Android使用外部SQLITE数据库
1、一定要把数据库放到assert下，本例我放的名字是carobd.db新建AssetsDatabaseManager类，其中使用了单例设计模式
package com.zk.outdatabase;
import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.HashMap;
import java.util.Map;
import android.content.Context;
import android.content.SharedPreferences;
import android.content.res.AssetManager;
import android.database.sqlite.SQLiteDatabase;
import android.util.Log;
public class AssetsDatabaseManager {
private static String tag = "AssetsDatabase"; // for LogCat
private static String databasepath = "/data/data/com.zk.outdatabase/databases"; // %s is packageName ，//注意自己记得替换成自己的包
// A mapping from assets database file to SQLiteDatabase object
private Map<String, SQLiteDatabase> databases = new HashMap<String, SQLiteDatabase>();
// Context of application
private Context context = null;
// Singleton Pattern
private static AssetsDatabaseManager mInstance = null;
/**
* Initialize AssetsDatabaseManager
* @param context, context of application
*/
public static void initManager(Context context){
if(mInstance == null){
mInstance = new AssetsDatabaseManager(context);
}
}
/**
* Get a AssetsDatabaseManager object
* @return, if success return a AssetsDatabaseManager object, else return null
*/
public static AssetsDatabaseManager getManager(){
return mInstance;
}
private AssetsDatabaseManager(Context context){
this.context = context;
}
/**
* Get a assets database, if this database is opened this method is only return a copy of the opened database
* @param dbfile, the assets file which will be opened for a database
* @return, if success it return a SQLiteDatabase object else return null
*/
public SQLiteDatabase getDatabase(String dbfile) {
if(databases.get(dbfile) != null){
Log.i(tag, String.format("Return a database copy of %s", dbfile));
Log.e("my","数据库已经存在此文件了");
return (SQLiteDatabase) databases.get(dbfile);
}
if(context==null)
return null;
Log.i(tag, String.format("Create database %s", dbfile));
String spath = getDatabaseFilepath();
String sfile = getDatabaseFile(dbfile);
File file = new File(sfile);
SharedPreferences dbs = context.getSharedPreferences(AssetsDatabaseManager.class.toString(), 0);
boolean flag = dbs.getBoolean(dbfile, false); // Get Database file flag, if true means this database file was copied and valid
if(!flag || !file.exists()){
file = new File(spath);
if(!file.exists() && !file.mkdirs()){
Log.i(tag, "Create \""+spath+"\" fail!");
return null;
}
if(!copyAssetsToFilesystem(dbfile, sfile)){
Log.i(tag, String.format("Copy %s to %s fail!", dbfile, sfile));
return null;
}
dbs.edit().putBoolean(dbfile, true).commit();
}else{
//Log.e("my","数据库已经存在此文件了");
}
SQLiteDatabase db = SQLiteDatabase.openDatabase(sfile, null, SQLiteDatabase.NO_LOCALIZED_COLLATORS);
if(db != null){
databases.put(dbfile, db);
}
return db;
}
private String getDatabaseFilepath(){
return String.format(databasepath, context.getApplicationInfo().packageName);
}
private String getDatabaseFile(String dbfile){
return getDatabaseFilepath()+"/"+dbfile;
}
private boolean copyAssetsToFilesystem(String assetsSrc, String des){
Log.i(tag, "Copy "+assetsSrc+" to "+des);
InputStream istream = null;
OutputStream ostream = null;
try{
AssetManager am = context.getAssets();
istream = am.open(assetsSrc);
ostream = new FileOutputStream(des);
byte[] buffer = new byte[1024];
int length;
while ((length = istream.read(buffer))>0){
ostream.write(buffer, 0, length);
}
istream.close();
ostream.close();
}
catch(Exception e){
e.printStackTrace();
try{
if(istream!=null)
istream.close();
if(ostream!=null)
ostream.close();
}
catch(Exception ee){
ee.printStackTrace();
}
return false;
}
return true;
}
/**
* Close assets database
* @param dbfile, the assets file which will be closed soon
* @return, the status of this operating
*/
public boolean closeDatabase(String dbfile){
if(databases.get(dbfile) != null){
SQLiteDatabase db = (SQLiteDatabase) databases.get(dbfile);
db.close();
databases.remove(dbfile);
return true;
}
return false;
}
/**
* Close all assets database
*/
static public void closeAllDatabase(){
Log.i(tag, "closeAllDatabase");
if(mInstance != null){
for(int i=0; i<mInstance.databases.size(); ++i){
if(mInstance.databases.get(i)!=null){
mInstance.databases.get(i).close();
}
}
mInstance.databases.clear();
}
}
}
2、在MainActivity中，写入操作代码
package com.zk.outdatabase;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import com.zhangkai.sqlitedatabase.DbOpenHelper;
import android.os.Bundle;
import android.app.Activity;
import android.database.sqlite.SQLiteDatabase;
import android.util.Log;
import android.view.Menu;
public class MainActivity extends Activity {
public DbOpenHelper dbOpenHelper;
private int startbyte = 0;
private int bitnum = 0;
private int startbit = 0;
private int bitsep = 0;
private double B = 0;
int C = 0;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// 初始化，只需要调用一次
AssetsDatabaseManager.initManager(getApplication());
// 获取管理对象，因为数据库需要通过管理对象才能够获取
AssetsDatabaseManager mg = AssetsDatabaseManager.getManager();
// 通过管理对象获取数据库
mg.getDatabase("carobd.db");
dbOpenHelper = new DbOpenHelper(this);
String tablename = "J1939_parainfo_CAN";
String selection = "name=?";
Map<String,String> map = new HashMap<String,String>();
String[] selectionArgs={"车速"};
map = dbOpenHelper.view(tablename, selection, selectionArgs);
Set<String> set = map.keySet();
Iterator<String> keys = set.iterator();
/*
* 打印本行所有的列值，进行查看读取。
*/
//从数据库读取相应参数。
while(keys.hasNext()){
String key = keys.next();
if(key.equals("startbyte"))
startbyte = Integer.parseInt(map.get(key));
if(key.equals("bitnum"))
bitnum = Integer.parseInt(map.get(key));
if(key.equals("startbit"))
startbit = Integer.parseInt(map.get(key));
if(key.equals("bitsep"))
bitsep = Integer.parseInt(map.get(key));
if(key.equals("B"))
B = Double.parseDouble(map.get(key));
if(key.equals("C"))
C = Integer.parseInt(map.get(key));
//String value = map.get(key);
Log.i("my","key_speed:"+key+"----value_speed:"+map.get(key));
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
}
3、运行结果图片如下：