See http://forum.hibernate.org/viewtopic.php?p=2310547#2310547

Given a mapping file:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated Jun 13, 2006 3:27:21 PM by Hibernate Tools 3.1.0.beta5 -->
<hibernate-mapping>
<class name="Sample" table="Sample">
<id name="id" type="java.lang.Long">
<column name="id" />
<generator class="native" />
</id>
<version name="version" column="version"/>
<property name="value" column="value" type="string"/>
</class>
</hibernate-mapping>

the following ejb is generated (via hbm2java, ejb3="true", jdk5="true":

// default package
// Generated Jun 16, 2006 3:23:35 PM by Hibernate Tools 3.1.0.beta5

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;

/**

• Sample generated by hbm2java
  */
  @Entity
  @Table(name="Sample"
  )
  public class Sample implements java.io.Serializable {

// Fields

private Long id;
private Integer version;
private String value;

// Constructors

/** default constructor */
public Sample() {
}

/** full constructor */
public Sample(String value) {
this.value = value;
}

// Property accessors
@Id @GeneratedValue

@Column(name="id", unique=false, nullable=false, insertable=true, updatable=true)
public Long getId() {
return this.id;
}

public void setId(Long id) {
this.id = id;
}

@Column(name="version", unique=false, nullable=false, insertable=true, updatable=true)
public Integer getVersion() {
return this.version;
}

public void setVersion(Integer version) {
this.version = version;
}

@Column(name="value", unique=false, nullable=true, insertable=true, updatable=true)
public String getValue() {
return this.value;
}

public void setValue(String value) {
this.value = value;
}
}

There should be a @Version annotation on the version property!