Jackson is "the Java JSON library" or "the best JSON parser for Java". Or simply as "JSON for Java".

Jackson Annotations Source Code files are provided in the source packge (jackson-annotations-2.12.4-sources.jar). You can download it at Jackson Maven Website.

You can also browse Jackson Annotations Source Code below:

⏎ com/fasterxml/jackson/databind/ser/std/ObjectArraySerializer.java

package com.fasterxml.jackson.databind.ser.std;

import java.io.IOException;
import java.util.Objects;

import com.fasterxml.jackson.annotation.JsonFormat;

import com.fasterxml.jackson.core.*;

import com.fasterxml.jackson.databind.*;
import com.fasterxml.jackson.databind.annotation.JacksonStdImpl;
import com.fasterxml.jackson.databind.introspect.AnnotatedMember;
import com.fasterxml.jackson.databind.jsonFormatVisitors.JsonArrayFormatVisitor;
import com.fasterxml.jackson.databind.jsonFormatVisitors.JsonFormatVisitorWrapper;
import com.fasterxml.jackson.databind.jsontype.TypeSerializer;
import com.fasterxml.jackson.databind.ser.ContainerSerializer;
import com.fasterxml.jackson.databind.ser.ContextualSerializer;
import com.fasterxml.jackson.databind.ser.impl.PropertySerializerMap;

/**
 * Generic serializer for Object arrays (<code>Object[]</code>).
 */
@JacksonStdImpl
@SuppressWarnings("serial")
public class ObjectArraySerializer
    extends ArraySerializerBase<Object[]>
    implements ContextualSerializer
{
    /**
     * Whether we are using static typing (using declared types, ignoring
     * runtime type) or not for elements.
     */
    protected final boolean _staticTyping;

    /**
     * Declared type of element entries
     */
    protected final JavaType _elementType;

    /**
     * Type serializer to use for values, if any.
     */
    protected final TypeSerializer _valueTypeSerializer;
    
    /**
     * Value serializer to use, if it can be statically determined.
     */
    protected JsonSerializer<Object> _elementSerializer;

    /**
     * If element type cannot be statically determined, mapping from
     * runtime type to serializer is handled using this object
     */
    protected PropertySerializerMap _dynamicSerializers;

    /*
    /**********************************************************
    /* Life-cycle
    /**********************************************************
     */

    public ObjectArraySerializer(JavaType elemType, boolean staticTyping,
            TypeSerializer vts, JsonSerializer<Object> elementSerializer)
    {
        super(Object[].class);
        _elementType = elemType;
        _staticTyping = staticTyping;
        _valueTypeSerializer = vts;
        _dynamicSerializers = PropertySerializerMap.emptyForProperties();
        _elementSerializer = elementSerializer;
    }

    public ObjectArraySerializer(ObjectArraySerializer src, TypeSerializer vts)
    {
        super(src);
        _elementType = src._elementType;
        _valueTypeSerializer = vts;
        _staticTyping = src._staticTyping;
        // 22-Nov-2018, tatu: probably safe (even with [databind#2181]) since it's just
        //   inclusion, type serializer but NOT serializer
        _dynamicSerializers = src._dynamicSerializers;
        _elementSerializer = src._elementSerializer;
    }

    @SuppressWarnings("unchecked")
    public ObjectArraySerializer(ObjectArraySerializer src,
            BeanProperty property, TypeSerializer vts, JsonSerializer<?> elementSerializer,
            Boolean unwrapSingle)
    {
        super(src,  property, unwrapSingle);
        _elementType = src._elementType;
        _valueTypeSerializer = vts;
        _staticTyping = src._staticTyping;
        // [databind#2181]: may not be safe to reuse, start from empty
        _dynamicSerializers = PropertySerializerMap.emptyForProperties();
        _elementSerializer = (JsonSerializer<Object>) elementSerializer;
    }

    @Override
    public JsonSerializer<?> _withResolved(BeanProperty prop, Boolean unwrapSingle) {
        return new ObjectArraySerializer(this, prop,
                _valueTypeSerializer, _elementSerializer, unwrapSingle);
    }
    
