com.fasterxml.jackson.core

Interface TreeNode

public interface TreeNode

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

Method Summary

Modifier and Type	Method and Description
JsonToken	asToken() Method that can be used for efficient type detection when using stream abstraction for traversing nodes.
TreeNode	at(JsonPointer ptr) Method for locating node specified by given JSON pointer instances.
TreeNode	at(String jsonPointerExpression) Convenience method that is functionally equivalent to:
Iterator<String>	fieldNames() Method for accessing names of all fields for this node, iff this node is an Object node.
TreeNode	get(int index) Method for accessing value of the specified element of an array node.
TreeNode	get(String fieldName) Method for accessing value of the specified field of an object node.
boolean	isArray() Method that returns true if this node is an Array node, false otherwise.
boolean	isContainerNode() Method that returns true for container nodes: Arrays and Objects.
boolean	isMissingNode() 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.
boolean	isObject() Method that returns true if this node is an Object node, false otherwise.
boolean	isValueNode() Method that returns true for all value nodes: ones that are not containers, and that do not represent "missing" nodes in the path.
JsonParser.NumberType	numberType() 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.
TreeNode	path(int index) Method for accessing value of the specified element of an array node.
TreeNode	path(String fieldName) Method for accessing value of the specified field of an object node.
int	size() 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.
JsonParser	traverse() Method for constructing a JsonParser instance for iterating over contents of the tree that this node is root of.
JsonParser	traverse(ObjectCodec codec) Same as traverse(), but additionally passes ObjectCodec to use if JsonParser.readValueAs(Class) is used (otherwise caller must call JsonParser.setCodec(com.fasterxml.jackson.core.ObjectCodec) on response explicitly).

Method Detail

asToken

JsonToken asToken()

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

numberType

JsonParser.NumberType numberType()

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.

size

int size()

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

isValueNode

boolean isValueNode()

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

isContainerNode

boolean isContainerNode()

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

isMissingNode

boolean isMissingNode()

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

isArray

boolean isArray()

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

isObject

boolean isObject()

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

get

TreeNode get(String fieldName)

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.

Parameters:

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

get

TreeNode get(int index)

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.

Parameters:

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

path

TreeNode path(String fieldName)

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.

Parameters:

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

path

TreeNode path(int index)

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.

Parameters:

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

fieldNames

Iterator<String> fieldNames()

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

at

TreeNode at(JsonPointer ptr)

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.

Parameters:

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

at

TreeNode at(String jsonPointerExpression)
     throws IllegalArgumentException

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.

Parameters:

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).

Throws:

IllegalArgumentException

Since:

2.3

traverse

JsonParser traverse()

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) will not work with calling JsonParser.setCodec(com.fasterxml.jackson.core.ObjectCodec)). It is often better to call traverse(ObjectCodec) to pass the codec explicitly.

Returns:

JsonParser that will stream over contents of this node

traverse

JsonParser traverse(ObjectCodec codec)

Same as traverse(), but additionally passes ObjectCodec to use if JsonParser.readValueAs(Class) is used (otherwise caller must call JsonParser.setCodec(com.fasterxml.jackson.core.ObjectCodec) 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().

Parameters:

codec - ObjectCodec to associate with parser constructed

Returns:

JsonParser that will stream over contents of this node

Since:

2.1