/*
* Copyright 2002-2009 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package net.sf.json.util;
import java.io.IOException;
import java.io.Writer;
import net.sf.json.JSONException;
/**
* JSONBuilder provides a quick and convenient way of producing JSON text. The
* texts produced strictly conform to JSON syntax rules. No whitespace is added,
* so the results are ready for transmission or storage. Each instance of
* JSONWriter can produce one JSON text.
* <p>
* A JSONBuilder instance provides a <code>value</code> method for appending
* values to the text, and a <code>key</code> method for adding keys before
* values in objects. There are <code>array</code> and <code>endArray</code>
* methods that make and bound array values, and <code>object</code> and
* <code>endObject</code> methods which make and bound object values. All of
* these methods return the JSONBuilder instance, permitting a cascade style.
* For example,
*
* <pre>
* new JSONBuilder(myWriter)
* .object()
* .key("JSON")
* .value("Hello, World!")
* .endObject();</pre>
*
* which writes
*
* <pre>
* {"JSON":"Hello, World!"}</pre>
*
* <p>
* The first method called must be <code>array</code> or <code>object</code>.
* There are no methods for adding commas or colons. JSONBuilder adds them for
* you. Objects and arrays can be nested up to 20 levels deep.
* <p>
* This can sometimes be easier than using a JSONObject to build a string.
*
* @author JSON.org
* @version 1
*/
public class JSONBuilder {
private static final int MAXDEPTH = 20;
/**
* The comma flag determines if a comma should be output before the next
* value.
*/
private boolean comma;
/**
* The current mode. Values: 'a' (array), 'd' (done), 'i' (initial), 'k'
* (key), 'o' (object).
*/
protected char mode;
/**
* The object/array stack.
*/
private char stack[];
/**
* The stack top index. A value of 0 indicates that the stack is empty.
*/
private int top;
/**
* The writer that will receive the output.
*/
protected Writer writer;
/**
* Make a fresh JSONBuilder. It can be used to build one JSON text.
*/
public JSONBuilder( Writer w ) {
this.comma = false;
this.mode = 'i';
this.stack = new char[MAXDEPTH];
this.top = 0;
this.writer = w;
}
/**
* Append a value.
*
* @param s A string value.
* @return this
* @throws JSONException If the value is out of sequence.
*/
private JSONBuilder append( String s ) {
if( s == null ){
throw new JSONException( "Null pointer" );
}
if( this.mode == 'o' || this.mode == 'a' ){
try{
if( this.comma && this.mode == 'a' ){
this.writer.write( ',' );
}
this.writer.write( s );
}catch( IOException e ){
throw new JSONException( e );
}
if( this.mode == 'o' ){
this.mode = 'k';
}
this.comma = true;
return this;
}
throw new JSONException( "Value out of sequence." );
}
/**
* Begin appending a new array. All values until the balancing
* <code>endArray</code> will be appended to this array. The
* <code>endArray</code> method must be called to mark the array's end.
*
* @return this
* @throws JSONException If the nesting is too deep, or if the object is
* started in the wrong place (for example as a key or after the end
* of the outermost array or object).
*/
public JSONBuilder array() {
if( this.mode == 'i' || this.mode == 'o' || this.mode == 'a' ){
this.push( 'a' );
this.append( "[" );
this.comma = false;
return this;
}
throw new JSONException( "Misplaced array." );
}
/**
* End something.
*
* @param m Mode
* @param c Closing character
* @return this
* @throws JSONException If unbalanced.
*/
private JSONBuilder end( char m, char c ) {
if( this.mode != m ){
throw new JSONException( m == 'o' ? "Misplaced endObject." : "Misplaced endArray." );
}
this.pop( m );
try{
this.writer.write( c );
}catch( IOException e ){
throw new JSONException( e );
}
this.comma = true;
return this;
}
/**
* End an array. This method most be called to balance calls to
* <code>array</code>.
*
* @return this
* @throws JSONException If incorrectly nested.
*/
public JSONBuilder endArray() {
return this.end( 'a', ']' );
}
/**
* End an object. This method most be called to balance calls to
* <code>object</code>.
*
* @return this
* @throws JSONException If incorrectly nested.
*/
public JSONBuilder endObject() {
return this.end( 'k', '}' );
}
/**
* Append a key. The key will be associated with the next value. In an
* object, every value must be preceded by a key.
*
* @param s A key string.
* @return this
* @throws JSONException If the key is out of place. For example, keys do not
* belong in arrays or if the key is null.
*/
public JSONBuilder key( String s ) {
if( s == null ){
throw new JSONException( "Null key." );
}
if( this.mode == 'k' ){
try{
if( this.comma ){
this.writer.write( ',' );
}
this.writer.write( JSONUtils.quote( s ) );
this.writer.write( ':' );
this.comma = false;
this.mode = 'o';
return this;
}catch( IOException e ){
throw new JSONException( e );
}
}
throw new JSONException( "Misplaced key." );
}
/**
* Begin appending a new object. All keys and values until the balancing
* <code>endObject</code> will be appended to this object. The
* <code>endObject</code> method must be called to mark the object's end.
*
* @return this
* @throws JSONException If the nesting is too deep, or if the object is
* started in the wrong place (for example as a key or after the end
* of the outermost array or object).
*/
public JSONBuilder object() {
if( this.mode == 'i' ){
this.mode = 'o';
}
if( this.mode == 'o' || this.mode == 'a' ){
this.append( "{" );
this.push( 'k' );
this.comma = false;
return this;
}
throw new JSONException( "Misplaced object." );
}
/**
* Pop an array or object scope.
*
* @param c The scope to close.
* @throws JSONException If nesting is wrong.
*/
private void pop( char c ) {
if( this.top <= 0 || this.stack[this.top - 1] != c ){
throw new JSONException( "Nesting error." );
}
this.top -= 1;
this.mode = this.top == 0 ? 'd' : this.stack[this.top - 1];
}
/**
* Push an array or object scope.
*
* @param c The scope to open.
* @throws JSONException If nesting is too deep.
*/
private void push( char c ) {
if( this.top >= MAXDEPTH ){
throw new JSONException( "Nesting too deep." );
}
this.stack[this.top] = c;
this.mode = c;
this.top += 1;
}
/**
* Append either the value <code>true</code> or the value
* <code>false</code>.
*
* @param b A boolean.
* @return this
* @throws JSONException
*/
public JSONBuilder value( boolean b ) {
return this.append( b ? "true" : "false" );
}
/**
* Append a double value.
*
* @param d A double.
* @return this
* @throws JSONException If the number is not finite.
*/
public JSONBuilder value( double d ) {
return this.value( new Double( d ) );
}
/**
* Append a long value.
*
* @param l A long.
* @return this
* @throws JSONException
*/
public JSONBuilder value( long l ) {
return this.append( Long.toString( l ) );
}
/**
* Append an object value.
*
* @param o The object to append. It can be null, or a Boolean, Number,
* String, JSONObject, or JSONArray, or an object with a
* toJSONString() method.
* @return this
* @throws JSONException If the value is out of sequence.
*/
public JSONBuilder value( Object o ) {
return this.append( JSONUtils.valueToString( o ) );
}
}