Как хранить в JSON в SQLite

у меня возникли проблемы с хранением данных JSON в sqlite. Это код, который я пытаюсь сейчас реализовать. Данные JSON не особенно велики, в них всего 40 строк.

основной вид деятельности:

public class DatabaseActivity extends Activity {
/** Called when the activity is first created. */

public DBAdapter
DBAdapter =new DBAdapter(this);

TextView txt;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
// Create a crude view - this should really be set via the layout resources  
// but since its an example saves declaring them in the XML.  
LinearLayout rootLayout = new LinearLayout(getApplicationContext());  
txt = new TextView(getApplicationContext());  
rootLayout.addView(txt);  
setContentView(rootLayout);  

// Set the text and call the connect function.  
txt.setText("Connecting..."); 
//call the method to run the data retreival
txt.setText(getServerData(KEY_13)); 

}

public static final String KEY_13 = "http://xxx.xxx.xxx/api/train.php";


private String getServerData(String returnString) {

InputStream is = null;

String result = "";
//the train line to send
ArrayList<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
nameValuePairs.add(new BasicNameValuePair("code","A"));

//http post
try{
        HttpClient httpclient = new DefaultHttpClient();
        HttpPost httppost = new HttpPost(KEY_13);
        httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
        HttpResponse response = httpclient.execute(httppost);
        HttpEntity entity = response.getEntity();
        is = entity.getContent();

}catch(Exception e){
        Log.e("log_tag", "Error in http connection "+e.toString());
}

//convert response to string
try{
        BufferedReader reader = new BufferedReader(new InputStreamReader(is,"iso-8859-1"),8);
        StringBuilder sb = new StringBuilder();
        String line = null;
        while ((line = reader.readLine()) != null) {
                sb.append(line + "n");
        }
        is.close();
        result=sb.toString();
}catch(Exception e){
        Log.e("log_tag", "Error converting result "+e.toString());
}

//parse json data
try{
        JSONArray jArray = new JSONArray(result);
        for(int i=0;i<jArray.length();i++){
                JSONObject json_data = jArray.getJSONObject(i);
                DBAdapter.insertTrain(json_data.getString("id"),
                                    json_data.getString("code"),
                                    json_data.getString("station"),
                                    json_data.getString("platform"),
                                    json_data.getString("timetillstation"),
                                    json_data.getString("traindestination"),

                //Get an output to the screen
                returnString += "nt" + jArray.getJSONObject(i); 
        }
}catch(JSONException e){
        Log.e("log_tag", "Error parsing data "+e.toString());
}
return returnString; 
}    

}

адаптер:

public class DBAdapter{
public static final String KEY_ID = "id";
public static final String KEY_Code = "code";
public static final String KEY_Station = "station";
public static final String KEY_Platform = "platform";
public static final String KEY_TimeTillStation = "timetillstation";
public static final String KEY_TrainDestination = "traindestination";
private static final String TAG = "DBAdapter";

private static final String DATABASE_NAME = "trains";
private static final String DATABASE_TABLE = "Mekerel";
private static final int DATABASE_VERSION = 1;
private static final String DATABASE_CREATE =
    "create table titles (id integer primary key, "
    + "code text not null,"
    + "station text not null,"
    + "platform text not null,"
    + "timetillstation text not null,"
    + "traindestination text not null);";

private final Context context; 

private DatabaseHelper DBHelper;
private SQLiteDatabase db;
public DBAdapter(Context ctx)
  {
      this.context = ctx;
      DBHelper = new DatabaseHelper(context);
      this.db=DBHelper.getWritableDatabase();
  }

private static class DatabaseHelper extends SQLiteOpenHelper 
{
    DatabaseHelper(Context context) 
    {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }
    @Override
    public void onCreate(SQLiteDatabase db) 
    {
        db.execSQL(DATABASE_CREATE);        }
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, 
    int newVersion) 
    {
        Log.w(TAG, "Upgrading database from version " + oldVersion 
                + " to "
                + newVersion + ", which will destroy all old data");
        db.execSQL("DROP TABLE IF EXISTS titles");
        onCreate(db);
    }
}    

//---opens the database---
public DBAdapter open() throws SQLException 
{
    db = DBHelper.getWritableDatabase();
    return this;
}
//---closes the database---    
public void close() 
{
    DBHelper.close();
}