    @Override
    public ContainerSerializer<?> _withValueTypeSerializer(TypeSerializer vts) {
        return new ObjectArraySerializer(_elementType, _staticTyping, vts, _elementSerializer);
    }

    public ObjectArraySerializer withResolved(BeanProperty prop,
            TypeSerializer vts, JsonSerializer<?> ser, Boolean unwrapSingle) {
        if ((_property == prop) && (ser == _elementSerializer)
                && (_valueTypeSerializer == vts) && (Objects.equals(_unwrapSingle, unwrapSingle))) {
            return this;
        }
        return new ObjectArraySerializer(this, prop, vts, ser, unwrapSingle);
    }

    /*
    /**********************************************************
    /* Post-processing
    /**********************************************************
     */

    @Override
    public JsonSerializer<?> createContextual(SerializerProvider serializers,
            BeanProperty property)
        throws JsonMappingException
    {
        TypeSerializer vts = _valueTypeSerializer;
        if (vts != null) {
            vts = vts.forProperty(property);
        }
        JsonSerializer<?> ser = null;
        Boolean unwrapSingle = null;

        // First: if we have a property, may have property-annotation overrides
        if (property != null) {
            AnnotatedMember m = property.getMember();
            final AnnotationIntrospector intr = serializers.getAnnotationIntrospector();
            if (m != null) {
                Object serDef = intr.findContentSerializer(m);
                if (serDef != null) {
                    ser = serializers.serializerInstance(m, serDef);
                }
            }
        }
        JsonFormat.Value format = findFormatOverrides(serializers, property, handledType());
        if (format != null) {
            unwrapSingle = format.getFeature(JsonFormat.Feature.WRITE_SINGLE_ELEM_ARRAYS_UNWRAPPED);
        }
        if (ser == null) {
            ser = _elementSerializer;
        }
        // [databind#124]: May have a content converter
        ser = findContextualConvertingSerializer(serializers, property, ser);
        if (ser == null) {
            // 30-Sep-2012, tatu: One more thing -- if explicit content type is annotated,
            //   we can consider it a static case as well.
            if (_elementType != null) {
                if (_staticTyping && !_elementType.isJavaLangObject()) {
                    ser = serializers.findContentValueSerializer(_elementType, property);
                }
            }
        }
        return withResolved(property, vts, ser, unwrapSingle);
    }

    /*
    /**********************************************************
    /* Accessors
    /**********************************************************
     */

    @Override
    public JavaType getContentType() {
        return _elementType;
    }

    @Override
    public JsonSerializer<?> getContentSerializer() {
        return _elementSerializer;
    }

    @Override
    public boolean isEmpty(SerializerProvider prov, Object[] value) {
        return value.length == 0;
    }

    @Override
    public boolean hasSingleElement(Object[] value) {
        return (value.length == 1);
    }

    /*
    /**********************************************************
    /* Actual serialization
    /**********************************************************
     */

    @Override
    public final void serialize(Object[] value, JsonGenerator gen, SerializerProvider provider) throws IOException
    {
        final int len = value.length;
        if (len == 1) {
            if (((_unwrapSingle == null) &&
                    provider.isEnabled(SerializationFeature.WRITE_SINGLE_ELEM_ARRAYS_UNWRAPPED))
                    || (_unwrapSingle == Boolean.TRUE)) {
                serializeContents(value, gen, provider);
                return;
            }
        }
        gen.writeStartArray(value, len);
        serializeContents(value, gen, provider);
        gen.writeEndArray();
    }

    @Override
    public void serializeContents(Object[] value, JsonGenerator gen, SerializerProvider provider) throws IOException
    {
        final int len = value.length;
        if (len == 0) {
            return;
        }
        if (_elementSerializer != null) {
            serializeContentsUsing(value, gen, provider, _elementSerializer);
            return;
        }
        if (_valueTypeSerializer != null) {
            serializeTypedContents(value, gen, provider);
            return;
        }
        int i = 0;
        Object elem = null;
        try {
            PropertySerializerMap serializers = _dynamicSerializers;
            for (; i < len; ++i) {
                elem = value[i];
                if (elem == null) {
                    provider.defaultSerializeNull(gen);
                    continue;
                }
                Class<?> cc = elem.getClass();
                JsonSerializer<Object> serializer = serializers.serializerFor(cc);
                if (serializer == null) {
                    if (_elementType.hasGenericTypes()) {
                        serializer = _findAndAddDynamic(serializers,
                                provider.constructSpecializedType(_elementType, cc), provider);
                    } else {
                        serializer = _findAndAddDynamic(serializers, cc, provider);
                    }
                }
                serializer.serialize(elem, gen, provider);
            }
        } catch (Exception e) {
            wrapAndThrow(provider, e, elem, i);
        }
    }

