合并JS文件并进行压缩，合并js压缩,做Web的都知道多个JS

合并JS文件并进行压缩，合并js压缩,做Web的都知道多个JS

做Web的都知道多个JS文件或者CSS文件都会产生过多的请求。现在都喜欢把多个图片弄成一张图片，当用户浏览的时候只会产生一次请求而不是多次的请求。

但觉得合并JS真的能做到优化吗？因为不同页面有可能有不同的JS但也有是公用的例如：jQuery。

说个例子，我表达能力差。多多见谅。

有A-Z个页面，而A-Z的页面都有一个共用的JS：jQuery[size:60K]，一个不共用的JS：A-Z.js[size:12K]。

如果合并的话那么每次新访问页面都会重新请求一个 72K 的js。

但如果不合并的话，第一次请求72K，但之后也只请求12K。

import java.io.BufferedReader;import java.io.File;import java.io.FileInputStream;import java.io.FileOutputStream;import java.io.FileReader;import java.io.FileWriter;import java.io.IOException;import java.io.InputStreamReader;import java.io.OutputStreamWriter;import java.io.PrintWriter;import java.io.Reader;import java.io.Writer;import java.util.List;import java.util.StringTokenizer;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import org.apache.commons.io.FileUtils;import org.apache.commons.io.IOUtils;import org.apache.commons.lang.StringUtils;import org.mozilla.javascript.ErrorReporter;import org.mozilla.javascript.EvaluatorException;import com.yahoo.platform.yui.compressor.JavaScriptCompressor;public class JSControl extends HttpServlet {    String alljs;    String jsPath = "js";    public JSControl() {        super();    }    public void destroy() {        super.destroy(); // Just puts "destroy" string in log        // Put your code here    }    public void doGet(HttpServletRequest request, HttpServletResponse response)            throws ServletException, IOException {        String allPath = getWebrootPath() + jsPath + File.separator; //获取JS存放目录的绝对路径        String minFilePath = allPath + alljs + ".min.js"; //生成的压缩文件名字        File minFile = new File(minFilePath);        if (!minFile.exists()) {//判断是否已经生成了,如没有这个文件既生成            Long startTime = System.currentTimeMillis();            String tempFilePath = allPath + alljs + ".js"; //先合并再压缩,所以这个是合并时的临时文件名            StringBuffer mergeNr = new StringBuffer();            alljs = request.getParameter("alljs");            StringTokenizer st = new StringTokenizer(alljs, ",");            File tempFile = new File(tempFilePath);            while (st.hasMoreTokens()) {                String jsName = st.nextToken();                File tempJsFile = new File(allPath + jsName + ".js");                if (tempJsFile.exists()) {                    List<String> stList = FileUtils.readLines(tempJsFile,                            "UTF-8");                    for (String str : stList) {                        mergeNr.append(str).append("\\n"); //这里之前我没加\\n丫的我知道错了,居然都被注释了.哈哈!                    }                }            }            FileUtils.writeStringToFile(tempFile, mergeNr.toString(), "UTF-8",                    false);            Reader reader = new InputStreamReader(new FileInputStream(tempFile),                    "UTF-8");            Writer writer = new OutputStreamWriter(new FileOutputStream(minFilePath),                    "UTF-8");            //这个是YUI Compressor的压缩方法.            JavaScriptCompressor compressor = new JavaScriptCompressor(reader,                    new ErrorReporter() {                        public void warning(String message, String sourceName,                                int line, String lineSource, int lineOffset) {                            if (line < 0) {                                System.err.println("\\n[WARNING] " + message);                            } else {                                System.err.println("\\n[WARNING] " + line + ':'                                        + lineOffset + ':' + message);                            }                        }                        public void error(String message, String sourceName,                                int line, String lineSource, int lineOffset) {                            if (line < 0) {                                System.err.println("\\n[ERROR] " + message);                            } else {                                System.err.println("\\n[ERROR] " + line + ':'                                        + lineOffset + ':' + message);                            }                        }                        public EvaluatorException runtimeError(String message,                                String sourceName, int line, String lineSource,                                int lineOffset) {                            error(message, sourceName, line, lineSource,                                    lineOffset);                            return new EvaluatorException(message);                        }                    });            compressor.compress(writer, -1, true, false, false, false);            reader.close();            writer.close();            tempFile.delete();            System.out.println("压缩时间>>>>>>>>>"                    + (System.currentTimeMillis() - startTime));        }        // response.sendRedirect(request.getContextPath() + "/js/" + alljs        // + ".min.js");        getServletContext().getRequestDispatcher(                request.getContextPath() + "/js/" + alljs + ".min.js").forward(request, response);    }    public void doPost(HttpServletRequest request, HttpServletResponse response)            throws ServletException, IOException {        this.doGet(request, response);    }    public void init() throws ServletException {    }    private final static String getWebrootPath() {        String root = JSControl.class.getResource("/").getFile();        try {            root = new File(root).getParentFile().getParentFile()                    .getCanonicalPath();            root += File.separator;        } catch (IOException e) {            throw new RuntimeException(e);        }        return root;    }}//该片段来自于http://byrx.net