java http怎样发送请求

在Java中，可以使用HttpURLConnection类或者第三方库Apache HttpClient来发送HTTP请求。这里我将为你提供两种方法的示例代码。

方法1：使用HttpURLConnection

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

public class Main {
    public static void main(String[] args) {
        try {
            String apiUrl = "https://api.example.com/data"; // 替换为你要请求的API URL
            URL url = new URL(apiUrl);
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            connection.setRequestMethod("GET"); // 设置请求方法，可以是GET、POST、PUT等
            connection.setRequestProperty("User-Agent", "Mozilla/5.0"); // 设置User-Agent
            connection.setConnectTimeout(5000); // 设置连接超时时间（毫秒）
            connection.setReadTimeout(5000); // 设置读取数据超时时间（毫秒）

            int responseCode = connection.getResponseCode(); // 获取响应状态码
            System.out.println("Response Code: " + responseCode);

            if (responseCode == HttpURLConnection.HTTP_OK) {
                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: " + response.toString());
            } else {
                System.out.println("GET request failed");
            }

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

方法2：使用Apache HttpClient

首先，需要添加Apache HttpClient库的依赖。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，可以使用以下代码发送HTTP请求：

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
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 Main {
    public static void main(String[] args) {
        CloseableHttpClient httpClient = HttpClients.createDefault();
        String apiUrl = "https://api.example.com/data"; // 替换为你要请求的API URL
        String response = "";

        try {
            HttpGet httpGet = new HttpGet(apiUrl);
            httpGet.setHeader("User-Agent", "Mozilla/5.0"); // 设置User-Agent
            HttpResponse httpResponse = httpClient.execute(httpGet);
            int responseCode = httpResponse.getStatusLine().getStatusCode(); // 获取响应状态码
            System.out.println("Response Code: " + responseCode);

            if (responseCode == 200) {
                HttpEntity httpEntity = httpResponse.getEntity();
                response = EntityUtils.toString(httpEntity);
                System.out.println("Response: " + response);
            } else {
                System.out.println("GET request failed");
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                httpClient.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

以上两种方法都可以用于发送HTTP请求。根据你的需求和项目结构，可以选择适合你的方法。