Servlet缓存
在运行ajax的图片浏览器的时候，仅有第一次运行的情况是正确的，能正确显示图片。JS的代码为：
var store = new Ext.data.JsonStore({ url: '../ImagesServlet', root: 'images', fields: ['name', 'url',{name:'size', type: 'float'}, {name:'lastmod', type:'date', dateFormat:'timestamp'}] });
JS调用ImageServlet,取得json类型的数据。然后根据json的数据显示图片。
ImageServlet代码为：
/** **/package org.eimhe;import java.io.File;import java.io.IOException;import java.io.PrintWriter;import javax.servlet.ServletContext;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;/** * @author liheng * ImagesServlet.java * 2009-2-23 */public class ImagesServlet extends HttpServlet{ private boolean is_first = true; private StringBuffer jsonString = new StringBuffer(); protected void doGet(HttpServletRequest request,HttpServletResponse response) throws ServletException,IOException { processRequest(request,response); }protected void doPost(HttpServletRequest request,HttpServletResponse response) throws ServletException,IOException{ processRequest(request,response); }protected void processRequest(HttpServletRequest request,HttpServletResponse response) throws ServletException,IOException { //json "" ServletContext ctx = getServletContext(); String cs = ctx.getRealPath("/upload"); //String cs = "c:/upload"; File f = new File(cs); /** * if(jsonString != null) *{ *System.out.println("the cache is: "+jsonString.toString()); *jsonString = new StringBuffer(); *is_first = true; *} */ jsonString.append("{\"images\":[");//append json string headif(f.isDirectory()) { File[] fs = f.listFiles(new picFilter()); for(int i=0,len=fs.length;i<len;i++){ if(fs.isFile()) { if(is_first) { is_first = false; } else { jsonString.append(","); } jsonString.append("{\"name\":\""+fs.getName()+"\",\"url\":\"../upload/"+fs.getName()+"\",\"size\":"+fs.length()+",\"lastmod\":"+fs.lastModified()+"}"); //jsonString.append("{\"name\":\""+fs.getName()+"\",\"url\":\""+fs.getPath()+"\",\"size\":"+fs.length()+",\"lastmod\":"+fs.lastModified()+"}"); } else if(fs.isDirectory()) { getJsonStringForDirectory(fs,fs.getName()); } } } jsonString.append("]}"); //append json string bottom response.setContentType("text/html"); response.setHeader("Pragma","No-cache"); response.setDateHeader("Expires",0); response.setHeader("Cache-Control","no-cache");PrintWriter out = response.getWriter(); out.print(jsonString.toString()); out.close(); }protected void getJsonStringForDirectory(File f,String directoryName) { File[] ifile = f.listFiles(new picFilter()); for(int i=0,len=ifile.length;i<len;i++) { if(ifile.isFile()) { if(is_first) { is_first = false; } else { jsonString.append(","); } jsonString.append("{\"name\":\""+ifile.getName()+"\",\"url\":\"../upload/"+directoryName+"/"+ifile.getName()+"\",\"size\":"+ifile.length()+",\"lastmod\":"+ifile.lastModified()+"}"); } else if(ifile.isDirectory()) { getJsonStringForDirectory(ifile,directoryName+"/"+ifile.getName()); } } } }
刷新的时候，图片老是不能正常显示，于是怀疑是现实的json的格式有问题，发现没刷新一次，json的数据就多一些。原来是jsonString 和is_first都缓存了数据，在第二次运行的时候没有设置为默认值，导致json的格式错误。
去掉代码中注释的那块，图片能正常显示啦。
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