Add serialization support for Bukkit's ConfigurationSerializable types

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

@@ -1,7 +1,8 @@
 package de.exlll.configlib;
 
-import java.util.HashMap;
+import java.lang.reflect.Type;
-import java.util.Map;
+import java.util.*;
+import java.util.function.Predicate;
 
 import static de.exlll.configlib.Validator.requireNonNull;
 
@@ -10,6 +11,7 @@ import static de.exlll.configlib.Validator.requireNonNull;
  */
 class ConfigurationProperties {
     private final Map<Class<?>, Serializer<?, ?>> serializersByType;
+    private final Map<Predicate<? super Type>, Serializer<?, ?>> serializersByCondition;
     private final FieldFormatter formatter;
     private final FieldFilter filter;
     private final boolean outputNulls;
@@ -24,6 +26,9 @@ class ConfigurationProperties {
      */
     protected ConfigurationProperties(Builder<?> builder) {
         this.serializersByType = Map.copyOf(builder.serializersByType);
+        this.serializersByCondition = Collections.unmodifiableMap(new LinkedHashMap<>(
+                builder.serializersByCondition
+        ));
         this.formatter = requireNonNull(builder.formatter, "field formatter");
         this.filter = requireNonNull(builder.filter, "field filter");
         this.outputNulls = builder.outputNulls;
@@ -68,7 +73,8 @@ class ConfigurationProperties {
      */
     public static abstract class Builder<B extends Builder<B>> {
         private final Map<Class<?>, Serializer<?, ?>> serializersByType = new HashMap<>();
-        /* change setter JavaDoc if default values are changed */
+        private final Map<Predicate<? super Type>, Serializer<?, ?>> serializersByCondition =
+                new LinkedHashMap<>();
         private FieldFormatter formatter = FieldFormatters.IDENTITY;
         private FieldFilter filter = FieldFilters.DEFAULT;
         private boolean outputNulls = false;
@@ -79,6 +85,7 @@ class ConfigurationProperties {
 
         protected Builder(ConfigurationProperties properties) {
             this.serializersByType.putAll(properties.serializersByType);
+            this.serializersByCondition.putAll(properties.serializersByCondition);
             this.formatter = properties.formatter;
             this.filter = properties.filter;
             this.outputNulls = properties.outputNulls;
@@ -131,6 +138,29 @@ class ConfigurationProperties {
             return getThis();
         }
 
+        /**
+         * Adds a serializer for the condition. The serializer is selected when the condition
+         * evaluates to true. The {@code test} method of the condition object is invoked with
+         * the type of a field. Serializers added by this method take precedence over all other
+         * serializers expect the ones that were added for a specific type by the
+         * {@link #addSerializer(Class, Serializer)} method. The conditions are checked in the order
+         * in which they were added.
+         *
+         * @param condition  the condition
+         * @param serializer the serializer
+         * @return this builder
+         * @throws NullPointerException if any argument is null
+         */
+        final B addSerializerByCondition(
+                Predicate<? super Type> condition,
+                Serializer<?, ?> serializer
+        ) {
+            requireNonNull(condition, "condition");
+            requireNonNull(serializer, "serializer");
+            serializersByCondition.put(condition, serializer);
+            return getThis();
+        }
+
         /**
          * Sets whether fields or collection elements whose value is null should be output
          * while serializing the configuration.
@@ -215,6 +245,18 @@ class ConfigurationProperties {
         return serializersByType;
     }
 
+    /**
+     * Returns an unmodifiable map of serializers by condition. The serializers returned by this
+     * method take precedence over any default serializers provided by this library expect the ones
+     * that were added for a specific type.
+     *
+     * @return serializers by condition
+     */
+    final Map<Predicate<? super Type>, Serializer<?, ?>> getSerializersByCondition() {
+        return serializersByCondition;
+    }
+
+
     /**
      * Returns whether null values should be output.
      *

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

@@ -42,6 +42,9 @@ final class SerializerSelector {
     }
 
     public Serializer<?, ?> select(Type type) {
+        final Serializer<?, ?> custom = selectCustomSerializer(type);
+        if (custom != null)
+            return custom;
         if (type instanceof Class<?> cls) {
             return selectForClass(cls);
         } else if (type instanceof ParameterizedType pType) {
@@ -60,9 +63,19 @@ final class SerializerSelector {
         throw new ConfigurationException(baseExceptionMessage(type));
     }
 
