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/* Jackson JSON-processor.
*
* Copyright (c) 2007- Tatu Saloranta, [email protected]
*/
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 {@link 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
*/
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 {@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 {@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.
*
* @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 {@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 {@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 {@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, {@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, {@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.
*
* @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.
*
* @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 {@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 {@link #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.
*
* @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, if (and only if)
* 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 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 {@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
* {@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 {@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.
*
* 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()}.
*
* Also note that calling this method will NOT 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 {@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).
*
* 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);
}