通过Java压缩JavaScript代码实例分享
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2023-12-04 11:46:34
通过移除空行和注释来压缩 javascript 代码
/**
* this file is part of the echo web application...
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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