Implementing the state pattern with Java and EclipseLink

Question

I would like to implement the state pattern in java for the following scenario:

• The whole story is persisted with EclipseLink

• A Person has a SecurityState (= Security Level).

• Depending on a persons previous SecurityState , an operation changeSecurityLevel (and probably other operations too) will have different behaviour.

Person Class

@Entity
public class Person extends DatabaseObject{
    // .... lots of properties....
    @ManyToOne(fetch=FetchType.LAZY)
    private SecurityState securityState;

    public changeSecurityState(SecurityState newState){
       securityState.changeSecurityState(newState);
    }  

}

SecurityState:

@Entity
public abstract class SecurityState extends DatabaseObject{
    private int level;   // 1 = low, 2 = medium, 3 = high
    private Person person;  

    public SecurityState(Person p){
        this.person = p;
    }

    public changeSecurityState(SecurityState newState){
       // not implemented
    }        

    public void someOtherOperation(){
    }

    // getter and setter

}

For example the HighSecurityState :

@Entity
public class HighSecurityState extends SecurityState {
    private int level = 3;

    public changeSecurityState(SecurityState newState){
        if(newState.getLevel() == 1){
           // do specific stuff for High-to-Low status changes

           person.securityState = new LowSecurityState();
        }else if(newState.getLevel() == 2){
           person.securityState = new MediumSecurityState();
        }else{ }
    }  
}

Questions: - Is the state-pattern more or less correctly implemented? I don't like the if-else somehow, this doesn't really feel right.

• How can I persist the SecurityState? Which class/table should be persisted, the abstract SecurityState ? Or the concrete state classes?

Answer 1

Don't worry about if-else for such simple cases; it's fine.

Maybe switch looks a little better - but it's essentially the same thing

switch(newState.getLevel())
    case 1:
             ...
    case ...

    default: throw new AssertionError();

Or you could even go apply Visitor pattern - is it really worth it though?

public changeSecurityState(LowSecurityState newState)
...    
public changeSecurityState(MediumSecurityState newState)
...    
public changeSecurityState(HighSecurityState newState)
...

On the 2nd question - security state is just a simple int; you don't need a separate table for it; it should just be an integer column in the person table. You can make it an enum type in Java if you like.