What is IOC Scope?

  • There are two type scope in IOC.
    1. Singleton
    2. Prototype
      • Request
      • Session
      • Websocket
      • ….

1. Singleton

When make Bean in spring, should write @Component or @Controller or @Service and so on and default scope type is Singleton.

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@Component
public class Single {

}

2. Prototype

If want scope type prototype, should write prototype in @Scope like below.

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@Component @Scope(value = "prototype")
public class Proto {

}

Check

Let’s check scope example about above code.

First, configure Single class like this.

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@Component
public class Single {

    @Autowired
    private Proto proto;

    public Proto getProto() {
        return proto;
    }
}

Second, configure Prototype class like this.

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@Component @Scope(value = "prototype")
public class Proto {

    @Autowired
    Single single;
}

As example above code, Single class type is Singleton and Proto class type is prototype.

Execute code for test like below.

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@Component
public class ScopeRunner implements ApplicationRunner {

    @Autowired
    ApplicationContext ctx;

    @Override
    public void run(ApplicationArguments args) throws Exception {
        System.out.println("proto");

        System.out.println(ctx.getBean(Proto.class));
        System.out.println(ctx.getBean(Proto.class));
        System.out.println(ctx.getBean(Proto.class));

        System.out.println("single");

        System.out.println(ctx.getBean(Single.class));
        System.out.println(ctx.getBean(Single.class));
        System.out.println(ctx.getBean(Single.class));
    }
}

As like result, every Singleton class hashcode are same and every prototype code are different. 

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proto
com.example.demo.scope.Proto@71466383
com.example.demo.scope.Proto@46d63dbb
com.example.demo.scope.Proto@4088741b
single
com.example.demo.scope.Single@178270b2
com.example.demo.scope.Single@178270b2
com.example.demo.scope.Single@178270b2

How about Proto class in Single class?

Let’s test.

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@Component
public class Single {

    @Autowired
    private Proto proto;

    public Proto getProto() {
        return proto;
    }
}
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@Component
public class ScopeRunner implements ApplicationRunner {

    @Autowired
    ApplicationContext ctx;
    @Override
    public void run(ApplicationArguments args) throws Exception {

        System.out.println("Proto by single");
        System.out.println(ctx.getBean(Single.class).getProto());
        System.out.println(ctx.getBean(Single.class).getProto());
        System.out.println(ctx.getBean(Single.class).getProto());
    }
}

The result is like this.

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Proto by single
com.example.demo.scope.Proto@38a1a26
com.example.demo.scope.Proto@38a1a26
com.example.demo.scope.Proto@38a1a26

Why every Prototype class’s hashcode are same even though configuration prototype?

That reason is that the Single class configuration is a Singleton.

When Bean Created, Single class already assigned prototype.

If want Proto class working like prototype in Singleton Bean, should write ‘proxyMode’ like below.

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@Component @Scope(value = "prototype", proxyMode = ScopedProxyMode.TARGET_CLASS)
public class Proto {

    @Autowired
    Single single;
}

The expected result was output.

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Proto by single
com.example.demo.scope.Proto@31ff6309
com.example.demo.scope.Proto@204e90f7
com.example.demo.scope.Proto@20a05b32