Added FieldFilter

If your configuration has a lot of fields and you want to exclude some
of these fields without making them final, static or transient, you can
configure your properties object to use additional FieldFilters.

A FieldFilter filters the fields of a configuration class by a specified
criterion. For example, if you only want to include fields whose names
don't start with 'ignore', you would add the following filter:

YamlProperties properties = YamlProperties.builder()
                .addFilter(field -> !field.getName().startsWith("ignore"))
                // ...
                .build();

ConfigLib-Bukkit/src/main/resources/plugin.yml

@@ -1,5 +1,5 @@
 name: ConfigLib
 author: Exlll
 
-version: 2.0.3
+version: 2.1.0
 main: de.exlll.configlib.ConfigLib

ConfigLib-Bungee/src/main/resources/plugin.yml

@@ -1,5 +1,5 @@
 name: ConfigLib
 author: Exlll
 
-version: 2.0.3
+version: 2.1.0
 main: de.exlll.configlib.ConfigLib

ConfigLib-Core/src/main/java/de/exlll/configlib/Configuration.java

@@ -1,10 +1,13 @@
 package de.exlll.configlib;
 
+import de.exlll.configlib.filter.FieldFilter;
+import de.exlll.configlib.filter.FieldFilters;
 import de.exlll.configlib.format.FieldNameFormatter;
 import de.exlll.configlib.format.FieldNameFormatters;
 
 import java.io.IOException;
-import java.util.*;
+import java.util.Map;
+import java.util.Objects;
 
 /**
  * Parent class of all configurations.
@@ -103,6 +106,7 @@ public abstract class Configuration<C extends Configuration<C>> {
      */
     protected static class Properties {
         private final FieldNameFormatter formatter;
+        private final FieldFilter filter;
 
         /**
          * Constructs a new {@code Properties} object.
@@ -112,6 +116,7 @@ public abstract class Configuration<C extends Configuration<C>> {
          */
         protected Properties(Builder<?> builder) {
             this.formatter = builder.formatter;
+            this.filter = builder.filter;
         }
 
         static Builder<?> builder() {
@@ -132,6 +137,15 @@ public abstract class Configuration<C extends Configuration<C>> {
             return formatter;
         }
 
+        /**
+         * Returns the {@code FieldFilter} of a configuration
+         *
+         * @return {@code FieldFilter} of a configuration
+         */
+        public final FieldFilter getFilter() {
+            return filter;
+        }
+
         /**
          * Builder classes are used for constructing {@code Properties}.
          *
@@ -139,6 +153,7 @@ public abstract class Configuration<C extends Configuration<C>> {
          */
         protected static abstract class Builder<B extends Builder<B>> {
             private FieldNameFormatter formatter = FieldNameFormatters.IDENTITY;
+            private FieldFilter filter = FieldFilters.DEFAULT;
 
             protected Builder() {}
 
@@ -154,13 +169,30 @@ public abstract class Configuration<C extends Configuration<C>> {
              *
              * @param formatter formatter for configuration
              * @return this {@code Builder}
-             * @throws NullPointerException if {@code formatter ist null}
+             * @throws NullPointerException if {@code formatter} is null
              */
             public final B setFormatter(FieldNameFormatter formatter) {
                 this.formatter = Objects.requireNonNull(formatter);
                 return getThis();
             }
 
+            /**
+             * Composes the given {@link FieldFilter} with the
+             * {@code FieldFilters.DEFAULT} instance and any other
+             * previously added filters.
+             * <p>
+             * The added filter is not evaluated for a field if the field has
+             * already been filtered or by some other {@code FieldFilter}.
+             *
+             * @param filter field filter that is added
+             * @return this {@code Builder}
+             * @throws NullPointerException if {@code filter} is null
+             */
+            public final B addFilter(FieldFilter filter) {
+                this.filter = this.filter.and(filter);
+                return getThis();
+            }
+
             /**
              * Builds a new {@code Properties} instance using the values set.
              *

