Java中的Post請求帶Json參數是通過HttpURLConnection來實現的。以下是實現步驟：

try {
URL url = new URL("http://example.com/your_endpoint");
HttpURLConnection con = (HttpURLConnection ) url.openConnection();
// 設置請求方法為POST
con.setRequestMethod("POST");
// 設置請求頭
con.setRequestProperty("Content-Type", "application/json;charset=utf-8");
con.setRequestProperty("Accept", "application/json");
// 開啟輸出流
con.setDoOutput(true);
// 構造請求Json數據
JSONObject jsonObject = new JSONObject();
jsonObject.put("name", "Jack");
jsonObject.put("age", "25");
String requestBody = jsonObject.toString();
// 發送請求并寫入數據
OutputStreamWriter out = new OutputStreamWriter(con.getOutputStream());
out.write(requestBody);
out.flush();
out.close();
// 獲取響應狀態碼
int responseCode = con.getResponseCode();
if(responseCode == 200) {
// 獲取響應內容
BufferedReader in = new BufferedReader(new InputStreamReader(con.getInputStream()));
String responseLine;
StringBuffer response = new StringBuffer();
while ((responseLine = in.readLine()) != null) {
response.append(responseLine);
}
in.close();
// 處理響應內容
JSONObject responseJson = new JSONObject(response.toString());
System.out.println(responseJson);
} else {
System.out.println("請求失敗:"+responseCode);
}
} catch (IOException e) {
e.printStackTrace();
}

以上代碼實現了一個簡單的Post請求帶Json參數的示例，可以根據需要進行修改和擴展。