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();

}

}

}

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