ConfigLib-Core/src/main/java/de/exlll/configlib/FieldMapper.java

@@ -1,18 +1,14 @@
 package de.exlll.configlib;
 
 import de.exlll.configlib.Converter.ConversionInfo;
+import de.exlll.configlib.filter.FieldFilter;
 import de.exlll.configlib.format.FieldNameFormatter;
 
 import java.lang.reflect.Field;
-import java.lang.reflect.Modifier;
-import java.util.Arrays;
 import java.util.LinkedHashMap;
-import java.util.List;
 import java.util.Map;
-import java.util.function.Predicate;
 
 import static de.exlll.configlib.Validator.*;
-import static java.util.stream.Collectors.toList;
 
 enum FieldMapper {
     ;
@@ -21,7 +17,8 @@ enum FieldMapper {
             Object inst, Configuration.Properties props
     ) {
         Map<String, Object> map = new LinkedHashMap<>();
-        for (Field field : FieldFilter.filterFields(inst.getClass())) {
+        FieldFilter filter = props.getFilter();
+        for (Field field : filter.filterDeclaredFieldsOf(inst.getClass())) {
             Object val = toConvertibleObject(field, inst, props);
             FieldNameFormatter fnf = props.getFormatter();
             String fn = fnf.fromFieldName(field.getName());
@@ -45,7 +42,8 @@ enum FieldMapper {
             Object inst, Map<String, Object> instMap,
             Configuration.Properties props
     ) {
-        for (Field field : FieldFilter.filterFields(inst.getClass())) {
+        FieldFilter filter = props.getFilter();
+        for (Field field : filter.filterDeclaredFieldsOf(inst.getClass())) {
             FieldNameFormatter fnf = props.getFormatter();
             String fn = fnf.fromFieldName(field.getName());
             Object mapValue = instMap.get(fn);
@@ -79,27 +77,4 @@ enum FieldMapper {
         Object val = Reflect.getValue(field, instance);
         checkNotNull(val, field.getName());
     }
-
-    enum FieldFilter implements Predicate<Field> {
-        DEFAULT;
-
-        static List<Field> filterFields(Class<?> cls) {
-            Field[] fields = cls.getDeclaredFields();
-            return Arrays.stream(fields)
-                    .filter(DEFAULT)
-                    .collect(toList());
-        }
-
-        @Override
-        public boolean test(Field field) {
-            if (field.isSynthetic()) {
-                return false;
-            }
-
-            int mods = field.getModifiers();
-            return !(Modifier.isFinal(mods) ||
-                    Modifier.isStatic(mods) ||
-                    Modifier.isTransient(mods));
-        }
-    }
 }

ConfigLib-Core/src/main/java/de/exlll/configlib/Validator.java

@@ -266,9 +266,9 @@ final class Validator {
         }
     }
 
-    static void checkConverterHasNoArgsConstructor(Class<?> convClass, String fn) {
-        if (!Reflect.hasNoArgConstructor(convClass)) {
-            String msg = "Converter '" + convClass.getSimpleName() + "' used " +
+    static void checkConverterHasNoArgsConstructor(Class<?> converterClass, String fn) {
+        if (!Reflect.hasNoArgConstructor(converterClass)) {
+            String msg = "Converter '" + converterClass.getSimpleName() + "' used " +
                     "on field '" + fn + "' doesn't have a no-args constructor.";
             throw new ConfigurationException(msg);
         }
@@ -284,14 +284,6 @@ final class Validator {
         }
     }
 
-    static boolean isTypeMap(Map<?, ?> map) {
-        return map.entrySet().stream().allMatch(entry -> {
-            Class<?> keyCls = entry.getKey().getClass();
-            Class<?> valCls = entry.getValue().getClass();
-            return (String.class == keyCls) && Reflect.isSimpleType(valCls);
-        });
-    }
-
     static void checkFieldTypeAssignableFrom(Class<?> type, ConversionInfo info) {
         Class<?> fieldType = info.getFieldType();
         if (!fieldType.isAssignableFrom(type)) {

