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/AsArrayTypeDeserializer.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_ARRAY}
 * inclusion mechanism. Simple since JSON structure used is always
 * the same, regardless of structure used for actual value: wrapping
 * is done using a 2-element JSON Array where type id is the first
 * element, and actual object data as second element.
 */
public class AsArrayTypeDeserializer
    extends TypeDeserializerBase
    implements java.io.Serializable
{
    private static final long serialVersionUID = 1L;

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

    public AsArrayTypeDeserializer(AsArrayTypeDeserializer src, BeanProperty property) {
        super(src, property);
    }
    
    @Override
    public TypeDeserializer forProperty(BeanProperty prop) {
        // usually if it's null:
        return (prop == _property) ? this : new AsArrayTypeDeserializer(this, prop);
    }
    
    @Override
    public As getTypeInclusion() { return As.WRAPPER_ARRAY; }

    /**
     * Method called when actual object is serialized as JSON Array.
     */
    @Override
    public Object deserializeTypedFromArray(JsonParser jp, DeserializationContext ctxt) throws IOException {
        return _deserialize(jp, ctxt);
    }

    /**
     * Method called when actual object is serialized as JSON Object
     */
    @Override
    public Object deserializeTypedFromObject(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);
            }
        }
        boolean hadStartArray = p.isExpectedStartArrayToken();
        String typeId = _locateTypeId(p, ctxt);
        JsonDeserializer<Object> deser = _findDeserializer(ctxt, typeId);
        // Minor complication: we may need to merge type id in?
        if (_typeIdVisible
                // 06-Oct-2014, tatu: To fix [databind#408], must distinguish between
                //   internal and external properties
                //  TODO: but does it need to be injected in external case? Why not?
                && !_usesExternalId()
                && 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();
        }
        // [databind#2467] (2.10): Allow missing value to be taken as "just use null value"
        if (hadStartArray && p.currentToken() == JsonToken.END_ARRAY) {
            return deser.getNullValue(ctxt);
        }
        Object value = deser.deserialize(p, ctxt);
        // And then need the closing END_ARRAY
        if (hadStartArray && p.nextToken() != JsonToken.END_ARRAY) {
            ctxt.reportWrongTokenException(baseType(), JsonToken.END_ARRAY,
                    "expected closing END_ARRAY after type information and deserialized value");
            // 05-May-2016, tatu: Not 100% what to do if exception is stored for
            //     future, and not thrown immediately: should probably skip until END_ARRAY

            // ... but for now, fall through
        }
        return value;
    }    
    
    protected String _locateTypeId(JsonParser p, DeserializationContext ctxt) throws IOException
    {
        if (!p.isExpectedStartArrayToken()) {
            // Need to allow even more customized handling, if something unexpected seen...
            // but should there be a way to limit this to likely success cases?
            if (_defaultImpl != null) {
                return _idResolver.idFromBaseType();
            }
             ctxt.reportWrongTokenException(baseType(), JsonToken.START_ARRAY,
                     "need JSON Array to contain As.WRAPPER_ARRAY type information for class "+baseTypeName());
             return null;
        }
        // And then type id as a String
        JsonToken t = p.nextToken();
        if (t == JsonToken.VALUE_STRING) {
            String result = p.getText();
            p.nextToken();
            return result;
        }

        // 11-Nov-2020, tatu: I don't think this branch ever gets executed by
        //    unit tests so do not think it would actually work; commented out
        //    in 2.12.0
/*        if (_defaultImpl != null) {
            p.nextToken();
            return _idResolver.idFromBaseType();
        }
        */

        // 11-Nov-202, tatu: points to wrong place since we don't pass JsonParser
        //   we actually use (which is usually TokenBuffer created)... should fix
        ctxt.reportWrongTokenException(baseType(), JsonToken.VALUE_STRING,
                "need JSON String that contains type id (for subtype of %s)", baseTypeName());
        return null;
    }

    /**
     * @since 2.5
     */
    protected boolean _usesExternalId() {
        return false;
    }
}

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

 

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