org.json
Class JSONObject

java.lang.Object
  org.json.JSONObject

public class JSONObject
extends java.lang.Object

A JSONObject is an unordered collection of name/value pairs. Its external form is a string wrapped in curly braces with colons between the names and values, and commas between the values and names. The internal form is an object having get and opt methods for accessing the values by name, and put methods for adding or replacing values by name. The values can be any of these types: Boolean, JSONArray, JSONObject, Number, String, or the JSONObject.NULL object. A JSONObject constructor can be used to convert an external form JSON text into an internal form whose values can be retrieved with the get and opt methods, or to convert values into a JSON text using the put and toString methods. A get method returns a value if one can be found, and throws an exception if one cannot be found. An opt method returns a default value instead of throwing an exception, and so is useful for obtaining optional values.

The generic get() and opt() methods return an object, which you can cast or query for type. There are also typed get and opt methods that do type checking and type coercion for you. The opt methods differ from the get methods in that they do not throw. Instead, they return a specified value, such as null.

The put methods add or replace values in an object. For example,

myString = new JSONObject().put("JSON", "Hello, World!").toString();

produces the string {"JSON": "Hello, World"}.

The texts produced by the toString methods strictly conform to the JSON syntax rules. The constructors are more forgiving in the texts they will accept:

• An extra , (comma) may appear just before the closing brace.
• Strings may be quoted with ' (single quote).
• Strings do not need to be quoted at all if they do not begin with a quote or single quote, and if they do not contain leading or trailing spaces, and if they do not contain any of these characters: { } [ ] / \ : , = ; # and if they do not look like numbers and if they are not the reserved words true, false, or null.
• Keys can be followed by = or => as well as by :.
• Values can be followed by ; (semicolon) as well as by , (comma).

Version:

2011-11-24

Author:

JSON.org

Field Summary

static java.lang.Object

NULL It is sometimes more convenient and less ambiguous to have a NULL object than to use Java's null value.

Constructor Summary

JSONObject()
Construct an empty JSONObject.

JSONObject(JSONObject jo, java.lang.String[] names)
Construct a JSONObject from a subset of another JSONObject.

JSONObject(JSONTokener x)
Construct a JSONObject from a JSONTokener.

JSONObject(java.util.Map map)
Construct a JSONObject from a Map.

JSONObject(java.lang.Object bean)
Construct a JSONObject from an Object using bean getters.

JSONObject(java.lang.Object object, java.lang.String[] names)
Construct a JSONObject from an Object, using reflection to find the public members.

JSONObject(java.lang.String source)
Construct a JSONObject from a source JSON text string.

JSONObject(java.lang.String baseName, java.util.Locale locale)
Construct a JSONObject from a ResourceBundle.

