http communication using java

Http communication overview

There are two main ways of Http communication: POST and GET. The former sends data to the server through the Http message entity, which has high security and no limit to the size of data transmission. The latter transmits the parameters to the server through the query string of the URL and displays it in the browser address bar in plain text. It has poor confidentiality and can transmit up to 2048 characters. . But GET requests are not useless - GET requests are mostly used for querying (reading resources) and are efficient. POST requests are used for operations such as registration and login with high security and writing data to the database.

Besides POST and GET, there are other ways of http communication! see http request method

Preparation before coding

Before coding, let's create one Servletthat Servletreceives the client's parameters (name and age) and responds to the client.

@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();
    }

}

Implement http communication using JDK

URLConnectionImplement a GET request using

1. instantiate an java.net.URLobject;
2. Get one through URLthe object's openConnection()methods java.net.URLConnection;
3. Obtain the input stream through URLConnectionthe method of the object ;getInputStream()
4. read input stream;
5. Close the resource.

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());
}

HttpURLConnectionImplement a POST request using

java.net.HttpURLConnectionYes java.net.URLsubclass, provides more operations on http (getXXX and setXXX methods). A series of HTTP status codes are defined in this class:

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());
}

use httpclientfor http communication

httpclient greatly simplifies the implementation of http communication in the JDK.

maven dependencies:

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

GET request

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 request

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);
}

 

 

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