网站常使用GZIP压缩算法对网页内容进行压缩，然后传给浏览器，以减小数据传输量，提高响应速度。浏览器接收到GZIP压缩数据后会自动解压并正确显示。GZIP加速常用于解决网速慢的瓶颈。
压缩Filter中需要先判断客户浏览器时候支持GZip自动解压，如果支持，则进行GZIP压缩，否则不压缩。判断的依据是浏览器提供的Header信息，代码如下：
GZipFilter.java
1 ?package com.rom.util;
2
3 import java.io.IOException;
4
5 import javax.servlet.Filter;
6 import javax.servlet.FilterChain;
7 import javax.servlet.FilterConfig;
8 import javax.servlet.ServletException;
9 import javax.servlet.ServletRequest;
10 import javax.servlet.ServletResponse;
11 import javax.servlet.http.HttpServletRequest;
12 import javax.servlet.http.HttpServletResponse;
13
14 /**
15 * Servlet Filter implementation class GzipFilter
16 */
17 public class GzipFilter implements Filter {
18
19 /**
20 * Default constructor.
21 */
22 public GzipFilter() {
23 // TODO Auto-generated constructor stub
24 }
25
26 /**
27 * @see Filter#destroy()
28 */
29 public void destroy() {
30 // TODO Auto-generated method stub
31 }
32
33 /**
34 * @see Filter#doFilter(ServletRequest, ServletResponse, FilterChain)
35 */
36 public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) {
37 // TODO Auto-generated method stub
38 // place your code here
39
40 System.out.println("压缩的");
41
42
43 // TODO Auto-generated method stub
44 HttpServletRequest request = (HttpServletRequest)req;
45 HttpServletResponse response =(HttpServletResponse)res;
46
47 String acceptEncoding =request.getHeader("Accept-Encoding");
48 //支持的编码方式
49
50 try {
51 if(acceptEncoding != null && acceptEncoding.toLowerCase().indexOf("gzip") != -1){
52
53 System.out.println("执行压缩的方法");
54
55 //如果客户浏览器支持GZIP格式，则使用GZIP压缩数据
56 GZipResponseWrapper gzipRes = new GZipResponseWrapper(response);
57
58 chain.doFilter(request, gzipRes);//doFilter,使用自定义的response
59 gzipRes.finishResponse();//输出压缩数据
60
61 }else{
62 System.out.println("没有压缩");
63
64 chain.doFilter(request, response);//否则不压缩
65 }
66 // chain.doFilter(request, response);
67 } catch (IOException e) {
68 e.printStackTrace();
69 } catch (ServletException e) {
70 e.printStackTrace();
71 }
72 }
73
74 /**
75 * @see Filter#init(FilterConfig)
76 */
77 public void init(FilterConfig fConfig) throws ServletException {
78 // TODO Auto-generated method stub
79 }
80
81 }
GZipResponseWrapper为自定义的response类，内部将对输出的内容进行GZIP压缩。它集成HttpServletResponseWrapper类，也是一个“伪装”的response，不真正输出内容到客户端。
GZipResponseWrapper.java
1 package com.rom.util;
2
3 import java.io.IOException;
4 import java.io.OutputStreamWriter;
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 GZipResponseWrapper extends HttpServletResponseWrapper {
12 // 默认的 response
13 private HttpServletResponse response;
14
15 // 自定义的 outputStream, 执行close()的时候对数据压缩，并输出
16 private GZipOutputStream gzipOutputStream;
17
18 // 自定义 printWriter，将内容输出到 GZipOutputStream 中
19 private PrintWriter writer;
20
21 public GZipResponseWrapper(HttpServletResponse response) throws IOException {
22 super(response);
23 this.response = response;
24 }
25
26 public ServletOutputStream getOutputStream() throws IOException {
27 if (gzipOutputStream == null)
28 gzipOutputStream = new GZipOutputStream(response);
29 return gzipOutputStream;
30 }
31
32 public PrintWriter getWriter() throws IOException {
33 if (writer == null)
34 writer = new PrintWriter(new OutputStreamWriter(
35 new GZipOutputStream(response), "UTF-8"));
36 return writer;
37 }
38
39 // 压缩后数据长度会发生变化 因此将该方法内容置空
40 public void setContentLength(int contentLength) {
41 }
42
43 public void flushBuffer() throws IOException {
44 gzipOutputStream.flush();
45 }
46
47 public void finishResponse() throws IOException {
48 if (gzipOutputStream != null)
49 gzipOutputStream.close();
50 if (writer != null)
51 writer.close();
52 }
53 }
getWriter()与getOutputStream()都使用了GZipOutputStream类。这是自定义的一个ServletOutputStream类，它先将数据缓存起来，然后使用JDK自带的GZIP压缩类将数据压缩，并输出到客户端浏览器。GZIP数据压缩与输出都在该类里实现的。
GZipOutputStream.java
1 package com.rom.util;
2
3 import java.io.ByteArrayOutputStream;
4 import java.io.IOException;
5 import java.util.zip.GZIPOutputStream;
6
7 import javax.servlet.ServletOutputStream;
8 import javax.servlet.http.HttpServletResponse;
9
10 public class GZipOutputStream extends ServletOutputStream {
11
12 private HttpServletResponse response;
13
14
15 private GZIPOutputStream gzipOutputStream;
16
17
18 private ByteArrayOutputStream byteArrayOutputStream;
19
20 public GZipOutputStream(HttpServletResponse response) throws IOException {
21 this.response = response;
22 byteArrayOutputStream = new ByteArrayOutputStream();
23 gzipOutputStream = new GZIPOutputStream(byteArrayOutputStream);
24 }
25
26 public void write(int b) throws IOException {
27 gzipOutputStream.write(b);
28 }
29
30 public void close() throws IOException {
31
32
33 gzipOutputStream.finish();
34
35
36 byte[] content = byteArrayOutputStream.toByteArray();
37
38
39 response.addHeader("Content-Encoding", "gzip");
40 response.addHeader("Content-Length", Integer.toString(content.length));
41
42
43 ServletOutputStream out = response.getOutputStream();
44 out.write(content);
45 out.close();
46 }
47
48 public void flush() throws IOException {
49 gzipOutputStream.flush();
50 }
51
52 public void write(byte[] b, int off, int len) throws IOException {
53 gzipOutputStream.write(b, off, len);
54 }
55
56 public void write(byte[] b) throws IOException {
57 gzipOutputStream.write(b);
58 }
59
60 }
添加xml配置文件
1 <filter> 2 <display-name>GzipFilter</display-name> 3 <filter-name>GzipFilter</filter-name> 4 <filter-class>com.rom.util.GzipFilter</filter-class> 5 </filter> 6 <filter-mapping> 7 <filter-name>GzipFilter</filter-name> 8 <url-pattern>/*</url-pattern> 9 </filter-mapping>
时间： 2024-08-24 09:44:08