Method Summary

JSONObject	accumulate(java.lang.String key, java.lang.Object value) Accumulate values under a key.
JSONObject	append(java.lang.String key, java.lang.Object value) Append values to the array under a key.
static java.lang.String	doubleToString(double d) Produce a string from a double.
java.lang.Object	get(java.lang.String key) Get the value object associated with a key.
boolean	getBoolean(java.lang.String key) Get the boolean value associated with a key.
double	getDouble(java.lang.String key) Get the double value associated with a key.
int	getInt(java.lang.String key) Get the int value associated with a key.
JSONArray	getJSONArray(java.lang.String key) Get the JSONArray value associated with a key.
JSONObject	getJSONObject(java.lang.String key) Get the JSONObject value associated with a key.
long	getLong(java.lang.String key) Get the long value associated with a key.
static java.lang.String[]	getNames(JSONObject jo) Get an array of field names from a JSONObject.
static java.lang.String[]	getNames(java.lang.Object object) Get an array of field names from an Object.
java.lang.String	getString(java.lang.String key) Get the string associated with a key.
boolean	has(java.lang.String key) Determine if the JSONObject contains a specific key.
JSONObject	increment(java.lang.String key) Increment a property of a JSONObject.
boolean	isNull(java.lang.String key) Determine if the value associated with the key is null or if there is no value.
java.util.Iterator	keys() Get an enumeration of the keys of the JSONObject.
int	length() Get the number of keys stored in the JSONObject.
JSONArray	names() Produce a JSONArray containing the names of the elements of this JSONObject.
static java.lang.String	numberToString(java.lang.Number number) Produce a string from a Number.
java.lang.Object	opt(java.lang.String key) Get an optional value associated with a key.
boolean	optBoolean(java.lang.String key) Get an optional boolean associated with a key.
boolean	optBoolean(java.lang.String key, boolean defaultValue) Get an optional boolean associated with a key.
double	optDouble(java.lang.String key) Get an optional double associated with a key, or NaN if there is no such key or if its value is not a number.
double	optDouble(java.lang.String key, double defaultValue) Get an optional double associated with a key, or the defaultValue if there is no such key or if its value is not a number.
int	optInt(java.lang.String key) Get an optional int value associated with a key, or zero if there is no such key or if the value is not a number.
int	optInt(java.lang.String key, int defaultValue) Get an optional int value associated with a key, or the default if there is no such key or if the value is not a number.
JSONArray	optJSONArray(java.lang.String key) Get an optional JSONArray associated with a key.
JSONObject	optJSONObject(java.lang.String key) Get an optional JSONObject associated with a key.
long	optLong(java.lang.String key) Get an optional long value associated with a key, or zero if there is no such key or if the value is not a number.
long	optLong(java.lang.String key, long defaultValue) Get an optional long value associated with a key, or the default if there is no such key or if the value is not a number.
java.lang.String	optString(java.lang.String key) Get an optional string associated with a key.
java.lang.String	optString(java.lang.String key, java.lang.String defaultValue) Get an optional string associated with a key.
JSONObject	put(java.lang.String key, boolean value) Put a key/boolean pair in the JSONObject.
JSONObject	put(java.lang.String key, java.util.Collection value) Put a key/value pair in the JSONObject, where the value will be a JSONArray which is produced from a Collection.
JSONObject	put(java.lang.String key, double value) Put a key/double pair in the JSONObject.
JSONObject	put(java.lang.String key, int value) Put a key/int pair in the JSONObject.
JSONObject	put(java.lang.String key, long value) Put a key/long pair in the JSONObject.
JSONObject	put(java.lang.String key, java.util.Map value) Put a key/value pair in the JSONObject, where the value will be a JSONObject which is produced from a Map.
JSONObject	put(java.lang.String key, java.lang.Object value) Put a key/value pair in the JSONObject.
JSONObject	putOnce(java.lang.String key, java.lang.Object value) Put a key/value pair in the JSONObject, but only if the key and the value are both non-null, and only if there is not already a member with that name.
JSONObject	putOpt(java.lang.String key, java.lang.Object value) Put a key/value pair in the JSONObject, but only if the key and the value are both non-null.
static java.lang.String	quote(java.lang.String string) Produce a string in double quotes with backslash sequences in all the right places.
java.lang.Object	remove(java.lang.String key) Remove a name and its value, if present.
static java.lang.Object	stringToValue(java.lang.String string) Try to convert a string into a number, boolean, or null.
static void	testValidity(java.lang.Object o) Throw an exception if the object is a NaN or infinite number.
JSONArray	toJSONArray(JSONArray names) Produce a JSONArray containing the values of the members of this JSONObject.
java.lang.String	toString() Make a JSON text of this JSONObject.
java.lang.String	toString(int indentFactor) Make a prettyprinted JSON text of this JSONObject.
static java.lang.String	valueToString(java.lang.Object value) Make a JSON text of an Object value.
static java.lang.Object	wrap(java.lang.Object object) Wrap an object, if necessary.
java.io.Writer	write(java.io.Writer writer) Write the contents of the JSONObject as JSON text to a writer.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

NULL

public static final java.lang.Object NULL

It is sometimes more convenient and less ambiguous to have a NULL object than to use Java's null value. JSONObject.NULL.equals(null) returns true. JSONObject.NULL.toString() returns "null".

Constructor Detail

JSONObject

public JSONObject()

Construct an empty JSONObject.

JSONObject

public JSONObject(JSONObject jo,
                  java.lang.String[] names)

Construct a JSONObject from a subset of another JSONObject. An array of strings is used to identify the keys that should be copied. Missing keys are ignored.

Parameters:

jo - A JSONObject.

names - An array of strings.

Throws:

JSONException

JSONException - If a value is a non-finite number or if a name is duplicated.

JSONObject

public JSONObject(JSONTokener x)
           throws JSONException

Construct a JSONObject from a JSONTokener.

