使用java进行http通讯

Http通讯概述 Http通讯主要有两种方式POST方式和GET方式。前者经过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，后者经过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。可是GET请求并非一无可取——GET请求大多用于查询（读取资源），效率高。POST请求用于注册、登陆等安全性较高且向数据库中写入数据的操做。

除了POST和GET，http通讯还有其余方式！请参见http请求的方法

编码前的准备 在进行编码以前，咱们先建立一个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通讯 使用URLConnection实现GET请求 实例化一个java.net.URL对象； 经过URL对象的openConnection()方法获得一个java.net.URLConnection; 经过URLConnection对象的getInputStream()方法得到输入流； 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();                                                    // 打开链接
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的操做（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);        // 设置该链接是能够输出的
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");                   // 向链接中输出数据（至关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通讯 httpclient大大简化了JDK中http通讯的实现。

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{

// 建立HttpClient对象
HttpClient client = HttpClients.createDefault();

// 建立GET请求（在构造器中传入URL字符串便可）
HttpGet get = new HttpGet("http://127.0.0.1/http/demo.do?name=admin&age=40");

// 调用HttpClient对象的execute方法得到响应
HttpResponse response = client.execute(get);

// 调用HttpResponse对象的getEntity方法获得响应实体
HttpEntity httpEntity = response.getEntity();

// 使用EntityUtils工具类获得响应的字符串表示
String result = EntityUtils.toString(httpEntity,"utf-8");
System.out.println(result);

}

POST请求 public void httpclientPost() throws Exception{

// 建立HttpClient对象
HttpClient client = HttpClients.createDefault();

// 建立POST请求
HttpPost post = new HttpPost("http://127.0.0.1/http/demo.do");

// 建立一个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"));

// 获得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);

}

参考文档 httpclient官网