使用java进行http通信

1. 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

2. 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();

    }

 

}

3. 使用JDK实现http通信

 

3.1. 使用URLConnection实现GET请求

² 实例化一个java.net.URL对象；

² 通过URL对象的openConnection()方法得到一个java.net.URLConnection;

² 通过URLConnection对象的getInputStream()方法获得输入流；

² 读取输入流；

² 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());

}

 

3.2. 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());

}

4. 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);

}