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

/**
		 * 判断浏览器是否支持 gzip 压缩
		 * @param req
		 * @return boolean 值
		 */
		public static boolean isGzipSupport(HttpServletRequest req) {
			String headEncoding = req.getHeader("accept-encoding");
			if (headEncoding == null || (headEncoding.indexOf("gzip") == -1)) { // 客户端 不支持 gzip
				return false;
			} else { // 支持 gzip 压缩
				return true;
			}
		}

		/**
		 * 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，
		 * @param req
		 * @param resp
		 * @return
		 * @throws IOException
		 */
		public static PrintWriter createGzipPw(HttpServletRequest req, HttpServletResponse resp) throws IOException {
			PrintWriter pw = null;
			if (isGzipSupport(req)) { // 支持 gzip 压缩
				pw = new PrintWriter(new GZIPOutputStream(resp.getOutputStream()));
				// 在 header 中设置返回类型为 gzip
				resp.setHeader("content-encoding", "gzip");
			} else { // // 客户端 不支持 gzip
				pw = resp.getWriter();
			}
			return pw;
		}
	

servlet代码如下：

	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		response.setCharacterEncoding("utf-8");
		response.setHeader("Content-Encoding", "gzip");
		String ret = "{\"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\"}}";
		
		PrintWriter pw = new PrintWriter(new GZIPOutputStream(response.getOutputStream()));
		pw.write(ret);
		pw.close();
	}

	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		this.doPost(request, response);
	}

在代理软件中跟踪到的数据如下：

‹«VrÎÏ+IÍ+ñI¬L-R²ªV*É,ÉIU²R:rëÄÝM•ju”ÓS}2ó²‘e/m>üì̏ë«@òá©INEùåŨúŸ¬?pàØw¼g^Nf^*ÈTóo™R–™’šïœŸ[€¬àÔåc[ÁÖç8•–”äç¡»nÿª7@
¢òós3óÒ2“‘Uœþºýè–Ïg÷€Tå—$–¤› +r·¸ðä‡Zh¤†ˆ

实际数据如下：

{"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：

private static DefaultHttpClient getHttpClient() {
		DefaultHttpClient httpClient = new DefaultHttpClient();

		// 设置 连接超时时间
		httpClient.getParams().setParameter(
				HttpConnectionParams.CONNECTION_TIMEOUT, TIMEOUT_CONNECTION);
		// 设置 读数据超时时间
		httpClient.getParams().setParameter(HttpConnectionParams.SO_TIMEOUT,
				TIMEOUT_SOCKET);
		// 设置 字符集
		httpClient.getParams().setParameter("http.protocol.content-charset",
				UTF_8);
		return httpClient;
	}

得到HttpPost：

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

访问网络代码：

public static InputStream http_post_return_byte(String url,
			Map<String, String> params) throws AppException {
		DefaultHttpClient httpclient = null;
		HttpPost post = null;
		HttpResponse response = null;
		StringBuilder sb = null;
		StringEntity stringEntity = null;
		try {
			httpclient = getHttpClient();
			post = getHttpPost(url);
			sb = new StringBuilder();
			if (params != null && !params.isEmpty()) {
				Logger.d("In http_post the url is get here");
				for (Entry<String, String> entry : params.entrySet()) {
					sb.append(entry.getKey())
							.append("=")
							.append(URLEncoder.encode(entry.getValue(),
									HTTP.UTF_8)).append("&");
				}
				sb.deleteCharAt(sb.lastIndexOf("&"));
				Logger.d("In http_post the url is " + url + " and params is "
						+ sb.toString());
				stringEntity = new StringEntity(sb.toString());
				stringEntity
						.setContentType("application/x-www-form-urlencoded");
				post.setEntity(stringEntity);
			}

			response = httpclient.execute(post);
			int statusCode = response.getStatusLine().getStatusCode();
			Logger.d("statusCode is " + statusCode);
			if (statusCode != HttpStatus.SC_OK) {
				throw AppException.http(statusCode);
			}

			InputStream is = response.getEntity().getContent();

			Header contentEncoding = response
					.getFirstHeader("Content-Encoding");
			if (contentEncoding != null
					&& contentEncoding.getValue().equalsIgnoreCase("gzip")) {
				is = new GZIPInputStream(new BufferedInputStream(is));
			}
			return is;

		} catch (ClientProtocolException e) {
			e.printStackTrace();
			throw AppException.http(e);
		} catch (IOException e) {
			e.printStackTrace();
			throw AppException.network(e);
		} finally {

			/*
			 * if (!post.isAborted()) {
			 * 
			 * post.abort(); } httpclient = null;
			 */

		}

	}

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