运行此代码时出现异常。我想解析 url，它是一个 json 对象数组：
package com.example.compsci_734t;
import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.URL;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.StatusLine;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import android.app.Activity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
public class UoaCompsciActivity extends Activity {
private static String url = " http://redsox.tcs.auckland.ac.nz/734A/CSService.svc/courses";
//URL requestUrl = new URL(url);
JSONArray courses = null;
private static final String TAG_COURSES = "Courses";
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_uoa_compsci);
new MyTask().execute();
}
private class MyTask extends AsyncTask<URL, Void, JSONObject> {
@Override
protected JSONObject doInBackground(URL... urls) {
loadJSON(url);
return null;
}
protected void onPostExecute(JSONObject json) {
try {
courses = json.getJSONArray(TAG_COURSES);
// looping through all courses
for (int i = 0; i < courses.length(); i++) {
JSONObject c = courses.getJSONObject(i);
// Storing each json item in variable
String course_id = c.getString("courseField:");
String course_name = c.getString("titleField:");
String course_semester = c.getString("semesterField:");
Log.v("--", "Course: \n" + " " + course_id + " " + course_name
+ " " + course_semester);
}
} catch (JSONException e) {
e.printStackTrace();
}
}
}
public JSONObject loadJSON(String url) {
// Creating JSON Parser instance
JSONParser jParser = new JSONParser();
// getting JSON string from URL
JSONObject json = jParser.getJSONFromUrl(url);
return json;
}
}
这也是我的 logcat：
05-13 20:29:05.118: I/dalvikvm(770): threadid=3: reacting to signal 3
05-13 20:29:05.128: I/dalvikvm(770): Wrote stack traces to '/data/anr/traces.txt'
05-13 20:29:05.418: D/gralloc_goldfish(770): Emulator without GPU emulation detected.
05-13 20:31:46.128: I/dalvikvm(842): threadid=3: reacting to signal 3
05-13 20:31:46.218: I/dalvikvm(842): Wrote stack traces to '/data/anr/traces.txt'
05-13 20:31:46.408: D/gralloc_goldfish(842): Emulator without GPU emulation detected.
05-13 22:06:17.298: I/dalvikvm(918): threadid=3: reacting to signal 3
05-13 22:06:17.389: I/dalvikvm(918): Wrote stack traces to '/data/anr/traces.txt'
05-13 22:06:17.549: D/gralloc_goldfish(918): Emulator without GPU emulation detected.
05-13 22:06:17.829: W/dalvikvm(918): threadid=11: thread exiting with uncaught exception (group=0x409c01f8)
05-13 22:06:17.839: E/AndroidRuntime(918): FATAL EXCEPTION: AsyncTask #1
05-13 22:06:17.839: E/AndroidRuntime(918): java.lang.RuntimeException: An error occured while executing doInBackground()
05-13 22:06:17.839: E/AndroidRuntime(918): at android.os.AsyncTask$3.done(AsyncTask.java:278)
05-13 22:06:17.839: E/AndroidRuntime(918): at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
05-13 22:06:17.839: E/AndroidRuntime(918): at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
05-13 22:06:17.839: E/AndroidRuntime(918): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
05-13 22:06:17.839: E/AndroidRuntime(918): at java.util.concurrent.FutureTask.run(FutureTask.java:137)
05-13 22:06:17.839: E/AndroidRuntime(918): at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:208)
05-13 22:06:17.839: E/AndroidRuntime(918): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
05-13 22:06:17.839: E/AndroidRuntime(918): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
05-13 22:06:17.839: E/AndroidRuntime(918): at java.lang.Thread.run(Thread.java:856)
05-13 22:06:17.839: E/AndroidRuntime(918): Caused by: java.lang.IllegalArgumentException: Illegal character in scheme at index 0: http://redsox.tcs.auckland.ac.nz/734A/CSService.svc/courses
05-13 22:06:17.839: E/AndroidRuntime(918): at java.net.URI.create(URI.java:727)
05-13 22:06:17.839: E/AndroidRuntime(918): at org.apache.http.client.methods.HttpPost.<init>(HttpPost.java:79)
05-13 22:06:17.839: E/AndroidRuntime(918): at com.example.compsci_734t.JSONParser.getJSONFromUrl(JSONParser.java:36)
05-13 22:06:17.839: E/AndroidRuntime(918): at com.example.compsci_734t.UoaCompsciActivity.loadJSON(UoaCompsciActivity.java:78)
05-13 22:06:17.839: E/AndroidRuntime(918): at com.example.compsci_734t.UoaCompsciActivity$MyTask.doInBackground(UoaCompsciActivity.java:42)
05-13 22:06:17.839: E/AndroidRuntime(918): at com.example.compsci_734t.UoaCompsciActivity$MyTask.doInBackground(UoaCompsciActivity.java:1)
05-13 22:06:17.839: E/AndroidRuntime(918): at android.os.AsyncTask$2.call(AsyncTask.java:264)
05-13 22:06:17.839: E/AndroidRuntime(918): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
05-13 22:06:17.839: E/AndroidRuntime(918): ... 5 more
更新的日志猫：
05-13 22:15:01.438: I/dalvikvm(968): threadid=3: reacting to signal 3
05-13 22:15:01.598: I/dalvikvm(968): Wrote stack traces to '/data/anr/traces.txt'
05-13 22:15:01.718: D/gralloc_goldfish(968): Emulator without GPU emulation detected.