    public void serializeContentsUsing(Object[] value, JsonGenerator jgen, SerializerProvider provider,
            JsonSerializer<Object> ser) throws IOException
    {
        final int len = value.length;
        final TypeSerializer typeSer = _valueTypeSerializer;

        int i = 0;
        Object elem = null;
        try {
            for (; i < len; ++i) {
                elem = value[i];
                if (elem == null) {
                    provider.defaultSerializeNull(jgen);
                    continue;
                }
                if (typeSer == null) {
                    ser.serialize(elem, jgen, provider);
                } else {
                    ser.serializeWithType(elem, jgen, provider, typeSer);
                }
            }
        } catch (Exception e) {
            wrapAndThrow(provider, e, elem, i);
        }
    }

    public void serializeTypedContents(Object[] value, JsonGenerator jgen, SerializerProvider provider) throws IOException
    {
        final int len = value.length;
        final TypeSerializer typeSer = _valueTypeSerializer;
        int i = 0;
        Object elem = null;
        try {
            PropertySerializerMap serializers = _dynamicSerializers;
            for (; i < len; ++i) {
                elem = value[i];
                if (elem == null) {
                    provider.defaultSerializeNull(jgen);
                    continue;
                }
                Class<?> cc = elem.getClass();
                JsonSerializer<Object> serializer = serializers.serializerFor(cc);
                if (serializer == null) {
                    serializer = _findAndAddDynamic(serializers, cc, provider);
                }
                serializer.serializeWithType(elem, jgen, provider, typeSer);
            }
        } catch (Exception e) {
            wrapAndThrow(provider, e, elem, i);
        }
    }

    @Override
    public void acceptJsonFormatVisitor(JsonFormatVisitorWrapper visitor, JavaType typeHint)
        throws JsonMappingException
    {
        JsonArrayFormatVisitor arrayVisitor = visitor.expectArrayFormat(typeHint);
        if (arrayVisitor != null) {
            JavaType contentType = _elementType;

            // [databind#1793]: Was getting `null` for `typeHint`. But why would we even use it...
/*
            TypeFactory tf = visitor.getProvider().getTypeFactory();
            contentType = tf.moreSpecificType(_elementType, typeHint.getContentType());
            if (contentType == null) {
                visitor.getProvider().reportBadDefinition(_elementType,
                        "Could not resolve type: "+_elementType);
            }
*/
            JsonSerializer<?> valueSer = _elementSerializer;
            if (valueSer == null) {
                valueSer = visitor.getProvider().findContentValueSerializer(contentType, _property);
            }
            arrayVisitor.itemsFormat(valueSer, contentType);
        }
    }

    protected final JsonSerializer<Object> _findAndAddDynamic(PropertySerializerMap map,
            Class<?> type, SerializerProvider provider) throws JsonMappingException
    {
        PropertySerializerMap.SerializerAndMapResult result = map.findAndAddSecondarySerializer(type, provider, _property);
        // did we get a new map of serializers? If so, start using it
        if (map != result.map) {
            _dynamicSerializers = result.map;
        }
        return result.serializer;
    }

    protected final JsonSerializer<Object> _findAndAddDynamic(PropertySerializerMap map,
            JavaType type, SerializerProvider provider) throws JsonMappingException
    {
        PropertySerializerMap.SerializerAndMapResult result = map.findAndAddSecondarySerializer(type, provider, _property);
        // did we get a new map of serializers? If so, start using it
        if (map != result.map) {
            _dynamicSerializers = result.map;
        }
        return result.serializer;
    }
}

⏎ com/fasterxml/jackson/databind/ser/std/ObjectArraySerializer.java

 

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