ConfigLib-Core/src/main/java/de/exlll/configlib/filter/FieldFilter.java

@@ -0,0 +1,26 @@
+package de.exlll.configlib.filter;
+
+import java.lang.reflect.Field;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Objects;
+import java.util.function.Predicate;
+
+import static java.util.stream.Collectors.toList;
+
+@FunctionalInterface
+public interface FieldFilter extends Predicate<Field> {
+
+    @Override
+    default FieldFilter and(Predicate<? super Field> other) {
+        Objects.requireNonNull(other);
+        return (t) -> test(t) && other.test(t);
+    }
+
+    default List<? extends Field> filterDeclaredFieldsOf(Class<?> cls) {
+        Field[] fields = cls.getDeclaredFields();
+        return Arrays.stream(fields)
+                .filter(this)
+                .collect(toList());
+    }
+}

ConfigLib-Core/src/main/java/de/exlll/configlib/filter/FieldFilters.java

@@ -0,0 +1,20 @@
+package de.exlll.configlib.filter;
+
+import java.lang.reflect.Field;
+import java.lang.reflect.Modifier;
+
+public enum FieldFilters implements FieldFilter {
+    DEFAULT {
+        @Override
+        public boolean test(Field field) {
+            if (field.isSynthetic()) {
+                return false;
+            }
+
+            int mods = field.getModifiers();
+            return !(Modifier.isFinal(mods) ||
+                    Modifier.isStatic(mods) ||
+                    Modifier.isTransient(mods));
+        }
+    }
+}

ConfigLib-Core/src/test/java/de/exlll/configlib/ConfigurationTest.java

@@ -3,8 +3,6 @@ package de.exlll.configlib;
 import de.exlll.configlib.configs.mem.InSharedMemoryConfiguration;
 import org.junit.jupiter.api.Test;
 
-import java.io.IOException;
-
 import static org.hamcrest.Matchers.is;
 import static org.junit.Assert.assertThat;
 
@@ -14,7 +12,7 @@ class ConfigurationTest {
     }
 
     @Test
-    void configExecutesPreSaveHook() throws IOException {
+    void configExecutesPreSaveHook() {
         class A extends TestHook {
             int i = 0;
 
@@ -31,7 +29,7 @@ class ConfigurationTest {
     }
 
     @Test
-    void configExecutesPostLoadHook() throws IOException {
+    void configExecutesPostLoadHook() {
         class A extends TestHook {
             int i = 0;
 

ConfigLib-Core/src/test/java/de/exlll/configlib/FieldMapperHelpers.java

@@ -4,7 +4,6 @@ import de.exlll.configlib.annotation.ConfigurationElement;
 
 import java.util.Map;
 
-import static de.exlll.configlib.Configuration.Properties;
 import static de.exlll.configlib.configs.yaml.YamlConfiguration.YamlProperties.DEFAULT;
 import static org.hamcrest.Matchers.is;
 import static org.junit.Assert.assertThat;
@@ -43,14 +42,6 @@ public class FieldMapperHelpers {
         assertThat(ex.getMessage(), is(msg));
     }
 
-    public static void assertItmCfgExceptionMessage(
-            Object o, Properties props, String msg
-    ) {
-        ConfigurationException ex = assertItmThrowsCfgException(o, props);
-        assertThat(ex.getMessage(), is(msg));
-    }
-
-
     public static void assertIfmCfgExceptionMessage(
             Object o, Map<String, Object> map, String msg
     ) {
@@ -58,13 +49,6 @@ public class FieldMapperHelpers {
         assertThat(ex.getMessage(), is(msg));
     }
 
-    public static void assertIfmCfgExceptionMessage(
-            Object o, Map<String, Object> map, Properties props, String msg
-    ) {
-        ConfigurationException ex = assertIfmThrowsCfgException(o, map, props);
-        assertThat(ex.getMessage(), is(msg));
-    }
-
     public static ConfigurationException assertItmThrowsCfgException(Object o) {
         return assertThrows(
                 ConfigurationException.class,
@@ -72,15 +56,6 @@ public class FieldMapperHelpers {
         );
     }
 