//---insert a train into the database---
public long insertTrain(String id, String code, String station, String platform, String timetillstation, String traindestination) 
{
    ContentValues initialValues = new ContentValues();
    initialValues.put(KEY_ID, id);
    initialValues.put(KEY_Code, code);
    initialValues.put(KEY_Station, station);
    initialValues.put(KEY_Platform, platform);
    initialValues.put(KEY_TimeTillStation, timetillstation);
    initialValues.put(KEY_TrainDestination, traindestination);
    return db.insert(DATABASE_TABLE, null, initialValues);
}
//---retrieves all the ttrain---
public Cursor getAllTrains() 
{
    return db.query(DATABASE_TABLE, new String[] {
            KEY_ID,
            KEY_Code,
            KEY_Station,
            KEY_Platform,
            KEY_TimeTillStation,
            KEY_TrainDestination},
            null, 
            null, 
            null, 
            null, 
            null,
            null);
}
//---retrieves a particular train---
public Cursor getTrain(long id) throws SQLException 
{
    Cursor mCursor =
            db.query(true, DATABASE_TABLE, new String[] {
            KEY_ID,
            KEY_Code, 
            KEY_Station,
            KEY_Platform,
            KEY_TimeTillStation,
            KEY_TrainDestination}, 
        KEY_ID + "=" + id, 
        null,
        null, 
        null, 
        null, 
        null);
    if (mCursor != null) {
        mCursor.moveToFirst();
    }
    return mCursor;
}
//---updates a train---
public boolean updateTrain(long id, String code, String station, String platform, String timetillstation, String traindestination) 
{
    ContentValues args = new ContentValues();
    args.put(KEY_Code, code);
    args.put(KEY_Station, station);
    args.put(KEY_Platform, platform);
    args.put(KEY_TimeTillStation, timetillstation);
    args.put(KEY_TrainDestination, traindestination);
    return db.update(DATABASE_TABLE, args, 
                     KEY_ID + "=" + id, null) > 0;
}
}

Я не уверен, куда идти отсюда, так как есть еще вопросы. В журнале cat отображается следующее:

12-04 12:43:09.691: E/AndroidRuntime(21334): FATAL EXCEPTION: main
12-04 12:43:09.691: E/AndroidRuntime(21334): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{ta.dabase/ta.dabase.DatabaseActivity}: java.lang.NullPointerException
12-04 12:43:09.691: E/AndroidRuntime(21334):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1680)
12-04 12:43:09.691: E/AndroidRuntime(21334):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1784)
12-04 12:43:09.691: E/AndroidRuntime(21334):    at android.app.ActivityThread.access00(ActivityThread.java:123)
12-04 12:43:09.691: E/AndroidRuntime(21334):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:939)
12-04 12:43:09.691: E/AndroidRuntime(21334):    at android.os.Handler.dispatchMessage(Handler.java:99)
12-04 12:43:09.691: E/AndroidRuntime(21334):    at android.os.Looper.loop(Looper.java:130)
12-04 12:43:09.691: E/AndroidRuntime(21334):    at android.app.ActivityThread.main(ActivityThread.java:3835)
12-04 12:43:09.691: E/AndroidRuntime(21334):    at java.lang.reflect.Method.invokeNative(Native Method)
12-04 12:43:09.691: E/AndroidRuntime(21334):    at java.lang.reflect.Method.invoke(Method.java:507)
12-04 12:43:09.691: E/AndroidRuntime(21334):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:847)
12-04 12:43:09.691: E/AndroidRuntime(21334):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:605)
12-04 12:43:09.691: E/AndroidRuntime(21334):    at dalvik.system.NativeStart.main(Native Method)
12-04 12:43:09.691: E/AndroidRuntime(21334): Caused by: java.lang.NullPointerException
12-04 12:43:09.691: E/AndroidRuntime(21334):    at android.content.ContextWrapper.openOrCreateDatabase(ContextWrapper.java:203)
12-04 12:43:09.691: E/AndroidRuntime(21334):    at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:118)
12-04 12:43:09.691: E/AndroidRuntime(21334):    at ta.dabase.DBAdapter.<init>(DBAdapter.java:43)
12-04 12:43:09.691: E/AndroidRuntime(21334):    at ta.dabase.DatabaseActivity.<init>(DatabaseActivity.java:32)
12-04 12:43:09.691: E/AndroidRuntime(21334):    at java.lang.Class.newInstanceImpl(Native Method)
12-04 12:43:09.691: E/AndroidRuntime(21334):    at java.lang.Class.newInstance(Class.java:1409)
12-04 12:43:09.691: E/AndroidRuntime(21334):    at android.app.Instrumentation.newActivity(Instrumentation.java:1021)
12-04 12:43:09.691: E/AndroidRuntime(21334):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1672)
12-04 12:43:09.691: E/AndroidRuntime(21334):    ... 11 more

наконец, мне было интересно, может ли кто-нибудь помочь мне с отладкой в некотором смысле что и где разместить соответствующий код журнала, чтобы определить, где код идет не так? Спасибо