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/jsontype/TypeDeserializer.java

package com.fasterxml.jackson.databind.jsontype;

import java.io.IOException;

import com.fasterxml.jackson.core.*;
import com.fasterxml.jackson.databind.BeanProperty;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JavaType;
import com.fasterxml.jackson.databind.JsonDeserializer;
import com.fasterxml.jackson.annotation.JsonTypeInfo.As;


/**
 * Interface for deserializing type information from JSON content, to
 * type-safely deserialize data into correct polymorphic instance
 * (when type inclusion has been enabled for type handled).
 *<p>
 * Separate deserialization methods are needed because serialized
 * form for inclusion mechanism {@link As#PROPERTY}
 * is slighty different if value is not expressed as JSON Object:
 * and as such both type deserializer and serializer need to
 * JSON Object form (array, object or other (== scalar)) being used.
 */
public abstract class TypeDeserializer
{
    /*
    /**********************************************************
    /* Initialization
    /**********************************************************
     */

    /**
     * Method called to create contextual version, to be used for
     * values of given property. This may be the type itself
     * (as is the case for bean properties), or values contained
     * (for {@link java.util.Collection} or {@link java.util.Map}
     * valued properties).
     */
    public abstract TypeDeserializer forProperty(BeanProperty prop);

    /*
    /**********************************************************
    /* Introspection
    /**********************************************************
     */

    /**
     * Accessor for type information inclusion method
     * that deserializer uses; indicates how type information
     * is (expected to be) embedded in JSON input.
     */
    public abstract As getTypeInclusion();

    /**
     * Name of property that contains type information, if
     * property-based inclusion is used.
     */
    public abstract String getPropertyName();

    /**
     * Accessor for object that handles conversions between
     * types and matching type ids.
     */
    public abstract TypeIdResolver getTypeIdResolver();

    /**
     * Accessor for "default implementation" type; optionally defined
     * class to use in cases where type id is not
     * accessible for some reason (either missing, or cannot be
     * resolved)
     */
    public abstract Class<?> getDefaultImpl();

    /**
     * @since 2.12
     */
    public boolean hasDefaultImpl() { return getDefaultImpl() != null; }

    /*
    /**********************************************************
    /* Type deserialization methods
    /**********************************************************
     */

    /**
     * Method called to let this type deserializer handle 
     * deserialization of "typed" object, when value itself
     * is serialized as JSON Object (regardless of Java type).
     * Method needs to figure out intended
     * polymorphic type, locate {@link JsonDeserializer} to use, and
     * call it with JSON data to deserializer (which does not contain
     * type information).
     */
    public abstract Object deserializeTypedFromObject(JsonParser p, DeserializationContext ctxt) throws IOException;

    /**
     * Method called to let this type deserializer handle 
     * deserialization of "typed" object, when value itself
     * is serialized as JSON Array (regardless of Java type).
     * Method needs to figure out intended
     * polymorphic type, locate {@link JsonDeserializer} to use, and
     * call it with JSON data to deserializer (which does not contain
     * type information).
     */
    public abstract Object deserializeTypedFromArray(JsonParser p, DeserializationContext ctxt) throws IOException;

    /**
     * Method called to let this type deserializer handle 
     * deserialization of "typed" object, when value itself
     * is serialized as a scalar JSON value (something other
     * than Array or Object), regardless of Java type.
     * Method needs to figure out intended
     * polymorphic type, locate {@link JsonDeserializer} to use, and
     * call it with JSON data to deserializer (which does not contain
     * type information).
     */
    public abstract Object deserializeTypedFromScalar(JsonParser p, DeserializationContext ctxt) throws IOException;

    /**
     * Method called to let this type deserializer handle 
     * deserialization of "typed" object, when value itself
     * may have been serialized using any kind of JSON value
     * (Array, Object, scalar). Should only be called if JSON
     * serialization is polymorphic (not Java type); for example when
     * using JSON node representation, or "untyped" Java object
     * (which may be Map, Collection, wrapper/primitive etc).
     */
    public abstract Object deserializeTypedFromAny(JsonParser p, DeserializationContext ctxt) throws IOException;

    /*
    /**********************************************************
    /* Shared helper methods
    /**********************************************************
     */

    /**
     * Helper method used to check if given parser might be pointing to
     * a "natural" value, and one that would be acceptable as the
     * result value (compatible with declared base type)
     */
    public static Object deserializeIfNatural(JsonParser p, DeserializationContext ctxt, JavaType baseType) throws IOException {
        return deserializeIfNatural(p, ctxt, baseType.getRawClass());
    }

    @SuppressWarnings("incomplete-switch")
    public static Object deserializeIfNatural(JsonParser p, DeserializationContext ctxt,
            Class<?> base) throws IOException
    {
        final JsonToken t = p.currentToken();
        if (t == null) {
            return null;
        }
        switch (t) {
        case VALUE_STRING:
            if (base.isAssignableFrom(String.class)) {
                return p.getText();
            }
            break;
        case VALUE_NUMBER_INT:
            if (base.isAssignableFrom(Integer.class)) {
                return p.getIntValue();
            }
            break;

        case VALUE_NUMBER_FLOAT:
            if (base.isAssignableFrom(Double.class)) {
                return Double.valueOf(p.getDoubleValue());
            }
            break;
        case VALUE_TRUE:
            if (base.isAssignableFrom(Boolean.class)) {
                return Boolean.TRUE;
            }
            break;
        case VALUE_FALSE:
            if (base.isAssignableFrom(Boolean.class)) {
                return Boolean.FALSE;
            }
            break;
        }
        return null;
    }
}
    

⏎ com/fasterxml/jackson/databind/jsontype/TypeDeserializer.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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