-    public static ConfigurationException assertItmThrowsCfgException(
-            Object o, Configuration.Properties props
-    ) {
-        return assertThrows(
-                ConfigurationException.class,
-                () -> instanceToMap(o, props)
-        );
-    }
-
     public static ConfigurationException assertIfmThrowsCfgException(
             Object o, Map<String, Object> map
     ) {
@@ -90,31 +65,23 @@ public class FieldMapperHelpers {
         );
     }
 
-    public static ConfigurationException assertIfmThrowsCfgException(
-            Object o, Map<String, Object> map, Configuration.Properties props
-    ) {
-        return assertThrows(
-                ConfigurationException.class,
-                () -> instanceFromMap(o, map, props)
-        );
-    }
-
     public static Map<String, Object> instanceToMap(Object o) {
         return instanceToMap(o, DEFAULT);
     }
 
     public static Map<String, Object> instanceToMap(
-            Object o, Configuration.Properties props) {
+            Object o, Configuration.Properties props
+    ) {
         return FieldMapper.instanceToMap(o, props);
     }
 
     public static <T> T instanceFromMap(T o, Map<String, Object> map) {
-        FieldMapper.instanceFromMap(o, map, DEFAULT);
-        return o;
+        return instanceFromMap(o, map, DEFAULT);
     }
 
     public static <T> T instanceFromMap(
-            T o, Map<String, Object> map, Configuration.Properties props) {
+            T o, Map<String, Object> map, Configuration.Properties props
+    ) {
         FieldMapper.instanceFromMap(o, map, props);
         return o;
     }

ConfigLib-Core/src/test/java/de/exlll/configlib/FieldMapperTest.java

@@ -1,7 +1,6 @@
 package de.exlll.configlib;
 
 import de.exlll.configlib.Converter.ConversionInfo;
-import de.exlll.configlib.FieldMapper.FieldFilter;
 import de.exlll.configlib.annotation.ElementType;
 import de.exlll.configlib.annotation.NoConvert;
 import de.exlll.configlib.classes.TestClass;
@@ -12,13 +11,11 @@ import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
 import java.lang.reflect.Field;
-import java.lang.reflect.Modifier;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
 import java.util.function.Function;
-import java.util.function.Predicate;
 
 import static de.exlll.configlib.Converters.ENUM_CONVERTER;
 import static de.exlll.configlib.Converters.SIMPLE_TYPE_CONVERTER;
@@ -32,9 +29,6 @@ import static org.junit.jupiter.api.Assertions.assertThrows;
 
 @SuppressWarnings({"unused", "ThrowableNotThrown"})
 class FieldMapperTest {
-    private static final Class<ClassWithFinalStaticTransientField> CWFSTF =
-            ClassWithFinalStaticTransientField.class;
-    private static final Predicate<Field> filter = FieldFilter.DEFAULT;
     private static final TestClass t = TestClass.TEST_VALUES;
     private static final Configuration.Properties DEFAULT =
             Configuration.Properties.builder().build();
@@ -374,45 +368,6 @@ class FieldMapperTest {
         assertThat(instanceToMap(new Object()), instanceOf(LinkedHashMap.class));
     }
 
