Android中对assets目录下数据库操作

/**
* 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 smartTop
* @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();
}
}
}

// 初始化，只需要调用一次
AssetsDatabaseManager.initManager(getApplicationContext());
// 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
addressDB = mg.getDatabase("address.db");
注意：初始化话，只能初始化一次，最好在application中初始化