[Android]如何导入已有的外部数据库

我们平时见到的android数据库操作一般都是在程序开始时创建一个空的数据库,然后再进行相关操作。如果我们需要使用一个已有数据的数据库怎么办呢?
我们都知道android系统下数据库应该存放在 /data/data/com.*.*(package name)/ 目录下,所以我们需要做的是把已有的数据库传入那个目录下。操作方法是用FileInputStream读取原数据库,再用FileOutputStream把读取到的东西写入到那个目录。
操作方法:1. 把原数据库包括在项目源码的 res/raw 目录下,然后建立一个DBManager类,代码如下:

package com.android.ImportDatabase;

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

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.os.Environment;
import android.util.Log;

public class DBManager {
	private final int BUFFER_SIZE = 400000;
	public static final String DB_NAME = "countries.db"; //保存的数据库文件名
	public static final String PACKAGE_NAME = "com.android.ImportDatabase";
	public static final String DB_PATH = "/data"
			+ Environment.getDataDirectory().getAbsolutePath() + "/"
			+ PACKAGE_NAME;  //在手机里存放数据库的位置

	private SQLiteDatabase database;
	private Context context;

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

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

	private SQLiteDatabase openDatabase(String dbfile) {
		try {
			if (!(new File(dbfile).exists())) {  //判断数据库文件是否存在,若不存在则执行导入,否则直接打开数据库
				InputStream is = this.context.getResources().openRawResource(
						R.raw.countries); //欲导入的数据库
				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;
	}
   //do something else here
	public void closeDatabase() {
		this.database.close();
	}
}

然后在程序的首个Activity中示例化一个DBManager对象,然后对其执行openDatabase方法就可以完成导入了,可以把一些要对数据库进行的操作写在DBManager类里,然后通过DBManager类的对象调用;也可以在完成导入之后通过一个SQliteDatabase类的对象打开数据库,并执行操作。

我的做法是 在程序的首个Activity中导入数据库:

package com.android.ImportDatabase;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;

public class RootView extends Activity {

	public DBManager dbHelper;
	@Override
	public void onCreate(Bundle savedInstanceState) {

		super.onCreate(savedInstanceState);
		setContentView(R.layout.main);

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

	}
}

此时在DDMS中可以查看到,外部数据库已经成功导入

在需要使用数据库的类里:

package com.android.ImportDatabase;

import java.util.ArrayList;
import android.app.Activity;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;

public class TaxiActivity extends Activity {

	private SQLiteDatabase database;
        ArrayList<CityClass> CITY;

	@Override
	public void onCreate(Bundle savedInstanceState) {

		super.onCreate(savedInstanceState);
		setContentView(R.layout.main);
		
		database = SQLiteDatabase.openOrCreateDatabase(DBManager.DB_PATH + "/" + DBManager.DB_NAME, null);

		CITY = getCity();
		
        // do something with CITY

		database.close();
	}

	private ArrayList<CityClass> getCity() {
		
		Cursor cur = database.rawQuery("SELECT city.id_city, city.name FROM taxi, city WHERE city.id_city = taxi.id_city GROUP BY city.id_city", null);
		
		if (cur != null) {
			int NUM_CITY = cur.getCount();
			ArrayList<CityClass> taxicity = new ArrayList<CityClass>(NUM_CITY);
			if (cur.moveToFirst()) {
				do {
					String name = cur.getString(cur.getColumnIndex("name"));
					int id = cur.getInt(cur.getColumnIndex("id_city"));
					CityClass city = new CityClass("", 0);
					System.out.println(name);  //额外添加一句,把select到的信息输出到Logcat
					city.city_name = name;
					city.city_id = id;
					taxicity.add(city);
				} while (cur.moveToNext());
			}
			return taxicity;
		} else {
			return null;
		}
	}
}

查看输出的结果:

如果导入的数据库大小有问题,或使用InputStream读取出错了,请看此贴 [iPhone/Android] 导入程序的数据库大小与原数据库大小不一致怎么办?

posted @ 2011-01-03 22:09 木乃猫 阅读(...) 评论(...) 编辑 收藏