-    @Test
-    void filteredFieldsFiltersFields() throws NoSuchFieldException {
-        List<Field> fields = FieldFilter.filterFields(CWFSTF);
-        assertThat(fields.size(), is(0));
-
-        class A {
-            private int i;
-            private final int j = 0;
-            private transient int k;
-        }
-        fields = FieldFilter.filterFields(A.class);
-        assertThat(fields.size(), is(1));
-        assertThat(fields.get(0), is(A.class.getDeclaredField("i")));
-    }
-
-    @Test
-    void defaultFilterFiltersSyntheticFields() {
-        for (Field field : ClassWithSyntheticField.class.getDeclaredFields()) {
-            assertThat(field.isSynthetic(), is(true));
-            assertThat(filter.test(field), is(false));
-        }
-    }
-
-    @Test
-    void defaultFilterFiltersFinalStaticTransientFields()
-            throws NoSuchFieldException {
-        Field field = CWFSTF.getDeclaredField("i");
-        assertThat(Modifier.isFinal(field.getModifiers()), is(true));
-        assertThat(filter.test(field), is(false));
-
-        field = CWFSTF.getDeclaredField("j");
-        assertThat(Modifier.isStatic(field.getModifiers()), is(true));
-        assertThat(filter.test(field), is(false));
-
-        field = CWFSTF.getDeclaredField("k");
-        assertThat(Modifier.isTransient(field.getModifiers()), is(true));
-        assertThat(filter.test(field), is(false));
-    }
-
     private static Converter<Object, Object> converter = SIMPLE_TYPE_CONVERTER;
 
     private static ConversionInfo newInfo(String fieldName, Object o) {
@@ -479,8 +434,8 @@ class FieldMapperTest {
         for (String cls : classes) {
             for (Number number : numbers) {
                 ConversionInfo info = newInfo(cls);
-                Object conv = converter.convertFrom(number, info);
-                assertThat(conv, instanceOf(info.getFieldType()));
+                Object converted = converter.convertFrom(number, info);
+                assertThat(converted, instanceOf(info.getFieldType()));
             }
         }
     }
@@ -521,11 +476,30 @@ class FieldMapperTest {
         assertThat(a.ex, sameInstance(cls));
     }
 
-    private static final class ClassWithFinalStaticTransientField {
-        private final int i = 0;
-        private static int j;
-        private transient int k;
+    @Test
+    void fieldMapperUsesFiltersAdded() {
+        class A {
+            private int a = 1;
+            private int b = 2;
+            private int c = 3;
+            private transient int d = 4;
+            private final int e = 5;
+        }
+        Configuration.Properties props = Configuration.Properties.builder()
+                .addFilter(field -> !field.getName().equals("a"))
+                .addFilter(field -> !field.getName().equals("c"))
+                .build();
+
+        Map<String, Object> map = instanceToMap(new A(), props);
+        assertThat(map.size(), is(1));
+        assertThat(map, is(mapOf("b", 2)));
+
+        map = mapOf("a", -1, "b", -2, "c", -3, "d", -4, "e", -5);
+        A a = instanceFromMap(new A(), map, props);
+        assertThat(a.a, is(1));
+        assertThat(a.b, is(-2));
+        assertThat(a.c, is(3));
+        assertThat(a.d, is(4));
+        assertThat(a.e, is(5));
     }
-
-    private final class ClassWithSyntheticField {}
 }

ConfigLib-Core/src/test/java/de/exlll/configlib/ValidatorTest.java

@@ -1,6 +1,5 @@
 package de.exlll.configlib;
 
-import de.exlll.configlib.FieldMapperHelpers.*;
 import de.exlll.configlib.annotation.ConfigurationElement;
 import de.exlll.configlib.annotation.ElementType;
 import de.exlll.configlib.classes.TestSubClass;

ConfigLib-Core/src/test/java/de/exlll/configlib/classes/ClassWithFinalStaticTransientField.java

@@ -0,0 +1,7 @@
+package de.exlll.configlib.classes;
+
+public final class ClassWithFinalStaticTransientField {
+    private final int i = 0;
+    private static int j;
+    private transient int k;
+}

ConfigLib-Core/src/test/java/de/exlll/configlib/classes/TestSubClass.java

@@ -99,34 +99,6 @@ public final class TestSubClass {
         return string;
     }
 
-    public List<String> getList() {
-        return list;
-    }
-
-    public Set<String> getSet() {
-        return set;
-    }
-
-    public Map<String, Integer> getMap() {
-        return map;
-    }
-
-    public TestSubSubClass getTestSubSubClass() {
-        return testSubSubClass;
-    }
-
-    public List<TestSubSubClass> getSubClassList() {
-        return subClassList;
-    }
-
-    public Set<TestSubSubClass> getSubClassSet() {
-        return subClassSet;
-    }
-
-    public Map<String, TestSubSubClass> getSubClassMap() {
-        return subClassMap;
-    }
-
     @Override
     public String toString() {
         return "TestSubClass{" +

