android app无法连接互联网,该怎么处理

package com.android.network;import java.net.MalformedURLException;import java.net.URL;import java.io.InputStream;import android.app.Activity;import android.os.Bundle;import android.util.Log;import android.view.View;import android.widget.Button;public class ReadBytesActivity extends Activity{    private static final String DEBUG_TAG = "ReadBytesActivity";    @Override    protected void onCreate(Bundle savedInstanceState)    {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);                Log.i(DEBUG_TAG, "application start!");                Button go = (Button)findViewById(R.id.do_action);        go.setOnClickListener(new View.OnClickListener() {                        @Override            public void onClick(View v)            {                try                {                    URL text = new URL("http://www.liyebei.com/index.html");                        InputStream isText = text.openStream();                    byte[] bText = new byte[250];                    int readSize = isText.read(bText);                    Log.i(DEBUG_TAG, "read size = " + readSize);                    Log.i(DEBUG_TAG, "byte text = " + new String(bText));                                        isText.close();                }                catch(MalformedURLException e)                {                    e.printStackTrace();                    Log.i(DEBUG_TAG, "the URL cann't be find");                }                catch(Exception e)                {                    e.printStackTrace();                    Log.i(DEBUG_TAG, "there are some problems");                }            }        });    }    }

<?xml version="1.0" encoding="utf-8"?><LinearLayout    xmlns:android="http://schemas.android.com/apk/res/android"    android:orientation="vertical"    android:layout_width="fill_parent"    android:layout_height="fill_parent">    <LinearLayout        android:orientation="horizontal"        android:layout_width="fill_parent"        android:layout_height="wrap_content">        <TextView            android:id="@+id/instruct"            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:text="Press button for action" />        <Button            android:id="@+id/do_action"            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:text="Go!" />    </LinearLayout>    <TextSwitcher        android:id="@+id/status"        android:layout_width="fill_parent"        android:layout_height="wrap_content" />    <ImageSwitcher        android:id="@+id/images"        android:layout_width="fill_parent"        android:layout_height="wrap_content" />    <TextSwitcher        android:id="@+id/info"        android:layout_width="fill_parent"        android:layout_height="wrap_content" /></LinearLayout>