WIP: Add support for post-processing via annotated configuration elements

configlib-core/src/main/java/de/exlll/configlib/ConfigurationElementFilter.java

@@ -0,0 +1,57 @@
+package de.exlll.configlib;
+
+import java.util.function.Predicate;
+
+import static de.exlll.configlib.Validator.requireNonNull;
+
+
+/**
+ * Implementations of this interface test configuration elements for specific
+ * conditions.
+ */
+public interface ConfigurationElementFilter
+        extends Predicate<ConfigurationElement<?>> {
+    @Override
+    default ConfigurationElementFilter and(
+            Predicate<? super ConfigurationElement<?>> other
+    ) {
+        return element -> test(element) && other.test(element);
+    }
+
+    /**
+     * Creates a new {@code ConfigurationElementFilter} whose {@code test}
+     * method returns {@code true} if the tested configuration element is
+     * of the given type.
+     *
+     * @param type the type the filter is looking for
+     * @return new {@code ConfigurationElementFilter} that tests configuration
+     * elements for their type
+     * @throws NullPointerException if {@code type} is null
+     */
+    static ConfigurationElementFilter byType(Class<?> type) {
+        requireNonNull(type, "type");
+        return element -> element.type().equals(type);
+    }
+
+    /**
+     * Creates a new {@code ConfigurationElementFilter} whose {@code test}
+     * method returns {@code true} if the tested configuration element is
+     * annotated with a {@code PostProcess} annotation whose key equals
+     * {@code key}.
+     *
+     * @param key the key of the {@code PostProcess} annotation the filter is
+     *            looking for
+     * @return new {@code ConfigurationElementFilter} that tests configuration
+     * elements for {@code PostProcess} annotations with the given key
+     * @throws NullPointerException if {@code key} is null
+     */
+    static ConfigurationElementFilter byPostProcessKey(String key) {
+        requireNonNull(key, "post-process key");
+        return element -> {
+            final PostProcess postProcess = element.annotation(PostProcess.class);
+            if (postProcess == null) return false;
+            final String actualKey = postProcess.key();
+            return actualKey.equals(key);
+        };
+    }
+}

configlib-core/src/main/java/de/exlll/configlib/ConfigurationProperties.java

@@ -7,6 +7,7 @@ import java.util.LinkedHashMap;
 import java.util.Map;
 import java.util.function.Function;
 import java.util.function.Predicate;
+import java.util.function.UnaryOperator;
 
 import static de.exlll.configlib.Validator.requireNonNull;
 
@@ -14,10 +15,14 @@ import static de.exlll.configlib.Validator.requireNonNull;
  * A collection of values used to configure the serialization of configurations.
  */
 public class ConfigurationProperties {
-    private final Map<Class<?>, Serializer<?, ?>> serializersByType;
+    private final Map<Class<?>, Serializer<?, ?>>
+            serializersByType;
     private final Map<Class<?>, Function<? super SerializerContext, ? extends Serializer<?, ?>>>
             serializerFactoriesByType;
-    private final Map<Predicate<? super Type>, Serializer<?, ?>> serializersByCondition;
+    private final Map<Predicate<? super Type>, Serializer<?, ?>>
+            serializersByCondition;
+    private final Map<Predicate<? super ConfigurationElement<?>>, UnaryOperator<?>>
+            postProcessorsByCondition;
     private final NameFormatter formatter;
     private final FieldFilter filter;
     private final boolean outputNulls;
@@ -33,9 +38,12 @@ public class ConfigurationProperties {
     protected ConfigurationProperties(Builder<?> builder) {
         this.serializersByType = Map.copyOf(builder.serializersByType);
         this.serializerFactoriesByType = Map.copyOf(builder.serializerFactoriesByType);
-        this.serializersByCondition = Collections.unmodifiableMap(new LinkedHashMap<>(
+        this.serializersByCondition = Collections.unmodifiableMap(
-                builder.serializersByCondition
+                new LinkedHashMap<>(builder.serializersByCondition)
-        ));
+        );
+        this.postProcessorsByCondition = Collections.unmodifiableMap(
+                new LinkedHashMap<>(builder.postProcessorsByCondition)
+        );
         this.formatter = requireNonNull(builder.formatter, "name formatter");
         this.filter = requireNonNull(builder.filter, "field filter");
         this.outputNulls = builder.outputNulls;
@@ -79,11 +87,14 @@ public class ConfigurationProperties {
      * @param <B> the type of builder
      */
     public static abstract class Builder<B extends Builder<B>> {
-        private final Map<Class<?>, Serializer<?, ?>> serializersByType = new HashMap<>();
+        private final Map<Class<?>, Serializer<?, ?>>
+                serializersByType = new HashMap<>();
         private final Map<Class<?>, Function<? super SerializerContext, ? extends Serializer<?, ?>>>
                 serializerFactoriesByType = new HashMap<>();
-        private final Map<Predicate<? super Type>, Serializer<?, ?>> serializersByCondition =
+        private final Map<Predicate<? super Type>, Serializer<?, ?>>
-                new LinkedHashMap<>();
+                serializersByCondition = new LinkedHashMap<>();
+        private final Map<Predicate<? super ConfigurationElement<?>>, UnaryOperator<?>>
+                postProcessorsByCondition = new LinkedHashMap<>();
         private NameFormatter formatter = NameFormatters.IDENTITY;
         private FieldFilter filter = FieldFilters.DEFAULT;
         private boolean outputNulls = false;
@@ -96,6 +107,7 @@ public class ConfigurationProperties {
             this.serializersByType.putAll(properties.serializersByType);
             this.serializerFactoriesByType.putAll(properties.serializerFactoriesByType);
             this.serializersByCondition.putAll(properties.serializersByCondition);
+            this.postProcessorsByCondition.putAll(properties.postProcessorsByCondition);
             this.formatter = properties.formatter;
             this.filter = properties.filter;
             this.outputNulls = properties.outputNulls;
@@ -133,8 +145,9 @@ public class ConfigurationProperties {
         /**
          * Adds a serializer for the given type.
          * <p>
-         * If this library already provides a serializer for the given type (e.g. {@code BigInteger},
+         * If this library already provides a serializer for the given type
-         * {@code LocalDate}, etc.) the serializer added by this method takes precedence.
+         * (e.g. {@code BigInteger}, {@code LocalDate}, etc.) the serializer
+         * added by this method takes precedence.
          * <p>
          * If a factory is added via the {@link #addSerializerFactory(Class, Function)} method for
          * the same type, the serializer created by that factory takes precedence.
@@ -159,8 +172,9 @@ public class ConfigurationProperties {
         /**
          * Adds a serializer factory for the given type.
          * <p>
-         * If this library already provides a serializer for the given type (e.g. {@code BigInteger},
+         * If this library already provides a serializer for the given type
-         * {@code LocalDate}, etc.) the serializer created by the factory takes precedence.
+         * (e.g. {@code BigInteger}, {@code LocalDate}, etc.) the serializer
+         * created by the factory takes precedence.
          * <p>
          * If a serializer is added via the {@link #addSerializer(Class, Serializer)} method
          * for the same type, the serializer created by the factory that was added by this
@@ -204,6 +218,33 @@ public class ConfigurationProperties {
             return getThis();
         }
 
