How to detect JVM Shutdown

Runtime.getRuntime().addShutdownHook(new ShutdownHook());

boolean jvmShuttingDown = false;


private class ShutdownHook extends Thread {
        public void run() {
               jvmShuttingDown = true;
        }
}

How to lock a table in Mysql

in a session
use following
--> lock tables mySchema.myTable write;
In another session try to get
-->select count(*) from mySchema.myTable;

It will be locked till u say

--> unlock tables

How to get OpenJpa Sql Traces

Put the following item in your persistence.xml

<properties>
            <property name="openjpa.Log" value="SQL=TRACE"/>
</properties>

Lets do some XStream test

Aim: Keep a finite state machine configuration in a xml file.

A sample synthetic scenario for this ;
    Get messageBoxes of the users. Put the messageBoxes into a blockingQueue , let some threads process the mailboxes and get new and old messeges from the boxes and seperate them to different queues .
    Then process new messages (exm:delete if it is keeped longer than expected) and put some data for notification sms to the owner of expired message.Some threads will process this queue and will send smses and they will put some data to the edr queue.
    If the message is old (read message) threads on the oldMessageQueue put data to the edr queue directly without sending sms.

Maybe we want to use this states and conditions in a state manager base implementation/code generator which is not written yet ;)

public class StateList {
    public StateList () {
    }

    public List getFsm () {
        return fsm;
    }

    public void setFsm (List fsm) {
        this.fsm = fsm;
    }

    private Listfsm = new ArrayList();
}

public class State {
    public State () {
    }

    private String queueName;
    private int threadCount;
    private int queueSize;
    private String executorClassName;
    private List transitions = new java.util.ArrayList();

    public String getExecutorClassName () {
        return executorClassName;
    }

    public String getQueueName () {
        return queueName;
    }

    public int getThreadCount () {
        return threadCount;
    }

    public int getQueueSize () {
        return queueSize;
    }

    public List getTransitions () {
        return transitions;
    }

    public void setExecutorClassName (String executorClassName) {
        this.executorClassName = executorClassName;
    }

    public void setQueueName (String queueName) {
        this.queueName = queueName;
    }

    public void setThreadCount (int threadCount) {
        this.threadCount = threadCount;
    }

    public void setQueueSize (int queueSize) {
        this.queueSize = queueSize;
    }

    public void setTransitions (List transitions) {
        this.transitions = transitions;
    }
}

public class Transition {
    public Transition () {
    }

    public String getCondition () {
        return condition;
    }

    public String getName () {
        return name;
    }

    public void setCondition (String condition) {
        this.condition = condition;
    }

    public void setName (String name) {
        this.name = name;
    }

    private String name ;
    private String condition;
}

package XstreamTester;

import java.util.*;
import com.thoughtworks.xstream.*;
import java.io.*;

public class XStreamTester {
    public XStreamTester () {
     /* messageboxGetter->//newMsgProcessor ->SmsSender->EdrWrite
                                       ->//oldMsgProcessor ->EdrWrite
     */
    }

    public static void main (String[] args) {
        XStreamTester xstreamtester = new XStreamTester ();

        XStream stateConfiguration = new XStream ();
        stateConfiguration.alias ("state", State.class);
        stateConfiguration.alias ("transition", Transition.class);
        stateConfiguration.alias ("states", StateList.class);

        StateList stateConfig = new StateList();
        List stateList = new ArrayList();
        // messagebox state
        State mboxState = new State ();
        mboxState.setExecutorClassName ("MboxGetter");

        List mboxTransitions = new ArrayList();
        Transition newMessageTransition = new Transition ();
        newMessageTransition.setName ("newMessageQueue");
        newMessageTransition.setCondition ("new");
        mboxTransitions.add (newMessageTransition);
        Transition oldMessageTransition = new Transition ();
        oldMessageTransition.setName ("oldMessageQueue");
        oldMessageTransition.setCondition ("old");
        mboxTransitions.add (oldMessageTransition);
        mboxState.setTransitions (mboxTransitions);

        mboxState.setQueueName ("messageBoxQueue");
        mboxState.setThreadCount (10);
        mboxState.setQueueSize (1000);
        stateList.add (mboxState);


        // new message state
        State newMsgState = new State ();
        newMsgState.setExecutorClassName ("newMessageProcessor");

        List newMsgTransitionList = new ArrayList();
        Transition smsTransition = new Transition ();
        smsTransition.setName ("smsQueue");
        smsTransition.setCondition ("deleted");
        newMsgTransitionList.add (smsTransition);
        newMsgState.setTransitions(newMsgTransitionList);

        newMsgState.setQueueName ("newMessageQueue");
        newMsgState.setThreadCount (10);
        newMsgState.setQueueSize (1000);
        stateList.add (newMsgState);

        // old message state
        State oldMsgState = new State ();
        oldMsgState.setExecutorClassName ("oldMessageProcessor");

