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

Jackson Databind Source Code files are provided in the source packge (jackson-databind-2.14.0-sources.jar). You can download it at Jackson Maven Website.

You can also browse Jackson Databind Source Code below:

⏎ com/fasterxml/jackson/databind/deser/std/StdDelegatingDeserializer.java

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

import java.io.IOException;

import com.fasterxml.jackson.core.JsonParser;

import com.fasterxml.jackson.databind.*;
import com.fasterxml.jackson.databind.deser.ContextualDeserializer;
import com.fasterxml.jackson.databind.deser.ResolvableDeserializer;
import com.fasterxml.jackson.databind.jsontype.TypeDeserializer;
import com.fasterxml.jackson.databind.type.LogicalType;
import com.fasterxml.jackson.databind.util.ClassUtil;
import com.fasterxml.jackson.databind.util.Converter;

/**
 * Deserializer implementation where given Java type is first deserialized
 * by a standard Jackson deserializer into a delegate type; and then
 * this delegate type is converted using a configured
 * {@link Converter} into desired target type.
 * Common delegate types to use are {@link java.util.Map}
 * and {@link com.fasterxml.jackson.databind.JsonNode}.
 *<p>
 * Note that although types (delegate, target) may be related, they must not be same; trying
 * to do this will result in an exception.
 *<p>
 * Since 2.5 There is {@link StdNodeBasedDeserializer} that is a simplified version
 * for cases where intermediate type is {@link JsonNode}
 * 
 * @param <T> Target type to convert to, from delegate type
 * 
 * @since 2.1
 * 
 * @see StdNodeBasedDeserializer
 * @see Converter
 */
public class StdDelegatingDeserializer<T>
    extends StdDeserializer<T>
    implements ContextualDeserializer, ResolvableDeserializer
{
    private static final long serialVersionUID = 1L;

    /**
     * Converter that was used for creating {@link #_delegateDeserializer}.
     */
    protected final Converter<Object,T> _converter;

    /**
     * Fully resolved delegate type, with generic information if any available.
     */
    protected final JavaType _delegateType;

    /**
     * Underlying serializer for type <code>T</code>.
     */
    protected final JsonDeserializer<Object> _delegateDeserializer;

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

    @SuppressWarnings("unchecked")
    public StdDelegatingDeserializer(Converter<?,T> converter)
    {
        super(Object.class);
        _converter = (Converter<Object,T>)converter;
        _delegateType = null;
        _delegateDeserializer = null;
    }

    @SuppressWarnings("unchecked")
    public StdDelegatingDeserializer(Converter<Object,T> converter,
            JavaType delegateType, JsonDeserializer<?> delegateDeserializer)
    {
        super(delegateType);
        _converter = converter;
        _delegateType = delegateType;
        _delegateDeserializer = (JsonDeserializer<Object>) delegateDeserializer;
    }

    /**
     * @since 2.5
     */
    protected StdDelegatingDeserializer(StdDelegatingDeserializer<T> src)
    {
        super(src);
        _converter = src._converter;
        _delegateType = src._delegateType;
        _delegateDeserializer = src._delegateDeserializer;
    }

    /**
     * Method used for creating resolved contextual instances. Must be
     * overridden when sub-classing.
     */
    protected StdDelegatingDeserializer<T> withDelegate(Converter<Object,T> converter,
            JavaType delegateType, JsonDeserializer<?> delegateDeserializer)
    {
        ClassUtil.verifyMustOverride(StdDelegatingDeserializer.class, this, "withDelegate");
        return new StdDelegatingDeserializer<T>(converter, delegateType, delegateDeserializer);
    }

    /*
    /**********************************************************
    /* Contextualization
    /**********************************************************
     */

    // Note: unlikely to get called since most likely instances explicitly constructed;
    // if so, caller must ensure delegating deserializer is properly resolve()d.
    @Override
    public void resolve(DeserializationContext ctxt)
        throws JsonMappingException
    {
        if (_delegateDeserializer != null && _delegateDeserializer instanceof ResolvableDeserializer) {
            ((ResolvableDeserializer) _delegateDeserializer).resolve(ctxt);
        }
    }

