该封装只是在第一次使用数据库文件的时候把该文件夹拷贝到手机的/data/data/应用程序报名/database文件夹下，之后就直接从这个地方使用了。并且它允许你直接通过assets文件夹下的数据库名称来获取SQLiteDatabase对象，这样就极大的方便了你对数据库的使用。
package com.jemsn.database;
import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.HashMap;
import java.util.Map;
import android.content.Context;
import android.content.SharedPreferences;
import android.content.res.AssetManager;
import android.database.sqlite.SQLiteDatabase;
import android.util.Log;
/**
* This is a Assets Database Manager
* Use it, you can use a assets database file in you application
* It will copy the database file to "/data/data/[your application package name]/database" when you first time you use it
* Then you can get a SQLiteDatabase object by the assets database file
* @author RobinTang
* @time 2012-09-20
*
*
* How to use:
* 1. Initialize AssetsDatabaseManager
* 2. Get AssetsDatabaseManager
* 3. Get a SQLiteDatabase object through database file
* 4. Use this database object
*
* Using example:
* AssetsDatabaseManager.initManager(getApplication()); // this method is only need call one time
* AssetsDatabaseManager mg = AssetsDatabaseManager.getManager(); // get a AssetsDatabaseManager object
* SQLiteDatabase db1 = mg.getDatabase("db1.db"); // get SQLiteDatabase object, db1.db is a file in assets folder
* db1.??? // every operate by you want
* Of cause, you can use AssetsDatabaseManager.getManager().getDatabase("xx") to get a database when you need use a database
*/
public class AssetsDatabaseManager {
private static String tag = "AssetsDatabase"; // for LogCat
private static String databasepath = "/data/data/%s/database"; // %s is packageName
// A mapping from assets database file to SQLiteDatabase object
private Map<String, SQLiteDatabase> databases = new HashMap<String, SQLiteDatabase>();
// Context of application
private Context context = null;
// Singleton Pattern
private static AssetsDatabaseManager mInstance = null;
/**
* Initialize AssetsDatabaseManager
* @param context, context of application
*/
public static void initManager(Context context){
if(mInstance == null){
mInstance = new AssetsDatabaseManager(context);
}
}
/**
* Get a AssetsDatabaseManager object
* @return, if success return a AssetsDatabaseManager object, else return null
*/
public static AssetsDatabaseManager getManager(){
return mInstance;
}
private AssetsDatabaseManager(Context context){
this.context = context;
}
/**
* Get a assets database, if this database is opened this method is only return a copy of the opened database
* @param dbfile, the assets file which will be opened for a database
* @return, if success it return a SQLiteDatabase object else return null
*/
public SQLiteDatabase getDatabase(String dbfile) {
if(databases.get(dbfile) != null){
Log.i(tag, String.format("Return a database copy of %s", dbfile));
return (SQLiteDatabase) databases.get(dbfile);
}
if(context==null)
return null;
Log.i(tag, String.format("Create database %s", dbfile));
String spath = getDatabaseFilepath();
String sfile = getDatabaseFile(dbfile);
File file = new File(sfile);
SharedPreferences dbs = context.getSharedPreferences(AssetsDatabaseManager.class.toString(), 0);
boolean flag = dbs.getBoolean(dbfile, false); // Get Database file flag, if true means this database file was copied and valid
if(!flag || !file.exists()){
file = new File(spath);
if(!file.exists() && !file.mkdirs()){
Log.i(tag, "Create \""+spath+"\" fail!");
return null;
}
if(!copyAssetsToFilesystem(dbfile, sfile)){
Log.i(tag, String.format("Copy %s to %s fail!", dbfile, sfile));
return null;
}
dbs.edit().putBoolean(dbfile, true).commit();
}
SQLiteDatabase db = SQLiteDatabase.openDatabase(sfile, null, SQLiteDatabase.NO_LOCALIZED_COLLATORS);
if(db != null){
databases.put(dbfile, db);
}
return db;
}
private String getDatabaseFilepath(){
return String.format(databasepath, context.getApplicationInfo().packageName);
}
private String getDatabaseFile(String dbfile){
return getDatabaseFilepath()+"/"+dbfile;
}
private boolean copyAssetsToFilesystem(String assetsSrc, String des){
Log.i(tag, "Copy "+assetsSrc+" to "+des);
InputStream istream = null;
OutputStream ostream = null;
try{
AssetManager am = context.getAssets();
istream = am.open(assetsSrc);
ostream = new FileOutputStream(des);
byte[] buffer = new byte[1024];
int length;
while ((length = istream.read(buffer))>0){
ostream.write(buffer, 0, length);
}
istream.close();
ostream.close();
}
catch(Exception e){
e.printStackTrace();
try{
if(istream!=null)
istream.close();
if(ostream!=null)
ostream.close();
}
catch(Exception ee){
ee.printStackTrace();
}
return false;
}
return true;
}
/**
* Close assets database
* @param dbfile, the assets file which will be closed soon
* @return, the status of this operating
*/
public boolean closeDatabase(String dbfile){
if(databases.get(dbfile) != null){
SQLiteDatabase db = (SQLiteDatabase) databases.get(dbfile);
db.close();
databases.remove(dbfile);
return true;
}
return false;
}
/**
* Close all assets database
*/
static public void closeAllDatabase(){
Log.i(tag, "closeAllDatabase");
if(mInstance != null){
for(int i=0; i<mInstance.databases.size(); ++i){
if(mInstance.databases.get(i)!=null){
mInstance.databases.get(i).close();
}
}
mInstance.databases.clear();
}
}
}
使用的过程也很简单，应用程序开始的时候初始化一下，之后就可以在任意地方获取管理器在通过assets文件夹下的数据库文件名直接获取SQLiteDatabase对象，之后对数据库的操作就完全看你了。。。
简单的使用例子：
// 初始化，只需要调用一次 在HomeApplication中调用
AssetsDatabaseManager.initManager(getApplication());
// 获取管理对象，因为数据库需要通过管理对象才能够获取
AssetsDatabaseManager mg = AssetsDatabaseManager.getManager();
// 通过管理对象获取数据库
SQLiteDatabase db1 = mg.getDatabase("db1.db");
// 对数据库进行操作
db1.execSQL("insert into tb([ID],[content]) values(null, 'db1');");
