第七章过滤器 Filter（二）-阿里云开发者社区

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。

 1 package com.cy.wrapper;
 2 
 3 import javax.servlet.http.HttpServletRequest;
 4 import javax.servlet.http.HttpServletRequestWrapper;
 5 
 6 public class ReqWrapper extends HttpServletRequestWrapper{
 7 
 8     public ReqWrapper(HttpServletRequest request) {
 9         super(request);
10     }
11 
12     @Override
13     public String getHeader(String name) {
14         if("If-Modified-Since".equalsIgnoreCase(name)){
15             return null;
16         }else{
17             return super.getHeader(name);
18         }
19     }
20     
21     
22 
23 }

HttpServletResponseWrapper

 1 package com.cy.wrapper;
 2 
 3 import java.io.ByteArrayOutputStream;
 4 import java.io.IOException;
 5 import java.io.PrintWriter;
 6 
 7 import javax.servlet.ServletOutputStream;
 8 import javax.servlet.http.HttpServletResponse;
 9 import javax.servlet.http.HttpServletResponseWrapper;
10 
11 public class RespWrapper extends HttpServletResponseWrapper{
12     //创建一个缓存字节流对象，用于缓存servlet写入的数据
13     ByteArrayOutputStream baos = new ByteArrayOutputStream();
14     //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
15     MyOutputStream mos = new MyOutputStream(baos);
16     //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
17     PrintWriter pw = new PrintWriter(baos);
18     
19     
20     public RespWrapper(HttpServletResponse response) {
21         super(response);
22     }
23 
24     @Override
25     public ServletOutputStream getOutputStream() throws IOException {
26         return mos;
27     }
28         
29     @Override
30     public PrintWriter getWriter() throws IOException {
31         return pw;
32     }
33 
34 
35     /**
36      * 自定义一个ServletOutputStream的子类用于保存servlet端写入字节流数据
37      * @author hellokitty燕
38      *
39      */
40     private static class MyOutputStream extends ServletOutputStream{
41         private ByteArrayOutputStream baos ;
42         
43         public MyOutputStream(ByteArrayOutputStream baos){
44             this.baos = baos;
45         }
46         @Override
47         public void write(int b) throws IOException {
48             baos.write(b);
49         }
50         @Override
51         public void write(byte[] b, int off, int len) throws IOException {
52             baos.write(b, off, len);
53         }
54         @Override
55         public void write(byte[] b) throws IOException {
56             baos.write(b);
57         }
58         
59     }
60     
61     //将缓存流中的数据以String方式返回
62     public String toString(){
63         return baos.toString();
64     }
65     //将缓存流中的数据以字节数组方式返回
66     public byte[] toByteArray(){
67         return baos.toByteArray();
68     }
69     
70     
71 
72 }

将文本格式转化成所需的html格式

 1 package com.cy.filter;
 2 
 3 import java.io.IOException;
 4 import java.io.PrintWriter;
 5 import java.util.Date;
 6 
 7 import javax.servlet.Filter;
 8 import javax.servlet.FilterChain;
 9 import javax.servlet.FilterConfig;
10 import javax.servlet.ServletException;
11 import javax.servlet.ServletRequest;
12 import javax.servlet.ServletResponse;
13 import javax.servlet.http.HttpServletRequest;
14 import javax.servlet.http.HttpServletResponse;
15 
16 import com.cy.wrapper.ReqWrapper;
17 import com.cy.wrapper.RespWrapper;
18 
19 public class TextFilter implements Filter{
20 
21     @Override
22     public void destroy() {
23         // TODO Auto-generated method stub
24         
25     }
26 
27     @Override
28     public void doFilter(ServletRequest arg0, ServletResponse arg1,
29             FilterChain arg2) throws IOException, ServletException {
30         
31         ReqWrapper req = new ReqWrapper((HttpServletRequest)arg0);
32         RespWrapper resp = new RespWrapper((HttpServletResponse)arg1);
33         
34         arg2.doFilter(req, resp);        
35         arg1.setContentType("text/html;charset=utf-8");
36         PrintWriter pw = arg1.getWriter();
37         pw.print("<html>");
38         pw.print("<head>");
39         pw.print("</head>");
40         pw.print("<body style='background-color:green'>");
41         pw.print("<pre>");
42         pw.print("============== date:"+new Date().toString()+"===================<br/><br/>");
43         pw.print(resp.toString());
44         pw.print("<br/><br/>==========================================================");
45         pw.print("</pre>");
46         pw.print("</body>");
47         pw.print("</html>");
48         pw.close();
49         
50         
51     }
52 
53     @Override
54     public void init(FilterConfig arg0) throws ServletException {
55         // TODO Auto-generated method stub
56         
57     }
58 
59 }