+        /**
+         * Defines a post-processor for each configuration element that fulfils
+         * the given condition. Multiple post-processors are applied if an
+         * element fulfills more than one condition. The conditions are checked
+         * in the order in which they were added.
+         * <p>
+         * <b>NOTE</b>:
+         * It is the developer's responsibility to ensure that the type of the
+         * configuration element matches the type the post-processor expects.
+         *
+         * @param condition     the condition that is checked
+         * @param postProcessor the post-processor to be applied if the
+         *                      condition is true
+         * @return this builder
+         * @throws NullPointerException if any argument is null
+         * @see ConfigurationElementFilter
+         */
+        public final B addPostProcessor(
+                Predicate<? super ConfigurationElement<?>> condition,
+                UnaryOperator<?> postProcessor
+        ) {
+            requireNonNull(condition, "condition");
+            requireNonNull(postProcessor, "post-processor");
+            this.postProcessorsByCondition.put(condition, postProcessor);
+            return getThis();
+        }
+
         /**
          * Sets whether configuration elements, or collection elements whose value
          * is null should be output while serializing the configuration.
@@ -311,6 +352,16 @@ public class ConfigurationProperties {
         return serializersByCondition;
     }
 
+    /**
+     * Returns an unmodifiable map of post-processors by condition.
+     *
+     * @return post-processors by condition
+     */
+    public final Map<Predicate<? super ConfigurationElement<?>>, UnaryOperator<?>>
+    getPostProcessorsByCondition() {
+        return postProcessorsByCondition;
+    }
+
     /**
      * Returns whether null values should be output.
      *

configlib-core/src/main/java/de/exlll/configlib/ConfigurationSerializer.java

@@ -2,7 +2,6 @@ package de.exlll.configlib;
 
 import de.exlll.configlib.ConfigurationElements.FieldElement;
 
-import java.lang.reflect.Field;
 import java.util.List;
 import java.util.Map;
 
@@ -13,26 +12,13 @@ final class ConfigurationSerializer<T> extends TypeSerializer<T, FieldElement> {
 
     @Override
     public T deserialize(Map<?, ?> serializedConfiguration) {
-        final T result = Reflect.callNoParamConstructor(type);
+        final var deserializedElements = deserializeConfigurationElements(serializedConfiguration);
-
+        final var elements = elements();
-        for (final var element : elements()) {
+        final T result = newDefaultInstance();
-            final var formattedName = formatter.format(element.name());
+        for (int i = 0; i < deserializedElements.length; i++) {
-
+            final FieldElement fieldElement = elements.get(i);
-            if (!serializedConfiguration.containsKey(formattedName))
+            Reflect.setValue(fieldElement.element(), result, deserializedElements[i]);
-                continue;
-
-            final var serializedValue = serializedConfiguration.get(formattedName);
-            final var field = element.element();
-
-            if ((serializedValue == null) && properties.inputNulls()) {
-                requireNonPrimitiveFieldType(field);
-                Reflect.setValue(field, result, null);
-            } else if (serializedValue != null) {
-                Object deserializeValue = deserialize(element, serializedValue);
-                Reflect.setValue(field, result, deserializeValue);
-            }
         }
-
         return postProcessor.apply(result);
     }
 
@@ -64,15 +50,15 @@ final class ConfigurationSerializer<T> extends TypeSerializer<T, FieldElement> {
         return Reflect.callNoParamConstructor(type);
     }
 
-    private static void requireNonPrimitiveFieldType(Field field) {
-        if (field.getType().isPrimitive()) {
-            String msg = ("Cannot set field '%s' to null value. Primitive types " +
-                          "cannot be assigned null.").formatted(field);
-            throw new ConfigurationException(msg);
-        }
-    }
-
     Class<T> getConfigurationType() {
         return type;
     }
+
+    // This object must only be used for the `getDefaultValueOf` method below.
+    private final T defaultInstance = newDefaultInstance();
+
+    @Override
+    protected Object getDefaultValueOf(FieldElement element) {
+        return Reflect.getValue(element.element(), defaultInstance);
+    }
 }

configlib-core/src/main/java/de/exlll/configlib/PostProcess.java

@@ -22,7 +22,7 @@ import java.lang.annotation.Target;
  * method call. If the return type is {@code void}, then the method is simply
  * called on the given instance.
  */
-@Target({ElementType.FIELD, ElementType.METHOD})
+@Target({ElementType.FIELD, ElementType.METHOD, ElementType.RECORD_COMPONENT})
 @Retention(RetentionPolicy.RUNTIME)
 public @interface PostProcess {
     String key() default "";

configlib-core/src/main/java/de/exlll/configlib/RecordSerializer.java

@@ -2,7 +2,6 @@ package de.exlll.configlib;
 
 import de.exlll.configlib.ConfigurationElements.RecordComponentElement;
 
-import java.lang.reflect.RecordComponent;
 import java.util.Arrays;
 import java.util.List;
 import java.util.Map;
@@ -14,32 +13,8 @@ final class RecordSerializer<R> extends TypeSerializer<R, RecordComponentElement
 
     @Override
     public R deserialize(Map<?, ?> serializedConfiguration) {
-        final var elements = elements();
+        final var ctorArgs = deserializeConfigurationElements(serializedConfiguration);
-        final var constructorArguments = new Object[elements.size()];
+        final var result = Reflect.callCanonicalConstructor(type, ctorArgs);
-
-        for (int i = 0, size = elements.size(); i < size; i++) {
-            final var element = elements.get(i);
-            final var formattedName = formatter.format(element.name());
-
-            if (!serializedConfiguration.containsKey(formattedName)) {
-                constructorArguments[i] = Reflect.getDefaultValue(element.type());
-                continue;
-            }
-
-            final var serializedValue = serializedConfiguration.get(formattedName);
-            final var recordComponent = element.element();
-
-            if ((serializedValue == null) && properties.inputNulls()) {
-                requireNonPrimitiveComponentType(recordComponent);
-                constructorArguments[i] = null;
-            } else if (serializedValue == null) {
-                constructorArguments[i] = Reflect.getDefaultValue(element.type());
-            } else {
-                constructorArguments[i] = deserialize(element, serializedValue);
-            }
-        }
-
-        final R result = Reflect.callCanonicalConstructor(type, constructorArguments);
         return postProcessor.apply(result);
     }
 
@@ -72,16 +47,12 @@ final class RecordSerializer<R> extends TypeSerializer<R, RecordComponentElement
                 : Reflect.callCanonicalConstructorWithDefaultValues(type);
     }
 
-    private static void requireNonPrimitiveComponentType(RecordComponent component) {
-        if (component.getType().isPrimitive()) {
-            String msg = ("Cannot set component '%s' of record type '%s' to null. Primitive types " +
-                          "cannot be assigned null values.")
-                    .formatted(component, component.getDeclaringRecord());
-            throw new ConfigurationException(msg);
-        }
-    }
-
     Class<R> getRecordType() {
         return type;
     }
+
+    @Override
+    protected Object getDefaultValueOf(RecordComponentElement element) {
+        return Reflect.getDefaultValue(element.type());
+    }
 }

configlib-core/src/main/java/de/exlll/configlib/TypeSerializer.java

@@ -1,7 +1,12 @@
 package de.exlll.configlib;
 
+import de.exlll.configlib.ConfigurationElements.FieldElement;
+import de.exlll.configlib.ConfigurationElements.RecordComponentElement;
+
+import java.lang.reflect.Field;
 import java.lang.reflect.Method;
 import java.lang.reflect.Modifier;
+import java.lang.reflect.RecordComponent;
 import java.util.Arrays;
 import java.util.LinkedHashMap;
 import java.util.List;
@@ -101,10 +106,98 @@ sealed abstract class TypeSerializer<T, E extends ConfigurationElement<?>>
         return deserialized;
     }
 