+    private Serializer<?, ?> selectCustomSerializer(Type type) {
+        if (type instanceof Class<?> cls) {
+            if (properties.getSerializers().containsKey(cls)) // TODO move check out
+                return properties.getSerializers().get(cls);
+        }
+        for (var entry : properties.getSerializersByCondition().entrySet()) {
+            if (entry.getKey().test(type))
+                return entry.getValue();
+        }
+        return null;
+    }
+
     private Serializer<?, ?> selectForClass(Class<?> cls) {
-        if (properties.getSerializers().containsKey(cls))
-            return properties.getSerializers().get(cls);
         if (DEFAULT_SERIALIZERS.containsKey(cls))
             return DEFAULT_SERIALIZERS.get(cls);
         if (Reflect.isEnumType(cls)) {

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

@@ -1,10 +1,13 @@
 package de.exlll.configlib;
 
+import de.exlll.configlib.Serializers.StringSerializer;
 import org.junit.jupiter.api.Test;
 
 import java.awt.Point;
+import java.lang.reflect.Type;
 import java.util.Locale;
 import java.util.Map;
+import java.util.function.Predicate;
 
 import static de.exlll.configlib.TestUtils.assertThrowsNullPointerException;
 import static org.hamcrest.MatcherAssert.assertThat;
@@ -21,6 +24,7 @@ class ConfigurationPropertiesTest {
         assertThat(properties.outputNulls(), is(false));
         assertThat(properties.inputNulls(), is(false));
         assertThat(properties.getSerializers().entrySet(), empty());
+        assertThat(properties.getSerializersByCondition().entrySet(), empty());
         assertThat(properties.getFieldFormatter(), is(FieldFormatters.IDENTITY));
         assertThat(properties.getFieldFilter(), is(FieldFilters.DEFAULT));
     }
@@ -30,9 +34,11 @@ class ConfigurationPropertiesTest {
         FieldFormatter formatter = field -> field.getName().toLowerCase(Locale.ROOT);
         FieldFilter filter = field -> field.getName().startsWith("f");
         TestUtils.PointSerializer serializer = new TestUtils.PointSerializer();
+        Predicate<? super Type> predicate = type -> true;
 
         ConfigurationProperties properties = ConfigurationProperties.newBuilder()
                 .addSerializer(Point.class, serializer)
+                .addSerializerByCondition(predicate, serializer)
                 .setFieldFormatter(formatter)
                 .setFieldFilter(filter)
                 .outputNulls(true)
@@ -41,6 +47,7 @@ class ConfigurationPropertiesTest {
                 .build();
 
         assertThat(properties.getSerializers(), is(Map.of(Point.class, serializer)));
+        assertThat(properties.getSerializersByCondition(), is(Map.of(predicate, serializer)));
         assertThat(properties.outputNulls(), is(true));
         assertThat(properties.inputNulls(), is(true));
         assertThat(properties.serializeSetsAsLists(), is(false));
@@ -53,9 +60,11 @@ class ConfigurationPropertiesTest {
         FieldFormatter formatter = field -> field.getName().toLowerCase(Locale.ROOT);
         FieldFilter filter = field -> field.getName().startsWith("f");
         TestUtils.PointSerializer serializer = new TestUtils.PointSerializer();
+        Predicate<? super Type> predicate = type -> true;
 
