org.json.JSONObject：类型java.lang.String的值<？php无法转换为JSONObject

Question

我正在尝试将数据插入远程mysql数据库。我遇到的问题是位于远程服务器中时解析php文件。我总是得到类型java.lang.String的值php无法转换为JSONObject'错误。

这是我的php代码：

<?php
$response = array();
include 'db/connect.php';
include 'function.php';

$inputJSON = file_get_contents('php://input');
$input = json_decode($inputJSON, TRUE);

if(isset($input['user_ID']) && isset($input['submit_your_activity']) && isset($input['how_was_the_activity'])){
    $user_ID = $input['user_ID'];
    $submit_your_activity = $input['submit_your_activity'];
    $how_was_the_activity = $input['how_was_the_activity'];

    if(!userExists($user_ID)){
        $insertQuery = "INSERT INTO userdata(user_ID, submit_your_activity, how_was_the_activity) VALUES (?,?,?)";
        if($stmt = $conn->prepare($insertQuery)){
             $stmt->bind_param("sss",$user_ID,$submit_your_activity,$how_was_the_activity);
             $stmt->execute();
             $response["status"] = 0;
             $response["message"] = "Successful";
             $stmt->close();
        } else {
             $response["status"] = 1;
             $response["message"] = "Failed";
        }
    }
}
else{
    $response["status"] = 2;
    $response["message"] = "Missing mandatory parameters";
}
echo json_encode($response);
?>

这是我的Java代码，用于连接到远程服务器中的php代码。我已经使用GET方法连接到AWS S3。

    private void InsertData(){
        JSONObject request = new JSONObject();
        try{
            request.put(KEY_USER_ID, user_ID);
            request.put(KEY_SUBMIT_YOUR_ACTIVITY, submit_your_activity);
            request.put(KEY_HOW_WAS_YOUR_ACTIVITY, how_was_the_activity);
        }catch (JSONException e){
            e.printStackTrace();
        }

        JsonObjectRequest jsonObjectRequest = new JsonObjectRequest(Request.Method.GET, link, request, new Response.Listener<JSONObject>() {
            @Override
            public void onResponse(JSONObject response) {
                try {
                    if (response.getInt(KEY_STATUS) == 0) {
                        Toast.makeText(getApplicationContext(), "success", Toast.LENGTH_LONG).show();
                    } else if (response.getInt(KEY_STATUS) == 1) {
                        editText1.setError("User Already Exists");
                        editText1.requestFocus();
                    } else{
                        Toast.makeText(getApplicationContext(), response.getString(KEY_MESSAGE), Toast.LENGTH_LONG).show();
                    }
                } catch (JSONException e) {
                    e.printStackTrace();
                }
            }
        }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                Toast.makeText(getApplicationContext(), error.getLocalizedMessage(), Toast.LENGTH_LONG).show();
            }
        });
        MySingleton.getInstance(this).addToRequestQueue(jsonObjectRequest);
    }

在Response.ErrorListener中引发错误消息。