How to wrap Spring beans

Question

I am new to spring framework..

Here is my question: How i can wrap beans in runtime onto another class?

I have classes as follows for every data struct && java type:

@Component
    public class ByteCodec extends Codec<Byte> {
    public ByteCodec() {
        super(Byte.class);
    }

    public void encode(... buffer, Byte object) {
        buffer.writeByte(object);
    }

    public Byte decode(... buffer) {
        return buffer.readByte();
    }
}

and this class is a managed spring singleton. I need to wrap that codec by next class:

class OptionalCodec<T> extends Codec<Boolean> {
    public OptionalCodec(Codec<T> clazz) {
    }
    ... some implementation of encode && decode method's ...
}

How i can do this? Hint: i want automatic wrap in RUNTIME for every Codec instance..

And how to extend Autowired annotation, like that:

@AutowireCodec(targetClass=Integer.class, canBeNull=false)
private Codec<Integer> codec;

And how to do registry of the all runtime-created codecs with map:

Map<*MyCodecInfoClass*, Codec>

?? Thanks for any replies!

Answer 1

Spring allows you to inject beans by types and generic types out of the box, so for your use case I don't think it is really necessary to create a new Autowired annotation. You can simply use the existing @Autowired like this:

@Autowired
private Codec<Byte> codec;

Just keep in mind that if you define more than one bean for the same generic type and you use the code above, you'll get an error because more than one bean exist with that definition. You could get around that injecting a collection instead of a single object, for example:

@Autowired
private List<Codec<Byte>> byteCodecs;

Or if you want all codecs, regardless its generic type you can simply do something like this:

@Autowired
private List<Codec<?>> allCodecs;

Regarding your question on instance wrapping, I'm not sure if I fully understand what you're trying to achieve but you can inject a codec into another codec like I stated above, or you can take a look to Spring AOP and use it to wrap calls to your beans: http://docs.spring.io/spring/docs/current/spring-framework-reference/html/aop.html

---

I'm still not sure what would be the purpose of of the OptionalCodec as it will accept booleans on the encode/decode methods. The OptionalCodec is a different class than the base Codec interface, so if you do:

@Autowired
private OptionalCodec<Byte> codec;

Will inject the optional Byte codec. If you do:

@Autowired
private Codec<Byte> codec;

Will inject the original Byte codec. But if you do:

@Autowired
private Codec<Boolean> codec;

It will match all the OptionalCodec beans (because the type signature for an OptionalCodec is Codec<Boolean>) and throw an error as it will not be able to pick a single one.

That said, if you really need to fine tune the autowiring of same type of beans I suggest you to check this relevant section of Spring documentation where annotations like @Primary and @Qualifier are explained, and let you do exactly that: http://docs.spring.io/spring/docs/current/spring-framework-reference/html/beans.html#beans-autowired-annotation-qualifiers