我用google 的Geocoding API 接口来处理反向地理编码 ，但是运行时是空白界面，显示不出位置  下面是代码 ，请告诉我怎么办

public class MainActivity extends Activity {

public static final int SHOW_LOCATION=0;

private TextView positionTextView;

private LocationManager locationManager;

private String provider;

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

positionTextView=(TextView) findViewById(R.id.position_text_view);

locationManager=(LocationManager)getSystemService(Context.LOCATION_SERVICE);

//获取所有可用的位置提供器

List providerList=locationManager.getProviders(true);

if(providerList.contains(locationManager.GPS_PROVIDER)){

provider=locationManager.GPS_PROVIDER;

}else if(providerList.contains(LocationManager.NETWORK_PROVIDER)){

provider=LocationManager.NETWORK_PROVIDER;

}else{

//当没有可用的位置提供器时，弹出Toast提示用户

Toast.makeText(this, "No location Provider to use", Toast.LENGTH_SHORT).show();

return;

}

Location location=locationManager.getLastKnownLocation(provider);

if(location!=null){

//显示当前设备的位置信息

showLocation(location);

}

locationManager.requestLocationUpdates(provider, 5000, 1, locationListener);

}

protected void onDestroy(){

super.onDestroy();

if(locationManager!=null){

//关闭程序时将监听器移除

locationManager.removeUpdates(locationListener);

}

}

LocationListener locationListener=new LocationListener(){

@Override

public void onStatusChanged(String provider,int status,Bundle extras){

}

@Override

public void onProviderEnabled(String provider){}

@Override

public void onProviderDisabled(String provider){}

@Override

public void onLocationChanged(Location location){

//更新当前设备的位置信息

showLocation(location);

}

};

private void showLocation(final Location location){

//String currentPosition="latitude is"+location.getLatitude()+"\n"+

//"longitude is"+location.getLongitude();

// positionTextView.setText(currentPosition);

new Thread(new Runnable(){

@Override

public void run(){

try{

//组装反向地理编码的接口地址

StringBuilder url=new StringBuilder();

url.append("http://maps.googleapis.com/maps/api/geocode/json?latlng=");

url.append(location.getLatitude()).append(",");

url.append(location.getLongitude());

url.append("&sensor=false");

HttpClient httpclient=new DefaultHttpClient();

HttpGet httpget=new HttpGet(url.toString());

//在请求消息头中指定语言，保证服务器会返回中文数据

httpget.addHeader("Accept-Language","zh-CN");

HttpResponse httpResponse=httpclient.execute(httpget);

if(httpResponse.getStatusLine().getStatusCode()==200){

HttpEntity entity=httpResponse.getEntity();

String response=EntityUtils.toString(entity,"utf-8");

JSONObject jsonObject=new JSONObject(response);

//获取results节点下的位置信息

JSONArray resultArray=jsonObject.getJSONArray("results");

if(resultArray.length()>0){

JSONObject subObject=resultArray.getJSONObject(0);

//取出格式化后的位置信息

String address=subObject.getString("formatted_address");

Message message=new Message();

message.what=SHOW_LOCATION;

message.obj=address;

handler.sendMessage(message);

}

}

}catch(Exception e){

e.printStackTrace();

}

}

}).start();

}

private Handler handler=new Handler(){

public void handleMessage(Message msg){

switch(msg.what){

case SHOW_LOCATION:

String currentPosition=(String) msg.obj;

positionTextView.setText(currentPosition);

break;

default:

break;

}

}

};

}