使用JAVA实现http通信详解

Http通信概述

Http通信主要有两种方式POST方式和GET方式。前者通过Http消息实体发送数据给服务器，安全性高，数据传输大小没有限制，后者通过URL的查询字符串传递给服务器参数，以明文显示在浏览器地址栏，保密性差，最多传输2048个字符。但是GET请求并不是一无是处――GET请求大多用于查询（读取资源），效率高。POST请求用于注册、登录等安全性较高且向数据库中写入数据的操作。

除了POST和GET，http通信还有其他方式！请参见http请求的方法

编码前的准备

在进行编码之前，我们先创建一个Servlet，该Servlet接收客户端的参数(name和age)，并响应客户端。

@WebServlet(urlPatterns={"/demo.do"})public class DemoServlet extends HttpServlet {  private static final long serialVersionUID = 1L;  public void doGet(HttpServletRequest request, HttpServletResponse response)      throws ServletException, IOException {    request.setCharacterEncoding("utf-8");    response.setContentType("text/html;charset=utf-8");    String name = request.getParameter("name");    String age = request.getParameter("age");    PrintWriter pw = response.getWriter();    pw.print("您使用GET方式请求该Servlet。<br />" + "name = " + name + ",age = " + age);    pw.flush();    pw.close();  }  public void doPost(HttpServletRequest request, HttpServletResponse response)      throws ServletException, IOException {    request.setCharacterEncoding("utf-8");    response.setContentType("text/html;charset=utf-8");    String name = request.getParameter("name");    String age = request.getParameter("age");    PrintWriter pw = response.getWriter();    pw.print("您使用POST方式请求该Servlet。<br />" + "name = " + name + ",age = " + age);    pw.flush();    pw.close();  }}

使用JDK实现http通信

使用URLConnection实现GET请求

实例化一个java.net.URL对象；
通过URL对象的openConnection()方法得到一个java.net.URLConnection;
通过URLConnection对象的getInputStream()方法获得输入流；
读取输入流；
关闭资源。

public void get() throws Exception{  URL url = new URL("http://127.0.0.1/http/demo.do?name=Jack&age=10");  URLConnection urlConnection = url.openConnection();                          // 打开连接  BufferedReader br = new BufferedReader(new InputStreamReader(urlConnection.getInputStream(),"utf-8")); // 获取输入流  String line = null;  StringBuilder sb = new StringBuilder();  while ((line = br.readLine()) != null) {    sb.append(line + "/n");  }  System.out.println(sb.toString());}

使用HttpURLConnection实现POST请求

java.net.HttpURLConnection是java.net.URL的子类，提供了更多的关于http的操作（getXXX 和 setXXX方法）。该类中定义了一系列的HTTP状态码：

public void post() throws IOException{  URL url = new URL("http://127.0.0.1/http/demo.do");  HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();  httpURLConnection.setDoInput(true);  httpURLConnection.setDoOutput(true);    // 设置该连接是可以输出的  httpURLConnection.setRequestMethod("POST"); // 设置请求方式  httpURLConnection.setRequestProperty("charset", "utf-8");  PrintWriter pw = new PrintWriter(new BufferedOutputStream(httpURLConnection.getOutputStream()));  pw.write("name=welcome");          // 向连接中输出数据（相当于发送数据给服务器）  pw.write("&age=14");  pw.flush();  pw.close();  BufferedReader br = new BufferedReader(new InputStreamReader(httpURLConnection.getInputStream(),"utf-8"));  String line = null;  StringBuilder sb = new StringBuilder();  while ((line = br.readLine()) != null) {  // 读取数据    sb.append(line + "/n");  }  System.out.println(sb.toString());}

使用httpclient进行http通信

httpclient大大简化了JDK中http通信的实现。

maven依赖：

<dependency>  <groupId>org.apache.httpcomponents</groupId>  <artifactId>httpclient</artifactId>  <version>4.3.6</version></dependency>

GET请求

public void httpclientGet() throws Exception{  // 创建HttpClient对象  HttpClient client = HttpClients.createDefault();  // 创建GET请求（在构造器中传入URL字符串即可）  HttpGet get = new HttpGet("http://127.0.0.1/http/demo.do?name=admin&age=40");  // 调用HttpClient对象的execute方法获得响应  HttpResponse response = client.execute(get);  // 调用HttpResponse对象的getEntity方法得到响应实体  HttpEntity httpEntity = response.getEntity();  // 使用EntityUtils工具类得到响应的字符串表示  String result = EntityUtils.toString(httpEntity,"utf-8");  System.out.println(result);}

POST请求

public void httpclientPost() throws Exception{  // 创建HttpClient对象  HttpClient client = HttpClients.createDefault();  // 创建POST请求  HttpPost post = new HttpPost("http://127.0.0.1/http/demo.do");  // 创建一个List容器，用于存放基本键值对（基本键值对即：参数名-参数值）  List<BasicNameValuePair> parameters = new ArrayList<>();  parameters.add(new BasicNameValuePair("name", "张三"));  parameters.add(new BasicNameValuePair("age", "25"));  // 向POST请求中添加消息实体  post.setEntity(new UrlEncodedFormEntity(parameters, "utf-8"));  // 得到响应并转化成字符串  HttpResponse response = client.execute(post);  HttpEntity httpEntity = response.getEntity();  String result = EntityUtils.toString(httpEntity,"utf-8");  System.out.println(result);}

HttpClient是Apache Jakarta Common下的子项目，用来提供高效的、最新的、功能丰富的支持HTTP协议的客户端编程工具包，并且它支持HTTP协议最新的版本和建议。HttpClient已经应用在很多的项目中，比如Apache Jakarta上很著名的另外两个开源项目Cactus和HTMLUnit都使用了HttpClient。