+    protected final Object[] deserializeConfigurationElements(
+            Map<?, ?> serializedConfiguration
+    ) {
+        final var elements = elements();
+        final var result = new Object[elements.size()];
+
+        for (int i = 0, size = elements.size(); i < size; i++) {
+            final var element = elements.get(i);
+            final var formattedName = formatter.format(element.name());
+
+            if (!serializedConfiguration.containsKey(formattedName)) {
+                final Object defaultValue = getDefaultValueOf(element);
+                result[i] = applyPostProcessorForElement(element, defaultValue);
+//               TODO: if (result[i] == null) requireNonPrimitiveType(element);
+                continue;
+            }
+
+            final var serializedValue = serializedConfiguration.get(formattedName);
+            if ((serializedValue == null) && properties.inputNulls()) {
+                result[i] = null;
+            } else if (serializedValue == null) {
+                result[i] = getDefaultValueOf(element);
+            } else {
+                result[i] = deserialize(element, serializedValue);
+            }
+
+            if (result[i] == null) requireNonPrimitiveType(element);
+            result[i] = applyPostProcessorForElement(element, result[i]);
+            // TODO: PostProcessor could return null, check should be done after
+        }
+
+        return result;
+    }
+
+    private Object applyPostProcessorForElement(
+            ConfigurationElement<?> element,
+            Object deserializeValue
+    ) {
+        Object result = deserializeValue;
+        for (final var entry : properties.getPostProcessorsByCondition().entrySet()) {
+            final var condition = entry.getKey();
+
+            if (condition.test(element)) {
+                final var postProcessor = entry.getValue();
+                result = tryApplyPostProcessorForElement(postProcessor, result);
+            }
+        }
+        return result;
+    }
+
+    private static Object tryApplyPostProcessorForElement(
+            UnaryOperator<?> postProcessor,
+            Object value
+    ) {
+        // TODO: Properly throw a ClassCastException
+        // TODO: Add test: type of element does not match type postprocessor expects
+        @SuppressWarnings("unchecked")
+        final var pp = (UnaryOperator<Object>) postProcessor;
+        return pp.apply(value);
+    }
+
+    private static void requireNonPrimitiveType(ConfigurationElement<?> element) {
+        if (element instanceof RecordComponentElement recordComponentElement) {
+            final RecordComponent component = recordComponentElement.element();
+
+            if (!component.getType().isPrimitive()) return;
+
+            String msg = ("Cannot set component '%s' of record type '%s' to null. " +
+                          "Primitive types cannot be assigned null values.")
+                    .formatted(component, component.getDeclaringRecord());
+            throw new ConfigurationException(msg);
+        }
+
+        if (element instanceof FieldElement fieldElement) {
+            final Field field = fieldElement.element();
+
+            if (!field.getType().isPrimitive()) return;
+
+            String msg = ("Cannot set field '%s' to null value. " +
+                          "Primitive types cannot be assigned null.")
+                    .formatted(field);
+            throw new ConfigurationException(msg);
+        }
+
+        throw new ConfigurationException("Unhandled ConfigurationElement: " + element);
+    }
+
     final UnaryOperator<T> createPostProcessorFromAnnotatedMethod() {
         final List<Method> list = Arrays.stream(type.getDeclaredMethods())
-                .filter(Predicate.not(Method::isSynthetic))
                 .filter(method -> method.isAnnotationPresent(PostProcess.class))
+                .filter(Predicate.not(Method::isSynthetic))
+                .filter(this::isNotAccessorMethod)
                 .toList();
 
         if (list.isEmpty())
@@ -157,11 +250,27 @@ sealed abstract class TypeSerializer<T, E extends ConfigurationElement<?>>
         };
     }
 
+    private boolean isNotAccessorMethod(Method method) {
+        if (!type.isRecord()) return true;
+        return Arrays.stream(type.getRecordComponents())
+                .map(RecordComponent::getName)
+                .noneMatch(s -> s.equals(method.getName()));
+    }
+
     protected abstract void requireSerializableElements();
 
     protected abstract String baseDeserializeExceptionMessage(E element, Object value);
 
     protected abstract List<E> elements();
 
+    /**
+     * Returns the default value of a field or record component before any
+     * post-processing has been performed.
+     *
+     * @param element the configuration element
+     * @return the default value for that element
+     */
+    protected abstract Object getDefaultValueOf(E element);
+
     abstract T newDefaultInstance();
 }

configlib-core/src/test/java/de/exlll/configlib/ConfigurationElementFilterTest.java

@@ -0,0 +1,119 @@
+package de.exlll.configlib;
+
+import de.exlll.configlib.ConfigurationElements.FieldElement;
+import de.exlll.configlib.ConfigurationElements.RecordComponentElement;
+import org.junit.jupiter.api.Test;
+
+import static de.exlll.configlib.TestUtils.assertThrowsNullPointerException;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+class ConfigurationElementFilterTest {
+    static final class FieldElementHolder {
+        private final int x = 10;
+        @PostProcess
+        private final int y = 10;
+        @PostProcess(key = "key1")
+        private final int z = 10;
+        @PostProcess(key = "key2")
+        private final int w = 10;
+
+        private final double dbl = 10;
+        private final Object obj = new Object();
+    }
+
+    record RecordComponentElementHolder(
+            int x,
+            @PostProcess int y,
+            @PostProcess(key = "key1") int z,
+            @PostProcess(key = "key2") int w,
+            double dbl,
+            Object obj
+    ) {}
+
+    private static final Class<?> FE_HOLDER_TYPE = FieldElementHolder.class;
+    private static final Class<?> RCE_HOLDER_TYPE = RecordComponentElementHolder.class;
+    private static final FieldElement FE_X;
+    private static final FieldElement FE_Y;
+    private static final FieldElement FE_Z;
+    private static final FieldElement FE_W;
+    private static final FieldElement FE_DBL;
+    private static final FieldElement FE_OBJ;
+    private static final RecordComponentElement RCE_X;
+    private static final RecordComponentElement RCE_Y;
+    private static final RecordComponentElement RCE_Z;
+    private static final RecordComponentElement RCE_W;
+    private static final RecordComponentElement RCE_DBL;
+    private static final RecordComponentElement RCE_OBJ;
+
+    static {
+        try {
+            FE_X = new FieldElement(FE_HOLDER_TYPE.getDeclaredField("x"));
+            FE_Y = new FieldElement(FE_HOLDER_TYPE.getDeclaredField("y"));
+            FE_Z = new FieldElement(FE_HOLDER_TYPE.getDeclaredField("z"));
+            FE_W = new FieldElement(FE_HOLDER_TYPE.getDeclaredField("w"));
+            FE_DBL = new FieldElement(FE_HOLDER_TYPE.getDeclaredField("dbl"));
+            FE_OBJ = new FieldElement(FE_HOLDER_TYPE.getDeclaredField("obj"));
+            RCE_X = new RecordComponentElement(RCE_HOLDER_TYPE.getRecordComponents()[0]);
+            RCE_Y = new RecordComponentElement(RCE_HOLDER_TYPE.getRecordComponents()[1]);
+            RCE_Z = new RecordComponentElement(RCE_HOLDER_TYPE.getRecordComponents()[2]);
+            RCE_W = new RecordComponentElement(RCE_HOLDER_TYPE.getRecordComponents()[3]);
+            RCE_DBL = new RecordComponentElement(RCE_HOLDER_TYPE.getRecordComponents()[4]);
+            RCE_OBJ = new RecordComponentElement(RCE_HOLDER_TYPE.getRecordComponents()[5]);
+        } catch (NoSuchFieldException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    @Test
+    void byPostProcessKeyRequiresNonNull() {
+        assertThrowsNullPointerException(
+                () -> ConfigurationElementFilter.byPostProcessKey(null),
+                "post-process key"
+        );
+    }
+
+    @Test
+    void byPostProcessKeyOnFields() throws NoSuchFieldException {
+        final var filter = ConfigurationElementFilter.byPostProcessKey("key2");
+        assertFalse(filter.test(FE_X));
+        assertFalse(filter.test(FE_Y));
+        assertFalse(filter.test(FE_Z));
+        assertTrue(filter.test(FE_W));
+        assertFalse(filter.test(FE_DBL));
+        assertFalse(filter.test(FE_OBJ));
+    }
+
+    @Test
+    void byTypeOnFields() {
+        final var filter = ConfigurationElementFilter.byType(int.class);
+        assertTrue(filter.test(FE_X));
+        assertTrue(filter.test(FE_Y));
+        assertTrue(filter.test(FE_Z));
+        assertTrue(filter.test(FE_W));
+        assertFalse(filter.test(FE_DBL));
+        assertFalse(filter.test(FE_OBJ));
+    }
+
+    @Test
+    void byPostProcessKeyOnRecordComponents() {
+        final var filter = ConfigurationElementFilter.byPostProcessKey("key2");
+        assertFalse(filter.test(RCE_X));
+        assertFalse(filter.test(RCE_Y));
+        assertFalse(filter.test(RCE_Z));
+        assertTrue(filter.test(RCE_W));
+        assertFalse(filter.test(RCE_DBL));
+        assertFalse(filter.test(RCE_OBJ));
+    }
+
+    @Test
+    void byTypeOnRecordComponents() {
+        final var filter = ConfigurationElementFilter.byType(Object.class);
+        assertFalse(filter.test(RCE_X));
+        assertFalse(filter.test(RCE_Y));
+        assertFalse(filter.test(RCE_Z));
+        assertFalse(filter.test(RCE_W));
+        assertFalse(filter.test(RCE_DBL));
+        assertTrue(filter.test(RCE_OBJ));
+    }
+}