         ConfigurationProperties properties = ConfigurationProperties.newBuilder()
                 .addSerializer(Point.class, serializer)
+                .addSerializerByCondition(predicate, serializer)
                 .setFieldFormatter(formatter)
                 .setFieldFilter(filter)
                 .outputNulls(true)
@@ -66,6 +75,7 @@ class ConfigurationPropertiesTest {
                 .build();
 
         assertThat(properties.getSerializers(), is(Map.of(Point.class, serializer)));
+        assertThat(properties.getSerializersByCondition(), is(Map.of(predicate, serializer)));
         assertThat(properties.outputNulls(), is(true));
         assertThat(properties.inputNulls(), is(true));
         assertThat(properties.serializeSetsAsLists(), is(false));
@@ -76,11 +86,16 @@ class ConfigurationPropertiesTest {
     @Test
     void builderSerializersUnmodifiable() {
         ConfigurationProperties properties = ConfigurationProperties.newBuilder().build();
-        Map<Class<?>, Serializer<?, ?>> map = properties.getSerializers();
+        var serializersByType = properties.getSerializers();
+        var serializersByCondition = properties.getSerializersByCondition();
 
         assertThrows(
                 UnsupportedOperationException.class,
-                () -> map.put(Point.class, new TestUtils.PointSerializer())
+                () -> serializersByType.put(Point.class, new TestUtils.PointSerializer())
+        );
+        assertThrows(
+                UnsupportedOperationException.class,
+                () -> serializersByCondition.put(t -> true, new TestUtils.PointSerializer())
         );
     }
 
@@ -104,9 +119,9 @@ class ConfigurationPropertiesTest {
         }
 
         @Test
-        void addSerializerRequiresNonNull() {
+        void addSerializerByTypeRequiresNonNull() {
             assertThrowsNullPointerException(
-                    () -> builder.addSerializer(null, new Serializers.StringSerializer()),
+                    () -> builder.addSerializer(null, new StringSerializer()),
                     "serialized type"
             );
 
@@ -115,5 +130,18 @@ class ConfigurationPropertiesTest {
                     "serializer"
             );
         }
+
+        @Test
+        void addSerializerByConditionRequiresNonNull() {
+            assertThrowsNullPointerException(
+                    () -> builder.addSerializerByCondition(null, new StringSerializer()),
+                    "condition"
+            );
+
+            assertThrowsNullPointerException(
+                    () -> builder.addSerializerByCondition(type -> true, null),
+                    "serializer"
+            );
+        }
     }
 }

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

@@ -178,7 +178,7 @@ class SerializerSelectorTest {
     }
 
     @Test
-    void selectSerializerCustomType() {
+    void selectSerializerByCustomType() {
         var properties = ConfigurationProperties.newBuilder()
                 .addSerializer(Point.class, POINT_SERIALIZER)
                 .build();
@@ -188,7 +188,7 @@ class SerializerSelectorTest {
     }
 
     @Test
-    void selectSerializerCustomSerializerTakesPrecedence() {
+    void selectSerializerByCustomTypeTakesPrecedence() {
         var properties = ConfigurationProperties.newBuilder()
                 .addSerializer(BigInteger.class, CUSTOM_BIG_INTEGER_SERIALIZER)
                 .build();
@@ -198,6 +198,41 @@ class SerializerSelectorTest {
         assertThat(bigIntegerSerializer, sameInstance(CUSTOM_BIG_INTEGER_SERIALIZER));
     }
 
+    @Test
+    void selectSerializerByCondition() {
+        var properties = ConfigurationProperties.newBuilder()
+                .addSerializerByCondition(t -> t == Point.class, POINT_SERIALIZER)
+                .build();
+        SerializerSelector selector = new SerializerSelector(properties);
+        var pointSerializer = selector.select(Point.class);
+        assertThat(pointSerializer, sameInstance(POINT_SERIALIZER));
+    }
+
+    @Test
+    void selectSerializerByConditionTakesPrecedence() {
+        var properties = ConfigurationProperties.newBuilder()
+                .addSerializerByCondition(t -> t == BigInteger.class, CUSTOM_BIG_INTEGER_SERIALIZER)
+                .build();
+        SerializerSelector selector = new SerializerSelector(properties);
+        var bigIntegerSerializer = selector.select(BigInteger.class);
+        assertThat(bigIntegerSerializer, instanceOf(TestUtils.CustomBigIntegerSerializer.class));
+        assertThat(bigIntegerSerializer, sameInstance(CUSTOM_BIG_INTEGER_SERIALIZER));
+    }
+
+    @Test
+    void selectSerializerByCustomTypeTakesPrecedenceOverCustomType() {
+        var serializer1 = IdentifiableSerializer.of(1);
+        var serializer2 = IdentifiableSerializer.of(2);
+        var properties = ConfigurationProperties.newBuilder()
+                .addSerializerByCondition(t -> t == int.class, serializer1)
+                .addSerializer(int.class, serializer2)
+                .build();
+        SerializerSelector selector = new SerializerSelector(properties);
+        var serializer = selector.select(int.class);
+        assertThat(serializer, instanceOf(IdentifiableSerializer.class));
+        assertThat(serializer, sameInstance(serializer2));
+    }
+
     @Test
     void selectSerializerList() {
         class A {