ConfigLib-Core/src/test/java/de/exlll/configlib/classes/TestSubSubClass.java

@@ -46,26 +46,6 @@ public final class TestSubSubClass {
         return asMap;
     }
 
-    public int getPrimInt() {
-        return primInt;
-    }
-
-    public String getString() {
-        return string;
-    }
-
-    public List<String> getList() {
-        return list;
-    }
-
-    public Set<String> getSet() {
-        return set;
-    }
-
-    public Map<String, Integer> getMap() {
-        return map;
-    }
-
     @Override
     public String toString() {
         return "TestSubSubClass{" +

ConfigLib-Core/src/test/java/de/exlll/configlib/configs/yaml/YamlConfigurationTest.java

@@ -40,7 +40,7 @@ class YamlConfigurationTest {
     }
 
     @Test
-    void loadAndSaveExecutesPostLoadHook() throws IOException {
+    void loadAndSaveExecutesPostLoadHook() {
         class A extends YamlConfiguration {
             int i = 0;
 
@@ -58,7 +58,7 @@ class YamlConfigurationTest {
     }
 
     @Test
-    void loadAndSaveSavesConfiguration() throws IOException {
+    void loadAndSaveSavesConfiguration() {
         YamlConfiguration configuration = new TestClass(
                 configPath, TestClass.TEST_VALUES
         );
@@ -71,7 +71,7 @@ class YamlConfigurationTest {
     }
 
     @Test
-    void loadAndSaveLoadsConfiguration() throws IOException {
+    void loadAndSaveLoadsConfiguration() {
         new TestClass(configPath, TestClass.TEST_VALUES).save();
 
         YamlConfiguration configuration = new TestClass(configPath);
@@ -81,7 +81,7 @@ class YamlConfigurationTest {
     }
 
     @Test
-    void loadLoadsConfig() throws IOException {
+    void loadLoadsConfig() {
         setupConfigPath();
         Configuration configuration = new TestClass(configPath);
         assertThat(configuration, is(not(TestClass.TEST_VALUES)));
@@ -89,7 +89,7 @@ class YamlConfigurationTest {
         assertThat(configuration, is((TestClass.TEST_VALUES)));
     }
 
-    private void setupConfigPath() throws IOException {
+    private void setupConfigPath() {
         Configuration configuration = new TestClass(
                 configPath, TestClass.TEST_VALUES
         );
@@ -97,14 +97,14 @@ class YamlConfigurationTest {
     }
 
     @Test
-    void loadThrowsExceptionIfTypesDontMatch() throws IOException {
+    void loadThrowsExceptionIfTypesDoNotMatch() {
         Configuration configuration = new TestClass(configPath);
         configuration.save();
         assertThrows(IllegalArgumentException.class, configuration::load);
     }
 
     @Test
-    void saveCreatesConfig() throws IOException {
+    void saveCreatesConfig() {
         assertThat(Files.exists(testPath), is(false));
         Configuration configuration = new TestClass(testPath);
         configuration.save();

