Compresses a String containing JavaScript by removing comments and whitespace.
/*
* 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();
}
}
}
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