那，如果想要用一個已有的資料庫怎麼辦？


因為Android系統下的資料庫是存放在/data/data/com.*.*(package name)/目錄下,所以我們可以這樣：1.將.db檔案放到專案原始碼的res/raw目錄下；
2.用FileInputStream讀取原資料；
3.用FileOutPutStream把讀取到的資料寫入那個目錄


具體原始碼如下：

1.把.db檔案放到res/raw下



插個題外話，關於SQLite，可以用Navicat這個圖形工具建好我們的資料庫，即可得到我們的.db資料庫檔案了。

2.寫資料庫管理類DBManager.java

package com.cssystem.dao;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.os.Environment;
import android.util.Log;
import android.widget.Toast;

import com.cssystem.activity.ObjKey;
import com.cssystem.activity.R;
import com.cssystem.domain.Selected;
import com.cssystem.domain.Student;
import com.cssystem.domain.User;

public class DBManager {
	
    private final int BUFFER_SIZE = 400000;
    public static final String DB_NAME = "cssystem.db"; //儲存的資料庫檔名
    public static final String PACKAGE_NAME = "com.cssystem.activity";
    public static final String DB_PATH = "/data"
            + Environment.getDataDirectory().getAbsolutePath() + "/"
            + PACKAGE_NAME;  //在手機裡存放資料庫的位置(/data/data/com.cssystem.activity/cssystem.db)
    
    
    private SQLiteDatabase database;
    private Context context;

    public DBManager(Context context) {
        this.context = context;
    }

    public SQLiteDatabase getDatabase() {
        return database;
    }

    public void setDatabase(SQLiteDatabase database) {
        this.database = database;
    }

    public void openDatabase() {
    	System.out.println(DB_PATH + "/" + DB_NAME);
        this.database = this.openDatabase(DB_PATH + "/" + DB_NAME);
    }

    private SQLiteDatabase openDatabase(String dbfile) {

        try {
            if (!(new File(dbfile).exists())) {
            	//判斷資料庫檔案是否存在，若不存在則執行匯入，否則直接開啟資料庫
                InputStream is = this.context.getResources().openRawResource(
                        R.raw.cssystem); //欲匯入的資料庫
                FileOutputStream fos = new FileOutputStream(dbfile);
                byte[] buffer = new byte[BUFFER_SIZE];
                int count = 0;
                while ((count = is.read(buffer)) > 0) {
                    fos.write(buffer, 0, count);
                }
                fos.close();
                is.close();
            }

            SQLiteDatabase db = SQLiteDatabase.openOrCreateDatabase(dbfile,null);
            return db;

        } catch (FileNotFoundException e) {
            Log.e("Database", "File not found");
            e.printStackTrace();
        } catch (IOException e) {
            Log.e("Database", "IO exception");
            e.printStackTrace();
        }
        return null;
    }
    
    public void closeDatabase() {
        this.database.close();

    }
}

package com.cssystem.activity;


import android.app.Activity;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;

import com.cssystem.dao.DBManager;
import com.cssystem.domain.User;
import com.cssystem.service.UserService;

public class LoginActivity extends Activity {

	public DBManager dbHelper;
	private User u;
	private UserService us;
	private Intent intent;
	
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_login);
        
        //首次執行匯入.db檔案
        dbHelper = new DBManager(this);
        dbHelper.openDatabase();
        dbHelper.closeDatabase();
        ……
    ｝    
｝

1）可以把一些資料庫的操作寫在DBManager類裡，然後通過DBManager類的物件呼叫；
 

DBManager dbHelper = new DBManager(this);
dbHelper.openDatabase();

SQLiteDatabase database;

database = SQLiteDatabase.openOrCreateDatabase(DBManager.DB_PATH + "/" + DBManager.DB_NAME, null);