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 append()

* 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 JavaScriptCompressor 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();

}

}

}