https://github.com/FasterXML/jackson-core: Core Jackson processing abstractions (aka Streaming API), implementation for JSON (FasterXML)
  • Tatu Saloranta 
/* Jackson JSON-processor.
 *
 * Copyright (c) 2007- Tatu Saloranta, tatu.saloranta@iki.fi
 */

package com.fasterxml.jackson.core;

import java.util.Iterator;


Marker interface used to denote JSON Tree nodes, as far as the core package knows them (which is very little): mostly needed to allow ObjectCodec to have some level of interoperability. Most functionality is within JsonNode
base class in mapper package.


Note that in Jackson 1.x JsonNode itself
was part of core package: Jackson 2.x refactored this
since conceptually Tree Model is part of mapper package,
and so part visible to core package should
be minimized.


NOTE: starting with Jackson 2.2, there is more functionality
available via this class, and the intent was that this should
form actual base for multiple alternative tree representations;
for example, immutable trees could use different implementation
than mutable trees.

Since:2.2
/**
 * Marker interface used to denote JSON Tree nodes, as far as
 * the core package knows them (which is very little): mostly
 * needed to allow {@link ObjectCodec} to have some level
 * of interoperability.
 * Most functionality is within <code>JsonNode</code>
 * base class in <code>mapper</code> package.
 *<p>
 * Note that in Jackson 1.x <code>JsonNode</code> itself
 * was part of core package: Jackson 2.x refactored this
 * since conceptually Tree Model is part of mapper package,
 * and so part visible to <code>core</code> package should
 * be minimized.
 *<p>
 * NOTE: starting with Jackson 2.2, there is more functionality
 * available via this class, and the intent was that this should
 * form actual base for multiple alternative tree representations;
 * for example, immutable trees could use different implementation
 * than mutable trees.
 * 
 * @since 2.2
 */
public interface TreeNode
{
    /*
    /**********************************************************
    /* Minimal introspection methods
    /**********************************************************
     */
    
    
Method that can be used for efficient type detection when using stream abstraction for traversing nodes. Will return the first JsonToken that equivalent stream event would produce (for most nodes there is just one token but for structured/container types multiple) 
Returns:JsonToken that is most closely associated with the node type
/**
     * 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)
     *
     * @return {@link JsonToken} that is most closely associated with the node type
     */
    JsonToken asToken();

    
If this node is a numeric type (as per JsonToken.isNumeric), returns native type that node uses to store the numeric value; otherwise returns null. 
Returns:Type of number contained, if any; or null if node does not
 contain numeric value.
/**
     * If this node is a numeric type (as per {@link JsonToken#isNumeric}),
     * returns native type that node uses to store the numeric value;
     * otherwise returns null.
     * 
     * @return Type of number contained, if any; or null if node does not
     *  contain numeric value.
     */
    JsonParser.NumberType numberType();

    
Method that returns number of child nodes this node contains:
for Array nodes, number of child elements, for Object nodes,
number of fields, and for all other nodes 0.

Returns:For non-container nodes returns 0; for arrays number of
  contained elements, and for objects number of fields.
Since:2.2
/**
     * Method that returns number of child nodes this node contains:
     * for Array nodes, number of child elements, for Object nodes,
     * number of fields, and for all other nodes 0.
     *
     * @return For non-container nodes returns 0; for arrays number of
     *   contained elements, and for objects number of fields.
     * 
     * @since 2.2
     */
    int size();

    
Method that returns true for all value nodes: ones that 
are not containers, and that do not represent "missing" nodes
in the path. Such value nodes represent String, Number, Boolean
and null values from JSON.

 Note: one and only one of methods isValueNode, isContainerNode and isMissingNode ever returns true for any given node. 
Returns:True if this node is considered a value node; something that represents either a scalar value or explicit null
Since:2.2
/**
     * Method that returns true for all value nodes: ones that 
     * are not containers, and that do not represent "missing" nodes
     * in the path. Such value nodes represent String, Number, Boolean
     * and null values from JSON.
     *<p>
     * Note: one and only one of methods {@link #isValueNode},
     * {@link #isContainerNode} and {@link #isMissingNode} ever
     * returns true for any given node.
     *
     * @return True if this node is considered a value node; something that
     *    represents either a scalar value or explicit {@code null}
     * 
     * @since 2.2
     */
    boolean isValueNode();

    
Method that returns true for container nodes: Arrays and Objects.

