Android中用文件初始化sqlite 数据库的文(一)

很多时候在应用安装初始化时，需要创建本地数据库，同时为数据库添加数据，之后再从数据库中读取数据。

这里有2个思路

1.先在本地创建一个能支持android使用的sqlite数据库文件,启动时,用现成的sqlite的二进制文件进行直接copy到Android系统的数据库路径

2.可以考虑在第一次启动时,执行数据库初始化的sql文件.

 

方法1:

1.在本地准备android能使用的sqlite数据库文件

使用sqlite数据库管理工具,看个人爱好(SQLite Database Browser ,Navicat Premium,)

打开数据库,创建"android_metadata"数据表

CREATE TABLE "android_metadata" ("_id"  INTEGER PRIMARY KEY AUTOINCREMENT,"locale" TEXT DEFAULT 'en_US');//创建表
INSERT INTO "android_metadata" VALUES (1,'en_US');//插入值

 创建其他应用需要的表..此处省略.

 

2.复制文件到应用中.

把第一步创建的数据库文件复制到应用中的assets文件夹,然后创建DateBaseHelper extends SQLiteOpenHelper的类文件.

代码如下:

public class DataBaseHelper extends SQLiteOpenHelper {
	//The Android's default system path of your application database.
	private static String DB_PATH = "/data/data/YOUR_PACKAGE/databases/";
	private static String DB_NAME = "myDBName";
	private SQLiteDatabase myDataBase;
	private final Context myContext;
	/**
	 * Constructor
	 * Takes and keeps a reference of the passed context in order to access to the application assets and resources.
	 * @param context
	 */
	public DataBaseHelper(Context context) {
		super(context, DB_NAME, null, 1);
		this.myContext = context;
	}

	/**
	 * Creates a empty database on the system and rewrites it with your own database.
	 * */
	public void createDataBase()throws IOException {
		boolean dbExist = checkDataBase();
		if (dbExist) {
			//do nothing - database already exist
		} else {
			//By calling this method and empty database will be created into the default system path
			//of your application so we are gonna be able to overwrite that database with our database.
			this.getReadableDatabase();
			try {
				copyDataBase();
			} catch (IOException e) {
				throw new Error("Error copying database");
			}
		}
	}

	/**
	 * Check if the database already exist to avoid re-copying the file each time you open the application.
	 * @return true if it exists, false if it doesn't
	 */
	private boolean checkDataBase() {
		SQLiteDatabase checkDB = null;
		try {
			String myPath = DB_PATH + DB_NAME;
			checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
		} catch (SQLiteException e) {
			//database does't exist yet.
		}

		if (checkDB != null) {
			checkDB.close();
		}
		return checkDB != null ? true : false;
	}

	/**
	 * Copies your database from your local assets-folder to the just created empty database in the
	 * system folder, from where it can be accessed and handled.
	 * This is done by transfering bytestream.
	 * */
	private void copyDataBase()throws IOException {
		//Open your local db as the input stream
		InputStream myInput = myContext.getAssets().open(DB_NAME);
		// Path to the just created empty db
		String outFileName = DB_PATH + DB_NAME;
		//Open the empty db as the output stream
		OutputStream myOutput = new FileOutputStream(outFileName);
		//transfer bytes from the inputfile to the outputfile
		byte[]buffer = new byte[1024];
		int length;
		while ((length = myInput.read(buffer)) > 0) {
			myOutput.write(buffer, 0, length);
		}

		//Close the streams
		myOutput.flush();
		myOutput.close();
		myInput.close();
	}

	public void openDataBase()throws SQLException {
		//Open the database
		String myPath = DB_PATH + DB_NAME;
		myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
	}

	@Override
	public synchronized void close() {
		if (myDataBase != null)
			myDataBase.close();
		super.close();
	}

	@Override
	public void onCreate(SQLiteDatabase db) {}

	@Override
	public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {}
	// Add your public helper methods to access and get content from the database.
	// You could return cursors by doing "return myDataBase.query(....)" so it'd be easy
	// to you to create adapters for your views.
}

 

3.现在我们可以创建DateBaseHelper的实现操作了.

createDataBase() //创建

openDataBase()//打开只读数据库

记得要更改"YOUR_PACKAGE"为你的应用的包名

如:com.examplename.myapp

大概代码如下:

...
DataBaseHelper myDbHelper = new DataBaseHelper();
myDbHelper = new DataBaseHelper(this);
try {
	myDbHelper.createDataBase();
} catch (IOException ioe) {
	throw new Error("Unable to create database");
}
try {
	myDbHelper.openDataBase();
} catch (SQLException sqle) {
	throw sqle;
}
...