Java中HTTP请求怎么发送

在Java中发送HTTP请求，你可以使用多种方法。以下是一些常用的方法：

1. 使用java.net.HttpURLConnection（适用于Java 1.1及以上版本）：

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;

public class HttpGetRequest {
    public static void main(String[] args) {
        try {
            URL url = new URL("http://example.com");
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            connection.setRequestMethod("GET");

            int responseCode = connection.getResponseCode();
            System.out.println("Response Code: " + responseCode);

            BufferedReader in = new BufferedReader(new InputStreamReader(connection.getInputStream()));
            String inputLine;
            StringBuilder response = new StringBuilder();

            while ((inputLine = in.readLine()) != null) {
                response.append(inputLine);
            }
            in.close();

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

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

2. 使用java.net.URL和java.io.InputStream（适用于简单的GET请求）：

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.URL;

public class SimpleHttpGetRequest {
    public static void main(String[] args) {
        try {
            URL url = new URL("http://example.com");
            InputStream inputStream = url.openStream();
            BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));

            String line;
            while ((line = reader.readLine()) != null) {
                System.out.println(line);
            }
            reader.close();

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

3. 使用第三方库，如Apache HttpClient（适用于更复杂的HTTP请求和更好的错误处理）： 首先，你需要将Apache HttpClient库添加到项目的依赖中。如果你使用Maven，可以在pom.xml文件中添加以下依赖：

<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
    <version>4.5.13</version>
</dependency>

然后，你可以使用以下代码发送GET请求：

import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;

public class ApacheHttpClientExample {
    public static void main(String[] args) {
        try {
            HttpClient httpClient = HttpClients.createDefault();
            HttpGet httpGet = new HttpGet("http://example.com");

            HttpResponse httpResponse = httpClient.execute(httpGet);
            String responseBody = EntityUtils.toString(httpResponse.getEntity());

            System.out.println(responseBody);

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

这些方法中的每一个都可以用于发送HTTP请求。你可以根据你的需求和项目环境选择合适的方法。