configlib-core/src/test/java/de/exlll/configlib/ConfigurationPropertiesTest.java

@@ -8,6 +8,7 @@ import java.awt.Point;
 import java.lang.reflect.Type;
 import java.util.Map;
 import java.util.function.Predicate;
+import java.util.function.UnaryOperator;
 
 import static de.exlll.configlib.TestUtils.assertThrowsNullPointerException;
 import static org.hamcrest.MatcherAssert.assertThat;
@@ -18,11 +19,14 @@ class ConfigurationPropertiesTest {
     private static final NameFormatter FORMATTER = String::toLowerCase;
     private static final FieldFilter FILTER = field -> field.getName().startsWith("f");
     private static final PointSerializer SERIALIZER = new PointSerializer();
-    private static final Predicate<? super Type> PREDICATE = type -> true;
+    private static final Predicate<? super Type> PREDICATE_TYPE = type -> true;
+    private static final Predicate<? super ConfigurationElement<?>> PREDICATE_CE = ce -> true;
+    private static final UnaryOperator<?> POST_PROCESSOR = UnaryOperator.identity();
     private static final ConfigurationProperties.Builder<?> BUILDER = ConfigurationProperties.newBuilder()
             .addSerializer(Point.class, SERIALIZER)
             .addSerializerFactory(Point.class, ignored -> SERIALIZER)
-            .addSerializerByCondition(PREDICATE, SERIALIZER)
+            .addSerializerByCondition(PREDICATE_TYPE, SERIALIZER)
+            .addPostProcessor(PREDICATE_CE, POST_PROCESSOR)
             .setNameFormatter(FORMATTER)
             .setFieldFilter(FILTER)
             .outputNulls(true)
@@ -57,7 +61,8 @@ class ConfigurationPropertiesTest {
 
     private static void assertConfigurationProperties(ConfigurationProperties properties) {
         assertThat(properties.getSerializers(), is(Map.of(Point.class, SERIALIZER)));
-        assertThat(properties.getSerializersByCondition(), is(Map.of(PREDICATE, SERIALIZER)));
+        assertThat(properties.getSerializersByCondition(), is(Map.of(PREDICATE_TYPE, SERIALIZER)));
+        assertThat(properties.getPostProcessorsByCondition(), is(Map.of(PREDICATE_CE, POST_PROCESSOR)));
         assertThat(properties.outputNulls(), is(true));
         assertThat(properties.inputNulls(), is(true));
         assertThat(properties.serializeSetsAsLists(), is(false));
@@ -90,6 +95,17 @@ class ConfigurationPropertiesTest {
         );
     }
 
+    @Test
+    void builderPostProcessorsUnmodifiable() {
+        ConfigurationProperties properties = ConfigurationProperties.newBuilder().build();
+
+        var postProcessorsByCondition = properties.getPostProcessorsByCondition();
+        assertThrows(
+                UnsupportedOperationException.class,
+                () -> postProcessorsByCondition.put(t -> true, UnaryOperator.identity())
+        );
+    }
+
     public static final class BuilderTest {
         private static final ConfigurationProperties.Builder<?> builder = ConfigurationProperties.newBuilder();
 
@@ -147,5 +163,18 @@ class ConfigurationPropertiesTest {
                     "serializer"
             );
         }
+
+        @Test
+        void addPostProcessorByConditionRequiresNonNull() {
+            assertThrowsNullPointerException(
+                    () -> builder.addPostProcessor(null, UnaryOperator.identity()),
+                    "condition"
+            );
+
+            assertThrowsNullPointerException(
+                    () -> builder.addPostProcessor(type -> true, null),
+                    "post-processor"
+            );
+        }
     }
 }

configlib-core/src/test/java/de/exlll/configlib/ConfigurationSerializerTest.java

@@ -8,6 +8,7 @@ import de.exlll.configlib.configurations.ExampleInitializer;
 import org.junit.jupiter.api.Test;
 
 import java.awt.Point;
+import java.lang.reflect.Field;
 import java.math.BigDecimal;
 import java.time.LocalDate;
 import java.util.List;
@@ -18,6 +19,7 @@ import java.util.function.Consumer;
 import static de.exlll.configlib.TestUtils.*;
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.is;
+import static org.hamcrest.Matchers.nullValue;
 import static org.junit.jupiter.api.Assertions.*;
 
 @SuppressWarnings("FieldMayBeFinal")
@@ -63,13 +65,14 @@ class ConfigurationSerializerTest {
         );
     }
 
+    @Configuration
+    static final class A {
+        int value1 = 1;
+        int someValue2 = 2;
+    }
+
     @Test
     void serializeAppliesFormatter() {
-        @Configuration
-        class A {
-            int value1 = 1;
-            int someValue2 = 2;
-        }
         ConfigurationSerializer<A> serializer = newSerializer(
                 A.class,
                 builder -> builder.setNameFormatter(NameFormatters.UPPER_UNDERSCORE)
@@ -225,6 +228,35 @@ class ConfigurationSerializerTest {
         int j = 2;
     }
 