Parameters:

x - A JSONTokener object containing the source string.

Throws:

JSONException - If there is a syntax error in the source string or a duplicated key.

JSONObject

public JSONObject(java.util.Map map)

Construct a JSONObject from a Map.

Parameters:

map - A map object that can be used to initialize the contents of the JSONObject.

Throws:

JSONException

JSONObject

public JSONObject(java.lang.Object bean)

Construct a JSONObject from an Object using bean getters. It reflects on all of the public methods of the object. For each of the methods with no parameters and a name starting with "get" or "is" followed by an uppercase letter, the method is invoked, and a key and the value returned from the getter method are put into the new JSONObject. The key is formed by removing the "get" or "is" prefix. If the second remaining character is not upper case, then the first character is converted to lower case. For example, if an object has a method named "getName", and if the result of calling object.getName() is "Larry Fine", then the JSONObject will contain "name": "Larry Fine".

Parameters:

bean - An object that has getter methods that should be used to make a JSONObject.

JSONObject

public JSONObject(java.lang.Object object,
                  java.lang.String[] names)

Construct a JSONObject from an Object, using reflection to find the public members. The resulting JSONObject's keys will be the strings from the names array, and the values will be the field values associated with those keys in the object. If a key is not found or not visible, then it will not be copied into the new JSONObject.

Parameters:

object - An object that has fields that should be used to make a JSONObject.

names - An array of strings, the names of the fields to be obtained from the object.

JSONObject

public JSONObject(java.lang.String source)
           throws JSONException

Construct a JSONObject from a source JSON text string. This is the most commonly used JSONObject constructor.

Parameters:

source - A string beginning with { (left brace) and ending with } (right brace).

Throws:

JSONException - If there is a syntax error in the source string or a duplicated key.

JSONObject

public JSONObject(java.lang.String baseName,
                  java.util.Locale locale)
           throws JSONException

Construct a JSONObject from a ResourceBundle.

Parameters:

baseName - The ResourceBundle base name.

locale - The Locale to load the ResourceBundle for.

Throws:

JSONException - If any JSONExceptions are detected.

Method Detail

accumulate

public JSONObject accumulate(java.lang.String key,
                             java.lang.Object value)
                      throws JSONException

Accumulate values under a key. It is similar to the put method except that if there is already an object stored under the key then a JSONArray is stored under the key to hold all of the accumulated values. If there is already a JSONArray, then the new value is appended to it. In contrast, the put method replaces the previous value. If only one value is accumulated that is not a JSONArray, then the result will be the same as using put. But if multiple values are accumulated, then the result will be like append.

Parameters:

key - A key string.

value - An object to be accumulated under the key.

Returns:

this.

Throws:

JSONException - If the value is an invalid number or if the key is null.

append

public JSONObject append(java.lang.String key,
                         java.lang.Object value)
                  throws JSONException

Append values to the array under a key. If the key does not exist in the JSONObject, then the key is put in the JSONObject with its value being a JSONArray containing the value parameter. If the key was already associated with a JSONArray, then the value parameter is appended to it.

Parameters:

key - A key string.

value - An object to be accumulated under the key.

Returns:

this.

Throws:

JSONException - If the key is null or if the current value associated with the key is not a JSONArray.

doubleToString

public static java.lang.String doubleToString(double d)

Produce a string from a double. The string "null" will be returned if the number is not finite.

Parameters:

d - A double.

Returns:

A String.

get

public java.lang.Object get(java.lang.String key)
                     throws JSONException

Get the value object associated with a key.

Parameters:

key - A key string.

Returns:

The object associated with the key.

Throws:

JSONException - if the key is not found.

getBoolean

public boolean getBoolean(java.lang.String key)
                   throws JSONException

Get the boolean value associated with a key.

Parameters:

key - A key string.

Returns:

The truth.

Throws:

JSONException - if the value is not a Boolean or the String "true" or "false".

getDouble

public double getDouble(java.lang.String key)
                 throws JSONException

Get the double value associated with a key.

Parameters:

key - A key string.

Returns:

The numeric value.

Throws:

JSONException - if the key is not found or if the value is not a Number object and cannot be converted to a number.

getInt

public int getInt(java.lang.String key)
           throws JSONException

Get the int value associated with a key.

