Android Memory Database

In Android, a database is typically stored as a file on disk, and the memory database resides in memory, so it can be used as a caching technology scenario. So how does Android use SQLite's in-memory database?

Look at the source of Sqlitedatabase:

/**     * create a memory backed sqlite database.   its contents will be destroyed     * when the  database is closed.     *     * <p >sets the locale of the database to the  the system ' s  current locale.     * call {@link   #setLocale} if  you would like something else.</p>     *      *  @param  factory an optional factory class that is  called to instantiate a     *             cursor when query is called      *  @return  a&nbsP Sqlitedatabase object, or null if the database can ' t be created      */    public static sqlitedatabase create ( Cursorfactory factory)  {        // this is a  magic string with special meaning for SQLite.         return opendatabase (memory_db_path, factory, create_if_necessary);     }

Create_if_necessary indicates that the database will be created when it does not exist. You can tell by method annotations that this method can create a memory database and that the data will be purged when the database is closed.

Another way, please see Sqliteopenhelper Source:

Public synchronized sqlitedatabase getwritabledatabase ()  {                 boolean success = false;         SQLiteDatabase db = null;         if  (Mdatabase != null)  mdatabase.lock ();         try {             mIsInitializing = true;             if  (mname == null)  {                 db = sqlitedatabase.create (NULL);             } else {               &nbSp; db = mcontext.openorcreatedatabase (Mname, 0, mfactory, merrorhandler);             }             ...             OnOpen (db);            success = true;             return db;         } finally {             mIsInitializing = false;             if  (Success)  {                 if  (mdatabase != null)  {            &nbsP;        try { mdatabase.close (); } catch  ( Exception e)  { }                     mdatabase.unlock ();                 }                 mDatabase = db;             } else {                 if  (Mdatabase != null)  mdatabase.unlock ();                 if  (Db != null)  db.close ();            }         }    } 

You can tell from the code that when Mname (the database name) is NULL, the memory database is created.

I wrote a demo, please read the code:

Package dw.test;import android.content.contentvalues;import android.database.cursor;import  android.database.sqlite.SQLiteDatabase;import android.provider.BaseColumns;import  android.util.log;public final class memorydbtester {private static final  String log_tag = memorydbtester.class.getsimplename ();p rivate static final  string table_name =  "T_user";p rivate sqlitedatabase mmemorydb;private  Memorydbtester () {mmemorydb = creatememorydb ();} Private static memorydbtester sdefault = new memorydbtester ();p ublic static  memorydbtester getdefault () {return sdefault;} public interface columns extends basecolumns {public static final  string uname =  "UNAME";} /** *  Creating the Memory Database  */private sqlitedatabase creatememorydb () {sqlitedatabase database& NBsp;= sqlitedatabase.create (NULL); string t_user_sql =  "create table " +table_name+ "(_id integer primary  Key autoincrement, "+columns.uname+"  varchar ";d atabase.execsql (t_user_sql); return database;} /** *  inserts a data into the in-memory Database  */public void testinsert ()  {sqlitedatabase db =  mmemorydb;check (DB); Contentvalues values = new contentvalues (); Values.put (columns.uname,  "DW");d B.insert ( table_name, null, values);} /** *  querying the data in the in-memory Database  */public void testquery () {sqlitedatabase db =  Mmemorydb;check (DB); Cursor c = db.rawquery ("Select uname from t_user",  null); while (C.moveToNext ()) {string name = c.getstring (0); LOG.I (log_tag,  "NAME:"  + name);}} @Overrideprotected  void finalize ()  throws throwable {releasememory (); Super.finalize () ;} Public void&nbSp;releasememory () {sqlitedatabase db = mmemorydb;if (db!=null) {db.close ();mMemoryDb =  null;}} Private void check (sqlitedatabase db)  {if (db==null | |  !db.isopen ()) {throw new illegalstateexception ("memory database already closed") ;}}}

This article is from the "Itlife" blog, make sure to keep this source http://xwteacher.blog.51cto.com/9653444/1584554

Android Memory Database