struts和hibernate简单问题

大家帮忙看一下,小弟实在没招了.

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程序是这样的

public abstract class AbstractCustomer implements Serializable{

private int hashValue = 0;

private java.lang.Integer id;

private java.util.Set bookSet;

private java.lang.String firstname;

private java.lang.String lastname;

private java.lang.Integer age;

public AbstractCustomer(){

}

public AbstractCustomer(java.lang.Integer id){

this.setId(id);

}

public java.lang.Integer getId()

{

return id;

}

public void setId(java.lang.Integer id){

this.hashValue = 0;

this.id = id;

}

public java.lang.String getFirstname(){

return this.firstname;

}

public void setFirstname(java.lang.String firstname){