05-13 22:15:02.288: E/JSON Parser(968): Error parsing data org.json.JSONException: Value <?xml of type java.lang.String cannot be converted to JSONObject
05-13 22:15:02.288: D/AndroidRuntime(968): Shutting down VM
05-13 22:15:02.288: W/dalvikvm(968): threadid=1: thread exiting with uncaught exception (group=0x409c01f8)
05-13 22:15:02.298: E/AndroidRuntime(968): FATAL EXCEPTION: main
05-13 22:15:02.298: E/AndroidRuntime(968): java.lang.NullPointerException
05-13 22:15:02.298: E/AndroidRuntime(968): at com.example.compsci_734t.UoaCompsciActivity$MyTask.onPostExecute(UoaCompsciActivity.java:49)
05-13 22:15:02.298: E/AndroidRuntime(968): at com.example.compsci_734t.UoaCompsciActivity$MyTask.onPostExecute(UoaCompsciActivity.java:1)
05-13 22:15:02.298: E/AndroidRuntime(968): at android.os.AsyncTask.finish(AsyncTask.java:602)
05-13 22:15:02.298: E/AndroidRuntime(968): at android.os.AsyncTask.access$600(AsyncTask.java:156)
05-13 22:15:02.298: E/AndroidRuntime(968): at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:615)
05-13 22:15:02.298: E/AndroidRuntime(968): at android.os.Handler.dispatchMessage(Handler.java:99)
05-13 22:15:02.298: E/AndroidRuntime(968): at android.os.Looper.loop(Looper.java:137)
05-13 22:15:02.298: E/AndroidRuntime(968): at android.app.ActivityThread.main(ActivityThread.java:4424)
05-13 22:15:02.298: E/AndroidRuntime(968): at java.lang.reflect.Method.invokeNative(Native Method)
05-13 22:15:02.298: E/AndroidRuntime(968): at java.lang.reflect.Method.invoke(Method.java:511)
05-13 22:15:02.298: E/AndroidRuntime(968): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
05-13 22:15:02.298: E/AndroidRuntime(968): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
05-13 22:15:02.298: E/AndroidRuntime(968): at dalvik.system.NativeStart.main(Native Method)
05-13 22:15:02.889: I/dalvikvm(968): threadid=3: reacting to signal 3
05-13 22:15:02.919: I/dalvikvm(968): Wrote stack traces to '/data/anr/traces.txt'
完整日志猫：
05-13 22:15:01.438: I/dalvikvm(968): threadid=3: 对信号 3 做出反应
05-13 22:15:01.598：I/dalvikvm(968)：将堆栈跟踪写入“/data/anr/traces.txt”
05-13 22:15:01.718：D/gralloc_goldfish(968)：检测到没有 GPU 模拟的模拟器。
05-13 22:15:02.288：E/JSON 解析器（968）：解析数据 org.json.JSONException 时出错：值 
该错误本身是可以解释的：
java.lang.IllegalArgumentException：方案中存在非法字符index 0
您需要删除 URL 中的开头空格字符：
private static String url = "http://redsox.tcs.auckland.ac.nz/734A/CSService.svc/courses";
Update:
更新问题后，现在问题出现在这一行：
courses = json.getJSONArray(TAG_COURSES);
因为你还没有初始化或设置值courses这就是为什么它给予NullPointerException error.
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