首先看一个文件manifest文件：

1<manifest xmlns:android="http://schemas.android.com/apk/res/android"package="com.jj.upgrade" android:versioncode="1"android:versionname="1.0">  </manifest>

我们可以很清楚的看到versionCode和versionName,我们一般用versionCode来实现, 实现原理很简单：服务器端有个serverVersion，我们本地有个localVersion.服务器端serverVersion>localVersion,这个时候我们就需要进行升级版本.原理大致就是这样。

具体实现请看下面:

01package com.jj.upgrade;
02  
03import com.jj.Service.UpdateService;
04  
05import android.app.AlertDialog;
06import android.app.Application;
07import android.content.DialogInterface;
08import android.content.Intent;
09import android.content.pm.PackageInfo;
10import android.content.pm.PackageManager.NameNotFoundException;
11  
12/***
13 * MyApplication
14 *
15 * @author zhangjia
16 *
17 */
18public class MyApplication extends Application {
19  
20    public static int localVersion = 0;// 本地安装版本
21  
22    public static int serverVersion = 2;// 服务器版本
23  
24    public static String downloadDir = "jj/";// 安装目录
25  
26    @Override
27    public void onCreate() {
28        super.onCreate();
29        try {
30            PackageInfo packageInfo = getApplicationContext()
31                    .getPackageManager().getPackageInfo(getPackageName(),0);
32            localVersion = packageInfo.versionCode;
33        } catch (NameNotFoundException e) {
34            e.printStackTrace();
35        }
36  
37        /***
38         * 在这里写一个方法用于请求获取服务器端的serverVersion.
39         */
40  
41    }
42  
43}

我们一般把全局的东西放到application里面.

01public class MainActivity extends Activity {
02    private MyApplication myApplication;
03  
04    @Override
05    public void onCreate(Bundle savedInstanceState) {
06        super.onCreate(savedInstanceState);
07        setContentView(R.layout.main);
08          
09        checkVersion();
10    }
11  
12    /***
13     * 检查是否更新版本
14     */
15    public void checkVersion() {
16        myApplication = (MyApplication) getApplication();
17        if (myApplication.localVersion < myApplication.serverVersion) {
18  
19            // 发现新版本，提示用户更新
20            AlertDialog.Builder alert = new AlertDialog.Builder(this);
21            alert.setTitle("软件升级")
22                    .setMessage("发现新版本,建议立即更新使用.")
23                    .setPositiveButton("更新",
24                            new DialogInterface.OnClickListener() {
25                                public void onClick(DialogInterface dialog,
26                                        int which) {
27                                    Intent updateIntent = new Intent(
28                                            MainActivity.this,
29                                            UpdateService.class);
30                                    updateIntent.putExtra(
31                                            "app_name",
32                                            getResources().getString(
33                                                    R.string.app_name));
34                                    startService(updateIntent);
35                                }
36                            })
37                    .setNegativeButton("取消",
38                            new DialogInterface.OnClickListener() {
39                                public void onClick(DialogInterface dialog,
40                                        int which) {
41                                    dialog.dismiss();
42                                }
43                            });
44            alert.create().show();
45  
46        }
47    }
48}

我们在运行应用的时候要checkVersion();进行检查版本是否要进行升级. 最主要的是UpdateService服务类

01@Override
02    public int onStartCommand(Intent intent, int flags, int startId) {
03  
04        app_name = intent.getStringExtra("app_name");
05        // 创建文件
06        FileUtil.createFile(app_name);// 创建文件
07  
08        createNotification();// 首次创建
09  
10        createThread();// 线程下载
11  
12        return super.onStartCommand(intent, flags, startId);
13  
14    }

创建路径及文件，这里就不介绍了，不明白了下载源码看。

首先我们先 看createNotification().这个方法：

01/***
02     * 创建通知栏
03     */
04    RemoteViews contentView;
05    public void createNotification() {
06        notificationManager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
07        notification = new Notification();
08        notification.icon = R.drawable.ic_launcher;// 这个图标必须要设置，不然下面那个RemoteViews不起作用.
09        // 这个参数是通知提示闪出来的值.
10        notification.tickerText = "开始下载";
11        //
12        // updateIntent = new Intent(this, MainActivity.class);
13        // pendingIntent = PendingIntent.getActivity(this, 0, updateIntent, 0);
14        //
15        // // 这里面的参数是通知栏view显示的内容
16        // notification.setLatestEventInfo(this, app_name, "下载：0%",
17        // pendingIntent);
18        //
19        // notificationManager.notify(notification_id, notification);
20  
21        /***
22         * 在这里我们用自定的view来显示Notification
23         */
24        contentView = new RemoteViews(getPackageName(),
25                R.layout.notification_item);
26        contentView.setTextViewText(R.id.notificationTitle, "正在下载");
27        contentView.setTextViewText(R.id.notificationPercent, "0%");
28        contentView.setProgressBar(R.id.notificationProgress, 100, 0,false);
29  
30        notification.contentView = contentView;
31  
32        updateIntent = new Intent(this, MainActivity.class);
33        updateIntent.addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP);
34        pendingIntent = PendingIntent.getActivity(this, 0, updateIntent, 0);
35  
36        notification.contentIntent = pendingIntent;
37  
38        notificationManager.notify(notification_id, notification);
39  
40    }

