java发送post json数据

以下是使用Java发送POST请求并发送JSON数据的示例代码：

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

public class HttpPostJsonExample {

    public static void main(String[] args) throws Exception {

        String url = "http://example.com/api/endpoint";
        String jsonInputString = "{\"name\": \"John\", \"age\": 30, \"city\": \"New York\"}";

        URL obj = new URL(url);
        HttpURLConnection con = (HttpURLConnection) obj.openConnection();
        con.setRequestMethod("POST");
        con.setRequestProperty("Content-Type", "application/json");

        con.setDoOutput(true);
        OutputStream os = con.getOutputStream();
        os.write(jsonInputString.getBytes());
        os.flush();
        os.close();

        int responseCode = con.getResponseCode();
        System.out.println("Response Code : " + responseCode);

        BufferedReader in = new BufferedReader(
                new InputStreamReader(con.getInputStream()));
        String inputLine;
        StringBuffer response = new StringBuffer();
        while ((inputLine = in.readLine()) != null) {
            response.append(inputLine);
        }
        in.close();

        // Print response
        System.out.println(response.toString());

    }
}

在上面的示例中，我们使用HttpURLConnection类来创建一个HTTP POST请求，并将JSON数据作为请求正文发送。然后，我们可以读取响应并把它打印出来。请注意，在设置请求头时，我们设置了Content-Type为application/json，这样服务器就知道我们发送的是JSON数据。