The Bean Validation API (JSR0303) can be hooked up with JPA so that you have validation of an objects values prior to persistence, update and deletion. To do this

• Put the javax.validation "validation-api" jar in your CLASSPATH, along with the Bean Validation implementation jar of your choice
• Set the persistence property javax.persistence.validation.mode to one of auto (default), none , or callback
• Optionally set the persistence property(s) javax.persistence.validation.group.pre-persist , javax.persistence.validation.group.pre-update , javax.persistence.validation.group.pre-remove to fine tune the behaviour
• Use JPA as you normally would for persisting objects

To give a simple example of what you can do with the Bean Validation API

@Entity
public class Person 
{
    @Id
    @NotNull
    private Long id;

    @NotNull
    @Size(min = 3, max = 80)
    private String name;

    ...
}

So we are validating that instances of the Person class will have an "id" that is not null and that the "name" field is not null and between 3 and 80 characters. If it doesn't validate then at persist/update an exception will be thrown.