第七章过滤器 Filter（二）

一过滤器API

由容器实现的接口

–javax.servlet.Filter

–javax.servlet.FilterChain

–javax.servlet.FilterConfig

四个包装器类

–javax.servlet.ServletRequestWrapper

–javax.servlet.ServletResponseWrapper

–javax.servlet.http.HttpServletRequestWrapper

–javax.servlet.http.HttpServletResponseWrapper

二使用请求和响应包装器

示例：

假如我们有个老系统用来产生普通的ASCII文本格式的报表，并将报表保存在扩展名为.txt的文本文件中。现在我们想让这些报表可以通过浏览器访问。我们把文件保存在/text/a.txt。

如果 If-Modified-Since 值指定的时间内容资源没有更改过，那么服务器就不需要发送资源。

将请求包装在 HttpServletRequestWrapper 中并覆盖 getHeader()方法。

 package com.cy.wrapper;

 import javax.servlet.http.HttpServletRequest;

 import javax.servlet.http.HttpServletRequestWrapper;

 public class ReqWrapper extends HttpServletRequestWrapper{

     public ReqWrapper(HttpServletRequest request) {

         super(request);

     }

     @Override

     public String getHeader(String name) {

         if("If-Modified-Since".equalsIgnoreCase(name)){

             return null;

         }else{

             return super.getHeader(name);

         }

     }

 }

HttpServletResponseWrapper

 package com.cy.wrapper;

 import java.io.ByteArrayOutputStream;

 import java.io.IOException;

 import java.io.PrintWriter;

 import javax.servlet.ServletOutputStream;

 import javax.servlet.http.HttpServletResponse;

 import javax.servlet.http.HttpServletResponseWrapper;

 public class RespWrapper extends HttpServletResponseWrapper{

     //创建一个缓存字节流对象，用于缓存servlet写入的数据

     ByteArrayOutputStream baos = new ByteArrayOutputStream();

     //创建一个自定义的字节输出流对象，提供给servlet调用。以便把数据写入缓存流对象

     MyOutputStream mos = new MyOutputStream(baos);

     //创建一个自定义的字符输出流对象，提供给servlet调用。以便把数据写入缓存流对象

     PrintWriter pw = new PrintWriter(baos);

     public RespWrapper(HttpServletResponse response) {

         super(response);

     }

     @Override

     public ServletOutputStream getOutputStream() throws IOException {

         return mos;

     }

     @Override

     public PrintWriter getWriter() throws IOException {

         return pw;

     }

     /**

      * 自定义一个ServletOutputStream的子类用于保存servlet端写入字节流数据

      * @author hellokitty燕

      *

      */

     private static class MyOutputStream extends ServletOutputStream{

         private ByteArrayOutputStream baos ;

         public MyOutputStream(ByteArrayOutputStream baos){

             this.baos = baos;

         }

         @Override

         public void write(int b) throws IOException {

             baos.write(b);

         }

         @Override

         public void write(byte[] b, int off, int len) throws IOException {

             baos.write(b, off, len);

         }

         @Override

         public void write(byte[] b) throws IOException {

             baos.write(b);

         }

     }

     //将缓存流中的数据以String方式返回

     public String toString(){

         return baos.toString();

     }

     //将缓存流中的数据以字节数组方式返回

     public byte[] toByteArray(){

         return baos.toByteArray();

     }

 }

将文本格式转化成所需的html格式

 package com.cy.filter;

 import java.io.IOException;

 import java.io.PrintWriter;

 import java.util.Date;

 import javax.servlet.Filter;

 import javax.servlet.FilterChain;

 import javax.servlet.FilterConfig;

 import javax.servlet.ServletException;

 import javax.servlet.ServletRequest;

 import javax.servlet.ServletResponse;

 import javax.servlet.http.HttpServletRequest;

 import javax.servlet.http.HttpServletResponse;

 import com.cy.wrapper.ReqWrapper;

 import com.cy.wrapper.RespWrapper;

 public class TextFilter implements Filter{

     @Override

     public void destroy() {

         // TODO Auto-generated method stub

     }

     @Override

     public void doFilter(ServletRequest arg0, ServletResponse arg1,

             FilterChain arg2) throws IOException, ServletException {

         ReqWrapper req = new ReqWrapper((HttpServletRequest)arg0);