ConfigLib-Core/src/test/java/de/exlll/configlib/filter/FieldFilterTest.java

@@ -0,0 +1,58 @@
+package de.exlll.configlib.filter;
+
+import de.exlll.configlib.classes.ClassWithFinalStaticTransientField;
+import org.junit.jupiter.api.Test;
+
+import java.lang.reflect.Field;
+import java.lang.reflect.Modifier;
+import java.util.List;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.is;
+
+class FieldFilterTest {
+    private static final FieldFilter filter = FieldFilters.DEFAULT;
+    private static final Class<ClassWithFinalStaticTransientField> CWFSTF =
+            ClassWithFinalStaticTransientField.class;
+
+    @Test
+    void filteredFieldsFiltersFields() throws NoSuchFieldException {
+        List<? extends Field> fields = filter.filterDeclaredFieldsOf(CWFSTF);
+        assertThat(fields.size(), is(0));
+
+        class A {
+            private int i;
+            private final int j = 0;
+            private transient int k;
+        }
+        fields = filter.filterDeclaredFieldsOf(A.class);
+        assertThat(fields.size(), is(1));
+        assertThat(fields.get(0), is(A.class.getDeclaredField("i")));
+    }
+
+    @Test
+    void defaultFilterFiltersSyntheticFields() {
+        for (Field field : ClassWithSyntheticField.class.getDeclaredFields()) {
+            assertThat(field.isSynthetic(), is(true));
+            assertThat(filter.test(field), is(false));
+        }
+    }
+
+    @Test
+    void defaultFilterFiltersFinalStaticTransientFields()
+            throws NoSuchFieldException {
+        Field field = CWFSTF.getDeclaredField("i");
+        assertThat(Modifier.isFinal(field.getModifiers()), is(true));
+        assertThat(filter.test(field), is(false));
+
+        field = CWFSTF.getDeclaredField("j");
+        assertThat(Modifier.isStatic(field.getModifiers()), is(true));
+        assertThat(filter.test(field), is(false));
+
+        field = CWFSTF.getDeclaredField("k");
+        assertThat(Modifier.isTransient(field.getModifiers()), is(true));
+        assertThat(filter.test(field), is(false));
+    }
+
+    private final class ClassWithSyntheticField {}
+}

ConfigLib-Core/src/test/java/de/exlll/configlib/util/CollectionFactory.java

@@ -46,6 +46,14 @@ public final class CollectionFactory {
         return map;
     }
 
+    public static <K, V> Map<K, V> mapOf(
+            K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5
+    ) {
+        Map<K, V> map = mapOf(k1, v1, k2, v2, k3, v3, k4, v4);
+        map.put(k5, v5);
+        return map;
+    }
+
     public static <K, V> Map.Entry<K, V> mapEntry(K k, V v) {
         return new MapEntry<>(k, v);
     }

README.md

@@ -325,6 +325,24 @@ YamlProperties properties = YamlProperties.builder()
 
 Note: Changing the configuration style may break adding comments using the `@Comment` annotation.
 
+##### Adding field filters
+If your configuration has a lot of fields and you want to exclude some of these fields without
+making them final, static or transient, you can configure your properties object to use additional
+`FieldFilter`s. A `FieldFilter` filters the fields of a configuration class by a specified criterion.
+
+For example, if you only want to include fields whose names don't start with _ignore_, you would add
+the following filter:
+
+```java
+YamlProperties properties = YamlProperties.builder()
+                .addFilter(field -> !field.getName().startsWith("ignore"))
+                // ...
+                .build();
+```
+
+Note: A filter is not evaluated for a field if the field has already been filtered or by some
+other `FieldFilter`.
+
 #### Adding custom converters
 Any field can be converted using a custom converter. This can be useful if you don't like the default
 conversion mechanism or if you have classes that cannot be annotated as `ConfigurationElement`s
@@ -447,14 +465,14 @@ public final class DatabasePlugin extends JavaPlugin {
 <dependency>
     <groupId>de.exlll</groupId>
     <artifactId>configlib-bukkit</artifactId>
-    <version>2.0.3</version>
+    <version>2.1.0</version>
 </dependency>
 
 <!-- for Bungee plugins -->
 <dependency>
     <groupId>de.exlll</groupId>
     <artifactId>configlib-bungee</artifactId>
-    <version>2.0.3</version>
+    <version>2.1.0</version>
 </dependency>
 ```
 #### Gradle
@@ -466,9 +484,9 @@ repositories {
 }
 dependencies {
     // for Bukkit plugins
-    compile group: 'de.exlll', name: 'configlib-bukkit', version: '2.0.3'
+    compile group: 'de.exlll', name: 'configlib-bukkit', version: '2.1.0'
 
     // for Bungee plugins
-    compile group: 'de.exlll', name: 'configlib-bungee', version: '2.0.3'
+    compile group: 'de.exlll', name: 'configlib-bungee', version: '2.1.0'
 }
 ```

build.gradle

@@ -1,6 +1,6 @@
 allprojects {
     group 'de.exlll'
-    version '2.0.3'
+    version '2.1.0'
 }
 subprojects {
     apply plugin: 'java'

docs/tutorial.md

@@ -1,5 +1,3 @@
-## Tutorial
-
 This tutorial is intended to show most of the features of this library, so let's say that
 we want to create the following configuration file for some kind of game:
 
