java post请求带body参数

在Java中发送POST请求带有body参数，通常会使用`HttpURLConnection`或者更现代的库如`org.apache.httpcomponents.client5`或`okhttp`。这里是一个基本的例子使用`HttpURLConnection`：

URL url = new URL("http://example.com/api/endpoint");
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setRequestMethod("POST");
connection.setDoOutput(true);

try (OutputStream os = connection.getOutputStream()) {
    String requestBody = "key1=value1&key2=value2"; // JSON or form data format
    byte[] requestBodyBytes = requestBody.getBytes(StandardCharsets.UTF_8);
    os.write(requestBodyBytes);

    int responseCode = connection.getResponseCode();
    if (responseCode == HttpURLConnection.HTTP_OK) {
        BufferedReader in = new BufferedReader(new InputStreamReader(connection.getInputStream()));
        String inputLine;
        StringBuffer response = new StringBuffer();

        while ((inputLine = in.readLine()) != null) {
            response.append(inputLine);
        }
        in.close();
        System.out.println(response.toString());
    } else {
        System.err.println("Failed : HTTP error code : " + responseCode);
    }
} catch (IOException e) {
    e.printStackTrace();
}

这里的关键是设置`setDoOutput(true)`来启用输出流，并通过`OutputStream`写入请求体。如果是JSON数据，可能还需要添加适当的Content-Type头。