实体的@Override Equals方法处的对象为null

Question

I'm currently developing one of my company's project. I use JSF and PrimeFaces. According to the project requirements, I use PrimeFaces SelectOneMenu to show the employee list like the following...

<p:selectOneMenu id="employee" value="#{employeeBean.employee}"
converter="employeeConverter">
    <f:selectItem itemLabel="" itemValue="" />
    <f:selectItems value="#{employeeBean.employeeList}" var="emp"
    itemLabel="#{emp.name}" itemValue="#{emp}" />
</p>

Here is my Employee Object's Equals Method...

@Override
public boolean equals(Object obj) {
    if (!(obj instanceOf Employee)) {
        return false;
    }
    Employee employee = (Employee) obj;
    return this.id.equals(employee.getId());
}

If I create the employee object Employee employee = new Employee(); at Employee Bean init Method @PostConstruct public void init(){} , the employee object represented by this becomes null. If I don't create the employee object, everything works fine. Why? I have no idea. Thank you so much for your help!

Answer 1

This line,

return this.id.equals(employee.getId());

is not null safe. It will still throw NPE when id is null , which may be the case when you create the entity instance manually using new operator without setting any of its properties instead of obtaining an instance from the DB by JPA means. Fix it accordingly:

return id != null ? id.equals(employee.id) : employee == this;

Note that I also improved the reflexivity of the comparison by adding employee == this . See further also the first point of the contract of equals() .