这样的实体类BO大家见过吗？怎么回事？

在hiberate中些了个实体类bo，一般还要些一个相应的映射文件，把它映射到数据库中。但是像这样的bo大家见过吗？怎么回事？

import java.io.Serializable;
import java.util.Date;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;
import javax.persistence.Transient;

@Entity
@Table(name = "tree", catalog = "tree")
public class Capacity extends RemovableBO implements OptimizationLockedBOStyleTwo {

// Fields

/**
 * 
 */
private static final long serialVersionUID = 2772774L;

private String capacityId;

private String driverLicence;

// Property accessors
@Id
@Column(name = "CAPACITY_ID", unique = true, nullable = false, length = 16)
public String getCapacityId() {
    return this.capacityId;
}

public void setCapacityId(String capacityId) {
    this.capacityId = capacityId;
}

@Column(name = "DRIVER_LICENCE", length = 64)
public String getDriverLicence() {
    return driverLicence;
}


@Override
@Transient
public Serializable getEntityId() {
    return this.getCapacityId();
}

}

[b]问题补充：[/b]
各位gg能讲的再详细点吗？谢谢/

自己看实例
http://www.blogjava.net/bolo/archive/2008/09/19/229823.html

http://developer.51cto.com/art/200909/154974.htm

jpa中使用的标注，不需要映射文件了

看ejb3的实体bean或者hibernate3.2的jpa就懂了

你都已经用了注解的方式，自然就不需要映射文件了

就是o/r mapping 把数据库表中的字段和你的实体类作了映射