通过Java压缩JavaScript代码实例分享

通过移除空行和注释来压缩 javascript 代码

/**
 * 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();
    }
  }
}

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