jsontokenizer.as

用于flash/flex的 as3的 2D图形图像图表的动态生成

/*
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*/

package com.adobe.serialization.json {

      /**
       * @private
       */
	public class JSONTokenizer {
	
		/** The object that will get parsed from the JSON string */
		private var obj:Object;
		
		/** The JSON string to be parsed */
		private var jsonString:String;
		
		/** The current parsing location in the JSON string */
		private var loc:int;
		
		/** The current character in the JSON string during parsing */
		private var ch:String;
		
		/**
		 * Constructs a new JSONDecoder to parse a JSON string 
		 * into a native object.
		 *
		 * @param s The JSON string to be converted
		 *		into a native object
		 */
		public function JSONTokenizer( s:String ) {
			jsonString = s;
			loc = 0;
			
			// prime the pump by getting the first character
			nextChar();
		}
		
		/**
		 * Gets the next token in the input sting and advances
		* the character to the next character after the token
		 */
		public function getNextToken():JSONToken {
			var token:JSONToken = new JSONToken();
			
			// skip any whitespace / comments since the last 
			// token was read
			skipIgnored();
						
			// examine the new character and see what we have...
			switch ( ch ) {
				
				case '{':
					token.type = JSONTokenType.LEFT_BRACE;
					token.value = '{';
					nextChar();
					break
					
				case '}':
					token.type = JSONTokenType.RIGHT_BRACE;
					token.value = '}';
					nextChar();
					break
					
				case '[':
					token.type = JSONTokenType.LEFT_BRACKET;
					token.value = '[';
					nextChar();
					break
					
				case ']':
					token.type = JSONTokenType.RIGHT_BRACKET;
					token.value = ']';
					nextChar();
					break
				
				case ',':
					token.type = JSONTokenType.COMMA;
					token.value = ',';
					nextChar();
					break
					
				case ':':
					token.type = JSONTokenType.COLON;
					token.value = ':';
					nextChar();
					break;
					
				case 't': // attempt to read true
					var possibleTrue:String = "t" + nextChar() + nextChar() + nextChar();
					
					if ( possibleTrue == "true" ) {
						token.type = JSONTokenType.TRUE;
						token.value = true;
						nextChar();
					} else {
						parseError( "Expecting 'true' but found " + possibleTrue );
					}
					
					break;
					
				case 'f': // attempt to read false
					var possibleFalse:String = "f" + nextChar() + nextChar() + nextChar() + nextChar();
					
					if ( possibleFalse == "false" ) {
						token.type = JSONTokenType.FALSE;
						token.value = false;
						nextChar();
					} else {
						parseError( "Expecting 'false' but found " + possibleFalse );
					}
					
					break;
					
				case 'n': // attempt to read null
				
					var possibleNull:String = "n" + nextChar() + nextChar() + nextChar();
					
					if ( possibleNull == "null" ) {
						token.type = JSONTokenType.NULL;
						token.value = null;
						nextChar();
					} else {
						parseError( "Expecting 'null' but found " + possibleNull );
					}
					
					break;
					
				case '"': // the start of a string
					token = readString();
					break;
					
				default: 
					// see if we can read a number
					if ( isDigit( ch ) || ch == '-' ) {
						token = readNumber();
					} else if ( ch == '' ) {
						// check for reading past the end of the string
						return null;
					} else {						
						// not sure what was in the input string - it's not
						// anything we expected
						parseError( "Unexpected " + ch + " encountered" );
					}
			}
			
			return token;
		}
		
		/**
		 * Attempts to read a string from the input string.  Places
		 * the character location at the first character after the
		 * string.  It is assumed that ch is " before this method is called.
		 *
		 * @return the JSONToken with the string value if a string could
		 *		be read.  Throws an error otherwise.
		 */
		private function readString():JSONToken {
			// the token for the string we'll try to read
			var token:JSONToken = new JSONToken();
			token.type = JSONTokenType.STRING;
			
			// the string to store the string we'll try to read
			var string:String = "";
			
			// advance past the first "
			nextChar();
			
			while ( ch != '"' && ch != '' ) {
								
				// unescape the escape sequences in the string
				if ( ch == '\\' ) {
					
					// get the next character so we know what
					// to unescape
					nextChar();
					
					switch ( ch ) {
						
						case '"': // quotation mark
							string += '"';
							break;
						
						case '/':	// solidus
							string += "/";
							break;
							
						case '\\':	// reverse solidus
							string += '\\';
							break;
							
						case 'b':	// bell
							string += '\b';
							break;
							
						case 'f':	// form feed
							string += '\f';
							break;
							
						case 'n':	// newline
							string += '\n';
							break;
							
						case 'r':	// carriage return
							string += '\r';
							break;
							
						case 't':	// horizontal tab
							string += '\t'
							break;
						
						case 'u':
							// convert a unicode escape sequence
							// to it's character value - expecting
							// 4 hex digits
							
							// save the characters as a string we'll convert to an int
							var hexValue:String = "";
							
							// try to find 4 hex characters
							for ( var i:int = 0; i < 4; i++ ) {
								// get the next character and determine
								// if it's a valid hex digit or not
								if ( !isHexDigit( nextChar() ) ) {
									parseError( " Excepted a hex digit, but found: " + ch );
								}
								// valid, add it to the value
								hexValue += ch;
							}
							
							// convert hexValue to an integer, and use that
							// integrer value to create a character to add
							// to our string.
							string += String.fromCharCode( parseInt( hexValue, 16 ) );
							
							break;
					
						default:
							// couldn't unescape the sequence, so just
							// pass it through
							string += '\\' + ch;
						
