我們平時見到的android數據庫操作一般都是在程序開始時創建一個空的數據庫，然後再進行相關操作。如果我們需要使用一個已有數據的數據庫怎麼辦呢？
我們都知道android系統下數據庫應該存放在 /data/data/com.*.*(package name)/ 目錄下，所以我們需要做的是把已有的數據庫傳入那個目錄下。操作方法是用FileInputStream讀取原數據庫，再用FileOutputStream把讀取到的東西寫入到那個目錄。
操作方法：1. 把原數據庫包括在項目源碼的 res/raw 目錄下，然後建立一個DBManager類，代碼如下：
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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";
//保存的數據庫文件名 public
static final
String PACKAGE_NAME = "com.android.ImportDatabase"; public
static final
String DB_PATH = "/data" + Environment.getDataDirectory().getAbsolutePath() +
"/" + PACKAGE_NAME;
//在手機裏存放數據庫的位置 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())) { //判斷數據庫文件是否存在，若不存在則執行導入，否則直接打開數據庫 InputStream is =
this.context.getResources().openRawResource( R.raw.countries);
//欲導入的數據庫 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; } |
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//do something else here<br> |
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public
void closeDatabase() { this.database.close(); }} |
然後在程序的首個Activity中示例化一個DBManager對象，然後對其執行openDatabase方法就可以完成導入了，可以把一些要對數據庫進行的操作寫在DBManager類裏，然後通過DBManager類的對象調用；也可以在完成導入之後通過一個SQliteDatabase類的對象打開數據庫，並執行操作。
我的做法是 在程序的首個Activity中導入數據庫：
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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(); }} |
此時在DDMS中可以查看到，外部數據庫已經成功導入
在需要使用數據庫的類裏：
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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);
//額外添加一句，把select到的信息輸出到Logcat city.city_name = name; city.city_id = id; taxicity.add(city); }
while (cur.moveToNext()); } return
taxicity; }
else { return
null; } }} |
查看輸出的結果：
