Do Spring @Component classes have to be public?

Question

I'd like to expose a component's interface as an interface and the implementing class would be package protected (and maybe in some other package):

package baz.iface

interface Foo {
    void bar();
}  


package baz.whatever

@Component
class SpringyFoo implements baz.iface.Foo {
    public void bar() { frobnicate(); }
}

Assuming baz.whatever is in the component-scan, will Spring be able to autowire a baz.iface.Foo somewhere else?

class FooClient {
    @Autowired
    private baz.iface.Foo;
}

I just noticed another issue with this code: `baz.iface.Foo` isn't visible in `baz.whatever`. You'll need to make the interface `public`. — chrylis -cautiouslyoptimistic-, Aug 21 '13 at 07:28

score 14 · Answer 1 · edited Sep 13 '22 at 10:01

14

No, components don't have to be public. The only requirement is that they have a no-arg constructor.

edited Sep 13 '22 at 10:01

Ahmed Ashour

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answered Aug 19 '13 at 12:51

Evgeniy Dorofeev

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you can also use arguments in constructors for constructor injection: http://static.springsource.org/spring/docs/3.0.x/reference/beans.html#beans-constructor-injection – Christopher Taylor Aug 20 '13 at 09:51

score 1 · Answer 2 · answered Aug 19 '13 at 12:27

1

Yes, Spring will search for objects of type Foo.
SpringyFoo implements Foo and can be used in place of object of type Foo.

answered Aug 19 '13 at 12:27

Ajinkya

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To be clear, you're saying that **no**, components **do not** have to be public. – drew moore May 03 '16 at 08:53

chrylis -cautiouslyoptimistic- · Answer 3 · 2013-08-19T12:48:36.380

0

You can't make your bar() "package-protected" because it has to be public:

Every method declaration in the body of an interface is implicitly public.

Spring's reflection system will find all of your classes, even ones with default access, but it's a compile-time error for your bar() method not to be public.

edited Aug 19 '13 at 12:48

answered Aug 19 '13 at 12:41

chrylis -cautiouslyoptimistic-

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That is probably a typo in `SpringyFoo`. Also you don't have to declare interface methods to be `public` as [they are always public](http://stackoverflow.com/questions/5376970/protected-in-interfaces). – Adam Gent Aug 19 '13 at 12:45
This question is poorly written and asks two diametrically opposed questions. I'm restating. – chrylis -cautiouslyoptimistic- Aug 19 '13 at 12:47
2

Well the real issue is that he should just try it. With Java Reflection / Byte code manipulation and a corresponding loose security manager you can do just about anything including even setting final fields. – Adam Gent Aug 19 '13 at 12:48
yes, the missing `public` before `bar()` was a typo in `SpringyFoo`. I've updated the question. I did try it and it seemed to work. However, all the docs/examples I could find always used public classes, so I wanted to know if this was supported behaviour. – Christopher Taylor Aug 20 '13 at 09:44
I'm editing your question; let me know if it's not what you meant. – chrylis -cautiouslyoptimistic- Aug 20 '13 at 09:45

Do Spring @Component classes have to be public?

3 Answers3