我试图通过JSON从mySQL数据库获取数据到我的android应用程序，并将它们显示在ListView中。但是我得到了一个JSONException。如果这不是从数据库获取数据并在ListView上显示的最佳方法，请帮助我找到其他方法来执行此操作。我是android编程的新手。
public class ListTest extends ListActivity {
// Progress Dialog
private ProgressDialog pDialog;
// Creating JSON Parser object
JSONParser jParser = new JSONParser();
ArrayList<HashMap<String, String>> productsList;
// url to get all products list
private static String url_all_products = "http://10.0.2.2/shareity/include/get_all.php";
// JSON Node names
private static final String TAG_SUCCESS = "success";
private static final String TAG_PRODUCTS = "products";
private static final String TAG_PID = "eid";
private static final String TAG_NAME = "ename";
// products JSONArray
JSONArray products = null;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.all_events);
// Hashmap for ListView
productsList = new ArrayList<HashMap<String, String>>();
// Loading products in Background Thread
new LoadAllProducts().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 pid = ((TextView) view.findViewById(R.id.pid)).getText()
.toString();
// Starting new intent
Intent in = new Intent(getApplicationContext(), ListTest.class);
// sending pid to next activity
in.putExtra(TAG_PID, pid);
// 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
* */
class LoadAllProducts extends AsyncTask<String, String, String> {
/**
* Before starting background thread Show Progress Dialog
* */
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(ListTest.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("All Products: ", json.toString());
try {
// Checking for SUCCESS TAG
int success = json.getInt(TAG_SUCCESS);
if (success == 1) {
// products found
// Getting Array of Products
products = json.getJSONArray(TAG_PRODUCTS);
// 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 name = c.getString(TAG_NAME);
// 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_NAME, name);
// adding HashList to ArrayList
productsList.add(map);
}
} else {
// no products found
// Launch Add New product Activity
Intent i = new Intent(getApplicationContext(),
ListTest.class);
// Closing all previous activities
i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(i);
}
} 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(ListTest.this,
productsList, R.layout.list_item, new String[] {
TAG_PID, TAG_NAME }, new int[] { R.id.pid,
R.id.name });
// updating listview
setListAdapter(adapter);
}
});
}
}
}
这是我的logcat
Error parsing data org.json.JSONException: End of input at character 0 of
FATAL EXCEPTION: AsyncTask #1
Process: com.example.shareity, PID: 3556
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:818)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String org.json.JSONObject.toString()' on a null object reference
at com.example.shareity.ListTest$LoadAllProducts.doInBackground(ListTest.java:134)
at com.example.shareity.ListTest$LoadAllProducts.doInBackground(ListTest.java:1)
at android.os.AsyncTask$2.call(AsyncTask.java:288)
at java.util.concurrent.FutureTask.run(FutureTask.java:237)
... 4 more
这是我的php API
<?php
/*
* Following code will list all the products
*/
// array for JSON response
$response = array();
// include db connect class
require_once 'DB_Connect.php';
// connecting to db
$this->db = new DB_Connect();
$this->db->connect();
// get all products from products table
$result = mysql_query("SELECT *FROM event") or die(mysql_error());
// check for empty result
if (mysql_num_rows($result) > 0) {
// looping through all results
// products node
$response["event"] = array();
while ($row = mysql_fetch_array($result)) {
// temp user array
$event = array();
$event["eid"] = $row["eid"];
$event["ename"] = $row["ename"];
//$event["edesc"] = $row["edesc"];
//$event["created_at"] = $row["created_at"];
//$event["createdBy"] = $row["createdBy"];
// push single product into final response array
array_push($response["event"], $event);
}
// success
