在Java中获取URL响应引发异常

我对Java还是个新手，正在做一个类项目，这将使我感到毛骨悚然。我正在尝试从iTunesAPI中提取JSON信息。正在提取的信息来自某个相册。我在WebClass.java类的getURLStringResponse（）方法中使用了try/catch，它抛出了内置异常，我不知道为什么，也无法从我的老师那里得到帮助。因此，我正在向大脑伸出援手

如果有帮助，这里是我的github链接

这是我的主要活动

package com.agvinsant.java1application;

import java.net.MalformedURLException;
import java.net.URL;
import java.util.ArrayList;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import com.agvinsant.lib.BasicLayout;
import com.agvinsant.lib.WebClass;

import android.os.AsyncTask;
import android.os.Bundle;
import android.app.Activity;
import android.content.Context;
import android.content.res.Resources;
import android.util.Log;
import android.view.Menu;
import android.view.View;
import android.view.ViewGroup.LayoutParams;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemSelectedListener;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.LinearLayout;
import android.widget.Spinner;
import android.widget.TextView;
import android.widget.Toast;


public class MainActivity extends Activity {

Context context;
String[] songName;
Resources res;
TextView results;
Spinner viewSpinner;
TextView jsonView;
TextView connectedView;
String trackName;
String artistName;
String albumName;
String trackSite;

ArrayList<String> trackNameList = new ArrayList<String>();
ArrayList<String> artistNameList = new ArrayList<String>();
ArrayList<String> albumNameList = new ArrayList<String>();
ArrayList<String> trackSiteList = new ArrayList<String>();

Boolean connected = false;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    context = this;
    res = getResources();

    // setting the linear layout
    LinearLayout ll = new LinearLayout(this);
    LinearLayout ml = BasicLayout.layoutWithButton(this, "Show Info");
    ll.setOrientation(LinearLayout.VERTICAL);
    LayoutParams lp = new LayoutParams(LayoutParams.MATCH_PARENT,LayoutParams.MATCH_PARENT);
    ll.setLayoutParams(lp);

    // Creating button from BasicLayout class
    Button mb = (Button) ml.findViewById(1);
    mb.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            // Get selected song info
            int pos = viewSpinner.getSelectedItemPosition();
            String tName = trackNameList.get(pos).toString();
            String arName = artistNameList.get(pos).toString();
            String alName = albumNameList.get(pos).toString();  
            String tSite = trackSiteList.get(pos).toString();

            jsonView.setText("Song Name: " +tName+ "\r\n" + "Artist Name: " +arName+ "\r\n" +"Album Name: "+alName+ "\r\n" + "Song Website: " +tSite);
        }

    });



    connectedView = new TextView(context);

    //Detecting network settings
            connected = WebClass.getConnectionStatus(context);
            if(connected){
                Log.i("Network Connection", WebClass.getConnectionType(context));
                connectedView.setText("Network Connection: " + WebClass.getConnectionType(context)+"\n");
            }
            else{
                    connectedView.setText(""+WebClass.getConnectionType(context)+"\n");
            }


    // calling the getSongInfo function 
    getSongInfo();

    // song length display
    int songNum = res.getStringArray(R.array.songArray).length;
    TextView tv = new TextView(context);
    tv.setText("Check out one of the "+songNum+" songs on the album");

    //spinner adapter
    ArrayAdapter<String> spinnerAdapter = new ArrayAdapter<String>(context, android.R.layout.simple_spinner_item, songName);
    spinnerAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);

    //creating the spinner
    viewSpinner = new Spinner(context);
    viewSpinner.setAdapter(spinnerAdapter);
    lp = new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT);
    viewSpinner.setLayoutParams(lp);

    //spinner onClick function
    viewSpinner.setOnItemSelectedListener(new OnItemSelectedListener(){

        @Override
        public void onItemSelected(AdapterView<?> parent, View view,
                int position, long id) {
            Toast.makeText(context, "You selected " + songName[position], Toast.LENGTH_LONG).show();
        }

        @Override
        public void onNothingSelected(AdapterView<?> arg0) {
            // TODO Auto-generated method stub

        }

    });


    // setting different layout parts to the main layout
    ll.addView(ml);
    ll.addView(tv);
    ll.addView(viewSpinner);
    //ll.addView(connectedView);
    ll.addView(jsonView);


    // setting the content view
    setContentView(ll);




