我还是Java的新手，正在开展一个即将让我脱发的课程项目。我试图从iTunes API中提取JSON信息。被提取的信息来自某张专辑。我在WebClass.java类中的getURLStringResponse（）方法中使用了try / catch，它抛出了内置的异常，我不明白为什么也无法得到老师的帮助。所以我正在接触大脑！
如果有帮助，这是我的github链接
https://github.com/agvinsant/Java1/tree/master/week3
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();
}
}
}
}
这是WebClass
package com.agvinsant.lib;
import java.io.BufferedInputStream;
import java.net.URL;
import java.net.URLConnection;
import android.content.Context;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.util.Log;
public class WebClass {
static Boolean connection = false;
static String connectionType = "Unavailable";
public static String getConnectionType(Context context){
webInfo(context);
return connectionType;
}
public static Boolean getConnectionStatus(Context context){
webInfo(context);
return connection;
}
private static void webInfo(Context context){
ConnectivityManager cm = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo ni = cm.getActiveNetworkInfo();
if(ni != null){
if(ni.isConnected()){
connectionType = ni.getTypeName();
connection = true;
}
}
}
public static String getURLStringResponse(URL url){
String response = "";
try{
URLConnection conn = url.openConnection();
BufferedInputStream bin = new BufferedInputStream(conn.getInputStream());
byte[] contentBytes = new byte[1024];
int bytesRead = 0;
StringBuffer responseBuffer = new StringBuffer();
while((bytesRead = bin.read(contentBytes)) != -1){
response = new String(contentBytes,0,bytesRead);
responseBuffer.append(response);
}
return responseBuffer.toString();
}
catch(Exception e){
// This is the exception that is being thrown
Log.e("URL RESPONSE ERROR", "getURLStringResponse");
}
return response;
}
}
这也是一个处理一些文件响应的FileClass
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在运行时显示的内容
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
答案 0 :(得分：2)
使用您的onCreate方法
ArrayAdapter<String> spinnerAdapter = new ArrayAdapter<String>(context, android.R.layout.simple_spinner_item, songName);
但
String[] songName;
已声明但未初始化，即。它默认为null。您需要对其进行初始化并填充它。
ArrayAdapter构造函数尝试使用此代码创建ArrayList（不是java.util类型）
ArrayList(E[] array) {
if (array==null)
throw new NullPointerException();
a = array;
}
所以你得到NullPointerException。
请学习使用调试器并阅读堆栈跟踪。