    @Override
    public JsonDeserializer<?> createContextual(DeserializationContext ctxt, BeanProperty property)
        throws JsonMappingException
    {
        // First: if already got deserializer to delegate to, contextualize it:
        if (_delegateDeserializer != null) {
            JsonDeserializer<?> deser = ctxt.handleSecondaryContextualization(_delegateDeserializer,
                    property, _delegateType);
            if (deser != _delegateDeserializer) {
                return withDelegate(_converter, _delegateType, deser);
            }
            return this;
        }
        // Otherwise: figure out what is the fully generic delegate type, then find deserializer
        JavaType delegateType = _converter.getInputType(ctxt.getTypeFactory());
        return withDelegate(_converter, delegateType,
                ctxt.findContextualValueDeserializer(delegateType, property));
    }

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

    @Override
    public JsonDeserializer<?> getDelegatee() {
        return _delegateDeserializer;
    }

    @Override
    public Class<?> handledType() {
        return _delegateDeserializer.handledType();
    }

    @Override // since 2.12
    public LogicalType logicalType() {
        return _delegateDeserializer.logicalType();
    }
    
    @Override // since 2.9
    public Boolean supportsUpdate(DeserializationConfig config) {
        return _delegateDeserializer.supportsUpdate(config);
    }

    /*
    /**********************************************************
    /* Serialization
    /**********************************************************
     */
    
    @Override
    public T deserialize(JsonParser p, DeserializationContext ctxt) throws IOException
    {
        Object delegateValue = _delegateDeserializer.deserialize(p, ctxt);
        if (delegateValue == null) {
            return null;
        }
        return convertValue(delegateValue);
    }

    @Override
    public Object deserializeWithType(JsonParser p, DeserializationContext ctxt,
            TypeDeserializer typeDeserializer) throws IOException
    {
        /* 12-Apr-2016, tatu: As predicted, earlier handling does not work
         *   (see [databind#1189] for details). There does not seem to be any compelling
         *   way to combine polymorphic types, Converters, but the least sucky way
         *   is probably to use Converter and ignore polymorphic type. Alternative
         *   would be to try to change `TypeDeserializer` to accept `Converter` to
         *   invoke... but that is more intrusive, yet not guaranteeing success.
         */
        // method called up to 2.7.3:
//        Object delegateValue = _delegateDeserializer.deserializeWithType(p, ctxt, typeDeserializer);

        // method called since 2.7.4
        Object delegateValue = _delegateDeserializer.deserialize(p, ctxt);
        if (delegateValue == null) {
            return null;
        }
        return convertValue(delegateValue);
    }

    @SuppressWarnings("unchecked")
    @Override
    public T deserialize(JsonParser p, DeserializationContext ctxt, Object intoValue)
        throws IOException
    {
        if (_delegateType.getRawClass().isAssignableFrom(intoValue.getClass())){
            return (T) _delegateDeserializer.deserialize(p, ctxt, intoValue);
        }
        return (T) _handleIncompatibleUpdateValue(p, ctxt, intoValue);
    }

    /**
     * Overridable handler method called when {@link #deserialize(JsonParser, DeserializationContext, Object)}
     * has been called with a value that is not compatible with delegate value.
     * Since no conversion are expected for such "updateValue" case, this is normally not
     * an operation that can be permitted, and the default behavior is to throw exception.
     * Sub-classes may choose to try alternative approach if they have more information on
     * exact usage and constraints.
     *
     * @since 2.6
     */
    protected Object _handleIncompatibleUpdateValue(JsonParser p, DeserializationContext ctxt, Object intoValue)
        throws IOException
    {
        throw new UnsupportedOperationException(String.format
                ("Cannot update object of type %s (using deserializer for type %s)"
                        +intoValue.getClass().getName(), _delegateType));
    }
    
    /*
    /**********************************************************
    /* Overridable methods
    /**********************************************************
     */

    /**
     * Method called to convert from "delegate value" (which was deserialized
     * from JSON using standard Jackson deserializer for delegate type)
     * into desired target type.
     *<P>
     * The default implementation uses configured {@link Converter} to do
     * conversion.
     * 
     * @param delegateValue
     * 
     * @return Result of conversion
     */
    protected T convertValue(Object delegateValue) {
        return _converter.convert(delegateValue);
    }
}

⏎ com/fasterxml/jackson/databind/deser/std/StdDelegatingDeserializer.java

Or download all of them as a single archive file:

File name: jackson-databind-2.14.0-sources.jar
File size: 1187952 bytes
Release date: 2022-11-05
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