Parameters:

key - A key string.

Returns:

The integer value.

Throws:

JSONException - if the key is not found or if the value cannot be converted to an integer.

getJSONArray

public JSONArray getJSONArray(java.lang.String key)
                       throws JSONException

Get the JSONArray value associated with a key.

Parameters:

key - A key string.

Returns:

A JSONArray which is the value.

Throws:

JSONException - if the key is not found or if the value is not a JSONArray.

getJSONObject

public JSONObject getJSONObject(java.lang.String key)
                         throws JSONException

Get the JSONObject value associated with a key.

Parameters:

key - A key string.

Returns:

A JSONObject which is the value.

Throws:

JSONException - if the key is not found or if the value is not a JSONObject.

getLong

public long getLong(java.lang.String key)
             throws JSONException

Get the long value associated with a key.

Parameters:

key - A key string.

Returns:

The long value.

Throws:

JSONException - if the key is not found or if the value cannot be converted to a long.

getNames

public static java.lang.String[] getNames(JSONObject jo)

Get an array of field names from a JSONObject.

Returns:

An array of field names, or null if there are no names.

getNames

public static java.lang.String[] getNames(java.lang.Object object)

Get an array of field names from an Object.

Returns:

An array of field names, or null if there are no names.

getString

public java.lang.String getString(java.lang.String key)
                           throws JSONException

Get the string associated with a key.

Parameters:

key - A key string.

Returns:

A string which is the value.

Throws:

JSONException - if there is no string value for the key.

has

public boolean has(java.lang.String key)

Determine if the JSONObject contains a specific key.

Parameters:

key - A key string.

Returns:

true if the key exists in the JSONObject.

increment

public JSONObject increment(java.lang.String key)
                     throws JSONException

Increment a property of a JSONObject. If there is no such property, create one with a value of 1. If there is such a property, and if it is an Integer, Long, Double, or Float, then add one to it.

Parameters:

key - A key string.

Returns:

this.

Throws:

JSONException - If there is already a property with this name that is not an Integer, Long, Double, or Float.

isNull

public boolean isNull(java.lang.String key)

Determine if the value associated with the key is null or if there is no value.

Parameters:

key - A key string.

Returns:

true if there is no value associated with the key or if the value is the JSONObject.NULL object.

keys

public java.util.Iterator keys()

Get an enumeration of the keys of the JSONObject.

Returns:

An iterator of the keys.

length

public int length()

Get the number of keys stored in the JSONObject.

Returns:

The number of keys in the JSONObject.

names

public JSONArray names()

Produce a JSONArray containing the names of the elements of this JSONObject.

Returns:

A JSONArray containing the key strings, or null if the JSONObject is empty.

numberToString

public static java.lang.String numberToString(java.lang.Number number)
                                       throws JSONException

Produce a string from a Number.

Parameters:

number - A Number

Returns:

A String.

Throws:

JSONException - If n is a non-finite number.

opt

public java.lang.Object opt(java.lang.String key)

Get an optional value associated with a key.

Parameters:

key - A key string.

Returns:

An object which is the value, or null if there is no value.

optBoolean

public boolean optBoolean(java.lang.String key)

Get an optional boolean associated with a key. It returns false if there is no such key, or if the value is not Boolean.TRUE or the String "true".

Parameters:

key - A key string.

Returns:

The truth.

optBoolean

public boolean optBoolean(java.lang.String key,
                          boolean defaultValue)

Get an optional boolean associated with a key. It returns the defaultValue if there is no such key, or if it is not a Boolean or the String "true" or "false" (case insensitive).

Parameters:

key - A key string.

defaultValue - The default.

Returns:

The truth.

optDouble

public double optDouble(java.lang.String key)

Get an optional double associated with a key, or NaN if there is no such key or if its value is not a number. If the value is a string, an attempt will be made to evaluate it as a number.

Parameters:

key - A string which is the key.

Returns:

An object which is the value.

optDouble

public double optDouble(java.lang.String key,
                        double defaultValue)

Get an optional double associated with a key, or the defaultValue if there is no such key or if its value is not a number. If the value is a string, an attempt will be made to evaluate it as a number.

Parameters:

key - A key string.

defaultValue - The default.

