struts和hibernate简单问题

this.borrowallowed = borrowallowed;

}

public boolean equals(Object rhs){

if (rhs == null)

return false;

if (! (rhs instanceof Book))

return false;

Book that = (Book) rhs;

if (this.getId() == null || that.getId() == null)

return false;

return (this.getId().equals(that.getId()));

}

public int hashCode(){

if (this.hashValue == 0){

int result = 17;

int idValue = this.getId() == null ? 0 : this.getId().hashCode();

result = result * 37 + idValue;

this.hashValue = result;

}

return this.hashValue;

}

}

public class Book extends AbstractBook implements Serializable{

public Book(){

}

public Book(java.lang.Integer id){

super(id);

}

}

book类的映射文件是这样

<?xml version="1.0" encoding="UTF-8"?>