java 中如何 发送http请求

在 Java 中可以使用 HttpURLConnection 或 HttpClient 类来发送 HTTP 请求。

使用 HttpURLConnection 发送 HTTP 请求的示例：

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

public class HttpUrlConnectionExample {

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

        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());
    }
}

使用 HttpClient 发送 HTTP 请求的示例：

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

public class HttpClientExample {

    public static void main(String[] args) throws Exception {
        HttpClient httpClient = HttpClientBuilder.create().build();
        HttpGet request = new HttpGet("http://example.com");

        String response = httpClient.execute(request, response -> {
            int status = response.getStatusLine().getStatusCode();
            if (status >= 200 && status < 300) {
                return EntityUtils.toString(response.getEntity());
            } else {
                throw new Exception("Unexpected response status: " + status);
            }
        });

        System.out.println(response);
    }
}

需要注意的是，以上示例中的 URL 和请求方法需要根据实际情况进行修改。