gzip是http協議中使用的一種加密演算法,客戶端向web伺服器端發出了請求後，通常情況下伺服器端會將頁面檔案和其他資源，返回到客戶端，客戶端載入後渲染呈現，這種情況檔案一般都比較大，如果開啟Gzip ，那麼伺服器端響應後，會將頁面，JS,CSS等文字檔案或者其他檔案通過高壓縮演算法將其壓縮，然後傳輸到客戶端，由客戶端的瀏覽器負責解壓縮與呈現。通常能節省40%以上的流量（一般都有60%左右），一些PHP，JSP檔案也能夠進行壓縮。
1.Tomcat 直接開啟Gzip
開啟Tomcat 目錄下的conf下的server.xml，並找到如下資訊:
Xml程式碼

1. <!-- Note : To use gzip compression you could set the following properties :
2. compression="on"
3. compressionMinSize="2048"
4. noCompressionUserAgents="gozilla, traviata"
5. compressableMimeType="text/html,text/xml"
6. -->

<!-- Note : To use gzip compression you could set the following properties : compression="on" compressionMinSize="2048" noCompressionUserAgents="gozilla, traviata" compressableMimeType="text/html,text/xml" -->
 

把它們加入到你配置的<Connector port="80" .../>中去。如果要壓縮css 和 js，加入compressableMimeType="text/html,text/xml,text/css,text/javascript"。還要壓縮圖片,加入compressableMimeType="text/html,text/xml,text/css,text/javascript,image/gif,image/jpg"。
開啟後重啟Tomcat ，通過瀏覽器檢視headers資訊就能看到是否開啟。

2.使用filter,在程式碼級別完成web應用的gzip壓縮的開啟。

(1).CachedResponseWrapper類
實現定製輸出的關鍵是對HttpServletResponse 進行包裝，截獲所有的輸出，等到過濾器鏈處理完畢後，再對截獲的輸出進行處理，並寫入到真正的HttpServletResponse 物件中。JavaEE 框架已經定義了一個HttpServletResponseWrapper 類使得包裝HttpServletResponse 更加容易。我們擴充套件這個HttpServletResponseWrapper，截獲所有的輸出，並儲存到ByteArrayOutputStream 中。
定製的包裝響應能方便地從幫助類 HttpServletResponseWrapper 中匯出。這一類粗略地執行許多方法，允許我們簡單地覆蓋 getOutputStream() 方法以及 getWriter() 方法，提供了定製輸出流的例項。
HttpServletResponseWrapper這個類的使用包括以下五個步驟：
1）建立一個響應包裝器。擴充套件javax.servlet.http.HttpServletResponseWrapper。
2）提供一個快取輸出的PrintWriter。過載getWriter方法，返回一個儲存傳送給它的所有東西的PrintWriter，並把結果存進一個可以稍後訪問的欄位中。
3）傳遞該包裝器給doFilter。此呼叫是合法的，因為HttpServletResponseWrapper實現HttpServletResponse。
4）提取和修改輸出。在呼叫FilterChain的doFilter方法後，原資源的輸出只要利用步驟2中提供的機制就可以得到。只要對你的應用適合，就可以修改或替換它。
5）傳送修改過的輸出到客戶機。因為原資源不再發送輸出到客戶機（這些輸出已經存放到你的響應包裝器中了），所以必須傳送這些輸出。這樣，你的過濾器需要從原響應物件中獲得PrintWriter或OutputStream，並傳遞修改過的輸出到該流中。
Java程式碼

