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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