// BlogBridge -- RSS feed reader, manager, and web based service
// Copyright (C) 2002-2006 by R. Pito Salas
//
// This program is free software; you can redistribute it and/or modify it under
// the terms of the GNU General Public License as published by the Free Software Foundation;
// either version 2 of the License, or (at your option) any later version.
//
// This program 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 General Public License for more details.
//
// You should have received a copy of the GNU General Public License along with this program;
// if not, write to the Free Software Foundation, Inc., 59 Temple Place,
// Suite 330, Boston, MA 02111-1307 USA
//
// Contact: R. Pito Salas
// mailto:pitosalas@users.sourceforge.net
// More information: about BlogBridge
// http://www.blogbridge.com
// http://sourceforge.net/projects/blogbridge
//
// $Id: AbstractSchemaMigrationStep.java,v 1.8 2006/07/28 10:39:53 spyromus Exp $
//
package com.salas.bb.persistence.backend;
import com.salas.bb.utils.i18n.Strings;
import com.salas.bb.persistence.backend.migration.ISchemaMigrationStep;
import com.salas.bb.persistence.backend.migration.MigrationException;
import java.io.ByteArrayInputStream;
import java.io.ObjectInputStream;
import java.net.MalformedURLException;
import java.net.URL;
import java.sql.Connection;
import java.sql.SQLException;
import java.sql.Statement;
/**
* Abstract database migration step.
*/
abstract class AbstractSchemaMigrationStep implements ISchemaMigrationStep
{
private static final int ERR_UNKNOWN_CONSTRAINT = -40;
private static final int ERR_UNKNOWN_TABLE = -22;
protected Connection connection;
protected HsqlPersistenceManager manager;
/**
* Migrates from some version to the other.
*
* @param aConnection connection to use.
* @param aManager persistence manager to use for data operations.
*
* @throws MigrationException in case of any problems with procedure.
*/
public final void perform(Connection aConnection, HsqlPersistenceManager aManager)
throws MigrationException
{
connection = aConnection;
manager = aManager;
try
{
perform();
} catch (SQLException e)
{
throw new MigrationException(Strings.error("db.failed.to.update.database"), e);
}
}
/**
* Migrates from some version to the other.
*
* @throws MigrationException in case of any problems with procedure.
* @throws SQLException in case of any database problems.
*/
protected abstract void perform() throws MigrationException, SQLException;
/**
* Converts String to URL.
*
* @param string string to convert.
*
* @return URL or <code>NULL</code> if string is <code>NULL</code> or unconvertable.
*/
protected static URL urlFromString(String string)
{
URL url = null;
if (string != null)
{
try
{
url = new URL(string);
} catch (MalformedURLException e)
{
// Bad URL
}
}
return url;
}
/**
* Deserializes URL from bytes stream.
*
* @param stream stream of bytes.
*
* @return URL or NULL if the stream was empty or damaged.
*/
protected static URL urlFromStream(byte[] stream)
{
URL url = null;
if (stream != null)
{
ByteArrayInputStream is = new ByteArrayInputStream(stream);
try
{
ObjectInputStream os = new ObjectInputStream(is);
url = (URL)os.readObject();
} catch (Exception e)
{
url = null;
}
}
return url;
}
/**
* Looks for a table in database with a given name.
*
* @param con connection to use.
* @param table name of the target table.
*
* @return <code>TRUE</code> if table is there.
*
* @throws SQLException if database error happened.
*/
protected boolean isTablePresent(Connection con, String table)
throws SQLException
{
boolean present = true;
try
{
con.createStatement().executeQuery("SELECT * FROM " + table + " WHERE 1=0");
} catch (SQLException e)
{
if (e.getErrorCode() == ERR_UNKNOWN_TABLE)
{
present = false;
} else
{
throw e;
}
}
return present;
}
/**
* Drops the list of tables if they are in database. It's not a problem if tables aren't there.
*
* @param con connection to use.
* @param tables list of tables.
*
* @throws SQLException if there's database error.
*/
protected static void dropTables(Connection con, String[] tables)
throws SQLException
{
for (int i = 0; i < tables.length; i++)
{
String table = tables[i];
dropTable(con, table);
}
}
/**
* Drops database table with a given name. It's not a problem if table isn't there.
*
* @param con conneciton to use.
* @param table name of the table.
*
* @throws SQLException if there's database error.
*/
private static void dropTable(Connection con, String table)
throws SQLException
{
Statement stmt = con.createStatement();
stmt.execute("DROP TABLE " + table + " IF EXISTS;");
}
/**
* Drops the constraint on the table.
*
* @param con connection to use.
* @param table name of the table.
* @param constraint constraint name.
*
* @throws SQLException if there's database error.
*/
protected void dropConstraint(Connection con, String table, String constraint)
throws SQLException
{
Statement stmt = con.createStatement();
try
{
stmt.execute("ALTER TABLE " + table + " DROP CONSTRAINT " + constraint + ";");
} catch (SQLException e)
{
int errorCode = e.getErrorCode();
if (errorCode != ERR_UNKNOWN_CONSTRAINT && errorCode != ERR_UNKNOWN_TABLE) throw e;
}
}
/**
* Returns <code>TRUE</code> if the statement should be skipped for some reason.
* For example, it's empty, or it's a forbidden statement ("CREATE USER...", "CREATE ALIAS..."
* and so on).
*
* @param stmt statement questioned.
*
* @return <code>TRUE</code> if statement shouldn't be executed.
*/
static boolean skipStatement(String stmt)
{
boolean skip = true;
if (stmt != null && (stmt = stmt.trim()).length() > 0)
{
skip = stmt.startsWith("CREATE USER") || stmt.startsWith("CREATE ALIAS");
}
return skip;
}
/**
* Performs update operation and returns number of row changed.
*
* @param stmt statement to execute.
*
* @return number of rows changed.
*
* @throws SQLException if database operation fails.
*/
int update(String stmt)
throws SQLException
{
return connection.createStatement().executeUpdate(stmt);
}
}