利用Java來壓縮 JavaScript 代碼

通過移除空行和注釋來壓縮 JavaScript 代碼

/**


This file is part of the Echo Web Application Framework (hereinafter \"Echo\").
Copyright (C) 2002-2009 NextApp, Inc.
*
Compresses a String containing JavaScript by removing comments and whitespace.
*/
public class JavaScriptCompressor {
private static final char LINE_FEED = \'\n\';
 private static final char CARRIAGE_RETURN = \'\r\';
 private static final char SPACE = \' \';
 private static final char TAB = \'\t\';
/**

Compresses a String containing JavaScript by removing comments and 
whitespace.

@param script the String to compress
@return a compressed version
*/
public static String compress(String script) {
 JavaScriptCompressor jsc = new JavaScriptCompressor(script);
 return jsc.outputBuffer.toString();
}
/* Original JavaScript text. /
private String script;
/**

Compressed output buffer.
This buffer may only be modified by invoking the <code>append()</code>
method.
*/
private StringBuffer outputBuffer;
/* Current parser cursor position in original text. /
private int pos;
/* Character at parser cursor position. /
private char ch;
/* Last character appended to buffer. /
private char lastAppend;
/* Flag indicating if end-of-buffer has been reached. /
private boolean endReached;
/* Flag indicating whether content has been appended after last identifier. /
private boolean contentAppendedAfterLastIdentifier = true;
/**

Creates a new <code>JavaScriptCompressor</code> instance.

@param script
*/
private JavaScriptCompressor(String script) {
 this.script = script;
 outputBuffer = new StringBuffer(script.length());
 nextChar();
while (!endReached) {

 if (Character.isJavaIdentifierStart(ch)) {
     renderIdentifier();
 } else if (ch == \' \') {
     skipWhiteSpace();
 } else if (isWhitespace()) {
     // Compress whitespace
     skipWhiteSpace();
 } else if ((ch == \'\"\') || (ch == \'\\\'\')) {
     // Handle strings
     renderString();
 } else if (ch == \'/\') {
     // Handle comments
     nextChar();
     if (ch == \'/\') {
         nextChar();
         skipLineComment();
     } else if (ch == \'*\') {
         nextChar();
         skipBlockComment();
     } else {
         append(\'/\');
     }
 } else {
     append(ch);
     nextChar();
 }

}
}
/**

Append character to output.

@param ch the character to append
*/
private void append(char ch) {
 lastAppend = ch;
 outputBuffer.append(ch);
 contentAppendedAfterLastIdentifier = true;
}
/**

Determines if current character is whitespace.

@return true if the character is whitespace
*/
private boolean isWhitespace() {
 return ch == CARRIAGE_RETURN || ch == SPACE || ch == TAB || ch == LINE_FEED;

}
/**

Load next character.
*/
private void nextChar() {
 if (!endReached) {

 if (pos < script.length()) {
     ch = script.charAt(pos++);
 } else {
     endReached = true;
     ch = 0;
 }

}
}
/**

Adds an identifier to output.
*/
private void renderIdentifier() {
 if (!contentAppendedAfterLastIdentifier)

 append(SPACE);

append(ch);
 nextChar();
 while (Character.isJavaIdentifierPart(ch)) {

 append(ch);
 nextChar();

}
 contentAppendedAfterLastIdentifier = false;
}
/**

Adds quoted String starting at current character to output.
*/
private void renderString() {
 char startCh = ch; // Save quote char
 append(ch);
 nextChar();
 while (true) {

 if ((ch == LINE_FEED) || (ch == CARRIAGE_RETURN) || (endReached)) {
     // JavaScript error: string not terminated
     return;
 } else {
     if (ch == \'\\\\\') {
         append(ch);
         nextChar();
         if ((ch == LINE_FEED) || (ch == CARRIAGE_RETURN) || (endReached)) {
             // JavaScript error: string not terminated
             return;
         }
         append(ch);
         nextChar();
     } else {
         append(ch);
         if (ch == startCh) {
             nextChar();
             return;
         }
         nextChar();
     }
 }

}
}
/**

Moves cursor past a line comment.
*/
private void skipLineComment() {
 while ((ch != CARRIAGE_RETURN) && (ch != LINE_FEED)) {

 if (endReached) {
     return;
 }
 nextChar();

}
}
/**

Moves cursor past a block comment.
*/
private void skipBlockComment() {
 while (true) {

 if (endReached) {
     return;
 }
 if (ch == \'*\') {
     nextChar();
     if (ch == \'/\') {
         nextChar();
         return;
     }
 } else
     nextChar();

}
}
/**

Renders a new line character, provided previously rendered character 
is not a newline.
*/
private void renderNewLine() {
 if (lastAppend != \'\n\' && lastAppend != \'\r\') {

 append(\'\\n\');

}
}
/**

Moves cursor past white space (including newlines).
*/
private void skipWhiteSpace() {
 if (ch == LINE_FEED || ch == CARRIAGE_RETURN) {
 renderNewLine();

 } else {
 append(ch);

 }
 nextChar();
 while (ch == LINE_FEED || ch == CARRIAGE_RETURN || ch == SPACE || ch == TAB) {
 if (ch == LINE_FEED || ch == CARRIAGE_RETURN) {
     renderNewLine();
 }
 nextChar();

 }
}
}</pre>