我使用asynctask从远程url获取json数据，但有时这个url会在json数据中返回错误，如下所示：
{
"error": {
"message": "(#803) Some of the aliases you requested do not exist: RNN.NES",
"type": "OAuthException",
"code": 803
}
}
在doInBackground中，我检查json是否有错误..
if（true）{取消asynctask并使用消息显示toast
cancel(true)
但是当我尝试输入包含错误对象的无效网址时，它看不到条件并强制停止应用
这是我的代码：
@Override
protected Void doInBackground(String... params) {
db.open();
try {
// Creating JSON Parser instance
JSONParser jParser = new JSONParser();
// getting JSON string from URL
JSONObject json = jParser.getJSONFromUrl(params[0]);
// addPageData(params[0]);
if (json.has("error") == true) {
Log.e("error", "true");
toastMsg = "This username is invalid";
cancel(true);
} else {
name = json.getString("name");
Log.e("error", name);
// category = json.getString("category");
fid = json.getString("id");
if (db.checkPage(fid)) {
toastMsg = "This page is already added";
cancel(true);
}
String picture = json.getJSONObject("picture").getJSONObject("data").getString("url");
picName = downloadImage(picture, fid);
}
db.closeDatabase();
} catch (JSONException e) {
e.printStackTrace();
}
return null;
}
@Override
protected void onCancelled() {
mProgressDialog.dismiss();
Toast.makeText(context, toastMsg, Toast.LENGTH_LONG).show();
}
jsonParser.java
package com.engahmedphp.facebookcollector;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.ParseException;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.client.methods.HttpUriRequest;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.util.EntityUtils;
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() {
}
// ==============================================================================
public JSONObject getJSONFromUrl(String url) {
// Making HTTP request
// try {
// defaultHttpClient
// DefaultHttpClient httpClient = new DefaultHttpClient();
// // HttpFeed httpFeed = new HttpFeed(url);
//
// HttpGet httpGet = new HttpGet(url);
//
// HttpResponse httpResponse = httpClient.execute(httpGet);
// HttpEntity httpEntity = httpResponse.getEntity();
// is = httpEntity.getContent();
try {
URL newURL = new URL(url);
HttpURLConnection con = (HttpURLConnection) newURL.openConnection();
is = con.getInputStream();
} catch (MalformedURLException e2) {
// TODO Auto-generated catch block
e2.printStackTrace();
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
// DefaultHttpClient httpClient = new DefaultHttpClient();
// // HttpFeed httpFeed = new HttpFeed(url);
//
// HttpGet httpGet = new HttpGet(url);
// HttpResponse httpResponse = null;
// try {
// httpResponse = httpClient.execute(httpGet);
//
// } catch (UnsupportedEncodingException e) {
// e.printStackTrace();
// } catch (ClientProtocolException e) {
// e.printStackTrace();
// } catch (IOException e) {
// e.printStackTrace();
// }
try {
// HttpEntity httpEntity = httpResponse.getEntity();
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();
// System.out.println(json);
// System.out.println(httpEntity);
} catch (ParseException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
// 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;
}
}
它认为它不包含错误对象然后他移动到else子句并强制关闭
这是我的logcat ..我认为它包含一些可能对您有用的信息
10-06 15:04:45.539: E/JSON Parser(7183): Error parsing data org.json.JSONException: End of input at character 0 of
10-06 15:04:45.539: W/System.err(7183): org.json.JSONException: No value for name
10-06 15:04:45.539: W/System.err(7183): at org.json.JSONObject.get(JSONObject.java:354)
10-06 15:04:45.539: W/System.err(7183): at org.json.JSONObject.getString(JSONObject.java:510)
10-06 15:04:45.539: W/System.err(7183): at com.engahmedphp.facebookcollector.General$MyAsyncTask.doInBackground(General.java:148)
10-06 15:04:45.539: W/System.err(7183): at com.engahmedphp.facebookcollector.General$MyAsyncTask.doInBackground(General.java:1)
10-06 15:04:45.539: W/System.err(7183): at android.os.AsyncTask$2.call(AsyncTask.java:185)
