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();          }      }  }