Android数据存储

1.保存数据到data

//保存数据到data    public void save2data(View view) throws Exception{        //data/data/包名/files/a.txt        //写文件        FileOutputStream fos = openFileOutput("a.txt", MODE_PRIVATE);        fos.write("小明".getBytes());        fos.close();        //读文件        FileInputStream fis = openFileInput("a.txt");        BufferedReader br = new BufferedReader(new InputStreamReader(fis));        String line = br.readLine();        Toast.makeText(this, line, Toast.LENGTH_SHORT).show();        fis.close();        //删除文件        deleteFile("a.txt");    }

2.保存数据到sdcard

//保存数据到sdcard    public void save2sdcard(View view) throws Exception{        //data/data/包名//a.txt        String state = Environment.getExternalStorageState();        if(Environment.MEDIA_MOUNTED.equals(state)){            File dir = Environment.getExternalStorageDirectory();            File file = new File(dir,"b.txt");            FileWriter fw = new FileWriter(file);            fw.write("小明名");            fw.close();        }    }

3.存储到SharedPreferences

//存储到SharedPreferences    public void save2sp(View view) throws Exception{        // /data/data/包名/shared_prefs/c.xml        SharedPreferences sp = getSharedPreferences("c", MODE_PRIVATE);        //保存数据        sp.edit().putString("name", "小明").commit();        //获取数据        String string = sp.getString("name", "提示默认值");        Toast.makeText(this, string, Toast.LENGTH_SHORT).show();        //删除数据        sp.edit().remove("name").commit();        sp.edit().clear().commit();        }    //存储到SharedPreferences    public void save2sp2(View view) throws Exception{        // /data/data/包名/shared_prefs/c.xml        SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(this);        //保存数据        sp.edit().putString("name", "小明").apply();        //获取数据        String name = sp.getString("name", "");        Toast.makeText(this, name, Toast.LENGTH_SHORT).show();        //删除数据        sp.edit().remove("name").apply();    }

commit()与apply()方法的区别在于：

1. apply没有返回值而commit返回boolean表明修改是否提交成功
2. apply是将修改数据原子提交到内存, 而后异步真正提交到硬件磁盘, 而commit是同步的提交到硬件磁盘，因此，在多个并发的提交commit的时候，他们会等待正在处理的commit保存到磁盘后在操作，从而降低了效率。而apply只是原子的提交到内容，后面有调用apply的函数的将会直接覆盖前面的内存数据，这样从一定程度上提高了很多效率。
3. apply方法不会提示任何失败的提示。
   由于在一个进程中，sharedPreference是单实例，一般不会出现并发冲突，如果对提交的结果不关心的话，建议使用apply，当然需要确保提交成功且有后续操作的话，还是需要用commit的。

4.存储到SQLite中

//存储到SQLite中    public void save2sqlite(View view){        //data/data/包名/databases/t_user.db        MySQLiteOpenHelper openHelper = new MySQLiteOpenHelper(this, "t_user.db", null, 1);        SQLiteDatabase database = openHelper.getReadableDatabase();        //添加        ContentValues values = new ContentValues();        values.put("name", "小明");        database.insert("t_user", null, values );        //查询        Cursor cursor = database.query("t_user", new String[]{"name","id"}, "id>?",new String[]{"1","小明"},null, null, null);        while(cursor.moveToNext()){            int index = cursor.getColumnIndex("name");            String name = cursor.getString(index);            int id = cursor.getInt(1);        }        cursor.close();        database.close();    }    class MySQLiteOpenHelper extends SQLiteOpenHelper{        public MySQLiteOpenHelper(Context context, String name,                CursorFactory factory, int version) {            super(context, name, factory, version);        }        @Override        public void onCreate(SQLiteDatabase db) {            String sql = "create table t_user (id integer primary key,name varchar(20))";            db.execSQL(sql );        }        @Override        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {            // TODO Auto-generated method stub        }    }