         RespWrapper resp = new RespWrapper((HttpServletResponse)arg1);

         arg2.doFilter(req, resp);

         arg1.setContentType("text/html;charset=utf-8");

         PrintWriter pw = arg1.getWriter();

         pw.print("<html>");

         pw.print("<head>");

         pw.print("</head>");

         pw.print("<body style='background-color:green'>");

         pw.print("<pre>");

         pw.print("============== date:"+new Date().toString()+"===================<br/><br/>");

         pw.print(resp.toString());

         pw.print("<br/><br/>==========================================================");

         pw.print("</pre>");

         pw.print("</body>");

         pw.print("</html>");

         pw.close();

     }

     @Override

     public void init(FilterConfig arg0) throws ServletException {

         // TODO Auto-generated method stub

     }

 }

Servlet

 package com.cy.servlet;

 import java.io.FileInputStream;

 import java.io.IOException;

 import javax.servlet.ServletException;

 import javax.servlet.ServletOutputStream;

 import javax.servlet.http.HttpServlet;

 import javax.servlet.http.HttpServletRequest;

 import javax.servlet.http.HttpServletResponse;

 public class TextServlet extends HttpServlet{

     @Override

     protected void doGet(HttpServletRequest req, HttpServletResponse resp)

             throws ServletException, IOException {

         //获取刚才覆盖以后的字节数出流。

         ServletOutputStream sos = resp.getOutputStream();

         String uri = req.getRequestURI();

         String name = uri.substring(uri.lastIndexOf("/")+1);

         String path = "/text/"+name;

         //将相对路径转换为物理路径

         path = getServletContext().getRealPath(path);

         FileInputStream fis = new FileInputStream(path);

         byte[] b = new byte[100];

         int length = 0;

         while(-1!=(length = fis.read(b, 0, 100))){

             sos.write(b, 0, length);

         }

         sos.close();

         fis.close();

     }

     @Override

     protected void doPost(HttpServletRequest req, HttpServletResponse resp)

             throws ServletException, IOException {

         doGet(req, resp);

     }

 }

web.xml

 <?xml version="1.0" encoding="UTF-8"?>

 <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">

   <display-name>Filter</display-name>

   <welcome-file-list>

     <welcome-file>index.html</welcome-file>

     <welcome-file>index.htm</welcome-file>

     <welcome-file>index.jsp</welcome-file>

     <welcome-file>default.html</welcome-file>

     <welcome-file>default.htm</welcome-file>

     <welcome-file>default.jsp</welcome-file>

   </welcome-file-list>

   <servlet>

       <servlet-name>s_text</servlet-name>

       <servlet-class>com.cy.servlet.TextServlet</servlet-class>

   </servlet>

   <servlet-mapping>

       <servlet-name>s_text</servlet-name>

       <url-pattern>*.txt</url-pattern>

   </servlet-mapping>

    <filter>

       <filter-name>text</filter-name>

       <filter-class>com.cy.filter.TextFilter</filter-class>

   </filter>

   <filter-mapping>

       <filter-name>text</filter-name>

       <url-pattern>*.txt</url-pattern>

   </filter-mapping> 

 </web-app>

应用HttpServletResponseWrapper对象，压缩内容。

 package com.cy.wrapper;

 import java.io.ByteArrayOutputStream;

 import java.io.IOException;

 import java.io.UnsupportedEncodingException;

 import javax.servlet.ServletOutputStream;

 import javax.servlet.http.HttpServletResponse;

 import javax.servlet.http.HttpServletResponseWrapper;

 public class RespGzipWrapper extends HttpServletResponseWrapper {

     public MyOutputStream mos=new MyOutputStream();

     public RespGzipWrapper(HttpServletResponse response) {

         super(response);

     }

     @Override

     public ServletOutputStream getOutputStream() throws IOException {

         return mos;

     }

     public class MyOutputStream extends ServletOutputStream{

       ByteArrayOutputStream baos=new ByteArrayOutputStream();

         @Override

         public void write(int b) throws IOException {

             baos.write(b);

         }

         @Override

         public void write(byte[] b) throws IOException {

             baos.write(b);