        List oldMsgTransitionList = new ArrayList();
        Transition edrTransition = new Transition ();
        edrTransition.setName ("edrQueue");
        edrTransition.setCondition ("deleted");
        oldMsgTransitionList.add (edrTransition);
        oldMsgState.setTransitions(oldMsgTransitionList);

        oldMsgState.setQueueName ("oldMessageQueue");
        oldMsgState.setThreadCount (10);
        oldMsgState.setQueueSize (1000);
        stateList.add (oldMsgState);


        //sms state
        State smsState = new State ();
        smsState.setExecutorClassName ("smsQueueProcessor");

        List smsTransitionList = new ArrayList();
        Transition sms2EdrTransition = new Transition ();
        sms2EdrTransition.setName ("edr");
        sms2EdrTransition.setCondition ("smsSent");
        smsTransitionList.add (sms2EdrTransition);

        smsState.setTransitions(smsTransitionList);
        smsState.setQueueName ("smsQueue");
        smsState.setThreadCount (10);
        smsState.setQueueSize (1000);
        stateList.add (smsState);


        //edr state
        State edrState = new State ();
        smsState.setExecutorClassName ("edrQueueProcessor");

        edrState.setQueueName ("edrQueue");
        edrState.setThreadCount (10);
        edrState.setQueueSize (1000);
        stateList.add (edrState);


        stateConfig.setFsm(stateList);
        String xml = stateConfiguration.toXML (stateConfig);
        try {
            BufferedWriter out = new BufferedWriter (new FileWriter (
                "/home/serkans/jbproject/UM_Test/xml/stateConfiguration.xml"));
            out.write (xml);
            out.close ();
        } catch (IOException e) {
            e.printStackTrace ();
        }
        System.exit (0);
    }
}

Generated xml will be something like this.
<states>
  <fsm>
    <state>
      <queueName>messageBoxQueue</queueName>
      <threadCount>10</threadCount>
      <queueSize>1000</queueSize>
      <executorClassName>MboxGetter</executorClassName>
      <transitions>
        <transition>
          <name>newMessage</name>
          <condition>new</condition>
        </transition>
        <transition>
          <name>oldMessage</name>
          <condition>old</condition>
        </transition>
      </transitions>
    </state>
    <state>
      <queueName>newMessageQueue</queueName>
      <threadCount>10</threadCount>
      <queueSize>1000</queueSize>
      <executorClassName>newMessageProcessor</executorClassName>
      <transitions>
        <transition>
          <name>sms</name>
          <condition>deleted</condition>
        </transition>
      </transitions>
    </state>
    <state>
      <queueName>oldMessageQueue</queueName>
      <threadCount>10</threadCount>
      <queueSize>1000</queueSize>
      <executorClassName>oldMessageProcessor</executorClassName>
      <transitions>
        <transition>
          <name>edr</name>
          <condition>deleted</condition>
        </transition>
      </transitions>
    </state>
    <state>
      <queueName>smsQueue</queueName>
      <threadCount>10</threadCount>
      <queueSize>1000</queueSize>
      <executorClassName>edrQueueProcessor</executorClassName>
      <transitions>
        <transition>
          <name>edr</name>
          <condition>smsSent</condition>
        </transition>
      </transitions>
    </state>
    <state>
      <queueName>edrQueue</queueName>
      <threadCount>10</threadCount>
      <queueSize>1000</queueSize>
      <transitions/>
    </state>
  </fsm>
</states>

Are u sure about Oracle ROWNUM ?

http://www.oracle.com/technology/oramag/oracle/06-sep/o56asktom.html

A simple implementation with JPA  on oracle dbms

    /*
     I had to make some improvements in query with oracle bec.of performance of the default jpa implementation.
     */
    public User[] getUsersInPage (int startIndex, int stopIndex) throws Exception {

        EntityManager em = createEntityManager ();
        List ret = new ArrayList();
        try {
            if (isOracle()){
                Query selectQuery = em.createNativeQuery ("SELECT * FROM (select a.*,rownum rnum from (select * from provisioning_subsys.VIP_USERS) a where ROWNUM <= " +
                    stopIndex + ") where rnum >=" + startIndex + "", User.class);
                ret = (List) selectQuery.getResultList ();
            }else{
                String qry = "select u from User u";
                Query selectQuery = em.createQuery (qry);
                selectQuery.setMaxResults (stopIndex - startIndex);
                selectQuery.setFirstResult (startIndex);
                ret = (List) selectQuery.getResultList ();
            }
        } finally {
            em.close ();
        }

        return getUserArrayFromList (ret);
    }

    private boolean isOracle () {
        if (emf instanceof EntityManagerFactoryImpl) {
            Properties jpaProperties = ((EntityManagerFactoryImpl) emf).getProperties ();
            String dbms = (String) jpaProperties.get ("Platform");
            if (dbms.indexOf ("Oracle") != -1) {
                return true;
            } else return false;
        }
        return false;
    }