[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：

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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;     }

1	//do something else here<br>

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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：

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package com.android.ImportDatabase;   import android.app.Activity; import android.content.Intent; import android.os.Bundle;   public class RootView extends Activity {       public DBManager dbHelper;

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@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：

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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;         }     } }