Re: [JBoss-user] Question about CMP entity

[Marco Garbelini]

----- Original Message -----

From: "Marco Tedone" <[EMAIL PROTECTED]>

To: <[EMAIL PROTECTED]>

Sent: Wednesday, June 25, 2003 8:19 PM

Subject: Re: [JBoss-user] Question about CMP entity

> Could you please forward some example?

You can use this same bean to create ids for any entity, or create a sequence bean for each entity to get some performance boost.

 

Observe the for (;;) loop and the TransactionRolledbackException catch, thatīs the tricky part.

 

there you go:

--------------------------------------------------

package com.ped.server.util.sequence;

 

import javax.ejb.EntityBean;
import javax.ejb.EntityContext;
import javax.ejb.CreateException;

 

import org.jboss.logging.Logger;

 

/**
 * Class to implement Sequence entity
 * @ejb.bean
 *      cmp-version = "2.x"
 *      name = "Sequence"
 *      local-jndi-name = "ped/server/SequenceLocal"
 *      type = "CMP"
 *      view-type = "local"
 * @ejb.persistence
 *      table-name="tb_sequence"
 * @ejb.pk
 *      class = "com.ped.server.util.sequence.SequencePk" 
 */
public abstract class SequenceBean implements EntityBean {

 

    private EntityContext context; //EJB context
    private static final Logger logger = Logger.getLogger(SequenceBean.class);

 

    // EJB Default Methods -----------------------------------------------------

 

    /**
     *
     */   
    public void setEntityContext(EntityContext context) {
        this.context = context;
    }

 

    /**
     *
     */
    public void ejbActivate() {
    }

 

    /**
     *
     */
    public void ejbPassivate() {
    }

 

    /**
     *
     * @param sequenceName
     * @return
     * @throws CreateException
     * @ejb.create-method
     */
    public SequencePk ejbCreate(String sequenceName) throws CreateException {

 

        setSequenceName(sequenceName);
        setCurrentKeyValue(0); //Set initial value
        return null;

 

    }

 

    /**
     *
     * @param sequenceName
     * @throws CreateException
     */
    public void ejbPostCreate(String sequenceName) throws CreateException {
    }

 

    /**
     *
     */
    public void ejbRemove() {
    }

 

    /**
     *
     */
    public void unsetEntityContext() {
        context = null;
    }

 

    /**
     *
     */
    public void ejbLoad() {
    }

 

    /**
     *
     */
    public void ejbStore() {

 

    }

 

    /**
     *
     * @param blockSize
     * @return
     * @ejb.interface-method
     *      view-type = "local"
     */
    public int getNextBlockFirstKey(int blockSize) {

 

        int nextCounter = getCurrentKeyValue();
        nextCounter += blockSize;
        setCurrentKeyValue(nextCounter);

 

        return nextCounter;
    }

 

    //CMP methods --------------------------------------------------------------

 

    /**
     * Get sequene name
     * @ejb.persistent-field
     * @ejb.pk-field
     * @ejb.persistence
     *      column-name="sequencename"
     * @ejb.interface-method
     *      view-type = "local"
     */
    public abstract String getSequenceName();
   
    /**
     *
     * @param sequenceName
     */
    public abstract void setSequenceName(String sequenceName);

 

    /**
     * @ejb.persistent-field
     * @ejb.persistence
     *      column-name="currentkey"
     * @ejb.interface-method
     *      view-type = "local"
     * @return
     */
    public abstract int getCurrentKeyValue();
   
    /**
     *
     * @param currentKeyValue
     * @ejb.interface-method
     *      view-type = "local"
     */
    public abstract void setCurrentKeyValue(int currentKeyValue);

 

}

 

package com.ped.server.util.sequence;

 

import java.util.HashMap;

 

import javax.ejb.CreateException;
import javax.ejb.FinderException;
import javax.ejb.SessionBean;
import javax.ejb.SessionContext;
import javax.naming.InitialContext;
import javax.naming.NamingException;
import javax.transaction.TransactionRolledbackException;

 

import org.jboss.logging.Logger;

 

/**
 * Implements a facade to obtain primary keys
 * @ejb.bean
 *     name="SequenceTool"
 *     type="Stateless"
 *     local-jndi-name = "ped/server/SequenceToolLocal"
 *     view-type = "local"
 */
public class SequenceToolBean implements SessionBean {

 

    private static final Logger logger =
        Logger.getLogger(SequenceToolBean.class);
    private SessionContext sessionCtx;
    private HashMap blocks;
    private SequenceLocalHome sequenceHome;

 

    private static final int BLOCK_SIZE = 10;
    private static final int RETRY_MAX_COUNT = 5;
    private int retryCount;
   
    /**
     * Constructor
     */
    public SequenceToolBean() {
    }

 

    /**
     * @param aContext Context passed by container
     */
    public void setSessionContext(SessionContext sessionCtx) {
        this.sessionCtx = sessionCtx;
    }

 

    /**
    * EJB Activation
    */
    public void ejbActivate() {
    }

 

    /**
     * EJB Passivation
     */
    public void ejbPassivate() {
    }

 

    /**
     * EJB Creation
     * @ejb.create-method
     */
    public void ejbCreate() throws CreateException, NamingException {
       
        blocks = new HashMap();       

 

        retryCount = 0;
        sequenceHome =
            (SequenceLocalHome) (new InitialContext()).lookup(
                SequenceLocalHome.JNDI_NAME);

 

    }

 

    /**
     * EJB Post Creation   
     */
    public void ejbPostCreate() throws CreateException {
    }

 

    /**
     * EJB Remotion
     */
    public void ejbRemove() {
    }

 

    // Enterprise Bean methods ----------------------------------------------------------

 

    /**
     * Get next id on cached block
     * @param sequenceName sequence to get next id
     * @return next id
     * @ejb.interface-method
     *      view-type = "local"
     */
    public Integer getNextId(String sequenceName)
        throws FinderException, SequenceException, CreateException {

 

        //Get cached block           
        Integer nextId = (Integer) blocks.get(sequenceName);

 

        if (nextId == null || ((nextId.intValue() % BLOCK_SIZE) == 0)) {
            nextId = getNextBlockStart(sequenceName);
        }
        nextId = new Integer(nextId.intValue() + 1);
        blocks.put(sequenceName, nextId);

 

        return nextId;

 

    }

 

    /**
     * Gext next sequence block.
     * @param sequenceName
     */
    private Integer getNextBlockStart(String sequenceName)
        throws SequenceException, CreateException {

 

        SequenceLocal sequence;

 

        //Try to find Sequence
        try {
            sequence =
                (SequenceLocal) sequenceHome.findByPrimaryKey(
                    new SequencePk(sequenceName));
        } catch (FinderException e) {
            sequence = sequenceHome.create(sequenceName);
        }

 

        int retries = 0;
        int nextBlockKey;
        for (;;) {
            try {
                nextBlockKey = sequence.getNextBlockFirstKey(BLOCK_SIZE);
                break;
            } catch (Exception e) {
                if (e instanceof TransactionRolledbackException) {
                    retries++;
                    if (retries > RETRY_MAX_COUNT) {
                        throw new SequenceException(
                            "Couldnīt get the next primary key block, too many retries ("
                                + Integer.toBinaryString(retries)
                                + ")");
                    }
                } else {
                    throw new SequenceException(
                        "Unknown exception:\n" + e.getMessage());
                }
            }
        }

 

        Integer newVal = new Integer(nextBlockKey);
        blocks.put(sequenceName, newVal);

 

        return newVal;

 

    }

 

}