发送post请求 Content-type : application/json

1使用 HttpURLConnection：（不过测试的时候会出现url访问不了的情况，建议第二种）

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

public class Main {
    public static void main(String[] args) {
        try {
            URL url = new URL("https://example.com/api/endpoint"); // 替换为目标 API 的 URL
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setDoOutput(true);
            conn.setRequestMethod("POST");
            conn.setRequestProperty("Content-Type", "application/json");

            // 构建请求体
            String requestBody = "{\"key1\":\"value1\", \"key2\":\"value2\"}";

            // 发送请求
            DataOutputStream outputStream = new DataOutputStream(conn.getOutputStream());
            outputStream.writeBytes(requestBody);
            outputStream.flush();
            outputStream.close();

            // 获取响应
            BufferedReader reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));
            String line;
            StringBuilder response = new StringBuilder();
            while ((line = reader.readLine()) != null) {
                response.append(line);
            }
            reader.close();

            // 处理响应
            System.out.println(response.toString());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

2使用 HttpClient：

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.ContentType;
import org.apache.http.entity.StringEntity;
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) {
        try (CloseableHttpClient httpClient = HttpClients.createDefault()) {
            HttpPost httpPost = new HttpPost("https://example.com/api/endpoint"); // 替换为目标 API 的 URL
            httpPost.setHeader("Content-Type", "application/json");

            // 构建请求体
            String requestBody = "{\"key1\":\"value1\", \"key2\":\"value2\"}";
            StringEntity requestEntity = new StringEntity(requestBody, ContentType.APPLICATION_JSON);
            httpPost.setEntity(requestEntity);

            // 发送请求
            HttpResponse response = httpClient.execute(httpPost);

            // 处理响应
            HttpEntity entity = response.getEntity();
            String responseBody = EntityUtils.toString(entity);
            System.out.println(responseBody);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}