}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

//get URL
private void getSongInfo(){
    String baseURL = "https://itunes.apple.com/search?term=groove+logic+logical+thinking";
    URL finalURL;
    try{
        finalURL = new URL(baseURL);
        songRequest sr = new songRequest();
        sr.execute(finalURL);
    } catch (MalformedURLException e){
        Log.e("BAD URL", "MALFORMED URL");
        finalURL = null;
    }
}

//get data from URL
private class songRequest extends AsyncTask<URL, Void, String>{
    @Override
    protected String doInBackground(URL... urls){
        String response = "";
        for(URL url: urls){
            response = WebClass.getURLStringResponse(url);
        }
        return response;
    }

    //get data and add to arrays.
    @Override
    protected void onPostExecute(String result){
        try {

            Log.i("URL Response", result);
            JSONArray jsonArray = new JSONArray(result);

            int n = jsonArray.length();
            for(int i = 0;i<n; i++){
                JSONObject jsonObject = jsonArray.getJSONObject(i);

                trackName = jsonObject.getString("trackName");
                artistName= jsonObject.getString("artistName");
                albumName = jsonObject.getString("collectionName");
                trackSite= jsonObject.getString("trackViewUrl");
                trackNameList.add(trackName);
                artistNameList.add(artistName);
                albumNameList.add(albumName);  
                trackSiteList.add(trackSite);
            }

        } catch (JSONException e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();
        }
    }   
}

}

这也是一个FileClass，用于处理一些文件响应

package com.agvinsant.lib;

import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

import android.content.Context;
import android.util.Log;

// TODO: Auto-generated Javadoc
/**
 * The Class FileClass.
 */
public class FileClass {

    /**
     * Store string file.
     *
     * @param context the context
     * @param filename the filename
     * @param content the content
     * @param external the external
     * @return the boolean
     */
    @SuppressWarnings("resource")
    public static Boolean storeStringFile(Context context, String filename, String content, Boolean external){
        try{
            File file;
            FileOutputStream fos;
            if(external){
                file = new File(context.getExternalFilesDir(null), filename);
                fos = new FileOutputStream(file);
            }else{
                fos = context.openFileOutput(filename, Context.MODE_PRIVATE);
            }
            fos.write(content.getBytes());
            fos.close();
        } catch (IOException e){
            Log.e("WRITE ERROR", filename);
        }
        return true;
    }


    /**
     * Store object file.
     *
     * @param context the context
     * @param filename the filename
     * @param external the external
     * @return the boolean
     */
    public static Boolean storeObjectFile(Context context, String filename, Boolean external){

        return true;
    }


    /**
     * Store object file.
     *
     * @param context the context
     * @param filename the filename
     * @param content the content
     * @param external the external
     * @return the boolean
     */
    @SuppressWarnings("resource")
    public static Boolean storeObjectFile(Context context, String filename, Object content, Boolean external){
        try{
            File file;
            FileOutputStream fos;
            ObjectOutputStream oos;
            if(external){
                file = new File(context.getExternalFilesDir(null), filename);
                fos = new FileOutputStream(file);
            } else {
                fos = context.openFileOutput(filename, Context.MODE_PRIVATE);
            }
            oos = new ObjectOutputStream(fos);
            oos.writeObject(content);
            oos.close();
            fos.close();
        } catch (IOException e){
            Log.e("WRITE ERROR", filename);
        }
        return true;
    }


    /**
     * Read string file.
     *
     * @param context the context
     * @param filename the filename
     * @param external the external
     * @return the string
     */
    @SuppressWarnings("resource")
    public static String readStringFile(Context context, String filename, Boolean external){
        String content = "";
        try{
            File file;
            FileInputStream fin;
            if(external){
                file = new File(context.getExternalFilesDir(null), filename);
                fin = new FileInputStream(file);
            } else {
                file = new File(filename);
                fin = context.openFileInput(filename);
            }
            BufferedInputStream bin = new BufferedInputStream(fin);
            byte[] contentBytes = new byte[1024];
            int bytesRead = 0;
            StringBuffer contentBuffer = new StringBuffer();

            while((bytesRead = bin.read(contentBytes)) != -1){
                content = new String(contentBytes,0,bytesRead);
                contentBuffer.append(content);
            }
            content = contentBuffer.toString();
            fin.close();
        } catch (FileNotFoundException e) {
            Log.e("READ ERROR", "FILE NOT FOUND " + filename);
        } catch (IOException e){
            Log.e("READ ERROR", "I/O ERROR");
        }
        return content;
    }


