我正在尝试从数据库（phpmyadmin）获取数据并将其转换为json以将其放入ListView或TextView但是当我运行应用程序时它关闭并且当我检查日志时发现了一个例外。
这是我的代码：
MainActivity.java
public class MainActivity extends AppCompatActivity {
ProgressDialog pDialog;
// Creating JSON Parser object
ListView lv;
ArrayList<HashMap<String, String>> productsList;
// url to get all products list
private static String url_all_products = "http://192.168.0.100/takeofftravel/test.php";
// products JSONArray
JSONArray products = null;
int error=0;
// JSON Node names
private static final String TAG_SUCCESS = "success";
private static final String TAG_NOTIF = "notif";
private static final String TAG_PID = "id";
private static final String TAG_Type = "type";
private static final String TAG_REQUETE = "requete";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Hashmap for ListView.
productsList = new ArrayList<HashMap<String, String>>();
// Get listview
lv = (ListView)findViewById(R.id.listView);
// Loading products in Background Thread
new LoadAllProducts().execute();
// on seleting single product
// launching Edit Product Screen
lv.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
/* HashMap<String,String> map=new HashMap<String, String>();
map=(HashMap<String,String>)lv.getAdapter().getItem(position);
String ide=map.get(TAG_PID);
Toast.makeText(All.this,ide,Toast.LENGTH_LONG).show();
Intent i=new Intent(getApplicationContext(),Detail.class);
i.putExtra("id",ide);
startActivity(i);
finish();*/
}
});
}
class LoadAllProducts extends AsyncTask<String, String, String> {
/**
* Before starting background thread Show Progress Dialog
* */
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(MainActivity.this);
pDialog.setMessage("Loading...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(false);
pDialog.show();
}
/**
* getting All products from url
* */
protected String doInBackground(String... args) {
// Building Parameters
HashMap<String, String> params = new HashMap<String, String>();
JSONParser jParser = new JSONParser();
// getting JSON string from URL
JSONObject json = jParser.makeHttpRequest(url_all_products, "GET", params);
// Check your log cat for JSON reponse
Log.d("All Products: ", json.toString());
// Checking for SUCCESS TAG
int success = 0;
try {
success = json.getInt(TAG_SUCCESS);
if (success == 1) {
// products found
// Getting Array of Products
products = json.getJSONArray(TAG_NOTIF);
// looping through All Products
for (int i = 0; i < products.length(); i++) {
JSONObject c = products.getJSONObject(i);
// Storing each json item in variable
String id = c.getString(TAG_PID);
String type = c.getString(TAG_Type);
String requete=c.getString(TAG_REQUETE);
// creating new HashMap
HashMap<String, String> map = new HashMap<String, String>();
// adding each child node to HashMap key => value
map.put(TAG_PID, id);
map.put(TAG_Type, type);
map.put(TAG_REQUETE,requete);
// adding HashList to ArrayList
productsList.add(map);
}
} else {
}
} 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(
MainActivity.this, productsList,
R.layout.item, new String[] { TAG_PID,
TAG_Type,TAG_REQUETE},
new int[] { R.id.pid, R.id.nom,R.id.nature });
// updating listview
lv.setAdapter(adapter);
// }
// });
}
}
}
JSONParse.java文件：
public class JSONParser {
String charset = "UTF-8";
HttpURLConnection conn;
DataOutputStream wr;
StringBuilder result;
URL urlObj;
JSONObject jObj = null;
StringBuilder sbParams;
String paramsString;
public JSONObject makeHttpRequest(String url, String method,
HashMap<String, String> params) {
sbParams = new StringBuilder();
int i = 0;
for (String key : params.keySet()) {
try {
if (i != 0){
sbParams.append("&");
}
sbParams.append(key).append("=")
.append(URLEncoder.encode(params.get(key), charset));
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
}
i++;
}
if (method.equals("POST")) {
// request method is POST
try {
urlObj = new URL(url);
conn = (HttpURLConnection) urlObj.openConnection();
conn.setDoOutput(true);
conn.setRequestMethod("POST");
conn.setRequestProperty("Accept-Charset", charset);
conn.setReadTimeout(10000);
conn.setConnectTimeout(15000);
conn.connect();
paramsString = sbParams.toString();
wr = new DataOutputStream(conn.getOutputStream());
wr.writeBytes(paramsString);
wr.flush();
wr.close();
} catch (IOException e) {
e.printStackTrace();
}
}
else if(method.equals("GET")){
// request method is GET
if (sbParams.length() != 0) {
url += "?" + sbParams.toString();
}
try {
urlObj = new URL(url);
conn = (HttpURLConnection) urlObj.openConnection();
conn.setDoOutput(false);
conn.setRequestMethod("GET");
conn.setRequestProperty("Accept-Charset", charset);
conn.setConnectTimeout(15000);
conn.connect();
} catch (IOException e) {
e.printStackTrace();
}
}
try {
//Receive the response from the server
InputStream in = new BufferedInputStream(conn.getInputStream());
BufferedReader reader = new BufferedReader(new InputStreamReader(in));
result = new StringBuilder();
String line;
while ((line = reader.readLine()) != null) {
result.append(line);
}
Log.d("JSON Parser", "result: " + result.toString());
} catch (IOException e) {
e.printStackTrace();
}
conn.disconnect();
// try parse the string to a JSON object
try {
jObj = new JSONObject(result.toString());
} catch (JSONException e) {
Log.e("JSON Parser", "Error parsing data " + e.toString());
}
// return JSON Object
return jObj;
}
}
错误消息：
E/AndroidRuntime: FATAL EXCEPTION: AsyncTask #1
Process: com.example.asus.json, PID: 11657
java.lang.RuntimeException: An error occured while executing doInBackground()
at android.os.AsyncTask$3.done(AsyncTask.java:300)
at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
at java.util.concurrent.FutureTask.run(FutureTask.java:242)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
at java.lang.Thread.run(Thread.java:841)
Caused by: java.lang.NullPointerException
at com.example.asus.json.JSONParser.makeHttpRequest(JSONParser.java:124)
at com.example.asus.json.MainActivity$LoadAllProducts.doInBackground(MainActivity.java:100)
at com.example.asus.json.MainActivity$LoadAllProducts.doInBackground(MainActivity.java:75)
at android.os.AsyncTask$2.call(AsyncTask.java:288)
at java.util.concurrent.FutureTask.run(FutureTask.java:237)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
at java.lang.Thread.run(Thread.java:841)
答案 0 :(得分：0)
主要问题在于您的JSONParser类在第124行。这是因为JSONParser类没有返回任何JSON，并且生成的JSON为null并且您在null JSON对象上调用函数getInt（），这就是为什么NullPointerException。