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/jsontype/impl/AsWrapperTypeDeserializer.java

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

import java.io.IOException;

import com.fasterxml.jackson.annotation.JsonTypeInfo.As;
import com.fasterxml.jackson.core.*;
import com.fasterxml.jackson.core.util.JsonParserSequence;
import com.fasterxml.jackson.databind.*;
import com.fasterxml.jackson.databind.jsontype.TypeDeserializer;
import com.fasterxml.jackson.databind.jsontype.TypeIdResolver;
import com.fasterxml.jackson.databind.util.TokenBuffer;

/**
 * Type deserializer used with {@link As#WRAPPER_OBJECT}
 * inclusion mechanism. Simple since JSON structure used is always
 * the same, regardless of structure used for actual value: wrapping
 * is done using a single-element JSON Object where type id is the key,
 * and actual object data as the value.
 */
public class AsWrapperTypeDeserializer
    extends TypeDeserializerBase
    implements java.io.Serializable
{
    private static final long serialVersionUID = 1L;

    /**
     * @since 2.8
     */
    public AsWrapperTypeDeserializer(JavaType bt, TypeIdResolver idRes,
            String typePropertyName, boolean typeIdVisible, JavaType defaultImpl)
    {
        super(bt, idRes, typePropertyName, typeIdVisible, defaultImpl);
    }

    protected AsWrapperTypeDeserializer(AsWrapperTypeDeserializer src, BeanProperty property) {
        super(src, property);
    }
    
    @Override
    public TypeDeserializer forProperty(BeanProperty prop) {
        return (prop == _property) ? this : new AsWrapperTypeDeserializer(this, prop);
    }
    
    @Override
    public As getTypeInclusion() { return As.WRAPPER_OBJECT; }

    /**
     * Deserializing type id enclosed using WRAPPER_OBJECT style is straightforward
     */
    @Override
    public Object deserializeTypedFromObject(JsonParser jp, DeserializationContext ctxt) throws IOException {
        return _deserialize(jp, ctxt);
    }    

    @Override
    public Object deserializeTypedFromArray(JsonParser jp, DeserializationContext ctxt) throws IOException {
        return _deserialize(jp, ctxt);
    }

    @Override
    public Object deserializeTypedFromScalar(JsonParser jp, DeserializationContext ctxt) throws IOException {
        return _deserialize(jp, ctxt);
    }

    @Override
    public Object deserializeTypedFromAny(JsonParser jp, DeserializationContext ctxt) throws IOException {
        return _deserialize(jp, ctxt);
    }
    
    /*
    /***************************************************************
    /* Internal methods
    /***************************************************************
     */

    /**
     * Method that handles type information wrapper, locates actual
     * subtype deserializer to use, and calls it to do actual
     * deserialization.
     */
    @SuppressWarnings("resource")
    protected Object _deserialize(JsonParser p, DeserializationContext ctxt) throws IOException
    {
        // 02-Aug-2013, tatu: May need to use native type ids
        if (p.canReadTypeId()) {
            Object typeId = p.getTypeId();
            if (typeId != null) {
                return _deserializeWithNativeTypeId(p, ctxt, typeId);
            }
        }
        // first, sanity checks
        JsonToken t = p.currentToken();
        if (t == JsonToken.START_OBJECT) {
            // should always get field name, but just in case...
            if (p.nextToken() != JsonToken.FIELD_NAME) {
                ctxt.reportWrongTokenException(baseType(), JsonToken.FIELD_NAME,
                        "need JSON String that contains type id (for subtype of "+baseTypeName()+")");
            }
        } else if (t != JsonToken.FIELD_NAME) {
            ctxt.reportWrongTokenException(baseType(), JsonToken.START_OBJECT,
                    "need JSON Object to contain As.WRAPPER_OBJECT type information for class "+baseTypeName());
        }
        final String typeId = p.getText();
        JsonDeserializer<Object> deser = _findDeserializer(ctxt, typeId);
        p.nextToken();

        // Minor complication: we may need to merge type id in?
        if (_typeIdVisible && p.hasToken(JsonToken.START_OBJECT)) {
            // but what if there's nowhere to add it in? Error? Or skip? For now, skip.
            TokenBuffer tb = new TokenBuffer(null, false);
            tb.writeStartObject(); // recreate START_OBJECT
            tb.writeFieldName(_typePropertyName);
            tb.writeString(typeId);
            // 02-Jul-2016, tatu: Depending on for JsonParserSequence is initialized it may
            //   try to access current token; ensure there isn't one
            p.clearCurrentToken();
            p = JsonParserSequence.createFlattened(false, tb.asParser(p), p);
            p.nextToken();
        }
        
        Object value = deser.deserialize(p, ctxt);
        // And then need the closing END_OBJECT
        if (p.nextToken() != JsonToken.END_OBJECT) {
            ctxt.reportWrongTokenException(baseType(), JsonToken.END_OBJECT,
                    "expected closing END_OBJECT after type information and deserialized value");
        }
        return value;
    }
}

⏎ com/fasterxml/jackson/databind/jsontype/impl/AsWrapperTypeDeserializer.java

 

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