Returns:

An object which is the value.

optInt

public int optInt(java.lang.String key)

Get an optional int value associated with a key, or zero if there is no such key or if the value is not a number. If the value is a string, an attempt will be made to evaluate it as a number.

Parameters:

key - A key string.

Returns:

An object which is the value.

optInt

public int optInt(java.lang.String key,
                  int defaultValue)

Get an optional int value associated with a key, or the default if there is no such key or if the value is not a number. If the value is a string, an attempt will be made to evaluate it as a number.

Parameters:

key - A key string.

defaultValue - The default.

Returns:

An object which is the value.

optJSONArray

public JSONArray optJSONArray(java.lang.String key)

Get an optional JSONArray associated with a key. It returns null if there is no such key, or if its value is not a JSONArray.

Parameters:

key - A key string.

Returns:

A JSONArray which is the value.

optJSONObject

public JSONObject optJSONObject(java.lang.String key)

Get an optional JSONObject associated with a key. It returns null if there is no such key, or if its value is not a JSONObject.

Parameters:

key - A key string.

Returns:

A JSONObject which is the value.

optLong

public long optLong(java.lang.String key)

Get an optional long value associated with a key, or zero if there is no such key or if the value is not a number. If the value is a string, an attempt will be made to evaluate it as a number.

Parameters:

key - A key string.

Returns:

An object which is the value.

optLong

public long optLong(java.lang.String key,
                    long defaultValue)

Get an optional long value associated with a key, or the default if there is no such key or if the value is not a number. If the value is a string, an attempt will be made to evaluate it as a number.

Parameters:

key - A key string.

defaultValue - The default.

Returns:

An object which is the value.

optString

public java.lang.String optString(java.lang.String key)

Get an optional string associated with a key. It returns an empty string if there is no such key. If the value is not a string and is not null, then it is converted to a string.

Parameters:

key - A key string.

Returns:

A string which is the value.

optString

public java.lang.String optString(java.lang.String key,
                                  java.lang.String defaultValue)

Get an optional string associated with a key. It returns the defaultValue if there is no such key.

Parameters:

key - A key string.

defaultValue - The default.

Returns:

A string which is the value.

put

public JSONObject put(java.lang.String key,
                      boolean value)
               throws JSONException

Put a key/boolean pair in the JSONObject.

Parameters:

key - A key string.

value - A boolean which is the value.

Returns:

this.

Throws:

JSONException - If the key is null.

put

public JSONObject put(java.lang.String key,
                      java.util.Collection value)
               throws JSONException

Put a key/value pair in the JSONObject, where the value will be a JSONArray which is produced from a Collection.

Parameters:

key - A key string.

value - A Collection value.

Returns:

this.

Throws:

JSONException

put

public JSONObject put(java.lang.String key,
                      double value)
               throws JSONException

Put a key/double pair in the JSONObject.

Parameters:

key - A key string.

value - A double which is the value.

Returns:

this.

Throws:

JSONException - If the key is null or if the number is invalid.

put

public JSONObject put(java.lang.String key,
                      int value)
               throws JSONException

Put a key/int pair in the JSONObject.

Parameters:

key - A key string.

value - An int which is the value.

Returns:

this.

Throws:

JSONException - If the key is null.

put

public JSONObject put(java.lang.String key,
                      long value)
               throws JSONException

Put a key/long pair in the JSONObject.

Parameters:

key - A key string.

value - A long which is the value.

Returns:

this.

Throws:

JSONException - If the key is null.

put

public JSONObject put(java.lang.String key,
                      java.util.Map value)
               throws JSONException

Put a key/value pair in the JSONObject, where the value will be a JSONObject which is produced from a Map.

Parameters:

key - A key string.

value - A Map value.

Returns:

this.

Throws:

JSONException

put

public JSONObject put(java.lang.String key,
                      java.lang.Object value)
               throws JSONException

Put a key/value pair in the JSONObject. If the value is null, then the key will be removed from the JSONObject if it is present.

Parameters:

key - A key string.

value - An object which is the value. It should be of one of these types: Boolean, Double, Integer, JSONArray, JSONObject, Long, String, or the JSONObject.NULL object.

Returns:

this.

Throws:

JSONException - If the value is non-finite number or if the key is null.

putOnce

public JSONObject putOnce(java.lang.String key,
                          java.lang.Object value)
                   throws JSONException

Put a key/value pair in the JSONObject, but only if the key and the value are both non-null, and only if there is not already a member with that name.

