/*
* Copyright (C) 2012, Katy Hilgenberg.
* Special acknowledgments to: Knowledge & Data Engineering Group, University of Kassel (http://www.kde.cs.uni-kassel.de).
* Contact: sdcf@cs.uni-kassel.de
*
* This file is part of the SDCFramework (Sensor Data Collection Framework) project.
*
* The SDCFramework is free software: you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* The SDCFramework is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with the SDCFramework. If not, see <http://www.gnu.org/licenses/>.
*/
package de.unikassel.android.sdcframework.persistence;
import de.unikassel.android.sdcframework.persistence.facade.DatabaseAdapter;
import de.unikassel.android.sdcframework.persistence.facade.DatabaseCommand;
import de.unikassel.android.sdcframework.util.Logger;
import android.database.SQLException;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteFullException;
/**
* Abstract base class for database commands. It does allow homogeneous command
* execution using a database adapter, as well as a basic handling of open
* errors and exceptions.<br/>
* <br/>
* Any extending concrete command class has to implement the abstract protected
* {@link #applyCommand(DatabaseAdapter)} method, to implement the concrete
* command behavior on an open database.
*
* @author Katy Hilgenberg
* @param <T>
* the result type of the command
*
*/
public abstract class AbstractDatabaseCommand< T >
implements DatabaseCommand< T >
{
/**
* The default value for the count of repeated tries to open the database
*/
public final static int DEFAULT_DB_OPEN_RETRY_COUNT = 5;
/**
* The count of retries if we fail to open the database
*/
private final int dbOpenRetryCount;
/**
* The database open access flag
*/
private final boolean openReadOnly;
/**
* The command execution result
*/
private T result;
/**
* Constructor
*
* @param openReadOnly
* flag if database can be open read only to execute the command
* @param dbOpenRetryCount
* retry count for database open command
*/
public AbstractDatabaseCommand( boolean openReadOnly, int dbOpenRetryCount )
{
super();
this.openReadOnly = openReadOnly;
this.dbOpenRetryCount = dbOpenRetryCount;
result = null;
}
/**
* Constructor
*
* @param openReadOnly
* flag if database can be open read only to execute the command
*/
public AbstractDatabaseCommand( boolean openReadOnly )
{
this( openReadOnly, DEFAULT_DB_OPEN_RETRY_COUNT );
}
/*
* (non-Javadoc)
*
* @see
* de.unikassel.android.sdcframework.persistence.facade.DatabaseCommand#getResult
* ()
*/
@Override
public final T getResult()
{
return result;
}
/**
* Getter for the dbOpenRetryCount
*
* @return the dbOpenRetryCount
*/
public final int getDbOpenRetryCount()
{
return dbOpenRetryCount;
}
/**
* Getter for the openReadOnly flag
*
* @return the openReadOnly
*/
public final boolean isOpenReadOnly()
{
return openReadOnly;
}
/**
* Internal method to execute the command and store the result
*
* @param dbAdapter
* the database adapter to use for execution
* @throws SQLiteFullException
* if command execution fails due to the fact that the database is
* full
*/
protected final void internalExecute( DatabaseAdapter dbAdapter )
throws SQLiteFullException
{
try
{
// first open the database ( block until successful )
if ( openDatabase( dbAdapter ) )
{
// now try to execute the command itself
result = applyCommand( dbAdapter );
}
}
catch ( SQLiteFullException e )
{
// throw this special SQL exception to the caller
throw e;
}
catch ( SQLException e )
{
onSQLException( e );
}
finally
{
dbAdapter.close();
}
}
/**
* Method to open the database
*
* @param dbAdapter
* the database adapter result success true if successful
*/
private boolean openDatabase( DatabaseAdapter dbAdapter )
{
boolean success = false;
int cntTries = 0;
while ( !success && cntTries <= dbOpenRetryCount )
{
try
{
if ( openReadOnly )
{
dbAdapter.openForRead();
}
else
{
dbAdapter.open();
}
success = true;
}
catch ( SQLiteFullException e )
{
// throw this special SQL exception to the caller
throw e;
}
catch ( SQLiteException e )
{
cntTries++;
if ( cntTries < dbOpenRetryCount )
{
// do wait a moment before retry opening
try
{
Thread.sleep( 500 );
}
catch ( InterruptedException e1 )
{}
}
else
{
// log last exception
Logger.getInstance().error(
this,
"Failed to open database in "
+ ( openReadOnly ? "read" : "write" )
+ " mode: " + e.getMessage() );
}
}
}
return success;
}
/*
* (non-Javadoc)
*
* @see
* de.unikassel.android.sdcframework.persistence.facade.DatabaseCommand#execute
* (de.unikassel.android.sdcframework.persistence.facade.DatabaseAdapter)
*/
@Override
public boolean execute( DatabaseAdapter dbAdapter )
throws SQLiteFullException
{
internalExecute( dbAdapter );
return result != null;
}
/**
* Method to apply the basic database command operation.
*
* @param dbAdapter
* the database adapter to use
* @return the command result
*/
protected abstract T applyCommand( DatabaseAdapter dbAdapter );
/**
* SQLException handler
*
* @param e
* the exception
*/
private void onSQLException( SQLException e )
{
// default we do just log the exception
Logger.getInstance().error( this,
"SQLException in execute: " + e.getMessage() );
e.printStackTrace();
}
}