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 whitespaceskipWhiteSpace();} 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(); } }}总结
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