    /**
     * Read object file.
     *
     * @param context the context
     * @param filename the filename
     * @param external the external
     * @return the object
     */
    @SuppressWarnings("resource")
    public static Object readObjectFile(Context context, String filename, Boolean external){
        Object content = new Object();
        try{
            File file;
            FileInputStream fin;
            if(external){
                file = new File(context.getExternalFilesDir(null), filename);
                fin = new FileInputStream(file);
            } else {
                file = new File(filename);
                fin = context.openFileInput(filename);
            }

            ObjectInputStream ois = new ObjectInputStream(fin);
            try{
                content = (Object) ois.readObject();
            } catch (ClassNotFoundException e){
                Log.e("READ ERROR", "INVALID JAVA OBJECT FILE");
            }
            ois.close();
            fin.close();
        } catch (FileNotFoundException e) {
            Log.e("READ ERROR", "FILE NOT FOUND " + filename);
            return null;
        } catch (IOException e){
            Log.e("READ ERROR", "I/O ERROR");
        }
        return content;
    }

}

这是LogCat运行时显示的内容

09-11 21:11:25.496: E/Trace(2500): error opening trace file: No such file or directory (2)
09-11 21:11:25.676: I/Network Connection(2500): mobile
09-11 21:11:25.707: D/AndroidRuntime(2500): Shutting down VM
09-11 21:11:25.707: W/dalvikvm(2500): threadid=1: thread exiting with uncaught exception (group=0xb2f55288)
09-11 21:11:25.756: E/AndroidRuntime(2500): FATAL EXCEPTION: main
09-11 21:11:25.756: E/AndroidRuntime(2500): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.agvinsant.java1application/com.agvinsant.java1application.MainActivity}: java.lang.NullPointerException
09-11 21:11:25.756: E/AndroidRuntime(2500):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
09-11 21:11:25.756: E/AndroidRuntime(2500):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
09-11 21:11:25.756: E/AndroidRuntime(2500):     at android.app.ActivityThread.access$600(ActivityThread.java:130)
09-11 21:11:25.756: E/AndroidRuntime(2500):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
09-11 21:11:25.756: E/AndroidRuntime(2500):     at android.os.Handler.dispatchMessage(Handler.java:99)
09-11 21:11:25.756: E/AndroidRuntime(2500):     at android.os.Looper.loop(Looper.java:137)
09-11 21:11:25.756: E/AndroidRuntime(2500):     at android.app.ActivityThread.main(ActivityThread.java:4745)
09-11 21:11:25.756: E/AndroidRuntime(2500):     at java.lang.reflect.Method.invokeNative(Native Method)
09-11 21:11:25.756: E/AndroidRuntime(2500):     at java.lang.reflect.Method.invoke(Method.java:511)
09-11 21:11:25.756: E/AndroidRuntime(2500):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
09-11 21:11:25.756: E/AndroidRuntime(2500):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
09-11 21:11:25.756: E/AndroidRuntime(2500):     at dalvik.system.NativeStart.main(Native Method)
09-11 21:11:25.756: E/AndroidRuntime(2500): Caused by: java.lang.NullPointerException
09-11 21:11:25.756: E/AndroidRuntime(2500):     at java.util.Arrays$ArrayList.<init>(Arrays.java:38)
09-11 21:11:25.756: E/AndroidRuntime(2500):     at java.util.Arrays.asList(Arrays.java:154)
09-11 21:11:25.756: E/AndroidRuntime(2500):     at android.widget.ArrayAdapter.<init>(ArrayAdapter.java:128)
09-11 21:11:25.756: E/AndroidRuntime(2500):     at com.agvinsant.java1application.MainActivity.onCreate(MainActivity.java:121)
09-11 21:11:25.756: E/AndroidRuntime(2500):     at android.app.Activity.performCreate(Activity.java:5008)
09-11 21:11:25.756: E/AndroidRuntime(2500):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
09-11 21:11:25.756: E/AndroidRuntime(2500):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)
09-11 21:11:25.756: E/AndroidRuntime(2500):     ... 11 more
09-11 21:11:25.766: E/URL RESPONSE ERROR(2500): getURLStringResponse