+    @Configuration
+    static final class B14 {
+        private int i1;
+        private int i2 = 10;
+        private String s1;
+        private String s2 = null;
+        private String s3 = "s3";
+    }
+
+    @Test
+    void getDefaultValueOf() {
+        final var serializer = newSerializer(B14.class);
+
+        assertThat(serializer.getDefaultValueOf(fieldElementFor(B14.class, "i1")), is(0));
+        assertThat(serializer.getDefaultValueOf(fieldElementFor(B14.class, "i2")), is(10));
+        assertThat(serializer.getDefaultValueOf(fieldElementFor(B14.class, "s1")), nullValue());
+        assertThat(serializer.getDefaultValueOf(fieldElementFor(B14.class, "s2")), nullValue());
+        assertThat(serializer.getDefaultValueOf(fieldElementFor(B14.class, "s3")), is("s3"));
+    }
+
+    private static ConfigurationElements.FieldElement fieldElementFor(Class<?> type, String fieldName) {
+        try {
+            final Field field = type.getDeclaredField(fieldName);
+            return new ConfigurationElements.FieldElement(field);
+        } catch (NoSuchFieldException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
     @Configuration
     static final class B9 {
         int i;
@@ -311,4 +343,346 @@ class ConfigurationSerializerTest {
         assertThat(b13.b12.j, is(7));
         assertThat(b13.b12.b11.k, is(26));
     }
+
+    @Configuration
+    static final class PP_1 {
+        @PostProcess(key = "key1")
+        private int a1 = 10;
+        @PostProcess(key = "key1")
+        private int a2 = 20;
+
+        @PostProcess(key = "key2")
+        private int b1 = 10;
+        @PostProcess(key = "key2")
+        private int b2 = 20;
+
+        @PostProcess
+        private int c1 = 10;
+        @PostProcess
+        private int c2 = 20;
+
+        private int d1 = 10;
+        private int d2 = 20;
+    }
+
+    @Test
+    void postProcessFieldByKey1() {
+        final var serializer = newSerializer(
+                PP_1.class,
+                builder -> builder.addPostProcessor(
+                        ConfigurationElementFilter.byPostProcessKey("key1"),
+                        (Integer x) -> x * 2
+                )
+        );
+        PP_1 deserialized = serializer.deserialize(Map.of(
+                "a1", 10, "a2", 20,
+                "b1", 10, "b2", 20,
+                "c1", 10, "c2", 20,
+                "d1", 10, "d2", 20
+        ));
+        assertThat(deserialized.a1, is(20));
+        assertThat(deserialized.a2, is(40));
+        assertThat(deserialized.b1, is(10));
+        assertThat(deserialized.b2, is(20));
+        assertThat(deserialized.c1, is(10));
+        assertThat(deserialized.c2, is(20));
+        assertThat(deserialized.d1, is(10));
+        assertThat(deserialized.d2, is(20));
+    }
+
+    @Test
+    void postProcessFieldByEmptyKey() {
+        final var serializer = newSerializer(
+                PP_1.class,
+                builder -> builder.addPostProcessor(
+                        ConfigurationElementFilter.byPostProcessKey(""),
+                        (Integer x) -> x * 2
+                )
+        );
+        PP_1 deserialized = serializer.deserialize(Map.of(
+                "a1", 10, "a2", 20,
+                "b1", 10, "b2", 20,
+                "c1", 10, "c2", 20,
+                "d1", 10, "d2", 20
+        ));
+        assertThat(deserialized.a1, is(10));
+        assertThat(deserialized.a2, is(20));
+        assertThat(deserialized.b1, is(10));
+        assertThat(deserialized.b2, is(20));
+        assertThat(deserialized.c1, is(20));
+        assertThat(deserialized.c2, is(40));
+        assertThat(deserialized.d1, is(10));
+        assertThat(deserialized.d2, is(20));
+    }
+
+    @Configuration
+    static final class PP_2 {
+        private PP_1 pp1_1 = new PP_1();
+        @PostProcess(key = "key3")
+        private PP_1 pp1_2 = new PP_1();
+    }
+
+    @Test
+    void postProcessNestedFieldByKey2And3() {
+        final var serializer = newSerializer(
+                PP_2.class,
+                builder -> builder
+                        .addPostProcessor(
+                                ConfigurationElementFilter.byPostProcessKey("key2"),
+                                (Integer x) -> x * 2
+                        )
+                        .addPostProcessor(
+                                ConfigurationElementFilter.byPostProcessKey("key3"),
+                                (PP_1 pp1) -> {
+                                    pp1.a1 *= 10;
+                                    pp1.a2 *= 10;
+                                    pp1.b1 *= 10;
+                                    pp1.b2 *= 10;
+                                    pp1.c1 *= 10;
+                                    pp1.c2 *= 10;
+                                    pp1.d1 *= 10;
+                                    pp1.d2 *= 10;
+                                    return pp1;
+                                }
+                        )
+        );
+        PP_2 deserialized = serializer.deserialize(Map.of(
+                "pp1_1", Map.of(
+                        "a1", 10, "a2", 20,
+                        "b1", 10, "b2", 20,
+                        "c1", 10, "c2", 20,
+                        "d1", 10, "d2", 20
+                ),
+                "pp1_2", Map.of(
+                        "a1", 10, "a2", 20,
+                        "b1", 10, "b2", 20,
+                        "c1", 10, "c2", 20,
+                        "d1", 10, "d2", 20
+                )
+        ));
+        assertThat(deserialized.pp1_1.a1, is(10));
+        assertThat(deserialized.pp1_1.a2, is(20));
+        assertThat(deserialized.pp1_1.b1, is(20));
+        assertThat(deserialized.pp1_1.b2, is(40));
+        assertThat(deserialized.pp1_1.c1, is(10));
+        assertThat(deserialized.pp1_1.c2, is(20));
+        assertThat(deserialized.pp1_1.d1, is(10));
+        assertThat(deserialized.pp1_1.d2, is(20));
+
+        assertThat(deserialized.pp1_2.a1, is(100));
+        assertThat(deserialized.pp1_2.a2, is(200));
+        assertThat(deserialized.pp1_2.b1, is(200));
+        assertThat(deserialized.pp1_2.b2, is(400));
+        assertThat(deserialized.pp1_2.c1, is(100));
+        assertThat(deserialized.pp1_2.c2, is(200));
+        assertThat(deserialized.pp1_2.d1, is(100));
+        assertThat(deserialized.pp1_2.d2, is(200));
+    }
+
+    @Test
+    void postProcessFieldDefaultValueIfSerializationMissing() {
+        final var serializer = newSerializer(
+                PP_1.class,
+                builder -> builder
+                        .addPostProcessor(
+                                ConfigurationElementFilter.byPostProcessKey("key1"),
+                                (Integer x) -> x * 2
+                        )
+                        .addPostProcessor(
+                                ConfigurationElementFilter.byPostProcessKey("key2"),
+                                (Integer x) -> x * 5
+                        )
+        );
+        PP_1 deserialized = serializer.deserialize(Map.of(
+                "a1", 700,
+                "b1", 800
+        ));
+        assertThat(deserialized.a1, is(1400));
+        assertThat(deserialized.a2, is(40));
+        assertThat(deserialized.b1, is(4000));
+        assertThat(deserialized.b2, is(100));
+        assertThat(deserialized.c1, is(10));
+        assertThat(deserialized.c2, is(20));
+        assertThat(deserialized.d1, is(10));
+        assertThat(deserialized.d2, is(20));
+    }
+
+    @Configuration
+    static final class PP_3 {
+        @PostProcess
+        private int i;
+
+        @PostProcess
+        private void postProcess() {
+            i++;
+        }
+    }
+
+    @Test
+    void postProcessMethodAppliedAfterPostProcessAnnotation() {
+        final var serializer = newSerializer(
+                PP_3.class,
+                builder -> builder.addPostProcessor(
+                        ConfigurationElementFilter.byPostProcessKey(""),
+                        (Integer x) -> x * 2
+                )
+        );
+        PP_3 deserialized = serializer.deserialize(Map.of("i", 10));
+        assertThat(deserialized.i, is(21));
+    }
+
+    @Configuration
+    static final class PP_Ignored {
+        @PostProcess(key = "key1")
+        @Ignore
+        private int a1 = 10;
+        @PostProcess(key = "key1")
+        @Ignore
+        private int a2 = 20;
+
+        @PostProcess(key = "key2")
+        private final int b1 = 10;
+        @PostProcess(key = "key2")
+        private final int b2 = 20;
+
+        @PostProcess
+        private transient int c1 = 10;
+        @PostProcess
+        private transient int c2 = 20;
+
+        private int d1 = 10;
+        private int d2 = 20;
+    }
+
+    @Test
+    void ignoredFieldsAreNotPostProcessed() {
+        final var serializer = newSerializer(
+                PP_Ignored.class,
+                builder -> builder
+                        .addPostProcessor(
+                                ConfigurationElementFilter.byPostProcessKey("key1"),
+                                (Integer x) -> x * 2
+                        )
+                        .addPostProcessor(
+                                ConfigurationElementFilter.byPostProcessKey("key2"),
+                                (Integer x) -> x * 5
+                        )
+                        .addPostProcessor(
+                                ConfigurationElementFilter.byPostProcessKey(""),
+                                (Integer x) -> x * 7
+                        )
+        );
+        PP_Ignored deserialized = serializer.deserialize(Map.of(
+                "a1", 10, "a2", 20,
+                "b1", 10, "b2", 20,
+                "c1", 10, "c2", 20,
+                "d1", 10, "d2", 20
+        ));
+        assertThat(deserialized.a1, is(10));
+        assertThat(deserialized.a2, is(20));
+        assertThat(deserialized.b1, is(10));
+        assertThat(deserialized.b2, is(20));
+        assertThat(deserialized.c1, is(10));
+        assertThat(deserialized.c2, is(20));
+        assertThat(deserialized.d1, is(10));
+        assertThat(deserialized.d2, is(20));
+    }
+
+    @Configuration
+    static final class PP_Null {
+        @PostProcess(key = "integer")
+        private Integer i1;
+        @PostProcess(key = "integer")
+        private Integer i2;
+        @PostProcess(key = "integer")
+        private Integer i3 = 1;
+        private Integer i4;
+        @PostProcess(key = "string")
+        private String s1;
+        @PostProcess(key = "string")
+        private String s2;
+        @PostProcess(key = "string")
+        private String s3 = "a";
+        private String s4;
+    }
+
+    @Test
+    void postProcessFieldsThatAreAssignedNullValues() {
+        final var serializer = newSerializer(
+                PP_Null.class,
+                builder -> builder
+                        .inputNulls(true)
+                        .addPostProcessor(
+                                ConfigurationElementFilter.byPostProcessKey("integer"),
+                                (Integer x) -> (x == null) ? -1 : x * 2
+                        )
+                        .addPostProcessor(
+                                ConfigurationElementFilter.byPostProcessKey("string"),
+                                (String s) -> (s == null) ? "empty" : s.repeat(2)
+                        )
+        );
+        PP_Null deserialized = serializer.deserialize(TestUtils.asMap(
+                "i1", null, "i4", null,
+                "s1", null, "s4", null
+
+        ));
+        assertThat(deserialized.i1, is(-1));
+        assertThat(deserialized.i2, is(-1));
+        assertThat(deserialized.i3, is(2));
+        assertThat(deserialized.i4, nullValue());
+        assertThat(deserialized.s1, is("empty"));
+        assertThat(deserialized.s2, is("empty"));
+        assertThat(deserialized.s3, is("aa"));
+        assertThat(deserialized.s4, nullValue());
+    }
+
+    @Configuration
+    static final class PP_Null_2 {
+        @PostProcess(key = "integer")
+        private Integer i1 = 1;
+        @PostProcess(key = "integer")
+        private Integer i2 = 2;
+        @PostProcess(key = "integer")
+        private Integer i3 = null;
+        @PostProcess(key = "integer")
+        private Integer i4 = null;
+        @PostProcess(key = "string")
+        private String s1 = "a";
+        @PostProcess(key = "string")
+        private String s2 = "b";
+        @PostProcess(key = "string")
+        private String s3 = null;
+        @PostProcess(key = "string")
+        private String s4 = null;
+    }
+
+    @Test
+    void postProcessSerializedNullValuesWithInputNullsBeingFalse() {
+        final var serializer = newSerializer(
+                PP_Null_2.class,
+                builder -> builder
+                        .inputNulls(false)
+                        .addPostProcessor(
+                                ConfigurationElementFilter.byPostProcessKey("integer"),
+                                (Integer x) -> (x == null) ? -1 : x * 2
+                        )
+                        .addPostProcessor(
+                                ConfigurationElementFilter.byPostProcessKey("string"),
+                                (String s) -> (s == null) ? "empty" : s.repeat(2)
+                        )
+        );
+        PP_Null_2 deserialized = serializer.deserialize(TestUtils.asMap(
+                "i1", null, "i3", null,
+                "s1", null, "s3", null
+
+        ));
+        assertThat(deserialized.i1, is(2));
+        assertThat(deserialized.i2, is(4));
+        assertThat(deserialized.i3, is(-1));
+        assertThat(deserialized.i4, is(-1));
+        assertThat(deserialized.s1, is("aa"));
+        assertThat(deserialized.s2, is("bb"));
+        assertThat(deserialized.s3, is("empty"));
+        assertThat(deserialized.s4, is("empty"));
+    }
 }

