Java HTTP客户端如何发送GET请求

在Java中，您可以使用多种库来发送HTTP GET请求。以下是使用两种流行库的示例：java.net.HttpURLConnection（标准库）和Apache HttpClient。

方法1：使用java.net.HttpURLConnection

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

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

            // 设置请求方法为GET
            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: " + response.toString());

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

方法2：使用Apache HttpClient

首先，您需要将Apache HttpClient库添加到项目的依赖项中。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 HttpGetRequest {
    public static void main(String[] args) {
        HttpClient httpClient = HttpClients.createDefault();
        HttpGet httpGet = new HttpGet("https://api.example.com/data");

        try {
            HttpResponse response = httpClient.execute(httpGet);
            int statusCode = response.getStatusLine().getStatusCode();
            System.out.println("Response Code: " + statusCode);

            String responseBody = EntityUtils.toString(response.getEntity());
            System.out.println("Response: " + responseBody);

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

这两个示例都会发送一个GET请求到指定的URL，并打印响应代码和响应体。您可以根据需要修改这些示例。