Parameters:

key -

value -

Returns:

his.

Throws:

JSONException - if the key is a duplicate

putOpt

public JSONObject putOpt(java.lang.String key,
                         java.lang.Object value)
                  throws JSONException

Put a key/value pair in the JSONObject, but only if the key and the value are both non-null.

Parameters:

key - A key string.

value - An object which is the value. It should be of one of these types: Boolean, Double, Integer, JSONArray, JSONObject, Long, String, or the JSONObject.NULL object.

Returns:

this.

Throws:

JSONException - If the value is a non-finite number.

quote

public static java.lang.String quote(java.lang.String string)

Produce a string in double quotes with backslash sequences in all the right places. A backslash will be inserted within

Parameters:

string - A String

Returns:

A String correctly formatted for insertion in a JSON text.

remove

public java.lang.Object remove(java.lang.String key)

Remove a name and its value, if present.

Parameters:

key - The name to be removed.

Returns:

The value that was associated with the name, or null if there was no value.

stringToValue

public static java.lang.Object stringToValue(java.lang.String string)

Try to convert a string into a number, boolean, or null. If the string can't be converted, return the string.

Parameters:

string - A String.

Returns:

A simple JSON value.

testValidity

public static void testValidity(java.lang.Object o)
                         throws JSONException

Throw an exception if the object is a NaN or infinite number.

Parameters:

o - The object to test.

Throws:

JSONException - If o is a non-finite number.

toJSONArray

public JSONArray toJSONArray(JSONArray names)
                      throws JSONException

Produce a JSONArray containing the values of the members of this JSONObject.

Parameters:

names - A JSONArray containing a list of key strings. This determines the sequence of the values in the result.

Returns:

A JSONArray of values.

Throws:

JSONException - If any of the values are non-finite numbers.

toString

public java.lang.String toString()

Make a JSON text of this JSONObject. For compactness, no whitespace is added. If this would not result in a syntactically correct JSON text, then null will be returned instead.

Warning: This method assumes that the data structure is acyclical.

Overrides:

toString in class java.lang.Object

Returns:

a printable, displayable, portable, transmittable representation of the object, beginning with { (left brace) and ending with } (right brace).

toString

public java.lang.String toString(int indentFactor)
                          throws JSONException

Make a prettyprinted JSON text of this JSONObject.

Warning: This method assumes that the data structure is acyclical.

Parameters:

indentFactor - The number of spaces to add to each level of indentation.

Returns:

a printable, displayable, portable, transmittable representation of the object, beginning with { (left brace) and ending with } (right brace).

Throws:

JSONException - If the object contains an invalid number.

valueToString

public static java.lang.String valueToString(java.lang.Object value)
                                      throws JSONException

Make a JSON text of an Object value. If the object has an value.toJSONString() method, then that method will be used to produce the JSON text. The method is required to produce a strictly conforming text. If the object does not contain a toJSONString method (which is the most common case), then a text will be produced by other means. If the value is an array or Collection, then a JSONArray will be made from it and its toJSONString method will be called. If the value is a MAP, then a JSONObject will be made from it and its toJSONString method will be called. Otherwise, the value's toString method will be called, and the result will be quoted.

Warning: This method assumes that the data structure is acyclical.

Parameters:

value - The value to be serialized.

Returns:

a printable, displayable, transmittable representation of the object, beginning with { (left brace) and ending with } (right brace).

Throws:

JSONException - If the value is or contains an invalid number.

wrap

public static java.lang.Object wrap(java.lang.Object object)

Wrap an object, if necessary. If the object is null, return the NULL object. If it is an array or collection, wrap it in a JSONArray. If it is a map, wrap it in a JSONObject. If it is a standard property (Double, String, et al) then it is already wrapped. Otherwise, if it comes from one of the java packages, turn it into a string. And if it doesn't, try to wrap it in a JSONObject. If the wrapping fails, then null is returned.

Parameters:

object - The object to wrap

Returns:

The wrapped value

write

public java.io.Writer write(java.io.Writer writer)
                     throws JSONException

Write the contents of the JSONObject as JSON text to a writer. For compactness, no whitespace is added.

Warning: This method assumes that the data structure is acyclical.

Returns:

The writer.

Throws:

JSONException