Servlet

 1 package com.cy.servlet;
 2 
 3 import java.io.FileInputStream;
 4 import java.io.IOException;
 5 
 6 import javax.servlet.ServletException;
 7 import javax.servlet.ServletOutputStream;
 8 import javax.servlet.http.HttpServlet;
 9 import javax.servlet.http.HttpServletRequest;
10 import javax.servlet.http.HttpServletResponse;
11 
12 public class TextServlet extends HttpServlet{
13 
14     @Override
15     protected void doGet(HttpServletRequest req, HttpServletResponse resp)
16             throws ServletException, IOException {
17         //获取刚才覆盖以后的字节数出流。
18         ServletOutputStream sos = resp.getOutputStream();        
19         String uri = req.getRequestURI();
20         String name = uri.substring(uri.lastIndexOf("/")+1);
21         String path = "/text/"+name;
22         //将相对路径转换为物理路径
23         path = getServletContext().getRealPath(path);
24         FileInputStream fis = new FileInputStream(path);
25         byte[] b = new byte[100];
26         int length = 0;
27         while(-1!=(length = fis.read(b, 0, 100))){
28             sos.write(b, 0, length);
29         }
30         sos.close();
31         fis.close();
32     }
33 
34     @Override
35     protected void doPost(HttpServletRequest req, HttpServletResponse resp)
36             throws ServletException, IOException {
37         doGet(req, resp);
38     }
39 
40 }

web.xml

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <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">
 3   <display-name>Filter</display-name>
 4   <welcome-file-list>
 5     <welcome-file>index.html</welcome-file>
 6     <welcome-file>index.htm</welcome-file>
 7     <welcome-file>index.jsp</welcome-file>
 8     <welcome-file>default.html</welcome-file>
 9     <welcome-file>default.htm</welcome-file>
10     <welcome-file>default.jsp</welcome-file>
11   </welcome-file-list>
12  
13 
14   
15   <servlet>
16       <servlet-name>s_text</servlet-name>
17       <servlet-class>com.cy.servlet.TextServlet</servlet-class>
18   </servlet>
19   
20   <servlet-mapping>
21       <servlet-name>s_text</servlet-name>
22       <url-pattern>*.txt</url-pattern>
23   </servlet-mapping>
24   
25    <filter>
26       <filter-name>text</filter-name>
27       <filter-class>com.cy.filter.TextFilter</filter-class>
28   </filter>
29   
30   <filter-mapping>
31       <filter-name>text</filter-name>
32       <url-pattern>*.txt</url-pattern>
33   </filter-mapping> 
34   
35   
36 </web-app>

应用HttpServletResponseWrapper对象，压缩内容。

 1 package com.cy.wrapper;
 2 
 3 import java.io.ByteArrayOutputStream;
 4 import java.io.IOException;
 5 import java.io.UnsupportedEncodingException;
 6 
 7 import javax.servlet.ServletOutputStream;
 8 import javax.servlet.http.HttpServletResponse;
 9 import javax.servlet.http.HttpServletResponseWrapper;
10 
11 public class RespGzipWrapper extends HttpServletResponseWrapper {
12     
13     public MyOutputStream mos=new MyOutputStream();
14     public RespGzipWrapper(HttpServletResponse response) {
15         super(response);
16     }
17         
18     @Override
19     public ServletOutputStream getOutputStream() throws IOException {
20         return mos;
21     }
22     
23     
24     public class MyOutputStream extends ServletOutputStream{
25       ByteArrayOutputStream baos=new ByteArrayOutputStream();
26         @Override
27         public void write(int b) throws IOException {
28             baos.write(b);
29         }
30         @Override
31         public void write(byte[] b) throws IOException {
32             baos.write(b);
33         }
34         @Override
35         public void write(byte[] b, int off, int len) throws IOException {
36             baos.write(b, off, len);
37         }
38         
39          public String toString(String encode){
40         try {
41             return baos.toString(encode);
42         } catch (UnsupportedEncodingException e) {
43             e.printStackTrace();
44         }
45         return null;
46         
47     }
48          
49     }
50     
51     
52 }