         }

         @Override

         public void write(byte[] b, int off, int len) throws IOException {

             baos.write(b, off, len);

         }

          public String toString(String encode){

         try {

             return baos.toString(encode);

         } catch (UnsupportedEncodingException e) {

             e.printStackTrace();

         }

         return null;

     }

     }

 }

filter

 package com.cy.filter;

 import java.io.BufferedReader;

 import java.io.IOException;

 import java.io.StringReader;

 import javax.servlet.Filter;

 import javax.servlet.FilterChain;

 import javax.servlet.FilterConfig;

 import javax.servlet.ServletException;

 import javax.servlet.ServletRequest;

 import javax.servlet.ServletResponse;

 import javax.servlet.http.HttpServletRequest;

 import javax.servlet.http.HttpServletResponse;

 import com.cy.wrapper.RespGzipWrapper;

 public class GzipFilter implements Filter{

     @Override

     public void destroy() {

     }

     @Override

     public void doFilter(ServletRequest arg0, ServletResponse arg1,

             FilterChain arg2) throws IOException, ServletException {

         HttpServletRequest req=(HttpServletRequest)arg0;

         String uri=req.getRequestURI();

         //获取读取文件后缀名

         String exName=uri.substring(uri.lastIndexOf("."));

         RespGzipWrapper rgw=new RespGzipWrapper((HttpServletResponse)arg1);

         //调用后面的资源

         arg2.doFilter(arg0, rgw);

         //用返回的字符串创建字符读取流

         StringReader sr=new StringReader(rgw.mos.toString("utf-8"));

         //根据上面读取的流创建缓存读取流

         BufferedReader br=new BufferedReader(sr);

         String line="";

         //创建压缩后的文件缓存区

         StringBuffer sb=new StringBuffer();

         while((line=br.readLine())!=null){

             //追加到缓存区

             sb.append(line.trim());

         }

         //设置压缩后的文件大小

         arg1.setContentLength(sb.toString().getBytes("iso-8859-1").length);

         //根据请求后缀名来设置请求头

         if(".html".equals(exName)){

             arg1.setContentType("text/html;charset="+rgw.getCharacterEncoding());

         }else if(".js".equals(exName)){

             arg1.setContentType("text/javascript;charset="+rgw.getCharacterEncoding());

         }else if(".css".equals(exName)){

             arg1.setContentType("text/css;charset="+rgw.getCharacterEncoding());

         }

        //响应到客户端浏览器

         arg1.getWriter().print(sb.toString());

         arg1.getWriter().close();

     }

     @Override

     public void init(FilterConfig arg0) throws ServletException {

     }

 }

html;

 <!DOCTYPE html>

 <html>

   <head>

     <title>index.html</title>

     <meta name="keywords" content="keyword1,keyword2,keyword3">

     <meta name="description" content="this is my page">

     <meta name="content-type" content="text/html; charset=UTF-8">

     <link rel="stylesheet" type="text/css" href="../css/index.css">

     <script type="text/javascript" src="../js/index.js"></script>

   </head>

   <body>

     This is my HTML page！ <br>

   </body>

 </html>

css:

 *{

     margin:;

     padding:;

     color:red;

 }

window.onload=function(){ alert("hello"); };

web.xml

 <?xml version="1.0" encoding="UTF-8"?>

 <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">

   <display-name>GZIP</display-name>

   <welcome-file-list>

     <welcome-file>index.html</welcome-file>

     <welcome-file>index.htm</welcome-file>

     <welcome-file>index.jsp</welcome-file>

     <welcome-file>default.html</welcome-file>

     <welcome-file>default.htm</welcome-file>

     <welcome-file>default.jsp</welcome-file>

   </welcome-file-list> 

    <filter>

     <filter-name>GzipFilter</filter-name>

     <filter-class>com.cy.filter.GzipFilter</filter-class>

   </filter>

   <filter-mapping>

      <filter-name>GzipFilter</filter-name>

      <url-pattern>/*</url-pattern>

   </filter-mapping>

 </web-app>

最终结果：

。。。。

巴特西

第七章过滤器 Filter（二）

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巴特西

第七章 过滤器 Filter（二）

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第七章过滤器 Filter（二）