09-11 21:11:25.496:E/Trace（2500）：打开跟踪文件时出错：没有这样的文件或目录（2）
09-11 21:11:25.676:I/网络连接（2500）：移动
09-11 21:11:25.707:D/AndroidRuntime（2500）：关闭虚拟机
09-11 21:11:25.707:W/dalvikvm（2500）：threadid=1:线程退出时出现未捕获异常（组=0xb2f55288）
09-11 21:11:25.756:E/AndroidRuntime（2500）：致命异常：main
09-11 21:11:25.756:E/AndroidRuntime（2500）：java.lang.RuntimeException:无法启动活动组件信息{com.agvinsant.java1application/com.agvinsant.java1application.MainActivity}:java.lang.NullPointerException
09-11 21:11:25.756:E/AndroidRuntime（2500）：在android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2059）
09-11 21:11:25.756:E/AndroidRuntime（2500）：位于android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:2084）
09-11 21:11:25.756:E/AndroidRuntime（2500）：在android.app.ActivityThread.access$600（ActivityThread.java:130）
09-11 21:11:25.756:E/AndroidRuntime（2500）：在android.app.ActivityThread$H.handleMessage（ActivityThread.java:1195）
09-11 21:11:25.756:E/AndroidRuntime（2500）：在android.os.Handler.dispatchMessage（Handler.java:99）上
09-11 21:11:25.756:E/AndroidRuntime（2500）：在android.os.Looper.loop（Looper.java:137）
09-11 21:11:25.756:E/AndroidRuntime（2500）：位于android.app.ActivityThread.main（ActivityThread.java:4745）
09-11 21:11:25.756:E/AndroidRuntime（2500）：位于java.lang.reflect.Method.Invokenactive（本机方法）
09-11 21:11:25.756:E/AndroidRuntime（2500）：位于java.lang.reflect.Method.invoke（Method.java:511）
09-11 21:11:25.756:E/AndroidRuntime（2500）：在com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run（ZygoteInit.java:786）
09-11 21:11:25.756:E/AndroidRuntime（2500）：位于com.android.internal.os.ZygoteInit.main（ZygoteInit.java:553）
9-11 21:11:25.756:E/AndroidRuntime（2500）：在dalvik.system.NativeStart.main（本机方法）
09-11 21:11:25.756:E/AndroidRuntime（2500）：由以下原因引起：java.lang.NullPointerException
09-11 21:11:25.756:E/AndroidRuntime（2500）：位于java.util.Arrays$ArrayList。（Arrays.java:38）
09-11 21:11:25.756:E/AndroidRuntime（2500）：位于java.util.Arrays.asList（Arrays.java:154）
09-11 21:11:25.756:E/AndroidRuntime（2500）：在android.widget.ArrayAdapter.（ArrayAdapter.java:128）
09-11 21:11:25.756:E/AndroidRuntime（2500）：位于com.agvinsant.java1application.MainActivity.onCreate（MainActivity.java:121）
09-11 21:11:25.756:E/AndroidRuntime（2500）：在android.app.Activity.performCreate（Activity.java:5008）上
09-11 21:11:25.756:E/AndroidRuntime（2500）：在android.app.Instrumentation.callActivityOnCreate（Instrumentation.java:1079）上
2009-11 21:11:25.756:E/AndroidRuntime（2500）：在android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2023）
2009-11 21:11:25.756:E/AndroidRuntime（2500）：。。。还有11个
09-11 21:11:25.766:E/URL响应错误（2500）：getURLStringResponse

在您的

onCreate

方法中

ArrayAdapter<String> spinnerAdapter = new ArrayAdapter<String>(context, android.R.layout.simple_spinner_item, songName);

已声明但未初始化，即默认为

null

。您需要初始化它，并可能填充它

ArrayAdapter

构造函数尝试使用此代码创建

ArrayList

（而不是

java.util

类）

   ArrayList(E[] array) {
        if (array==null)
            throw new NullPointerException();
        a = array;
    }

因此，您会得到一个

NullPointerException

---

---

请学习使用调试器和读取堆栈跟踪。

谢谢，我已经修复了它，但它仍在崩溃。@user2789153它可能因为另一个原因崩溃。除非你告诉我们，否则我们无法知道。这些课程和导师并不是最好的。我明白了，thanks@user2789153一次只接受一个例外。如果你需要的话，可以问一个新问题，但先自己尝试一下。

String[] songName;

   ArrayList(E[] array) {
        if (array==null)
            throw new NullPointerException();
        a = array;
    }