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-2.12.4-sources.jar). You can download it at Jackson Maven Website.

You can also browse Jackson Databind Source Code below:

⏎ com/fasterxml/jackson/databind/deser/impl/MergingSettableBeanProperty.java

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

import java.io.IOException;

import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.deser.*;
import com.fasterxml.jackson.databind.introspect.AnnotatedMember;

/**
 * {@link SettableBeanProperty} implementation that will try to access value of
 * the property first, and if non-null value found, pass that for update
 * (using {@link com.fasterxml.jackson.databind.JsonDeserializer#deserialize(com.fasterxml.jackson.core.JsonParser, com.fasterxml.jackson.databind.DeserializationContext, Object)})
 * instead of constructing a new value. This is necessary to support "merging" properties.
 *<p>
 * Note that there are many similarities to {@link SetterlessProperty}, which predates
 * this variant; and that one is even used in cases where there is no mutator
 * available.
 *
 * @since 2.9
 */
public class MergingSettableBeanProperty
    extends SettableBeanProperty.Delegating
{
    private static final long serialVersionUID = 1L;

    /**
     * Member (field, method) used for accessing existing value.
     */
    protected final AnnotatedMember _accessor;

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

    protected MergingSettableBeanProperty(SettableBeanProperty delegate,
            AnnotatedMember accessor)
    {
        super(delegate);
        _accessor = accessor;
    }

    protected MergingSettableBeanProperty(MergingSettableBeanProperty src,
            SettableBeanProperty delegate)
    {
        super(delegate);
        _accessor = src._accessor;
    }

    public static MergingSettableBeanProperty construct(SettableBeanProperty delegate,
            AnnotatedMember accessor)
    {
        return new MergingSettableBeanProperty(delegate, accessor);
    }

    @Override
    protected SettableBeanProperty withDelegate(SettableBeanProperty d) {
        return new MergingSettableBeanProperty(d, _accessor);
    }

    /*
    /**********************************************************
    /* Deserialization methods
    /**********************************************************
     */

    @Override
    public void deserializeAndSet(JsonParser p, DeserializationContext ctxt,
            Object instance) throws IOException
    {
        Object oldValue = _accessor.getValue(instance);
        Object newValue;
        // 20-Oct-2016, tatu: Couple of possibilities of how to proceed; for
        //    now, default to "normal" handling without merging
        if (oldValue == null) {
            newValue = delegate.deserialize(p, ctxt);
        } else {
            newValue = delegate.deserializeWith(p, ctxt, oldValue);
        }
        if (newValue != oldValue) {
            // 18-Apr-2017, tatu: Null handling should occur within delegate, which may
            //     set/skip/transform it, or throw an exception.
            delegate.set(instance, newValue);
        }
    }

    @Override
    public Object deserializeSetAndReturn(JsonParser p,
            DeserializationContext ctxt, Object instance) throws IOException
    {
        Object oldValue = _accessor.getValue(instance);
        Object newValue;
        // 20-Oct-2016, tatu: Couple of possibilities of how to proceed; for
        //    now, default to "normal" handling without merging
        if (oldValue == null) {
            newValue = delegate.deserialize(p, ctxt);
        } else {
            newValue = delegate.deserializeWith(p, ctxt, oldValue);
        }
        // 23-Oct-2016, tatu: One possible complication here; should we always
        //    try calling setter on builder? Presumably should not be required,
        //    but may need to revise
        if (newValue != oldValue) {
            // 31-Oct-2016, tatu: Basically should just ignore as null can't really
            //    contribute to merging.
            if (newValue != null) {
                return delegate.setAndReturn(instance, newValue);
            }
        }
        return instance;
    }

    @Override
    public void set(Object instance, Object value) throws IOException {
        // 31-Oct-2016, tatu: Basically should just ignore as null can't really
        //    contribute to merging.
        if (value != null) {
            delegate.set(instance, value);
        }
    }

    @Override
    public Object setAndReturn(Object instance, Object value) throws IOException {
        // 31-Oct-2016, tatu: Basically should just ignore as null can't really
        //    contribute to merging.
        if (value != null) {
            return delegate.setAndReturn(instance, value);
        }
        return instance;
    }
}

⏎ com/fasterxml/jackson/databind/deser/impl/MergingSettableBeanProperty.java

 

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