@@ -220,9 +218,8 @@ public final class GameConfig extends BukkitYamlConfiguration {
 }
 ```
 
-`ConfigurationElement`s must have a no-args constructor which is to create
-instances of a given element. If the no-args constructor is a valid constructor
-for your program, it must initialize the fields to some non-`null` value.
+`ConfigurationElement`s must have a no-args constructor which is used to create
+instances of a given element.
 
 #### 7. Add `usersByName`
 
@@ -298,7 +295,7 @@ public final class GameConfig extends BukkitYamlConfiguration {
 The `arenaHeight` can simply be represented by an `int` field. The `arenaCenter`
 is of type `Location`. We could again use the `@NoConvert` annotation but this
 would result in a different representation. Instead, we are going to implement our
-`Converter`.
+own `Converter`.
 
 First we have to create a class that implements `Converter<Location, String>`:
 
@@ -351,8 +348,8 @@ public final class GameConfig extends BukkitYamlConfiguration {
 
 Before we can use our new configuration, we have to instantiate it by passing
 a `Path` and a `BukkitYamlProperties` object to its constructor. In this case
-the `BukkitYamlProperties` is used to change the formatting and to append
-additional text to the created configuration file.
+the `BukkitYamlProperties` is used to change the formatting of field names,
+to append text to the configuration file and to add an additional field filter.
 
 ```java
 public final class GamePlugin extends JavaPlugin {
@@ -362,12 +359,12 @@ public final class GamePlugin extends JavaPlugin {
         Path configPath = new File(getDataFolder(), "config.yml").toPath();
 
         BukkitYamlProperties properties = BukkitYamlProperties.builder()
+                .addFilter(field -> !field.getName().startsWith("ignore"))
                 .setFormatter(FieldNameFormatters.LOWER_UNDERSCORE)
                 .setAppendedComments(Arrays.asList(
                         "", "Remember to play fair!"
                 ))
                 .build();
-
         GameConfig config = new GameConfig(configPath, properties);
         config.loadAndSave();
     }
@@ -403,6 +400,7 @@ public final class GamePlugin extends JavaPlugin {
         Path configPath = new File(getDataFolder(), "config.yml").toPath();
 
         BukkitYamlProperties properties = BukkitYamlProperties.builder()
+                .addFilter(field -> !field.getName().startsWith("ignore"))
                 .setFormatter(FieldNameFormatters.LOWER_UNDERSCORE)
                 .setAppendedComments(Arrays.asList(
                         "", "Remember to play fair!"
@@ -442,6 +440,8 @@ final class GameConfig extends BukkitYamlConfiguration {
     private Location arenaCenter = new Location(
             Bukkit.getWorld("world"), 0, 128, 0
     );
+    private String ignoreMe = "1";
+    private String ignoreMeToo = "2";
 
     public GameConfig(Path path, BukkitYamlProperties properties) {
         super(path, properties);
@@ -503,6 +503,14 @@ final class User {
         this.credentials = new Credentials(username, password);
         this.email = email;
     }
+
+    public Credentials getCredentials() {
+        return credentials;
+    }
+
+    public String getEmail() {
+        return email;
+    }
 }
 
 @ConfigurationElement
@@ -517,5 +525,13 @@ final class Credentials {
         this.username = username;
         this.password = password;
     }
+
+    public String getUsername() {
+        return username;
+    }
+
+    public String getPassword() {
+        return password;
+    }
 }
 ```