Question

Is it somehow possible to annotate a Java Method in that way that i later can give another Method a Field Identifier or something like that, so that this Method can call the right one?

I know that normally you would do this with interfaces, but in my case this would be a immense count of interfaces… I need to use this in Entity Classes for my Database (and i’m not allowed to use a ORM Mapper)

For example: I have the Entity

public class Account{
    private String username;
    private String password;
    private String name;
    private String mail;


    public void setUserName(String username){
        this.username = username;
    }

    public String getUserName(){
        return username;
    }

    [all other getter/Setter...]
}

Now i want to tell a Method that it need to validate a Field, for example the username field.

The Method that does should look like this:

public void validateField(XXX Field, Entity entity) throws ValidationFailedException, EmptyFieldException;

where XXX is somehow the FieldIdentifier.

Is that in any way possible in Java?

My only guess it that i Use public static final ìnt stuff in there to give every field a Method or so…

Answer 1

What do you use? I don’t see any annotations from which I can guess your framework. If you use Hibernate, you can use something like @NotNull or something else, or even do your custom validation:
This is how you would go with your example:

public class Account{

    @NotNull(message="This field should not be null")
    private String username;
    @NotBlank(message="This string should not be empty or null")
    private String password;
    private String name;
    private String mail;


    public void setUserName(String username){
        this.username = username;
    }

    public String getUserName(){
        return username;
    }

    [all other getter/Setter...]
}

http://silentwalker.wordpress.com/2009/04/07/custom-validation-in-hibernate/

You can also create your own annotations without using any framework and use them @prepersist or whatever. Basically the sky is the limit.

P.S Since you don’t want to use any non internal code, here is how you can approach:

First, you can define an annotation

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface NotNull{
    public String message() default "";
}

Then, before persisting the class, you would inspect its fields:

So, you have something like this:

Field[] classFields = yourObjectPrePersist.getClass().getDeclaredFields();
for (int i = 0; i < classFields.length; i++) {
        classFields[i].setAccessible(true);//take notice that if you use a SecurityManager, you should work around it
        if (classFields[i].getAnnotation(NotNull.class) != null) {
            Object value = classFields[i].get(yourObjectPrePersist);
            //here check if value is null or not and then return the message
            if (value == null) {
                throw new SomeException(((NotNull) classFields[i].getAnnotation(NotNull.class)).message());
            }
        }
    }