Cómo almacenar JSON en SQLite

Tengo problemas con el almacenamiento de datos JSON a sqlite. Este es el código que estoy tratando de implementar ahora mismo. Los datos de JSON no son particularmente grandes con sólo 40 líneas en él.

La actividad principal es:

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 += "\n\t" + jArray.getJSONObject(i); } }catch(JSONException e){ Log.e("log_tag", "Error parsing data "+e.toString()); } return returnString; } }

El adaptador es:

 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; } }

No estoy seguro de dónde ir desde aquí, ya que todavía hay problemas. El logcat muestra lo siguiente:

 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.access$1500(ActivityThread.java:123) 12-04 12:43:09.691: E/AndroidRuntime(21334): at android.app.ActivityThread$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

Por último, me preguntaba si alguien podría ayudarme con la depuración en un sentido de qué y dónde colocar el código de registro adecuado para detectar dónde el código va mal exactamente? Gracias