java 数据库不从资产复制
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时间：2020-10-30 13:35:34 来源:igfitidea点击:
Database not copying from assets
提问by GGe
Little to say ill just paste my code hoping that someone will see what im missing:
没什么好说的，只是粘贴我的代码，希望有人能看到我遗漏了什么：
Database.Java
数据库.Java
package gr.peos;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import android.content.Context;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
public class Database extends SQLiteOpenHelper{
//The Android's default system path of your application database.
private static String DB_PATH = "/data/data/gr.peos/databases/";
//Name of the Database to be created.
private static String DB_NAME = "BLib";
private SQLiteDatabase myDataBase;
private final Context myContext;
/**
* Constructor
* Takes and keeps a reference of the passed context in order to access to the application assets and resources.
* @param context
*/
public Database(Context context) {
super(context, DB_NAME, null, 1);
this.myContext = context;
}
/**
* Creates a empty database on the system and rewrites it with your own database.
* */
public void createDataBase() throws IOException{
//First we check if the database already exists, Method declared later
boolean dbExist = checkDataBase();
if(dbExist){
//do nothing - database already exists
}else{
//By calling this method an empty database will be created into the default system path
//of your application so we are going to be able to overwrite that database with our database.
this.getReadableDatabase();
try {
copyDataBase(); //Method declared later
} catch (IOException e) {
throw new Error("Error copying database");
}
}
}
/**
* Check if the database already exist to avoid re-copying the file each time you open the application.
* @return true if it exists, false if it doesn't
*/
private boolean checkDataBase(){
SQLiteDatabase checkDB = null;
try{
String myPath = DB_PATH + DB_NAME;
checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
}catch(SQLiteException e){
//database does't exist yet.
}
if(checkDB != null){
checkDB.close();
}
return checkDB != null ? true : false;
}
/**
* Copies your database from your local assets-folder to the just created empty database in the
* system folder, from where it can be accessed and handled.
* This is done by transferring byte stream.
* */
private void copyDataBase() throws IOException{
//Open your local db as the input stream
InputStream myInput = myContext.getAssets().open(DB_NAME);
// Path to the just created empty db
String outFileName = DB_PATH + DB_NAME;
//Open the empty db as the output stream
OutputStream myOutput = new FileOutputStream(outFileName);
//transfer bytes from the inputfile to the outputfile
byte[] buffer = new byte[1024];
int length;
while ((length = myInput.read(buffer))>0){
myOutput.write(buffer, 0, length);
}
//Close the streams
myOutput.flush();
myOutput.close();
myInput.close();
}
//Opening the Database
public void openDataBase() throws SQLException{
//Open the database
String myPath = DB_PATH + DB_NAME;
myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
}
/
//Finally overriding a few methods as required
@Override
public synchronized void close() {
if(myDataBase != null)
myDataBase.close();
super.close();
}
@Override
public void onCreate(SQLiteDatabase db) {
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
}
}
The part to call this is on the onCreate method of my main activity (Tried others too it wasnt the problem).
调用它的部分是在我的主要活动的 onCreate 方法上（也试过其他人，这不是问题）。
Database myDbHelper = new Database(null);
myDbHelper = new Database(this);
try {
myDbHelper.createDataBase();
} catch (IOException ioe) {
throw new Error("Unable to create database");
}
try {
}catch(SQLException sqle){
throw sqle;
}
The weird part now. On my device (I dont have root access so cant extract the db after it's been created), my Data appears to be 48KB. When running the exact same code on the emulator the database isnt copied over (Im not picking on any exception). To be exact the android/metadata table seems to be getting copied but the other tables along with the data arent. Any ideas?
现在奇怪的部分。在我的设备上（我没有 root 访问权限，因此无法在创建后提取数据库），我的数据似乎是 48KB。在模拟器上运行完全相同的代码时，不会复制数据库（我没有选择任何异常）。确切地说，android/metadata 表似乎正在被复制，但其他表以及数据都没有。有任何想法吗？
回答by Jaydeep Khamar
I am giving you the complete code,plz reply if you success
我给你完整的代码，如果你成功请回复
public class DataBaseHelper extends SQLiteOpenHelper{
private Context mycontext;
private String DB_PATH = "/data/data/gr.peos/databases/";
//private String DB_PATH = mycontext.getApplicationContext().getPackageName()+"/databases/";
private static String DB_NAME = "BLib.sqlite";//the extension may be .sqlite or .db
public SQLiteDatabase myDataBase;
/*private String DB_PATH = "/data/data/"
+ mycontext.getApplicationContext().getPackageName()
+ "/databases/";*/
public DataBaseHelper(Context context) throws IOException {
super(context,DB_NAME,null,1);
this.mycontext=context;
boolean dbexist = checkdatabase();
if(dbexist)
{
//System.out.println("Database exists");
opendatabase();
}
else
{
System.out.println("Database doesn't exist");
createdatabase();
}
}
public void createdatabase() throws IOException{
boolean dbexist = checkdatabase();
if(dbexist)
{
//System.out.println(" Database exists.");
}
else{
this.getReadableDatabase();
try{
copydatabase();
}
catch(IOException e){
throw new Error("Error copying database");
}
}
}
private boolean checkdatabase() {
//SQLiteDatabase checkdb = null;
boolean checkdb = false;
try{
String myPath = DB_PATH + DB_NAME;
File dbfile = new File(myPath);
//checkdb = SQLiteDatabase.openDatabase(myPath,null,SQLiteDatabase.OPEN_READWRITE);
checkdb = dbfile.exists();
}
catch(SQLiteException e){
System.out.println("Database doesn't exist");
}
return checkdb;
}
private void copydatabase() throws IOException {
//Open your local db as the input stream
InputStream myinput = mycontext.getAssets().open(DB_NAME);
// Path to the just created empty db
String outfilename = DB_PATH + DB_NAME;
//Open the empty db as the output stream
OutputStream myoutput = new FileOutputStream("/data/data/gr.peos/databases/BLib.sqlite");
// transfer byte to inputfile to outputfile
byte[] buffer = new byte[1024];
int length;
while ((length = myinput.read(buffer))>0)
{
myoutput.write(buffer,0,length);
}
//Close the streams
myoutput.flush();
myoutput.close();
myinput.close();
}
public void opendatabase() throws SQLException
{
//Open the database
String mypath = DB_PATH + DB_NAME;
myDataBase = SQLiteDatabase.openDatabase(mypath, null, SQLiteDatabase.OPEN_READWRITE);
}
public synchronized void close(){
if(myDataBase != null){
myDataBase.close();
}
super.close();
}
回答by Niranj Patel
if your file name have extension in assets folder to must add in code.
如果您的文件名在资产文件夹中有扩展名，则必须添加代码。
like
喜欢
private static String DB_NAME = "BLib.extension";
extension is like as ".sqlite",".db" ...etc
扩展名就像“.sqlite”，“.db”...等
