我知道这个问题有几个问题，但它们都不适合我，我找不到错误，它让我疯狂。
我收到错误
NullPointerException：lock == null
错误
解析数据时出错org.json.JSONException：字符0处的输入结束。
我检查了我的JSON文件，这是有效的。我知道NullPointerException是什么，但我无法在我的代码中找到导致它的原因。
这是我的Android类：
package com.ipmedt4.challengeweek_v2;
import android.app.ListActivity;
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.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.TextView;
import org.apache.http.NameValuePair;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
public class OverzichtStudenten extends ListActivity {
// Progress Dialog
private ProgressDialog pDialog;
// Creating JSON Parser object
JSONParser jParser = new JSONParser();
ArrayList<HashMap<String, String>> studentList;
// url to get all products list
private static String url_all_products = "https://charlenemacdonald.com/getAlleStudenten.php";
// JSON Node names
private static final String TAG_SUCCESS = "success";
private static final String TAG_STUDENTEN = "studenten";
private static final String TAG_NAAM = "Naam";
private static final String TAG_STUDENTNUMMER = "Studentnummer";
private static final String TAG_KLAS = "Klas";
private static final String TAG_GROEP = "Groep";
// products JSONArray
JSONArray studenten = null;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_overzicht_studenten);
// Hashmap for ListView
studentList = new ArrayList<HashMap<String, String>>();
// Loading products in Background Thread
new LaadAlleStudenten().execute();
// Get listview
ListView lv = getListView();
// on seleting single product
// launching Edit Product Screen
lv.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
// getting values from selected ListItem
String Naam = ((TextView) view.findViewById(R.id.Naam)).getText()
.toString();
// Starting new intent
Intent in = new Intent(getApplicationContext(),
Beoordelingscherm.class);
// sending pid to next activity
in.putExtra(TAG_NAAM, Naam);
// starting new activity and expecting some response back
startActivityForResult(in, 100);
}
});
}
// Response from Edit Product Activity
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
// if result code 100
if (resultCode == 100) {
// if result code 100 is received
// means user edited/deleted product
// reload this screen again
Intent intent = getIntent();
finish();
startActivity(intent);
}
}
/**
* Background Async Task to Load all product by making HTTP Request
* */
private class LaadAlleStudenten extends AsyncTask<String, String, String> {
/**
* Before starting background thread Show Progress Dialog
* */
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(OverzichtStudenten.this);
pDialog.setMessage("Loading products. Please wait...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(false);
pDialog.show();
}
/**
* getting All products from url
* */
protected String doInBackground(String... args) {
// Building Parameters
List<NameValuePair> params = new ArrayList<NameValuePair>();
// getting JSON string from URL
JSONObject json = jParser.makeHttpRequest(url_all_products, "GET", params);
// Check your log cat for JSON reponse
Log.d("studenten: ", json.toString());
try {
int success = json.getInt(TAG_SUCCESS);
if (json != null && success == 1 ) {
// products found
// Getting Array of Products
studenten = json.getJSONArray(TAG_STUDENTEN);
// looping through All Products
for (int i = 0; i < studenten.length(); i++) {
JSONObject c = studenten.getJSONObject(i);
// Storing each json item in variable
String Naam = c.getString(TAG_NAAM);
String Studentnummer = c.getString(TAG_STUDENTNUMMER);
String Klas = c.getString(TAG_KLAS);
String Groep = c.getString(TAG_GROEP);
// creating new HashMap
HashMap<String, String> student = new HashMap<String, String>();
// adding each child node to HashMap key => value;
student.put(TAG_NAAM, Naam);
student.put(TAG_STUDENTNUMMER, Studentnummer);
student.put(TAG_KLAS, Klas);
student.put(TAG_GROEP, Groep);
// adding HashList to ArrayList
studentList.add(student);
}
}
} catch (JSONException e) {
e.printStackTrace();
}
return null;
}
/**
* After completing background task Dismiss the progress dialog
* **/
protected void onPostExecute(String file_url) {
// dismiss the dialog after getting all products
pDialog.dismiss();
// updating UI from Background Thread
runOnUiThread(new Runnable() {
public void run() {
/**
* Updating parsed JSON data into ListView
* */
ListAdapter adapter = new SimpleAdapter(
OverzichtStudenten.this, studentList,
R.layout.student_info, new String[] { TAG_NAAM,
TAG_STUDENTNUMMER, TAG_KLAS, TAG_GROEP},
new int[] { R.id.Naam, R.id.Studentnummer, R.id.Klas, R.id.Groep });
// updating listview
setListAdapter(adapter);
}
});
}
}
}
这是我的PHP文件：
/*
* Following code will list all the students
*/
$response = array();
$response["success"] = 0;
$response["message"] = "No students found";
// include db connect class
require_once __DIR__ . '/db_connect.php';
// connecting to db
$db = new DB_CONNECT();
// get all products from products table
$result = mysql_query("SELECT *FROM studenten");
// check for empty result
if ($result && mysql_num_rows($result) > 0) {
// looping through all results
// products node
$response["studenten"] = array();
while ($row = mysql_fetch_array($result)) {
// temp user array
$student = array();
$student["Naam"] = $row["Naam"];
$student["Studentnummer"] = $row["Studentnummer"];
$student["Klas"] = $row["Klas"];
$student["Groep"] = $row["Groep"];
// push single product into final response array
array_push($response["studenten"], $student);
}
// success
$response["success"] = 1;
}
// Echo JSON anyway!
echo json_encode($response);
die();
?>
?>
我的JSON Parser课程：
package com.ipmedt4.challengeweek_v2;
import android.util.Log;
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 java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.util.List;
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;
}
}
我知道这个问题已被多次询问，但在这些帖子中，我无法找到适合我的解决方案。如果你能告诉我如何解决这个错误，我将不胜感激。谢谢！