$response["success"] = 1;
// echoing JSON response
echo json_encode($response);
} else {
// no products found
$response["success"] = 0;
$response["message"] = "No products found";
// echo no users JSON
echo json_encode($response);
}
?>
答案 0 :(得分：0)
问题可能是您没有连接到数据库，结果是您获得Nullpointer异常。你应该：
或者您也可以使用我的JSONFunctions类
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.HttpVersion;
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.impl.client.DefaultHttpClient;
import org.apache.http.params.BasicHttpParams;
import org.apache.http.params.HttpConnectionParams;
import org.apache.http.params.HttpParams;
import org.apache.http.params.HttpProtocolParams;
import org.apache.http.protocol.HTTP;
import org.json.JSONException;
import org.json.JSONObject;
import android.util.Log;
public class JSONFunctions {
static InputStream is = null;
static JSONObject jObj = null;
static String json = null;
static HttpResponse httpResponse = null;
//GET
public static JSONObject getJSONFromUrl(String url) {
// Making HTTP request
try {
HttpParams params = new BasicHttpParams();
HttpConnectionParams.setConnectionTimeout(params, 10000);
HttpConnectionParams.setSoTimeout(params, 10000);
HttpProtocolParams.setVersion(params, HttpVersion.HTTP_1_1);
HttpProtocolParams.setContentCharset(params, HTTP.UTF_8);
HttpProtocolParams.setUseExpectContinue(params, true);
// defaultHttpClient
DefaultHttpClient httpClient = new DefaultHttpClient(params);
HttpGet httpPost = new HttpGet( url);
httpResponse = httpClient.execute( httpPost);
HttpEntity httpEntity = httpResponse.getEntity();
is = httpEntity.getContent();
} catch (UnsupportedEncodingException ee) {
Log.i("UnsupportedEncodingException...", is.toString());
} catch (ClientProtocolException e) {
Log.i("ClientProtocolException...", is.toString());
} catch (IOException e) {
Log.i("IOException...","error");
}
try {
BufferedReader reader = new BufferedReader(new InputStreamReader(
is, "iso-8859-1"), 8); //old charset iso-8859-1
StringBuilder sb = new StringBuilder();
String line = null;
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
is.close();
reader.close();
json = sb.toString();
Log.i("StringBuilder...", json);
} 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 (Exception e) {
Log.e("JSON Parser", "Error parsing data " + e.toString());
try {
jObj = new JSONObject(json.substring(json.indexOf("{"), json.lastIndexOf("}") + 1));
} catch (Exception e0) {
Log.e("JSON Parser0", "Error parsing data [" + e0.getMessage()+"] "+json);
Log.e("JSON Parser0", "Error parsing data " + e0.toString());
try {
jObj = new JSONObject(json.substring(1));
} catch (Exception e1) {
Log.e("JSON Parser1", "Error parsing data [" + e1.getMessage()+"] "+json);
Log.e("JSON Parser1", "Error parsing data " + e1.toString());
try {
jObj = new JSONObject(json.substring(2));
} catch (Exception e2) {
Log.e("JSON Parser2", "Error parsing data [" + e2.getMessage()+"] "+json);
Log.e("JSON Parser2", "Error parsing data " + e2.toString());
try {
jObj = new JSONObject(json.substring(3));
} catch (Exception e3) {
Log.e("JSON Parser3", "Error parsing data [" + e3.getMessage()+"] "+json);
Log.e("JSON Parser3", "Error parsing data " + e3.toString());
}
}
}
}
}
// return JSON String
return jObj;
}
// POST
public static JSONObject getJSONFromUrl（String url，List params）{
try {
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();
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
try {
BufferedReader reader = new BufferedReader(new InputStreamReader(
is, "utf-8"), 8);
StringBuilder sb = new StringBuilder();
String line = null;
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
is.close();
json = sb.toString();
Log.e("JSON", json);
} catch (Exception e) {
Log.e("Buffer Error", "Error converting result " + e.toString());
}
try {
jObj = new JSONObject(json);
} catch (JSONException e) {
Log.e("JSON Parser", "Error parsing data " + e.toString());
}
// return JSON String
return jObj;
}
}