need help here to download the apk and form install affter

package com.xaluan2;

import android.app.Activity;
import android.app.AlertDialog;
import android.content.Context;
import android.content.DialogInterface;
import android.content.SharedPreferences;
import android.content.DialogInterface.OnClickListener;
import android.content.Intent.ShortcutIconResource;
import android.content.Intent;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.net.Uri;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.util.Log;
import android.view.KeyEvent;
import android.view.Menu;
import android.view.MenuItem;
import android.view.Window;
import android.webkit.WebChromeClient;
import android.webkit.WebSettings;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.ProgressBar;

public class XaLuanActivity extends Activity{
    private static final String tag=XaLuanActivity.class.getCanonicalName();
    private static final int CHIASE_MENU=1;
    private static final int THOAT_MENU=2;
    private static final int TAILAI_MENU=3;
    private static final int TROGIUP_MENU=4;
    private static final int DANHGIA_MENU=5;

    private String mainUrl="http://www.xaluan.com/mobi.php";
    ProgressBar mProgressBar;
    WebView wbvContent;
    @SuppressWarnings("deprecation")
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        this.requestWindowFeature(Window.FEATURE_NO_TITLE);
        setContentView(R.layout.xaluan);
        wbvContent=(WebView) findViewById(R.id.wbvContent);
        mProgressBar=(ProgressBar)findViewById(R.id.progressBar);
        wbvContent.getSettings().setJavaScriptEnabled(true);

        //wbvContent.getSettings().setJavaScriptCanOpenWindowsAutomatically(true);
        //wbvContent.getSettings().setSupportMultipleWindows(true);

        wbvContent.getSettings().setPluginsEnabled(true);
        wbvContent.getSettings().setPluginState(WebSettings.PluginState.ON);
        wbvContent.setInitialScale(1);
        wbvContent.getSettings().setLoadWithOverviewMode(true);
        wbvContent.getSettings().setUseWideViewPort(true);
        wbvContent.getSettings().setSupportZoom(true);
        wbvContent.getSettings().setBuiltInZoomControls(true);
        //wbvContent.getSettings().setDefaultZoom(ZoomDensity.FAR);

        HelloWebViewClient wbvClient=new HelloWebViewClient();
        wbvContent.setWebViewClient(wbvClient);

        if(!isConnectedNetwork(this)) {
            new AlertDialog.Builder(this)
            .setIcon(android.R.drawable.ic_dialog_alert)
            .setTitle("Thông báo")
            .setMessage("Không có kết nối mạng, vui lòng kết nối mạng để sử dụng")
            .setPositiveButton("Thử lại", new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialog, int which) {
                    XaLuanActivity.this.finish();
                    startActivity(new Intent(XaLuanActivity.this, XaLuanActivity.class));
                }
            })
            .setNegativeButton("Thoát", new OnClickListener() {
                @Override
                public void onClick(DialogInterface dialog, int which) {
                    XaLuanActivity.this.finish();
                }
            })
            .show();
        }else {
             wbvContent.loadUrl(mainUrl);
             wbvContent.setWebChromeClient(new WebChromeClient() {

                 public void onProgressChanged(WebView view, int progress)  {
                    if(progress < 100 && mProgressBar.getVisibility() == ProgressBar.GONE){
                       mProgressBar.setVisibility(ProgressBar.VISIBLE);
                    }
                    mProgressBar.setProgress(progress);
                    if(progress == 100) {
                       mProgressBar.setVisibility(ProgressBar.GONE);
                    }
                 }
             });
        }

    }

    private static class HelloWebViewClient extends WebViewClient {
        @Override
        public boolean shouldOverrideUrlLoading(WebView view, String url) {
            if (url != null && url.startsWith("market://")) {
                view.getContext().startActivity(new Intent(Intent.ACTION_VIEW, Uri.parse(url)));
                //return true;
            }
            else if(url.endsWith(".apk"))
            {
                view.getContext().startActivity(new Intent(Intent.ACTION_VIEW ,Uri.parse(url)));
//need help here to download the apk and form install affter downloaded
            }
            else {
                view.loadUrl(url);
                //return false;
            }
            return true;
        }

    }



    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        menu.add(0, CHIASE_MENU, 0, "Chia Sẻ").setIcon(R.drawable.share);
        menu.add(0, TAILAI_MENU, 0, "Tải Lại").setIcon(R.drawable.refresh);
        menu.add(0, DANHGIA_MENU, 0, "Đánh Giá").setIcon(R.drawable.rate);
        menu.add(0, TROGIUP_MENU, 0, "Trợ Giúp").setIcon(R.drawable.about);
        menu.add(0, THOAT_MENU, 0, "Thoát").setIcon(R.drawable.exit);
        return super.onCreateOptionsMenu(menu);
    }
    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
        case CHIASE_MENU: // chia se
            Intent sharingIntent = new Intent(Intent.ACTION_SEND);
            sharingIntent.setType("text/plain");
            sharingIntent.putExtra(Intent.EXTRA_SUBJECT, wbvContent.getTitle());
            sharingIntent.putExtra(android.content.Intent.EXTRA_TEXT, wbvContent.getUrl());
            startActivity(Intent.createChooser(sharingIntent,"Chia sẻ"));
            break;
        case THOAT_MENU: // chia se
            System.exit(0);
            break;
        case TAILAI_MENU: // chia se
            wbvContent.reload();
            break;
        case TROGIUP_MENU: // chia se
            Intent intent1=new Intent(this, About.class);
            startActivity(intent1);
            break;
        case DANHGIA_MENU:
            String url="market://details?id="+getApplicationContext().getPackageName();
            Intent intent2 = new Intent(Intent.ACTION_VIEW,Uri.parse(url));
            startActivity(intent2);
            break;
        default:
            break;
        }
        return super.onOptionsItemSelected(item);
    }
    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        if (keyCode == KeyEvent.KEYCODE_BACK) {
            if(wbvContent.canGoBack()) {
                wbvContent.goBack();
                return false;
            }else {
                new AlertDialog.Builder(this)
                .setIcon(android.R.drawable.ic_dialog_alert)
                .setTitle("Thoát")
                .setMessage("Bạn có muốn thoát khỏi ứng dụng không")
                .setPositiveButton("Có", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        XaLuanActivity.this.finish();
                    }
                })
                .setNegativeButton("Không", null)
                .show();
            }
        }
        return super.onKeyDown(keyCode, event);
    }
    public static boolean isConnectedNetwork(Context context) {
        ConnectivityManager connectivityManager = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo activeNetworkInfo = connectivityManager.getActiveNetworkInfo();
        return activeNetworkInfo != null;
    }
}