1. class
   CachedResponseWrapper extends HttpServletResponseWrapper {
2. public static final int OUTPUT_NONE = 0;
3. public static final int OUTPUT_WRITER = 1;
4. public static final int OUTPUT_STREAM = 2;
5. private int outputType = OUTPUT_NONE;
6. private int status = SC_OK;
7. private ServletOutputStream output = null;
8. private
   PrintWriter writer = null;
9. private ByteArrayOutputStream buffer = null;
10. public CachedResponseWrapper(HttpServletResponse resp) throws IOException {
11. super(resp);
12. buffer = new ByteArrayOutputStream();
13. }
14. public int getStatus() {
15. return status;
16. }
17. public void setStatus(int status) {
18. super.setStatus(status);
19. this.status = status;
20. }
21. public void setStatus(int status, String string) {
22. super.setStatus(status, string);
23. this.status = status;
24. }
25. public void sendError(int status, String string) throws IOException {
26. super.sendError(status, string);
27. this.status = status;
28. }
29. public void sendError(int status) throws IOException {
30. super.sendError(status);
31. this.status = status;
32. }
33. public void sendRedirect(String location) throws IOException {
34. super.sendRedirect(location);
35. this.status = SC_MOVED_TEMPORARILY;
36. }
37. public PrintWriter getWriter() throws IOException {
38. if (outputType == OUTPUT_STREAM)
39. throw new IllegalStateException();
40. else if (outputType == OUTPUT_WRITER)
41. return writer;
42. else {
43. outputType = OUTPUT_WRITER;
44. writer = new PrintWriter(new OutputStreamWriter(buffer,
45. getCharacterEncoding()));
46. return writer;
47. }
48. }
49. public ServletOutputStream getOutputStream() throws IOException {
50. if (outputType == OUTPUT_WRITER)
51. throw new IllegalStateException();
52. else if (outputType == OUTPUT_STREAM)
53. return output;
54. else {
55. outputType = OUTPUT_STREAM;
56. output = new WrappedOutputStream(buffer);
57. return output;
58. }
59. }
60. public void flushBuffer() throws IOException {
61. if (outputType == OUTPUT_WRITER)
62. writer.flush();
63. if (outputType == OUTPUT_STREAM)
64. output.flush();
65. }
66. public void reset() {
67. outputType = OUTPUT_NONE;
68. buffer.reset();
69. }
70. public byte[] getResponseData() throws IOException {
71. flushBuffer();
72. return buffer.toByteArray();
73. }
74. class WrappedOutputStream extends ServletOutputStream {
75. private ByteArrayOutputStream buffer;
76. public WrappedOutputStream(ByteArrayOutputStream buffer) {
77. this.buffer = buffer;
78. }
79. public void write(int b) throws IOException {
80. buffer.write(b);
81. }
82. public byte[] toByteArray() {
83. return buffer.toByteArray();
84. }
85. }
86. }

 class CachedResponseWrapper extends HttpServletResponseWrapper { public static final int OUTPUT_NONE = 0; public static final int OUTPUT_WRITER = 1; public static final int OUTPUT_STREAM = 2; private int outputType = OUTPUT_NONE; private int status = SC_OK; private ServletOutputStream output = null; private PrintWriter writer = null; private ByteArrayOutputStream buffer = null; public CachedResponseWrapper(HttpServletResponse resp) throws IOException { super(resp); buffer = new ByteArrayOutputStream(); } public int getStatus() { return status; } public void setStatus(int status) { super.setStatus(status); this.status = status; } public void setStatus(int status, String string) { super.setStatus(status, string); this.status = status; } public void sendError(int status, String string) throws IOException { super.sendError(status, string); this.status = status; } public void sendError(int status) throws IOException { super.sendError(status); this.status = status; } public void sendRedirect(String location) throws IOException { super.sendRedirect(location); this.status = SC_MOVED_TEMPORARILY; } public PrintWriter getWriter() throws IOException { if (outputType == OUTPUT_STREAM) throw new IllegalStateException(); else if (outputType == OUTPUT_WRITER) return writer; else { outputType = OUTPUT_WRITER; writer = new PrintWriter(new OutputStreamWriter(buffer, getCharacterEncoding())); return writer; } } public ServletOutputStream getOutputStream() throws IOException { if (outputType == OUTPUT_WRITER) throw new IllegalStateException(); else if (outputType == OUTPUT_STREAM) return output; else { outputType = OUTPUT_STREAM; output = new WrappedOutputStream(buffer); return output; } } public void flushBuffer() throws IOException { if (outputType == OUTPUT_WRITER) writer.flush(); if (outputType == OUTPUT_STREAM) output.flush(); } public void reset() { outputType = OUTPUT_NONE; buffer.reset(); } public byte[] getResponseData() throws IOException { flushBuffer(); return buffer.toByteArray(); } class WrappedOutputStream extends ServletOutputStream { private ByteArrayOutputStream buffer; public WrappedOutputStream(ByteArrayOutputStream buffer) { this.buffer = buffer; } public void write(int b) throws IOException { buffer.write(b); } public byte[] toByteArray() { return buffer.toByteArray(); } } }