 Note: one and only one of methods isValueNode, isContainerNode and isMissingNode ever returns true for any given node. 
Returns:True for Array and Object nodes, false otherwise
Since:2.2
/**
     * Method that returns true for container nodes: Arrays and Objects.
     *<p>
     * Note: one and only one of methods {@link #isValueNode},
     * {@link #isContainerNode} and {@link #isMissingNode} ever
     * returns true for any given node.
     *
     * @return {@code True} for Array and Object nodes, {@code false} otherwise
     * 
     * @since 2.2
     */
    boolean isContainerNode();
    
    
Method that returns true for "virtual" nodes which represent
missing entries constructed by path accessor methods when
there is no actual node matching given criteria.

 Note: one and only one of methods isValueNode, isContainerNode and isMissingNode ever returns true for any given node. 
Returns:True if this node represents a "missing" node
Since:2.2
/**
     * Method that returns true for "virtual" nodes which represent
     * missing entries constructed by path accessor methods when
     * there is no actual node matching given criteria.
     *<p>
     * Note: one and only one of methods {@link #isValueNode},
     * {@link #isContainerNode} and {@link #isMissingNode} ever
     * returns true for any given node.
     *
     * @return {@code True} if this node represents a "missing" node
     * 
     * @since 2.2
     */
    boolean isMissingNode();
    
    
Method that returns true if this node is an Array node, false otherwise. Note that if true is returned, isContainerNode must also return true. 
Returns:True for Array nodes, false for everything else
Since:2.2
/**
     * Method that returns true if this node is an Array node, false
     * otherwise.
     * Note that if true is returned, {@link #isContainerNode}
     * must also return true.
     *
     * @return {@code True} for Array nodes, {@code false} for everything else
     *
     * @since 2.2
     */
    boolean isArray();

    
Method that returns true if this node is an Object node, false otherwise. Note that if true is returned, isContainerNode must also return true. 
Returns:True for Object nodes, false for everything else
Since:2.2
/**
     * Method that returns true if this node is an Object node, false
     * otherwise.
     * Note that if true is returned, {@link #isContainerNode}
     * must also return true.
     *
     * @return {@code True} for Object nodes, {@code false} for everything else
     * 
     * @since 2.2
     */
    boolean isObject();

    /*
    /**********************************************************
    /* Basic traversal through structured entries (Arrays, Objects)
    /**********************************************************
     */

    
Method for accessing value of the specified field of
an object node. If this node is not an object (or it
does not have a value for specified field name), or
if there is no field with such name, null is returned.


NOTE: handling of explicit null values may vary between
implementations; some trees may retain explicit nulls, others
not.

Params:
  • fieldName – Name of the field (of Object node) to access
Returns:Node that represent value of the specified field, if this node is an Object and has value for the specified field; null otherwise.
Since:2.2
/**
     * Method for accessing value of the specified field of
     * an object node. If this node is not an object (or it
     * does not have a value for specified field name), or
     * if there is no field with such name, null is returned.
     *<p>
     * NOTE: handling of explicit null values may vary between
     * implementations; some trees may retain explicit nulls, others
     * not.
     *
     * @param fieldName Name of the field (of Object node) to access
     *
     * @return Node that represent value of the specified field,
     *   if this node is an Object and has value for the specified
     *   field; {@code null} otherwise.
     * 
     * @since 2.2
     */
    TreeNode get(String fieldName);

    
Method for accessing value of the specified element of
an array node. For other nodes, null is returned.


For array nodes, index specifies
exact location within array and allows for efficient iteration
over child elements (underlying storage is guaranteed to
be efficiently indexable, i.e. has random-access to elements).
If index is less than 0, or equal-or-greater than
node.size(), null is returned; no exception is
thrown for any index.

