Android中使用gzip传递数据

HTTP协议上的GZIP编码是一种用来改进WEB应用程序性能的技术。大流量的WEB站点常常使用GZIP压缩技术来减少文件大小，减少文件大小有两个明显的好处，一是可以减少存储空间，二是通过网络传输文件时，可以减少传输的时间。作者在写这篇博客时经过测试，4.4MB的文本数据经过Gzip传输到客户端之后变为392KB，压缩效率极高。

一.服务端

服务端有2种方式去压缩，一种可以自己压缩，但是更推荐第二种方式，用PrintWriter作为输出流，工具类代码如下

[java] view plaincopy

1. /**
2. * 判断浏览器是否支持 gzip 压缩
3. * @param req
4. * @return boolean 值
5. */
6. public static boolean isGzipSupport(HttpServletRequest req) {
7. String headEncoding = req.getHeader("accept-encoding");
8. if (headEncoding == null || (headEncoding.indexOf("gzip") == -1)) { // 客户端 不支持 gzip
9. return false;
10. } else { // 支持 gzip 压缩
11. return true;
12. }
13. }
15. /**
16. * 创建 以 gzip 格式 输出的 PrintWriter 对象，如果浏览器不支持 gzip 格式，则创建普通的 PrintWriter 对象，
17. * @param req
18. * @param resp
19. * @return
20. * @throws IOException
21. */
22. public static PrintWriter createGzipPw(HttpServletRequest req, HttpServletResponse resp) throws IOException {
23. PrintWriter pw = null;
24. if (isGzipSupport(req)) { // 支持 gzip 压缩
25. pw = new PrintWriter(new GZIPOutputStream(resp.getOutputStream()));
26. // 在 header 中设置返回类型为 gzip
27. resp.setHeader("content-encoding", "gzip");
28. } else { // // 客户端 不支持 gzip
29. pw = resp.getWriter();
30. }
31. return pw;
32. }

servlet代码如下：
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1. public void doPost(HttpServletRequest request, HttpServletResponse response)
2. throws ServletException, IOException {
3. response.setCharacterEncoding("utf-8");
4. response.setHeader("Content-Encoding", "gzip");
5. String ret = "{\"ContentLayer\":{\"title\":\"内容层\"},\"PageLink\":{\"title\":\"页面跳转\"},\"WebBrowser\":{\"title\":\"浏览器\"},"
6. + "\"InlinePage\":{\"title\":\"内嵌页面\"},\"VideoComp\":{\"title\":\"视频\"},"
7. + "\"PopButton\":{\"title\":\"内容开关\"},\"ZoomingPic\":{\"title\":\"缩放大图\"},"
8. + "\"Rotate360\":{\"title\":\"360度旋转\"}}";
10. PrintWriter pw = new PrintWriter(new GZIPOutputStream(response.getOutputStream()));
11. pw.write(ret);
12. pw.close();
13. }
15. public void doGet(HttpServletRequest request, HttpServletResponse response)
16. throws ServletException, IOException {
17. this.doPost(request, response);
18. }

在代理软件中跟踪到的数据如下：
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1. ‹?Vr??+Ií+?I?L-R2aV*é,éIU2R:r??YM•ju”óS}2ó2‘e/m>üìì??@òá?INEù??¨úŸ??pà?w?g^Nf^*èTóo™R–™’š?œŸ[€?à??c[á??8•–”????n?a7@
2. ￠òós3óò2“‘Uœtoyè–?g÷€T?—$–¤› +r?e?‡Zh¤†ˆ

实际数据如下：

[html] view plaincopy

1. {"ContentLayer":{"title":"内容层"},"PageLink":{"title":"页面跳转"},"WebBrowser":{"title":"浏览器"},"InlinePage":{"title":"内嵌页面"},"VideoComp":{"title":"视频"},"PopButton":{"title":"内容开关"},"ZoomingPic":{"title":"缩放大图"},"Rotate360":{"title":"360度旋转"}}

二.Android客户端

得到HttpClient代码：

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1. private static DefaultHttpClient getHttpClient() {
2. DefaultHttpClient httpClient = new DefaultHttpClient();
4. // 设置 连接超时时间
5. httpClient.getParams().setParameter(
6. HttpConnectionParams.CONNECTION_TIMEOUT, TIMEOUT_CONNECTION);
7. // 设置 读数据超时时间
8. httpClient.getParams().setParameter(HttpConnectionParams.SO_TIMEOUT,
9. TIMEOUT_SOCKET);
10. // 设置 字符集
11. httpClient.getParams().setParameter("http.protocol.content-charset",
12. UTF_8);
13. return httpClient;
14. }

得到HttpPost：

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1. private static HttpPost getHttpPost(String url) {
2. HttpPost httpPost = new HttpPost(url);
3. // 设置 请求超时时间
4. httpPost.getParams().setParameter(HttpConnectionParams.SO_TIMEOUT,
5. TIMEOUT_SOCKET);
6. httpPost.setHeader("Connection", "Keep-Alive");
7. httpPost.addHeader("Accept-Encoding", "gzip");
8. return httpPost;
9. }

访问网络代码：

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1. public static InputStream http_post_return_byte(String url,
2. Map<String, String> params) throws AppException {
3. DefaultHttpClient httpclient = null;
4. HttpPost post = null;
5. HttpResponse response = null;
6. StringBuilder sb = null;
7. StringEntity stringEntity = null;
8. try {
9. httpclient = getHttpClient();
10. post = getHttpPost(url);
11. sb = new StringBuilder();
12. if (params != null && !params.isEmpty()) {
13. Logger.d("In http_post the url is get here");
14. for (Entry<String, String> entry : params.entrySet()) {
15. sb.append(entry.getKey())
16. .append("=")
17. .append(URLEncoder.encode(entry.getValue(),
18. HTTP.UTF_8)).append("&");
19. }
20. sb.deleteCharAt(sb.lastIndexOf("&"));
21. Logger.d("In http_post the url is " + url + " and params is "
22. + sb.toString());
23. stringEntity = new StringEntity(sb.toString());
24. stringEntity
25. .setContentType("application/x-www-form-urlencoded");
26. post.setEntity(stringEntity);
27. }
29. response = httpclient.execute(post);
30. int statusCode = response.getStatusLine().getStatusCode();
31. Logger.d("statusCode is " + statusCode);
32. if (statusCode != HttpStatus.SC_OK) {
33. throw AppException.http(statusCode);
34. }
36. InputStream is = response.getEntity().getContent();
38. Header contentEncoding = response
39. .getFirstHeader("Content-Encoding");
40. if (contentEncoding != null
41. && contentEncoding.getValue().equalsIgnoreCase("gzip")) {
42. is = new GZIPInputStream(new BufferedInputStream(is));
43. }
44. return is;
46. } catch (ClientProtocolException e) {
47. e.printStackTrace();
48. throw AppException.http(e);
49. } catch (IOException e) {
50. e.printStackTrace();
51. throw AppException.network(e);
52. } finally {
54. /*
55. * if (!post.isAborted()) {
56. *
57. * post.abort(); } httpclient = null;
58. */
60. }
62. }