src/main/java/com/fasterxml/jackson/databind/node/BaseJsonNode.java

package com.fasterxml.jackson.databind.node;

import java.io.IOException;

import com.fasterxml.jackson.core.*;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.JsonSerializable;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.databind.jsontype.TypeSerializer;

/**
 * Abstract base class common to all standard {@link JsonNode}
 * implementations.
 * The main addition here is that we declare that sub-classes must
 * implement {@link JsonSerializable}.
 * This simplifies object mapping aspects a bit, as no external serializers are needed.
 *<p>
 * Since 2.10, all implements have been {@link java.io.Serializable}.
 */
public abstract class BaseJsonNode
    extends JsonNode
    implements java.io.Serializable
{
    private static final long serialVersionUID = 1L;

    // Simplest way is by using a helper
    Object writeReplace() {
        return NodeSerialization.from(this);
    }

    protected BaseJsonNode() { }

    /*
    /**********************************************************
    /* Basic definitions for non-container types
    /**********************************************************
     */

    @Override
    public final JsonNode findPath(String fieldName)
    {
        JsonNode value = findValue(fieldName);
        if (value == null) {
            return MissingNode.getInstance();
        }
        return value;
    }

    // Also, force (re)definition (2.7)
    @Override public abstract int hashCode();

    /*
    /**********************************************************************
    /* Improved required-ness checks for standard JsonNode implementations
    /**********************************************************************
     */

    @Override
    public JsonNode required(String fieldName) {
        return _reportRequiredViolation("Node of type `%s` has no fields",
                getClass().getSimpleName());
    }

    @Override
    public JsonNode required(int index) {
        return _reportRequiredViolation("Node of type `%s` has no indexed values",
                getClass().getSimpleName());
    }

    /*
    /**********************************************************
    /* Support for traversal-as-stream
    /**********************************************************
     */

    @Override
    public JsonParser traverse() {
        return new TreeTraversingParser(this);
    }

    @Override
    public JsonParser traverse(ObjectCodec codec) {
        return new TreeTraversingParser(this, codec);
    }
    
    /**
     * Method that can be used for efficient type detection
     * when using stream abstraction for traversing nodes.
     * Will return the first {@link JsonToken} that equivalent
     * stream event would produce (for most nodes there is just
     * one token but for structured/container types multiple)
     */
    @Override
    public abstract JsonToken asToken();

    /**
     * Returns code that identifies type of underlying numeric
     * value, if (and only if) node is a number node.
     */
    @Override
    public JsonParser.NumberType numberType() {
        // most types non-numeric, so:
        return null; 
    }

    /*
    /**********************************************************
    /* JsonSerializable
    /**********************************************************
     */

    /**
     * Method called to serialize node instances using given generator.
     */
    @Override
    public abstract void serialize(JsonGenerator jgen, SerializerProvider provider)
        throws IOException, JsonProcessingException;

    /**
     * Type information is needed, even if JsonNode instances are "plain" JSON,
     * since they may be mixed with other types.
     */
   @Override
    public abstract void serializeWithType(JsonGenerator jgen, SerializerProvider provider,
            TypeSerializer typeSer)
        throws IOException, JsonProcessingException;

   /*
   /**********************************************************
   /* Standard method overrides
   /**********************************************************
    */

   @Override
   public String toString() {
       return InternalNodeMapper.nodeToString(this);
   }

   @Override
   public String toPrettyString() {
       return InternalNodeMapper.nodeToPrettyString(this);
   }
}