Java 如何实现 HTTP 请求

在 Java 中，可以使用多种方法实现 HTTP 请求。这里，我将向您展示如何使用 Java 的 HttpURLConnection 类和一个流行的库 Apache HttpClient 来实现 HTTP 请求。

方法 1：使用 HttpURLConnection

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

public class HttpRequestExample {
    public static void main(String[] args) {
        try {
            String apiUrl = "https://api.example.com/data"; // 替换为您要请求的 API URL
            URL url = new URL(apiUrl);
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();

            // 设置请求方法
            connection.setRequestMethod("GET");
            connection.setRequestProperty("User-Agent", "Mozilla/5.0");

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

            if (responseCode == HttpURLConnection.HTTP_OK) {
                // 读取响应内容
                BufferedReader in = new BufferedReader(new InputStreamReader(connection.getInputStream()));
                String inputLine;
                StringBuilder response = new StringBuilder();

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

                // 输出响应内容
                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，您需要将 Apache HttpClient 库添加到项目中。如果您使用 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，您可以使用以下代码实现 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 HttpRequestExample {
    public static void main(String[] args) {
        CloseableHttpClient httpClient = HttpClients.createDefault();
        String apiUrl = "https://api.example.com/data"; // 替换为您要请求的 API URL
        String response = "";

        try {
            HttpGet httpGet = new HttpGet(apiUrl);
            httpGet.setHeader("User-Agent", "Mozilla/5.0");

            HttpResponse httpResponse = httpClient.execute(httpGet);
            int responseCode = httpResponse.getStatusLine().getStatusCode();
            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();
            }
        }
    }
}

以上代码展示了如何使用 Java 的 HttpURLConnection 和 Apache HttpClient 库实现 HTTP GET 请求。您可以根据需要修改这些代码以适应不同的请求类型（如 POST、PUT、DELETE 等）和参数。