Dear All,
I'm using HSQLDB as embedded in-process mode for my web application. I used
to schedule every 1 minutes to check on the HSQLDB database. I open the db
when context initialized and close it when context destroyed. But when the
context reloaded I always get Java.lang.NullPointerException when trying to
execute SQL statement.
What is wrong ?? It looks like everytime the context is destroyed... the
hsqldb gets lock.
The snippet code like below :
=======================
import javax.servlet.ServletContext;
import javax.servlet.ServletContextListener;
import javax.servlet.ServletContextEvent;
import java.nio.channels.ClosedByInterruptException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.util.Random;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class ContextStartUp implements ServletContextListener {
private ServletContext context = null;
MyThread objThread = null;
ResultSet rs = null;
Connection conn = null;
public void openDB()
{
try {
conn = DriverManager.getConnection("jdbc:hsqldb:file:" +
context.getRealPath("/data/testdb") + ";ifexists=true;shutdown=true;", "sa",
"phidmspassword");
} catch (SQLException e) {
e.printStackTrace();
}
catch(Exception e)
{
e.printStackTrace();
}
}
public void closeDB()
{
Statement stmt = null;
try {
if(conn!=null)
{
stmt = conn.createStatement();
stmt.execute("SHUTDOWN COMPACT");
stmt.close();
conn.close();
stmt = null;
conn = null;
}
} catch (SQLException e) {
e.printStackTrace();
}
}
public class MyThread implements Runnable {
int nomor = 0;
Thread currentthread = null;
public MyThread() {
if (currentthread == null) {
currentthread = new Thread(this);
currentthread.setPriority(new Random().nextInt(5) + 1);
currentthread.start();
}
}
public void run() {
Statement stmt = null;
String sqltodo = "";
Thread myThread = Thread.currentThread();
while (myThread == currentthread) {
try {
stmt = conn.createStatement();
if (stmt.execute("A select statement...... "))
{
rs = stmt.getResultSet();
if (rs.next()) {
..........................
}
}
sqltodo = Update queries ......;
stmt.executeUpdate(sqltodo);
stmt.execute("SHUTDOWN");
stmt.close();
}
else
{
stmt.close();
}
} catch (SQLException e) {
e.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
} finally {
stmt = null;
}
try {
Thread.sleep(100000);
} catch (InterruptedException e) {
}
}
}
}
public void initThread() {
openDB();
objThread = new MyThread();
}
public void stopThread() {
objThread = null;
closeDB();
}
public void contextDestroyed(ServletContextEvent event) {
context = null;
stopThread();
}
public void contextInitialized(ServletContextEvent event) {
try {
Class.forName("org.hsqldb.jdbcDriver").newInstance();
} catch (InstantiationException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
context = event.getServletContext();
initThread();
}
}
==============================================================
--
Regards,
Feris
PT. Putera Handal Indotama
JL. KH. Moh. Mansyur No. 11 Blok B.8-12
Telp. +62-21-631 6688 (Hunting)
Fax. +62-21-6330211
Jakarta (10140) - INDONESIA