configlib-core/src/test/java/de/exlll/configlib/PolymorphicSerializerTest.java

@@ -22,19 +22,19 @@ class PolymorphicSerializerTest {
         assertThat(DEFAULT_PROPERTY, is("type"));
     }
 
+    @Polymorphic
+    @Configuration
+    static final class A {
+        String type = "";
+    }
+    @Configuration
+    @Polymorphic(property = "prop")
+    static final class B {
+        String prop = "";
+    }
+
     @Test
     void serializeDoesNotAllowConfigurationElementWithSameNameAsProperty() {
-        @Polymorphic
-        @Configuration
-        class A {
-            String type = "";
-        }
-        @Configuration
-        @Polymorphic(property = "prop")
-        class B {
-            String prop = "";
-        }
-
         record Config(A a, B b, List<A> as) {}
 
         var serializerA = (PolymorphicSerializer) SELECTOR.select(fieldAsElement(Config.class, "a"));

configlib-core/src/test/java/de/exlll/configlib/RecordSerializerTest.java

@@ -1,5 +1,6 @@
 package de.exlll.configlib;
 
+import de.exlll.configlib.ConfigurationElements.RecordComponentElement;
 import org.junit.jupiter.api.Test;
 
 import java.awt.Point;
@@ -159,7 +160,7 @@ class RecordSerializerTest {
     }
 
     @Test
-    void deserializeNullValuesAsNullIfInputNullsIsTrueFailsForPrimitiveFields() {
+    void deserializeNullValuesAsNullIfInputNullsIsTrueFailsForPrimitiveRecordComponents() {
         RecordSerializer<R2> serializer = newSerializer(R2.class, builder -> builder.inputNulls(true));
         RecordComponent[] components = R2.class.getRecordComponents();
 