10-06 15:04:45.539: W/System.err(7183): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
10-06 15:04:45.539: W/System.err(7183): at java.util.concurrent.FutureTask.run(FutureTask.java:137)
10-06 15:04:45.539: W/System.err(7183): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1068)
10-06 15:04:45.539: W/System.err(7183): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:561)
10-06 15:04:45.539: W/System.err(7183): at java.lang.Thread.run(Thread.java:1096)
10-06 15:04:45.589: W/dalvikvm(7183): threadid=1: thread exiting with uncaught exception (group=0x400207d8)
10-06 15:04:45.679: E/AndroidRuntime(7183): FATAL EXCEPTION: main
10-06 15:04:45.679: E/AndroidRuntime(7183): java.lang.IllegalArgumentException: the bind value at index 1 is null
10-06 15:04:45.679: E/AndroidRuntime(7183): at android.database.sqlite.SQLiteProgram.bindString(SQLiteProgram.java:234)
10-06 15:04:45.679: E/AndroidRuntime(7183): at android.database.sqlite.SQLiteQuery.bindString(SQLiteQuery.java:182)
10-06 15:04:45.679: E/AndroidRuntime(7183): at android.database.sqlite.SQLiteDirectCursorDriver.query(SQLiteDirectCursorDriver.java:48)
10-06 15:04:45.679: E/AndroidRuntime(7183): at android.database.sqlite.SQLiteDatabase.rawQueryWithFactory(SQLiteDatabase.java:1454)
10-06 15:04:45.679: E/AndroidRuntime(7183): at android.database.sqlite.SQLiteDatabase.queryWithFactory(SQLiteDatabase.java:1338)
10-06 15:04:45.679: E/AndroidRuntime(7183): at android.database.sqlite.SQLiteDatabase.query(SQLiteDatabase.java:1293)
10-06 15:04:45.679: E/AndroidRuntime(7183): at android.database.sqlite.SQLiteDatabase.query(SQLiteDatabase.java:1373)
10-06 15:04:45.679: E/AndroidRuntime(7183): at com.engahmedphp.facebookcollector.DAOPages.getPageData(DAOPages.java:183)
10-06 15:04:45.679: E/AndroidRuntime(7183): at com.engahmedphp.facebookcollector.General.getPagePrefs(General.java:180)
10-06 15:04:45.679: E/AndroidRuntime(7183): at com.engahmedphp.facebookcollector.General.insertPageAndSetAlarmAndPrefs(General.java:207)
10-06 15:04:45.679: E/AndroidRuntime(7183): at com.engahmedphp.facebookcollector.General$MyAsyncTask.onPostExecute(General.java:113)
10-06 15:04:45.679: E/AndroidRuntime(7183): at com.engahmedphp.facebookcollector.General$MyAsyncTask.onPostExecute(General.java:1)
10-06 15:04:45.679: E/AndroidRuntime(7183): at android.os.AsyncTask.finish(AsyncTask.java:417)
10-06 15:04:45.679: E/AndroidRuntime(7183): at android.os.AsyncTask.access$300(AsyncTask.java:127)
10-06 15:04:45.679: E/AndroidRuntime(7183): at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:429)
10-06 15:04:45.679: E/AndroidRuntime(7183): at android.os.Handler.dispatchMessage(Handler.java:99)
10-06 15:04:45.679: E/AndroidRuntime(7183): at android.os.Looper.loop(Looper.java:123)
10-06 15:04:45.679: E/AndroidRuntime(7183): at android.app.ActivityThread.main(ActivityThread.java:4633)
10-06 15:04:45.679: E/AndroidRuntime(7183): at java.lang.reflect.Method.invokeNative(Native Method)
10-06 15:04:45.679: E/AndroidRuntime(7183): at java.lang.reflect.Method.invoke(Method.java:521)
10-06 15:04:45.679: E/AndroidRuntime(7183): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:858)
10-06 15:04:45.679: E/AndroidRuntime(7183): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
10-06 15:04:45.679: E/AndroidRuntime(7183): at dalvik.system.NativeStart.main(Native Method)
答案 0 :(得分：2)
您的问题出现在您的JSON解析器中：
try {
jObj = new JSONObject(json);
} catch (JSONException e) {
Log.e("JSON Parser", "Error parsing data " + e.toString());
}
你以某种方式将一个完全空的字符串传递给对象json，因此它会抛出一个JSONException。
由于您正在为jObj使用静态成员，并且上面的catch块未将其设置为null以指示存在错误，因此您将从JSONParser的任何实例返回此方法的最后一个有效jObj，因此json.has("error")可能会返回false。
我看不出有任何理由将jObj存储为静态成员，因此我只想将其更改为在上面引用的代码之前声明的局部变量。然后在我上面引用的catch块中，在记录错误后返回null。在doInBackground方法中，您可以将if语句更改为：
if (json==null){
//Log whatever kind of error could cause this, toast user, and cancel(true).
} else if (json.has("error")) {
...