					}
					
				} else {
					// didn't have to unescape, so add the character to the string
					string += ch;
					
				}
				
				// move to the next character
				nextChar();
				
			}
			
			// we read past the end of the string without closing it, which
			// is a parse error
			if ( ch == '' ) {
				parseError( "Unterminated string literal" );
			}
			
			// move past the closing " in the input string
			nextChar();
			
			// attach to the string to the token so we can return it
			token.value = string;
			
			return token;
		}
		
		/**
		 * Attempts to read a number from the input string.  Places
		 * the character location at the first character after the
		 * number.
		 * 
		 * @return The JSONToken with the number value if a number could
		 * 		be read.  Throws an error otherwise.
		 */
		private function readNumber():JSONToken {
			// the token for the number we'll try to read
			var token:JSONToken = new JSONToken();
			token.type = JSONTokenType.NUMBER;
			
			// the string to accumulate the number characters
			// into that we'll convert to a number at the end
			var input:String = "";
			
			// check for a negative number
			if ( ch == '-' ) {
				input += '-';
				nextChar();
			}
			
			// read numbers while we can
			while ( isDigit( ch ) ) {
				input += ch;
				nextChar();
			}
			
			// check for a decimal value
			if ( ch == '.' ) {
				input += '.';
				nextChar();
				// read more numbers to get the decimal value
				while ( isDigit( ch ) ) {
					input += ch;
					nextChar();
				}
			} else if ( ch == 'x' || ch == 'X' ) {
				input += 'x';
				nextChar();
				// read more numbers to get the hexadecimal value
				while ( isHexDigit( ch ) ) {
					input += ch;
					nextChar();
				}
			}
			
			//Application.application.show( "number = " + input );
			
			// conver the string to a number value
			var num:Number = Number( input );
			
			if ( isFinite( num ) ) {
				token.value = num;
				return token;
			} else {
				parseError( "Number " + num + " is not valid!" );
			}
            return null;
		}

		/**
		 * Reads the next character in the input
		 * string and advances the character location.
		 *
		 * @return The next character in the input string, or
		 *		null if we've read past the end.
		 */
		private function nextChar():String {
			return ch = jsonString.charAt( loc++ );
		}
		
		/**
		 * Advances the character location past any
		 * sort of white space and comments
		 */
		private function skipIgnored():void {
			skipWhite();
			skipComments();
			skipWhite();
		}
		
		/**
		 * Skips comments in the input string, either
		 * single-line or multi-line.  Advances the character
		 * to the first position after the end of the comment.
		 */
		private function skipComments():void {
			if ( ch == '/' ) {
				// Advance past the first / to find out what type of comment
				nextChar();
				switch ( ch ) {
					case '/': // single-line comment, read through end of line
						
						// Loop over the characters until we find
						// a newline or until there's no more characters left
						do {
							nextChar();
						} while ( ch != '\n' && ch != '' )
						
						// move past the \n
						nextChar();
						
						break;
					
					case '*': // multi-line comment, read until closing */

						// move past the opening *
						nextChar();
						
						// try to find a trailing */
						while ( true ) {
							if ( ch == '*' ) {
								// check to see if we have a closing /
								nextChar();
								if ( ch == '/') {
									// move past the end of the closing */
									nextChar();
									break;
								}
							} else {
								// move along, looking if the next character is a *
								nextChar();
							}
							
							// when we're here we've read past the end of 
							// the string without finding a closing */, so error
							if ( ch == '' ) {
								parseError( "Multi-line comment not closed" );
							}
						}

						break;
					
					// Can't match a comment after a /, so it's a parsing error
					default:
						parseError( "Unexpected " + ch + " encountered (expecting '/' or '*' )" );
				}
			}
			
		}
		
		
		/**
		 * Skip any whitespace in the input string and advances
		 * the character to the first character after any possible
		 * whitespace.
		 */
		private function skipWhite():void {
			
			// As long as there are spaces in the input 
			// stream, advance the current location pointer
			// past them
			while ( isSpace( ch ) ) {
				nextChar();
			}
			
		}
		
		/**
		 * Determines if a character is whitespace or not.
		 *
		 * @return True if the character passed in is a whitespace
		 *	character
		 */
		private function isSpace( ch:String ):Boolean {
			return (ch == ' ' || ch == '\t' || ch == '\n' || ch == '\r');
		}
		
		/**
		 * Determines if a character is a digit [0-9].
		 *
		 * @return True if the character passed in is a digit
		 */
		private function isDigit( ch:String ):Boolean {
			return ( ch >= '0' && ch <= '9' );
		}
		
		/**
		 * Determines if a character is a digit [0-9].
		 *
		 * @return True if the character passed in is a digit
		 */
		private function isHexDigit( ch:String ):Boolean {
			// get the uppercase value of ch so we only have
			// to compare the value between 'A' and 'F'
			var uc:String = ch.toUpperCase();
			
			// a hex digit is a digit of A-F, inclusive ( using
			// our uppercase constraint )
			return ( isDigit( ch ) || ( uc >= 'A' && uc <= 'F' ) );
		}
	
		/**
		 * Raises a parsing error with a specified message, tacking
		 * on the error location and the original string.
		 *
		 * @param message The message indicating why the error occurred
		 */
		public function parseError( message:String ):void {
			throw new JSONParseError( message, loc, jsonString );
		}
	}
	
}