(2).GZipFilter類
Java程式碼

1. public class GZipFilter implements Filter {
2. public void init(FilterConfig arg0) throws ServletException {
3. }
4. public void doFilter(ServletRequest request, ServletResponse response,
5. FilterChain chain) throws IOException, ServletException {
6. HttpServletResponse httpResponse = (HttpServletResponse) response;
7. CachedResponseWrapper wrapper = new CachedResponseWrapper(httpResponse);
8. // 寫入wrapper:
9. chain.doFilter(request, wrapper);
10. // 對響應進行處理，這裡是進行GZip壓縮:
11. byte[] data = GZipUtil.gzip(wrapper.getResponseData());
12. httpResponse.setHeader("Content-Encoding", "gzip");
13. httpResponse.setContentLength(data.length);
14. ServletOutputStream output = response.getOutputStream();
15. output.write(data);
16. output.flush();
17. }
18. public void destroy() {
19. }
20. }

public class GZipFilter implements Filter { public void init(FilterConfig arg0) throws ServletException { } public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { HttpServletResponse httpResponse = (HttpServletResponse) response; CachedResponseWrapper wrapper = new CachedResponseWrapper(httpResponse); // 寫入wrapper: chain.doFilter(request, wrapper); // 對響應進行處理，這裡是進行GZip壓縮: byte[] data = GZipUtil.gzip(wrapper.getResponseData()); httpResponse.setHeader("Content-Encoding", "gzip"); httpResponse.setContentLength(data.length); ServletOutputStream output = response.getOutputStream(); output.write(data); output.flush(); } public void destroy() { } }

(3).GZipUtil類
Java程式碼

1. public final class GZipUtil {
2. public static byte[] gzip(byte[] data) {
3. ByteArrayOutputStream byteOutput = new ByteArrayOutputStream(10240);
4. GZIPOutputStream output = null;
5. try {
6. output = new GZIPOutputStream(byteOutput);
7. output.write(data);
8. } catch (IOException e) {
9. throw new RuntimeException("G-Zip failed.", e);
10. } finally {
11. if (output != null) {
12. try {
13. output.close();
14. } catch (IOException e) {
15. }
16. }
17. }
18. return byteOutput.toByteArray();
19. }
20. }

public final class GZipUtil { public static byte[] gzip(byte[] data) { ByteArrayOutputStream byteOutput = new ByteArrayOutputStream(10240); GZIPOutputStream output = null; try { output = new GZIPOutputStream(byteOutput); output.write(data); } catch (IOException e) { throw new RuntimeException("G-Zip failed.", e); } finally { if (output != null) { try { output.close(); } catch (IOException e) { } } } return byteOutput.toByteArray(); } }

(4).在web.xml中配置 GZipFilter
Xml程式碼

1. <filter>
2. <filter-name>GZipFilter</filter-name>
3. <filter-class>com.logcd.filter.GZipFilter</filter-class>
4. </filter>
5. <filter-mapping>
6. <filter-name>GZipFilter</filter-name>
7. <url-pattern>*.html</url-pattern>
8. </filter-mapping>