@@ -230,6 +231,18 @@ class RecordSerializerTest {
         assertThat(r.s, is("s"));
     }
 
+    @Test
+    void getDefaultValueOf() {
+        record R(int i, String s) {
+            R() {this(10, "s");}
+        }
+        final var rc1 = new RecordComponentElement(R.class.getRecordComponents()[0]);
+        final var rc2 = new RecordComponentElement(R.class.getRecordComponents()[1]);
+        final var serializer = newSerializer(R.class);
+        assertThat(serializer.getDefaultValueOf(rc1), is(0));
+        assertThat(serializer.getDefaultValueOf(rc2), nullValue());
+    }
+
     @Test
     void postProcessorIsAppliedInRecordDeserializer() {
         record R(int i, String s) {
@@ -280,4 +293,230 @@ class RecordSerializerTest {
         assertThat(r1.r2.j, is(7));
         assertThat(r1.r2.r3.k, is(26));
     }
+
+
+    record RP(int x, int y) {
+        @PostProcess
+        private void doSth1() {}
+
+        @PostProcess
+        private void doSth2() {}
+    }
+
+    @Test
+    void recordWithMultiplePostProcessMethodsCausesException() {
+        assertThrowsConfigurationException(
+                () -> newSerializer(RP.class),
+                """
+                Configuration types must not define more than one method for post-processing but \
+                type 'class de.exlll.configlib.RecordSerializerTest$RP' defines 2:
+                  private void de.exlll.configlib.RecordSerializerTest$RP.doSth1()
+                  private void de.exlll.configlib.RecordSerializerTest$RP.doSth2()\
+                """
+        );
+    }
+
+    record RR_1(
+            @PostProcess(key = "key1")
+            int a1,
+            @PostProcess(key = "key1")
+            int a2,
+            @PostProcess(key = "key2")
+            int b1,
+            @PostProcess(key = "key2")
+            int b2,
+            @PostProcess
+            int c1,
+            @PostProcess
+            int c2,
+            int d1,
+            int d2
+    ) {}
+
+    @Test
+    void postProcessRecordComponentByKey1() {
+        final var serializer = newSerializer(
+                RR_1.class,
+                builder -> builder.addPostProcessor(
+                        ConfigurationElementFilter.byPostProcessKey("key1"),
+                        (Integer x) -> x * 2
+                )
+        );
+        RR_1 deserialized = serializer.deserialize(Map.of(
+                "a1", 10, "a2", 20,
+                "b1", 10, "b2", 20,
+                "c1", 10, "c2", 20,
+                "d1", 10, "d2", 20
+        ));
+        assertThat(deserialized.a1, is(20));
+        assertThat(deserialized.a2, is(40));
+        assertThat(deserialized.b1, is(10));
+        assertThat(deserialized.b2, is(20));
+        assertThat(deserialized.c1, is(10));
+        assertThat(deserialized.c2, is(20));
+        assertThat(deserialized.d1, is(10));
+        assertThat(deserialized.d2, is(20));
+    }
+
+    @Test
+    void postProcessRecordComponentByEmptyKey() {
+        final var serializer = newSerializer(
+                RR_1.class,
+                builder -> builder.addPostProcessor(
+                        ConfigurationElementFilter.byPostProcessKey(""),
+                        (Integer x) -> x * 2
+                )
+        );
+        RR_1 deserialized = serializer.deserialize(Map.of(
+                "a1", 10, "a2", 20,
+                "b1", 10, "b2", 20,
+                "c1", 10, "c2", 20,
+                "d1", 10, "d2", 20
+        ));
+        assertThat(deserialized.a1, is(10));
+        assertThat(deserialized.a2, is(20));
+        assertThat(deserialized.b1, is(10));
+        assertThat(deserialized.b2, is(20));
+        assertThat(deserialized.c1, is(20));
+        assertThat(deserialized.c2, is(40));
+        assertThat(deserialized.d1, is(10));
+        assertThat(deserialized.d2, is(20));
+    }
+
+    record RR_2(RR_1 pp1_1, @PostProcess(key = "key3") RR_1 pp1_2) {}
+
+    @Test
+    void postProcessNestedRecordComponentByKey2And3() {
+        final var serializer = newSerializer(
+                RR_2.class,
+                builder -> builder
+                        .addPostProcessor(
+                                ConfigurationElementFilter.byPostProcessKey("key2"),
+                                (Integer x) -> x * 2
+                        )
+                        .addPostProcessor(
+                                ConfigurationElementFilter.byPostProcessKey("key3"),
+                                (RR_1 pp1) -> new RR_1(
+                                        pp1.a1 * 10,
+                                        pp1.a2 * 10,
+                                        pp1.b1 * 10,
+                                        pp1.b2 * 10,
+                                        pp1.c1 * 10,
+                                        pp1.c2 * 10,
+                                        pp1.d1 * 10,
+                                        pp1.d2 * 10
+                                )
+                        )
+        );
+        RR_2 deserialized = serializer.deserialize(Map.of(
+                "pp1_1", Map.of(
+                        "a1", 10, "a2", 20,
+                        "b1", 10, "b2", 20,
+                        "c1", 10, "c2", 20,
+                        "d1", 10, "d2", 20
+                ),
+                "pp1_2", Map.of(
+                        "a1", 10, "a2", 20,
+                        "b1", 10, "b2", 20,
+                        "c1", 10, "c2", 20,
+                        "d1", 10, "d2", 20
+                )
+        ));
+        assertThat(deserialized.pp1_1.a1, is(10));
+        assertThat(deserialized.pp1_1.a2, is(20));
+        assertThat(deserialized.pp1_1.b1, is(20));
+        assertThat(deserialized.pp1_1.b2, is(40));
+        assertThat(deserialized.pp1_1.c1, is(10));
+        assertThat(deserialized.pp1_1.c2, is(20));
+        assertThat(deserialized.pp1_1.d1, is(10));
+        assertThat(deserialized.pp1_1.d2, is(20));
+
+        assertThat(deserialized.pp1_2.a1, is(100));
+        assertThat(deserialized.pp1_2.a2, is(200));
+        assertThat(deserialized.pp1_2.b1, is(200));
+        assertThat(deserialized.pp1_2.b2, is(400));
+        assertThat(deserialized.pp1_2.c1, is(100));
+        assertThat(deserialized.pp1_2.c2, is(200));
+        assertThat(deserialized.pp1_2.d1, is(100));
+        assertThat(deserialized.pp1_2.d2, is(200));
+    }
+
+    @Test
+    void postProcessRecordComponentDefaultValueIfSerializationMissing() {
+        final var serializer = newSerializer(
+                RR_1.class,
+                builder -> builder
+                        .addPostProcessor(
+                                ConfigurationElementFilter.byPostProcessKey("key1"),
+                                (Integer x) -> x + 20
+                        )
+                        .addPostProcessor(
+                                ConfigurationElementFilter.byPostProcessKey("key2"),
+                                (Integer x) -> x + 500
+                        )
+        );
+        RR_1 deserialized = serializer.deserialize(Map.of(
+                "a1", 700,
+                "b1", 800
+        ));
+        assertThat(deserialized.a1, is(720));
+        assertThat(deserialized.a2, is(20));
+        assertThat(deserialized.b1, is(1300));
+        assertThat(deserialized.b2, is(500));
+        assertThat(deserialized.c1, is(0));
+        assertThat(deserialized.c2, is(0));
+        assertThat(deserialized.d1, is(0));
+        assertThat(deserialized.d2, is(0));
+    }
+
+    record RR_3(@PostProcess int i) {
+        @PostProcess
+        private RR_3 postProcess() {
+            return new RR_3(i + 1);
+        }
+    }
+
+    @Test
+    void postProcessMethodAppliedAfterPostProcessAnnotation() {
+        final var serializer = newSerializer(
+                RR_3.class,
+                builder -> builder.addPostProcessor(
+                        ConfigurationElementFilter.byPostProcessKey(""),
+                        (Integer x) -> x * 2
+                )
+        );
+        RR_3 deserialized = serializer.deserialize(Map.of("i", 10));
+        assertThat(deserialized.i, is(21));
+    }
+
+    record RR_Null(
+            @PostProcess(key = "integer")
+            Integer i1,
+            Integer i2,
+            @PostProcess(key = "string")
+            String s1,
+            String s2
+    ) {}
+
+    @Test
+    void postProcessRecordComponentsThatAreAssignedNullValues() {
+        final var serializer = newSerializer(
+                RR_Null.class,
+                builder -> builder
+                        .inputNulls(true)
+                        .addPostProcessor(
+                                ConfigurationElementFilter.byPostProcessKey("integer"),
+                                (Integer x) -> (x == null) ? -1 : x * 2
+                        )
+                        .addPostProcessor(
+                                ConfigurationElementFilter.byPostProcessKey("string"),
+                                (String s) -> (s == null) ? "empty" : s.repeat(2)
+                        )
+        );
+        RR_Null deserialized = serializer.deserialize(Map.of());
+        assertThat(deserialized.i1, is(-1));
+        assertThat(deserialized.i2, nullValue());
+        assertThat(deserialized.s1, is("empty"));
+        assertThat(deserialized.s2, nullValue());
+    }
 }

