Entities equals(), hashCode() and toString(). How to correctly implement them?

Question

I'm implementing equals(), hashCode() and toString() of my entities using all the available fields in the bean.

I'm getting some Lazy init Exception on the frontend when I try to compare the equality or when I print the obj state. That's because some list in the entity can be lazy initialized.

I'm wondering what's the correct way to for implementing equals() and toString() on an entity object.

Answer 1

equals() and hashCode() should be implemented using a business key - i.e. a set of properties that uniquely identify the object, but are not its auto-generated ID.

in toString() you can put whatever information is interesting - for example all fields.

Use your IDE (Eclipse, NetBeans, IntelliJ) to generate all these for you.

In order to avoid LazyInitializationException, no matter whether in equals() or in your view (jsp), you can use OpenSessionInView.

Answer 2

When you implement the equals and hashCode methods for Hibernate objects, it is important to

1. Use getters instead of directly accessing the class properties.
2. Not directly compare objects' classes, but use instanceof instead

More information:

Stackoverflow: overriding-equals-and-hashcode-in-java

Hibernate documentation: Equals and HashCode

Edit: the same rules about not accessing the class properties directly applies to toString method as well - only using the getters guarantees that the information really contained in the class is returned.