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

@@ -94,6 +94,28 @@ public final class TestUtils {
         }
     }
 
+    public static final class IdentifiableSerializer<S, T> implements Serializer<S, T> {
+        public int identifier;
+
+        public IdentifiableSerializer(int identifier) {
+            this.identifier = identifier;
+        }
+
+        public static IdentifiableSerializer<Integer, Integer> of(int identifier) {
+            return new IdentifiableSerializer<>(identifier);
+        }
+
+        @Override
+        public T serialize(S element) {
+            return null;
+        }
+
+        @Override
+        public S deserialize(T element) {
+            return null;
+        }
+    }
+
     public static final class PointIdentitySerializer implements Serializer<Point, Point> {
         @Override
         public Point serialize(Point element) {

configlib-paper/src/main/java/de/exlll/configlib/BukkitConfigurationSerializableSerializer.java

@@ -0,0 +1,31 @@
+package de.exlll.configlib;
+
+import org.bukkit.configuration.file.YamlConstructor;
+import org.bukkit.configuration.file.YamlRepresenter;
+import org.bukkit.configuration.serialization.ConfigurationSerializable;
+import org.yaml.snakeyaml.DumperOptions;
+import org.yaml.snakeyaml.Yaml;
+
+final class BukkitConfigurationSerializableSerializer
+        implements Serializer<ConfigurationSerializable, String> {
+    static BukkitConfigurationSerializableSerializer DEFAULT =
+            new BukkitConfigurationSerializableSerializer();
+    private final Yaml yaml;
+
+    BukkitConfigurationSerializableSerializer() {
+        DumperOptions options = new DumperOptions();
+        options.setIndent(2);
+        options.setDefaultFlowStyle(DumperOptions.FlowStyle.BLOCK);
+        this.yaml = new Yaml(new YamlConstructor(), new YamlRepresenter(), options);
+    }
+
+    @Override
+    public String serialize(ConfigurationSerializable element) {
+        return yaml.dump(element);
+    }
+
+    @Override
+    public ConfigurationSerializable deserialize(String element) {
+        return yaml.load(element);
+    }
+}

configlib-paper/src/main/java/de/exlll/configlib/ConfigLib.java

@@ -1,8 +1,31 @@
 package de.exlll.configlib;
 
+import org.bukkit.configuration.serialization.ConfigurationSerializable;
+import org.bukkit.inventory.ItemStack;
 import org.bukkit.plugin.java.JavaPlugin;
 
 /**
- * An empty plugin class that loads this library and its dependencies.
+ * The plugin class that loads this library and its dependencies.
  */
-public final class ConfigLib extends JavaPlugin {}
+public final class ConfigLib extends JavaPlugin {
+    /**
+     * A {@code YamlConfigurationProperties} object that provides serializers for several Bukkit
+     * classes like {@link  ItemStack} and other {@link ConfigurationSerializable} types.
+     * <p>
+     * You can configure these properties further by creating a new builder using the
+     * {@code toBuilder()} method of this object.
+     */
+    public static final YamlConfigurationProperties BUKKIT_DEFAULT_PROPERTIES =
+            initializeBukkitDefaultProperties();
+
+    private static YamlConfigurationProperties initializeBukkitDefaultProperties() {
+        return YamlConfigurationProperties
+                .newBuilder()
+                .addSerializerByCondition(
+                        type -> type instanceof Class<?> cls &&
+                                ConfigurationSerializable.class.isAssignableFrom(cls),
+                        BukkitConfigurationSerializableSerializer.DEFAULT
+                )
+                .build();
+    }
+}