Java tutorial
/* * This file is part of the Echo Web Application Framework (hereinafter "Echo"). * Copyright (C) 2002-2009 NextApp, Inc. * * Version: MPL 1.1/GPL 2.0/LGPL 2.1 * * The contents of this file are subject to the Mozilla Public License Version * 1.1 (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.mozilla.org/MPL/ * * Software distributed under the License is distributed on an "AS IS" basis, * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License for * the specific language governing rights and limitations under the License. * * Alternatively, the contents of this file may be used under the terms of * either the GNU General Public License Version 2 or later (the "GPL"), or the * GNU Lesser General Public License Version 2.1 or later (the "LGPL"), in which * case the provisions of the GPL or the LGPL are applicable instead of those * above. If you wish to allow use of your version of this file only under the * terms of either the GPL or the LGPL, and not to allow others to use your * version of this file under the terms of the MPL, indicate your decision by * deleting the provisions above and replace them with the notice and other * provisions required by the GPL or the LGPL. If you do not delete the * provisions above, a recipient may use your version of this file under the * terms of any one of the MPL, the GPL or the LGPL. */ /** * 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(); } } }