SpringBoot实战发送HTTP/HTTPS请求（HttpURLConnection、HttpClient、OkhttpRestTemplate）

在Spring Boot中，我们可以使用以下几种方式来发送HTTP/HTTPS请求：

1. 使用Java的HttpURLConnection类
2. 使用Apache的HttpClient库
3. 使用OkHttp库

以下是每种方法的示例代码：

1. 使用HttpURLConnection类：

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
 
public String sendRequestUsingHttpURLConnection(String url) {
    HttpURLConnection connection = null;
    BufferedReader reader = null;
 
    try {
        URL url = new URL(url);
        connection = (HttpURLConnection) url.openConnection();
        connection.setRequestMethod("GET");
 
        // 接收响应代码
        int responseCode = connection.getResponseCode();
        if (responseCode == HttpURLConnection.HTTP_OK) {
            reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));
            return reader.readLine();
        }
 
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        if (connection != null) {
            connection.disconnect();
        }
        try {
            if (reader != null) {
                reader.close();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    return null;
}

2. 使用Apache的HttpClient库：

首先，你需要在你的pom.xml文件中添加以下依赖：

<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
    <version>4.5.12</version>
</dependency>

然后，你可以使用以下代码：

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 String sendRequestUsingHttpClient(String url) {
    HttpClient client = HttpClients.createDefault();
    HttpGet request = new HttpGet(url);
    try {
        HttpResponse response = client.execute(request);
        return EntityUtils.toString(response.getEntity(), "UTF-8");
    } catch (Exception e) {
        e.printStackTrace();
    }
    return null;
}

3. 使用OkHttp库：

首先