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JSONBuilder.java

/*
 * Copyright 2002-2007 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;

/*
Copyright (c) 2002 JSON.org

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

The Software shall be used for Good, not Evil.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
*/

/**
 * 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
 */
00083 public class JSONBuilder {
   private static final int MAXDEPTH = 20;

   /**
    * The comma flag determines if a comma should be output before the next
    * value.
    */
00090    private boolean comma;

   /**
    * The current mode. Values: 'a' (array), 'd' (done), 'i' (initial), 'k'
    * (key), 'o' (object).
    */
00096    protected char mode;

   /**
    * The object/array stack.
    */
00101    private char stack[];

   /**
    * The stack top index. A value of 0 indicates that the stack is empty.
    */
00106    private int top;

   /**
    * The writer that will receive the output.
    */
00111    protected Writer writer;

   /**
    * Make a fresh JSONBuilder. It can be used to build one JSON text.
    */
00116    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.
    */
00131    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).
    */
00163    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.
    */
00181    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.
    */
00202    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.
    */
00213    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.
    */
00226    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).
    */
00257    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.
    */
00277    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.
    */
00291    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
    */
00308    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.
    */
00319    public JSONBuilder value( double d ) {
      return this.value( new Double( d ) );
   }

   /**
    * Append a long value.
    *
    * @param l A long.
    * @return this
    * @throws JSONException
    */
00330    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.
    */
00343    public JSONBuilder value( Object o ) {
      return this.append( JSONUtils.valueToString( o ) );
   }
}

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