Params:
  • index – Index of the Array node element to access
Returns:Node that represent value of the specified element, if this node is an array and has specified element; null otherwise.
Since:2.2
/**
     * Method for accessing value of the specified element of
     * an array node. For other nodes, null is returned.
     *<p>
     * For array nodes, index specifies
     * exact location within array and allows for efficient iteration
     * over child elements (underlying storage is guaranteed to
     * be efficiently indexable, i.e. has random-access to elements).
     * If index is less than 0, or equal-or-greater than
     * <code>node.size()</code>, null is returned; no exception is
     * thrown for any index.
     *
     * @param index Index of the Array node element to access
     *
     * @return Node that represent value of the specified element,
     *   if this node is an array and has specified element;
     *   {@code null} otherwise.
     * 
     * @since 2.2
     */
    TreeNode get(int index);

    
Method for accessing value of the specified field of an object node. For other nodes, a "missing node" (virtual node for which isMissingNode returns true) is returned. 
Params:
  • fieldName – Name of the field (of Object node) to access
Returns:Node that represent value of the specified field,
  if this node is an object and has value for the specified field;
  otherwise "missing node" is returned.
Since:2.2
/**
     * Method for accessing value of the specified field of
     * an object node.
     * For other nodes, a "missing node" (virtual node
     * for which {@link #isMissingNode} returns true) is returned.
     *
     * @param fieldName Name of the field (of Object node) to access
     *
     * @return Node that represent value of the specified field,
     *   if this node is an object and has value for the specified field;
     *   otherwise "missing node" is returned.
     * 
     * @since 2.2
     */
    TreeNode path(String fieldName);

    
Method for accessing value of the specified element of an array node. For other nodes, a "missing node" (virtual node for which isMissingNode returns true) is returned. 

For array nodes, index specifies
exact location within array and allows for efficient iteration
over child elements (underlying storage is guaranteed to
be efficiently indexable, i.e. has random-access to elements).
If index is less than 0, or equal-or-greater than
node.size(), "missing node" is returned; no exception is
thrown for any index.

Params:
  • index – Index of the Array node element to access
Returns:Node that represent value of the specified element,
  if this node is an array and has specified element;
  otherwise "missing node" is returned.
Since:2.2
/**
     * Method for accessing value of the specified element of
     * an array node.
     * For other nodes, a "missing node" (virtual node
     * for which {@link #isMissingNode} returns true) is returned.
     *<p>
     * For array nodes, index specifies
     * exact location within array and allows for efficient iteration
     * over child elements (underlying storage is guaranteed to
     * be efficiently indexable, i.e. has random-access to elements).
     * If index is less than 0, or equal-or-greater than
     * <code>node.size()</code>, "missing node" is returned; no exception is
     * thrown for any index.
     *
     * @param index Index of the Array node element to access
     *
     * @return Node that represent value of the specified element,
     *   if this node is an array and has specified element;
     *   otherwise "missing node" is returned.
     * 
     * @since 2.2
     */
    TreeNode path(int index);
    
    
Method for accessing names of all fields for this node, iff this node is an Object node. Number of field names accessible will be size. 
Returns:An iterator for traversing names of all fields this Object node has (if Object node); empty Iterator otherwise (never null).
Since:2.2
/**
     * Method for accessing names of all fields for this node, iff
     * this node is an Object node. Number of field names accessible
     * will be {@link #size}.
     *
     * @return An iterator for traversing names of all fields this Object node
     *   has (if Object node); empty {@link Iterator} otherwise (never {@code null}).
     *
     * @since 2.2
     */
    Iterator<String> fieldNames();

    
Method for locating node specified by given JSON pointer instances. Method will never return null; if no matching node exists, will return a node for which isMissingNode() returns true. 
Params:
  • ptr – JsonPointer expression for descendant node to return
Returns:Node that matches given JSON Pointer, if any: if no match exists, will return a "missing" node (for which isMissingNode() returns true).
Since:2.3
/**
     * Method for locating node specified by given JSON pointer instances.
     * Method will never return null; if no matching node exists, 
     * will return a node for which {@link TreeNode#isMissingNode()} returns true.
     *
     * @param ptr {@link JsonPointer} expression for descendant node to return
     *
     * @return Node that matches given JSON Pointer, if any: if no match exists,
     *   will return a "missing" node (for which {@link TreeNode#isMissingNode()}
     *   returns {@code true}).
     * 
     * @since 2.3
     */
    TreeNode at(JsonPointer ptr);

