如何检查服务器响应是否为 json？

Question

当我尝试通过注册用户向数据库添加一些数据时，我的应用程序遇到了问题，问题是 php 脚本是否有任何错误或者它没有返回 json 我得到一个错误，activity 被迫停止，而如果 php 没有错误并正确返回 json，一切正常，所以我想检查一下服务器响应知道它是否有效，所以我可以避免错误，这是我的代码：

import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
import org.apache.http.NameValuePair;
import org.apache.http.message.BasicNameValuePair;
import org.json.JSONException;
import org.json.JSONObject;
import java.util.ArrayList;
import java.util.List;

public class Register  extends Activity {

    Button back;
    Button register;
    EditText iname;
    EditText iemail;
    EditText ireEmail;
    EditText ipassword;
    EditText irePassword;
    EditText iid;
    EditText iphone;
    EditText iaddress1;
    EditText iaddress2;


    // Progress Dialog
    private ProgressDialog pDialog;

    JSONParser jsonParser = new JSONParser();

    // url to create new product
    private static String url_register = "http://192.168.0.103/perfectdelivery/register.php";

    // JSON Node names
    private static final String TAG_SUCCESS = "success";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.register);

        iname = (EditText) findViewById(R.id.editText1);
        iemail = (EditText) findViewById(R.id.editText2);
        ireEmail = (EditText) findViewById(R.id.editText3);
        ipassword = (EditText) findViewById(R.id.editText4);
        irePassword = (EditText) findViewById(R.id.editText5);
        iid = (EditText) findViewById(R.id.editText6);
        iphone = (EditText) findViewById(R.id.editText7);
        iaddress1 = (EditText) findViewById(R.id.editText8);
        iaddress2 = (EditText) findViewById(R.id.editText9);

        back = (Button) findViewById(R.id.button1);
        register = (Button) findViewById(R.id.button2);

        back.setOnClickListener(myhandler1);
        register.setOnClickListener(myhandler2);
    }

    View.OnClickListener myhandler1 = new View.OnClickListener() {
        public void onClick(View v) {
            Intent intent = new Intent(Register.this, MainPage.class);
            startActivity(intent);
        }
    };

    View.OnClickListener myhandler2 = new View.OnClickListener() {
        public void onClick(View v) {
            new NewAccount().execute();
        }
    };

    /**
     * Background Async Task to Create new product
     */
    class NewAccount extends AsyncTask<String, String, String> {

        /**
         * Before starting background thread Show Progress Dialog
         */
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            pDialog = new ProgressDialog(Register.this);
            pDialog.setMessage("Registering...");
            pDialog.setIndeterminate(false);
            pDialog.setCancelable(true);
            pDialog.show();
        }

        /**
         * Creating product
         */
        protected String doInBackground(String... args) {
            String name = iname.getText().toString();
            String email = iemail.getText().toString();
            String reEmail = ireEmail.getText().toString();
            String password = ipassword.getText().toString();
            String rePassword = irePassword.getText().toString();
            String id = iid.getText().toString();
            String phone = iphone.getText().toString();
            String address1 = iaddress1.getText().toString();
            String address2 = iaddress2.getText().toString();



            // Building Parameters
            List<NameValuePair> params = new ArrayList<NameValuePair>();
            params.add(new BasicNameValuePair("name", name));
            params.add(new BasicNameValuePair("email", email));
            params.add(new BasicNameValuePair("password", password));
            params.add(new BasicNameValuePair("id", id));
            params.add(new BasicNameValuePair("phone", phone));
            params.add(new BasicNameValuePair("address1", address1));
            params.add(new BasicNameValuePair("address2", address2));

            // getting JSON Object
            // Note that create product url accepts POST method
            JSONObject json = jsonParser.makeHttpRequest(url_register,
                    "POST", params);

            if(json != null) {

                // check log cat fro response
                Log.d("Create Response", json.toString());

                // check for success tag
                try {
                    int success = json.getInt(TAG_SUCCESS);

                    if (success == 1) {
                        // successfully created product
                        Intent i = new Intent(Register.this, MainPage.class);
                        startActivity(i);

                        // closing this screen
                        finish();
                    } else {
                        // failed to create product
                    }
                } catch (JSONException e) {
                    e.printStackTrace();
                }
            }

            else{

                Toast.makeText(getApplicationContext(), "An error occurred, please try again", Toast.LENGTH_LONG).show();
            }

            return null;
        }

        /**
         * After completing background task Dismiss the progress dialog
         * *
         */
        protected void onPostExecute(String file_url) {
            // dismiss the dialog once done
            pDialog.dismiss();
        }

    }
}

Answer 1

根据之前的评论：假设服务器正确设置了响应的 Content-Type header 字段，您可能会在尝试处理响应 body 之前检查它。

即如果返回json，则header的值应该是application/json。如果返回错误（可能不是 json 格式，否则您的问题将是一个有争议的问题），它可能是 text/html 或 text/plain 之类的东西。到底是哪个并不重要，只要服务器响应包含 'success' 和 'error'.

的不同内容类型值即可

检查 Content-Type header 看起来有点像这样：

HttpResponse response = ...
Header contentTypeHeader = response.getFirstHeader("Content-Type");
if ("application/json".equals(contentTypeHeader.getValue()) {
    // server returned json
} else {
    // server returned something else, potentially an error
}

由您来实施实际行为并处理 null 值等

Answer 2

当您在 onPostExecute() 中获得响应时，只需尝试通过在 JSONObject 的构造函数中传递该响应来将该字符串转换为 json 对象。看下面的代码

try {
     JSONObject json = new JSONObject("your_output");
} catch (JSONException e) {
     // your output is not in json format
     e.printStackTrace();
}

因此，如果您的输出是 JSON 格式，则对象创建成功。否则它会抛出异常。

如何检查服务器响应是否为 json？

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