Java-based HTTP request method and implementation

Java is one of the most popular programming languages ​​now, and HTTP requests are a very common way of interaction in Web development. Therefore, it is very important to master the method of implementing HTTP requests in Java. In this article, I will introduce you to the way to implement HTTP requests based on Java and related knowledge.

HTTP request is one of the most basic operations in web development. It refers to the process in which the client initiates a request to the server and obtains a response. In Java, implementing HTTP requests requires the use of Java's network programming class library. Java provides a variety of ways to implement HTTP requests, such as using the HttpURLConnection class, using the HttpClient class, etc.

1. Implement HTTP requests based on HttpURLConnection

The HttpURLConnection class is a tool class that comes with Java for accessing HTTP resources. It supports all request methods of the HTTP protocol. You can obtain the content of the server response through InputStream, and you can also write the request content to the server through OutputStream. The following is an example of implementing an HTTP GET request based on HttpURLConnection:

import java.net.*;
import java.io.*;

public class HttpDemo {
    public static void main(String[] args) throws Exception {
        URL url = new URL("https://www.example.com");
        
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setRequestMethod("GET");
        conn.setRequestProperty("User-Agent", "Mozilla/5.0");
        
        int responseCode = conn.getResponseCode();
        System.out.println("Response Code : " + responseCode);

        InputStream inputStream = conn.getInputStream();
        BufferedReader in = new BufferedReader(new InputStreamReader(inputStream));
        String inputLine;
        StringBuffer response = new StringBuffer();
        while ((inputLine = in.readLine()) != null) {
            response.append(inputLine);
        }
        in.close();

        System.out.println(response.toString());
    }
}

In this example, we use the URL class in Java to instantiate a URL object and specify the URL address to be accessed. After opening this URL connection, we set the request method to GET through an instance of the HttpURLConnection class, and set the request header information. Finally, we read the server's response through InputStream, store the response content in the StringBuffer object, and print the output.

2. Implement HTTP requests based on HttpClient

The HttpClient class is an open source Java-implemented HTTP client provided by Apache. It supports a variety of HTTP request methods, such as POST requests, GET requests, and PUT requests. etc. HttpClient has a more friendly API design than HttpURLConnection and is easier to understand and use. The following is an example of implementing an HTTP GET request based on HttpClient:

import org.apache.http.HttpEntity;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;

public class HttpDemo {
    public static void main(String[] args) throws Exception {
        CloseableHttpClient httpClient = HttpClients.createDefault();
        HttpGet httpGet = new HttpGet("https://www.example.com");
        
        CloseableHttpResponse response = httpClient.execute(httpGet);
        try {
            HttpEntity entity = response.getEntity();
            String result = EntityUtils.toString(entity, "UTF-8");
            System.out.println(result);
        } finally {
            response.close();
        }
    }
}

In this example, we create a closeable HttpClient instance by creating a CloseableHttpClient object, and then use the HttpGet class to create a GET request and set the request URL. . Finally, execute the execute method to make a request to the server and get the response. Obtaining the content of the response requires parsing the HttpEntity. You can use the EntityUtils tool class to parse the HttpEntity.

Summary:

There are many ways to implement HTTP requests in Java. This article mainly introduces two methods based on HttpURLConnection and HttpClient. Their implementation methods are different, but the principles are basically the same, and they can all implement HTTP requests in Java programs very conveniently.

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