configlib-core/src/test/java/de/exlll/configlib/TypeSerializerTest.java

@@ -13,7 +13,6 @@ import java.util.List;
 import java.util.Map;
 import java.util.Set;
 import java.util.UUID;
-import java.util.concurrent.atomic.AtomicInteger;
 import java.util.function.Consumer;
 
 import static de.exlll.configlib.TestUtils.assertThrowsConfigurationException;
@@ -299,28 +298,29 @@ class TypeSerializerTest {
         );
     }
 
-    @Test
+    @Configuration
-    void postProcessMustReturnVoidOrSameType() {
+    static class E {
-        @Configuration
+        int i;
-        class E {
-            int i;
 
-            @PostProcess
+        @PostProcess
-            E postProcess() {return null;}
+        E postProcess() {return null;}
-        }
+    }
-        class F extends E {
+    static class F extends E {
-            @Override
+        @Override
-            @PostProcess
+        @PostProcess
-            E postProcess() {return null;}
+        E postProcess() {return null;}
-        }
+    }
-        class G extends E {
+    static class G extends E {
-            @Override
+        @Override
-            @PostProcess
+        @PostProcess
-            G postProcess() {
+        G postProcess() {
-                return null;
+            return null;
-            }
         }
+    }
 
+
+    @Test
+    void postProcessMustReturnVoidOrSameType() {
         // both of these are okay:
         newTypeSerializer(E.class);
         newTypeSerializer(G.class);
@@ -331,31 +331,29 @@ class TypeSerializerTest {
                 The return type of post-processing methods must either be 'void' or the same \
                 type as the configuration type in which the post-processing method is defined. \
                 The return type of the post-processing method of \
-                type 'class de.exlll.configlib.TypeSerializerTest$1F' is neither 'void' nor 'F'.\
+                type 'class de.exlll.configlib.TypeSerializerTest$F' is neither 'void' nor 'F'.\
                 """
         );
     }
 
-    @Test
+    @Configuration
-    void postProcessorInvokesAnnotatedMethodWithVoidReturnType1() {
+    static final class H1 {
-        final AtomicInteger integer = new AtomicInteger(0);
+        int i;
-
-        @Configuration
-        class H1 {
-            int i;
 
-            @PostProcess
+        @PostProcess
-            void postProcess() {integer.set(20);}
+        void postProcess() {i += 20;}
-        }
+    }
 
+    @Test
+    void postProcessorInvokesAnnotatedMethodWithVoidReturnType1() {
         final var serializer = newTypeSerializer(H1.class);
         final var postProcessor = serializer.createPostProcessorFromAnnotatedMethod();
 
         final H1 h1_1 = new H1();
         final H1 h1_2 = postProcessor.apply(h1_1);
 
-        assertThat(h1_2, sameInstance(h1_2));
+        assertThat(h1_2, sameInstance(h1_1));
-        assertThat(integer.get(), is(20));
+        assertThat(h1_2.i, is(20));
     }
 
     static int postProcessorInvokesAnnotatedMethodWithVoidReturnType2_int = 0;
@@ -379,20 +377,20 @@ class TypeSerializerTest {
         assertThat(postProcessorInvokesAnnotatedMethodWithVoidReturnType2_int, is(10));
     }
 
-    @Test
+    @Configuration
-    void postProcessorInvokesAnnotatedMethodWithSameReturnType1() {
+    static final class H3 {
-        @Configuration
+        int i;
-        class H3 {
+
-            int i;
+        @PostProcess
-
+        H3 postProcess() {
-            @PostProcess
+            H3 h3 = new H3();
-            H3 postProcess() {
+            h3.i = i + 20;
-                H3 h3 = new H3();
+            return h3;
-                h3.i = i + 20;
-                return h3;
-            }
         }
+    }
 
+    @Test
+    void postProcessorInvokesAnnotatedMethodWithSameReturnType1() {
         final var serializer = newTypeSerializer(H3.class);
         final var postProcessor = serializer.createPostProcessorFromAnnotatedMethod();
 
@@ -425,12 +423,13 @@ class TypeSerializerTest {
         assertThat(h4_2.i, is(30));
     }
 
+    @Configuration
+    static final class J {
+        int i;
+    }
+
     @Test
     void postProcessorIsIdentityFunctionIfNoPostProcessAnnotationPresent() {
-        @Configuration
-        class J {
-            int i;
-        }
         final var serializer = newTypeSerializer(J.class);
         final var postProcessor = serializer.createPostProcessorFromAnnotatedMethod();
 
@@ -439,20 +438,20 @@ class TypeSerializerTest {
         assertThat(j_2, sameInstance(j_1));
     }
 
-    @Test
+    @Configuration
-    void postProcessOfParentClassNotCalled() {
+    static class A {
-        @Configuration
+        int i = 10;
-        class A {
-            int i = 10;
 
-            @PostProcess
+        @PostProcess
-            void postProcess() {
+        void postProcess() {
-                this.i = this.i + 10;
+            this.i = this.i + 10;
-            }
         }
+    }
 
-        class B extends A {}
+    static final class B extends A {}
 
+    @Test
+    void postProcessOfParentClassNotCalled() {
         final var serializer = newTypeSerializer(B.class);
         final var postProcessor = serializer.createPostProcessorFromAnnotatedMethod();
 

configlib-core/src/testFixtures/java/de/exlll/configlib/TestUtils.java

@@ -210,7 +210,7 @@ public final class TestUtils {
 
         // Suppressing this warning might lead to an exception.
         // Using proper generics for the MEntry class is possible.
-        // However, doing so increases the compilation type by several seconds
+        // However, doing so increases the compilation time by several seconds
         @SuppressWarnings("unchecked")
         Map<K, V> returnResult = (Map<K, V>) result;
         return returnResult;