    
Convenience method that is functionally equivalent to:

  return at(JsonPointer.valueOf(jsonPointerExpression));



 Note that if the same expression is used often, it is preferable to construct JsonPointer instance once and reuse it: this method will not perform any caching of compiled expressions. 
Params:
  • jsonPointerExpression – Expression to compile as a JsonPointer instance
Returns:Node that matches given JSON Pointer, if any: if no match exists, will return a "missing" node (for which isMissingNode() returns true).
Since:2.3
/**
     * Convenience method that is functionally equivalent to:
     *<pre>
     *   return at(JsonPointer.valueOf(jsonPointerExpression));
     *</pre>
     *<p>
     * Note that if the same expression is used often, it is preferable to construct
     * {@link JsonPointer} instance once and reuse it: this method will not perform
     * any caching of compiled expressions.
     * 
     * @param jsonPointerExpression Expression to compile as a {@link JsonPointer}
     *   instance
     *
     * @return Node that matches given JSON Pointer, if any: if no match exists,
     *   will return a "missing" node (for which {@link TreeNode#isMissingNode()}
     *   returns {@code true}).
     * 
     * @since 2.3
     */
    TreeNode at(String jsonPointerExpression) throws IllegalArgumentException;
    
    /*
    /**********************************************************
    /* Converting to/from Streaming API
    /**********************************************************
     */

    
Method for constructing a JsonParser instance for iterating over contents of the tree that this node is root of. Functionally equivalent to first serializing tree using ObjectCodec and then re-parsing but more efficient. 
 NOTE: constructed parser instance will NOT initially point to a token, so before passing it to deserializers, it is typically necessary to advance it to the first available token by calling JsonParser.nextToken(). 

Also note that calling this method will NOT pass ObjectCodec reference, so data-binding callback methods like JsonParser.readValueAs(Class<Object>) will not work with calling JsonParser.setCodec). It is often better to call traverse(ObjectCodec) to pass the codec explicitly. 
Returns:JsonParser that will stream over contents of this node
/**
     * Method for constructing a {@link JsonParser} instance for
     * iterating over contents of the tree that this node is root of.
     * Functionally equivalent to first serializing tree using
     * {@link ObjectCodec} and then re-parsing but
     * more efficient.
     *<p>
     * NOTE: constructed parser instance will NOT initially point to a token,
     * so before passing it to deserializers, it is typically necessary to
     * advance it to the first available token by calling {@link JsonParser#nextToken()}.
     *<p>
     * Also note that calling this method will <b>NOT</b> pass {@link ObjectCodec}
     * reference, so data-binding callback methods like {@link JsonParser#readValueAs(Class)}
     * will not work with calling {@link JsonParser#setCodec}).
     * It is often better to call {@link #traverse(ObjectCodec)} to pass the codec explicitly.
     *
     * @return {@link JsonParser} that will stream over contents of this node
     */
    JsonParser traverse();

    
Same as traverse(), but additionally passes ObjectCodec to use if JsonParser.readValueAs(Class<Object>) is used (otherwise caller must call JsonParser.setCodec on response explicitly). 
 NOTE: constructed parser instance will NOT initially point to a token, so before passing it to deserializers, it is typically necessary to advance it to the first available token by calling JsonParser.nextToken(). 
Params:
  • codec – ObjectCodec to associate with parser constructed
Returns:JsonParser that will stream over contents of this node
Since:2.1
/**
     * Same as {@link #traverse()}, but additionally passes {@link com.fasterxml.jackson.core.ObjectCodec}
     * to use if {@link JsonParser#readValueAs(Class)} is used (otherwise caller must call
     * {@link JsonParser#setCodec} on response explicitly).
     *<p>
     * NOTE: constructed parser instance will NOT initially point to a token,
     * so before passing it to deserializers, it is typically necessary to
     * advance it to the first available token by calling {@link JsonParser#nextToken()}.
     *
     * @param codec {@link ObjectCodec} to associate with parser constructed
     *
     * @return {@link JsonParser} that will stream over contents of this node
     * 
     * @since 2.1
     */
    JsonParser traverse(ObjectCodec codec);
}