上面实现的也不难理解.(主要是初始化Notification,用于提醒用户开始下载)接着我们要看createThread方法

01/***
02     * 开线程下载
03     */
04    public void createThread() {
05        /***
06         * 更新UI
07         */
08        final Handler handler = new Handler() {
09            @Override
10            public void handleMessage(Message msg) {
11                switch (msg.what) {
12                case DOWN_OK:
13                    // 下载完成，点击安装
14                    Uri uri = Uri.fromFile(FileUtil.updateFile);
15                    Intent intent = new Intent(Intent.ACTION_VIEW);
16                    intent.setDataAndType(uri,
17                            "application/vnd.android.package-archive");
18  
19                    pendingIntent = PendingIntent.getActivity(
20                            UpdateService.this, 0, intent, 0);
21  
22                    notification.setLatestEventInfo(UpdateService.this,
23                            app_name, "下载成功，点击安装", pendingIntent);
24  
25                    notificationManager.notify(notification_id, notification);
26  
27                    stopSelf();
28                    break;
29                case DOWN_ERROR:
30                    notification.setLatestEventInfo(UpdateService.this,
31                            app_name, "下载失败", pendingIntent);
32                    break;
33  
34                default:
35                    stopSelf();
36                    break;
37                }
38  
39            }
40  
41        };
42  
43        final Message message = new Message();
44  
45        new Thread(new Runnable() {
46            @Override
47            public void run() {
48  
49                try {
50                    long downloadSize = downloadUpdateFile(down_url,
51                            FileUtil.updateFile.toString());
52                    if (downloadSize > 0) {
53                        // 下载成功
54                        message.what = DOWN_OK;
55                        handler.sendMessage(message);
56                    }
57  
58                } catch (Exception e) {
59                    e.printStackTrace();
60                    message.what = DOWN_ERROR;
61                    handler.sendMessage(message);
62                }
63  
64            }
65        }).start();
66    }

这个方法有点小多，不过我想大家都看的明白，我在这里简单说名一下：首先我们创建一个handler用于检测最后下载ok还是not ok. 下面我们开启了线程进行下载数据。 我们接着看downloadUpdateFile这个方法：

01/***
02     * 下载文件
03     *
04     * @return
05     * @throws MalformedURLException
06     */
07    public long downloadUpdateFile(String down_url, String file)
08            throws Exception {
09        int down_step = 5;// 提示step
10        int totalSize;// 文件总大小
11        int downloadCount = 0;// 已经下载好的大小
12        int updateCount = 0;// 已经上传的文件大小
13        InputStream inputStream;
14        OutputStream outputStream;
15  
16        URL url = new URL(down_url);
17        HttpURLConnection httpURLConnection = (HttpURLConnection) url
18                .openConnection();
19        httpURLConnection.setConnectTimeout(TIMEOUT);
20        httpURLConnection.setReadTimeout(TIMEOUT);
21        // 获取下载文件的size
22        totalSize = httpURLConnection.getContentLength();
23        if (httpURLConnection.getResponseCode() == 404) {
24            throw new Exception("fail!");
25        }
26        inputStream = httpURLConnection.getInputStream();
27        outputStream = new FileOutputStream(file, false);// 文件存在则覆盖掉
28        byte buffer[] = new byte[1024];
29        int readsize = 0;
30        while ((readsize = inputStream.read(buffer)) != -1) {
31            outputStream.write(buffer, 0, readsize);
32            downloadCount += readsize;// 时时获取下载到的大小
33            /**
34             * 每次增张5%
35             */
36            if (updateCount == 0
37                    || (downloadCount * 100 / totalSize - down_step) >= updateCount) {
38                updateCount += down_step;
39                // 改变通知栏
40                // notification.setLatestEventInfo(this, "正在下载...", updateCount
41                // + "%" + "", pendingIntent);
42                contentView.setTextViewText(R.id.notificationPercent,
43                        updateCount + "%");
44                contentView.setProgressBar(R.id.notificationProgress,100,
45                        updateCount, false);
46                // show_view
47                notificationManager.notify(notification_id, notification);
48  
49            }
50  
51        }
52        if (httpURLConnection != null) {
53            httpURLConnection.disconnect();
54        }
55        inputStream.close();
56        outputStream.close();
57  
58        return downloadCount;
59  
60    }

注释已经写的很详细，相信大家都看的明白，如果哪里有不足的地方，请留您吉言指出。

这里我用别的app代替了，简单省事，正常的话，你要对你的APP进行数字签名。然后才可以进行升级应用。

示意图：

提示有新版
提示有新版

开始升级
开始升级

升级下载中
升级下载中
 

下载完毕，点击安装
下载完毕，点击安装