filter

 1 package com.cy.filter;
 2 
 3 import java.io.BufferedReader;
 4 import java.io.IOException;
 5 import java.io.StringReader;
 6 
 7 import javax.servlet.Filter;
 8 import javax.servlet.FilterChain;
 9 import javax.servlet.FilterConfig;
10 import javax.servlet.ServletException;
11 import javax.servlet.ServletRequest;
12 import javax.servlet.ServletResponse;
13 import javax.servlet.http.HttpServletRequest;
14 import javax.servlet.http.HttpServletResponse;
15 
16 import com.cy.wrapper.RespGzipWrapper;
17 
18 public class GzipFilter implements Filter{
19 
20     @Override
21     public void destroy() {
22         
23     }
24 
25     @Override
26     public void doFilter(ServletRequest arg0, ServletResponse arg1,
27             FilterChain arg2) throws IOException, ServletException {
28         HttpServletRequest req=(HttpServletRequest)arg0;
29         String uri=req.getRequestURI();
30         //获取读取文件后缀名
31         String exName=uri.substring(uri.lastIndexOf("."));       
32         RespGzipWrapper rgw=new RespGzipWrapper((HttpServletResponse)arg1);
33         //调用后面的资源
34         arg2.doFilter(arg0, rgw);
35         //用返回的字符串创建字符读取流
36         StringReader sr=new StringReader(rgw.mos.toString("utf-8"));
37         //根据上面读取的流创建缓存读取流
38         BufferedReader br=new BufferedReader(sr);
39         String line="";
40         //创建压缩后的文件缓存区
41         StringBuffer sb=new StringBuffer();
42         while((line=br.readLine())!=null){
43             //追加到缓存区
44             sb.append(line.trim());
45         }
46         //设置压缩后的文件大小
47         arg1.setContentLength(sb.toString().getBytes("iso-8859-1").length);
48         //根据请求后缀名来设置请求头
49         if(".html".equals(exName)){
50             arg1.setContentType("text/html;charset="+rgw.getCharacterEncoding());
51         }else if(".js".equals(exName)){
52             arg1.setContentType("text/javascript;charset="+rgw.getCharacterEncoding());
53         }else if(".css".equals(exName)){
54             arg1.setContentType("text/css;charset="+rgw.getCharacterEncoding());
55         }
56        //响应到客户端浏览器
57         arg1.getWriter().print(sb.toString());
58         arg1.getWriter().close();        
59     }
60 
61     @Override
62     public void init(FilterConfig arg0) throws ServletException {
63         
64     }
65 
66 }

html;

 1 <!DOCTYPE html>
 2 <html>
 3   <head>
 4     <title>index.html</title>
 5     
 6     <meta name="keywords" content="keyword1,keyword2,keyword3">
 7     <meta name="description" content="this is my page">
 8     <meta name="content-type" content="text/html; charset=UTF-8">
 9     
10     <link rel="stylesheet" type="text/css" href="../css/index.css">
11     <script type="text/javascript" src="../js/index.js"></script>
12 
13   </head>
14   
15   <body>
16     This is my HTML page！ <br>
17   </body>
18 </html>

css:

1 *{
2     
3     margin: 0;
4     padding: 0;
5     color:red;
6 }

1 window.onload=function(){ 2 alert("hello"); 3 };

web.xml

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <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">
 3   <display-name>GZIP</display-name>
 4   <welcome-file-list>
 5     <welcome-file>index.html</welcome-file>
 6     <welcome-file>index.htm</welcome-file>
 7     <welcome-file>index.jsp</welcome-file>
 8     <welcome-file>default.html</welcome-file>
 9     <welcome-file>default.htm</welcome-file>
10     <welcome-file>default.jsp</welcome-file>
11   </welcome-file-list> 
12   
13    <filter>
14     <filter-name>GzipFilter</filter-name>
15     <filter-class>com.cy.filter.GzipFilter</filter-class>
16   </filter>
17   <filter-mapping>
18      <filter-name>GzipFilter</filter-name>
19      <url-pattern>/*</url-pattern>  
20   </filter-mapping>
21 </web-app>