在 Android 中解析 JSON 数据时出错

Question

我正在开发一个测试 Android 应用程序，它必须显示来自 MySQL 数据库的一些数据。这是我的日志：

这里是班级JSONParser.java

package com.example.portal; 

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.util.List;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.client.utils.URLEncodedUtils;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONException;
import org.json.JSONObject;

import android.util.Log;


public class JSONParser {

    static InputStream is = null;
    static JSONObject jObj = null;
    static String json = "";

    // constructor
    public JSONParser() {

    }

    // function get json from url
    // by making HTTP POST or GET mehtod
    public JSONObject makeHttpRequest(String url, String method,
            List<NameValuePair> params) {

        // Making HTTP request
        try {

            // check for request method
            if(method == "POST"){
                // request method is POST
                // defaultHttpClient
                DefaultHttpClient httpClient = new DefaultHttpClient();
                HttpPost httpPost = new HttpPost(url);
                httpPost.setEntity(new UrlEncodedFormEntity(params));

                HttpResponse httpResponse = httpClient.execute(httpPost);
                HttpEntity httpEntity = httpResponse.getEntity();
                is = httpEntity.getContent();

            }else if(method == "GET"){
                // request method is GET
                DefaultHttpClient httpClient = new DefaultHttpClient();
                String paramString = URLEncodedUtils.format(params, "utf-8");
                url += "?" + paramString;
                HttpGet httpGet = new HttpGet(url);

                HttpResponse httpResponse = httpClient.execute(httpGet);
                HttpEntity httpEntity = httpResponse.getEntity();
                is = httpEntity.getContent();
            }           


        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

        try {
            BufferedReader reader = new BufferedReader(new InputStreamReader(
                    is, "iso-8859-1"), 8);
            StringBuilder sb = new StringBuilder();
            String line = null;
            while ((line = reader.readLine()) != null) {
                sb.append(line + "\n");
            }
            is.close();
            json = sb.toString();
        } catch (Exception e) {
            Log.e("Buffer Error", "Error converting result " + e.toString());
        }

        // try parse the string to a JSON object
        try {
            jObj = new JSONObject(json);
        } catch (JSONException e) {
            Log.e("JSON Parser", "Error parsing data " + e.toString());
        }

        // return JSON String
        return jObj;


    }

}

这是我用来显示所选数据的类：

package com.example.portal;

import java.util.ArrayList;
import java.util.List;
import org.apache.http.NameValuePair;
import org.apache.http.message.BasicNameValuePair;
import org.json.JSONException;
import org.json.JSONObject;

import com.example.portal.JSONParser;
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;

public class LogIn extends Activity{

    // Progress Dialog
    private ProgressDialog pDialog;
    JSONParser jsonParser = new JSONParser();

    EditText user;
    EditText pasword;

    // url to create new product
    private static String url_create_product = 

    "http://10.0.2.2/android_connect/create_product.php";

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






    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.login);

         user=(EditText)findViewById(R.id.username);
         pasword=(EditText)findViewById(R.id.pasword);
         Button login= (Button) findViewById(R.id.loginbutton);

    /**
     * Handling all button click events
     * */

    // Listening to News Feed button click
    login.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View view) {
            // Launching News Feed Screen
            //Intent i = new Intent(getApplicationContext(),MainMenu.class);
            //startActivity(i);
            new CreateNewProduct().execute();
        }
    });



    }



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

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

        /**
         * Creating product
         * */
        protected String doInBackground(String... args) {
            String name = user.getText().toString();
            String price = pasword.getText().toString();
            String description = user.getText().toString();

            // Building Parameters
            List<NameValuePair> params = new ArrayList<NameValuePair>();
            params.add(new BasicNameValuePair("name", name));
            params.add(new BasicNameValuePair("price", price));
            params.add(new BasicNameValuePair("description", description));

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

            // 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(getApplicationContext(), 

        MainMenu.class);
                    startActivity(i);

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

                e.printStackTrace();
            }

            return null;
        }

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


    }

}

这里是 PHP 文件：

    <?php

    /*
     * Following code will create a new product row
     * All product details are read from HTTP Post Request
    */

    // array for JSON response
    $response = array();
    $response["success"] = 0;
    $response["message"] = "No products found";

    // check for required fields
    if (isset($_POST['name']) && isset($_POST['price']) ) {

        $name = $_POST['name'];
        $price = $_POST['price'];


        // include db connect class
        require_once __DIR__ . '/db_connect.php';

        // connecting to db
        $db = new DB_CONNECT();

        // mysql inserting a new row
        $result = mysql_query("INSERT INTO products(name, price) VALUES('$name', '$price')");

        // check if row inserted or not
        if ($result) {
    // successfully inserted into database
    $response["success"] = 1;
    $response["message"] = "Product successfully created.";

    // echoing JSON response
            echo json_encode($response);
        } else {
            // failed to insert row
            $response["success"] = 0;
            $response["message"] = "Oops! An error occurred.";

            // echoing JSON response
            echo json_encode($response);
            die();
        }
    } else {
        // required field is missing
        $response["success"] = 0;
        $response["message"] = "Required field(s) is missing";

        // echoing JSON response
        echo json_encode($response);
        die();
    }
    ?>

谢谢

Answer 1

你遇到了异常

输入在字符 0 处结束

这意味着您的响应不是 JSON，而是 null。

原因可能是您的 url 不支持 POST 请求并且您正在发送 post 请求，结果您得到空值。

您的网址不支持获取请求，并且您正在发送获取请求，结果您得到空值。

看看下面的链接，这些链接可能对你有帮助

Getting a JSONException: end of input at character 0

org.json.JSON Exception : End of input at character 0