Spring Framework - ImportSelector Examples

package com.logicbig.example;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.*;
import org.springframework.core.type.AnnotationMetadata;

public class ImportSelectorExample {

    public static void main (String[] args) {
        System.setProperty("myProp", "someValue");

        ApplicationContext context =
                  new AnnotationConfigApplicationContext(
                            MainConfig.class);
        ClientBean bean = context.getBean(ClientBean.class);
        bean.doSomething();
    }

    @Configuration
    @Import(MyImportSelector.class)
    public static class MainConfig {

        @Bean
        ClientBean clientBean () {
            return new ClientBean();
        }

    }

    public static class ClientBean {
        @Autowired
        private AppBean appBean;

        public void doSomething () {
            System.out.println(appBean.getMessage());
        }

    }


    public static class MyImportSelector implements ImportSelector {

        @Override
        public String[] selectImports (AnnotationMetadata importingClassMetadata) {
            String prop = System.getProperty("myProp");
            if ("someValue".equals(prop)) {
                return new String[]{MyConfig1.class.getName()};
            } else {
                return new String[]{MyConfig2.class.getName()};
            }
        }
    }

    public static class AppBean {
        private String message;

        public AppBean (String message) {
            this.message = message;
        }

        public String getMessage () {
            return message;
        }
    }

    @Configuration
    public static class MyConfig1 {
        @Bean
        AppBean appBean () {
            return new AppBean("from config 1");
        }
    }

    @Configuration
    public static class MyConfig2 {
        @Bean
        AppBean appBean () {
            return new AppBean("from config 2");
        }
    }
}

package com.logicbig.example;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.*;
import org.springframework.core.annotation.AnnotationAttributes;
import org.springframework.core.type.AnnotationMetadata;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

public class ImportSelectorWithAnnotationExample {
    public static void main (String[] args) {
        ApplicationContext context =
                  new AnnotationConfigApplicationContext(
                            MainConfig.class);
        ClientBean bean = context.getBean(ClientBean.class);
        bean.doSomething();
    }

    @Configuration
    @EnableSomeModule("someValue")
    public static class MainConfig {
        @Bean
        ClientBean clientBean () {
            return new ClientBean();
        }
    }

    public static class ClientBean {
        @Autowired
        private AppBean appBean;

        public void doSomething () {
            System.out.println(appBean.getMessage());
        }
    }

    @Retention(RetentionPolicy.RUNTIME)
    @Target(ElementType.TYPE)
    @Import(MyImportSelector.class)
    public @interface EnableSomeModule {
        String value () default "";
    }


    public static class MyImportSelector implements ImportSelector {

        @Override
        public String[] selectImports (AnnotationMetadata importingClassMetadata) {
            AnnotationAttributes attributes = AnnotationAttributes.fromMap(
                      importingClassMetadata.getAnnotationAttributes(
                                EnableSomeModule.class.getName(), false));

            String value = attributes.getString("value");
            if ("someValue".equals(value)) {
                return new String[]{MyConfig1.class.getName()};
            } else {
                return new String[]{MyConfig2.class.getName()};
            }
        }
    }

    public static class AppBean {
        private String message;

        public AppBean (String message) {
            this.message = message;
        }

        public String getMessage () {
            return message;
        }
    }

    @Configuration
    public static class MyConfig1 {
        @Bean
        AppBean appBean () {
            return new AppBean("from config 1");
        }
    }

    @Configuration
    public static class MyConfig2 {
        @Bean
        AppBean appBean () {
            return new AppBean("from config 2");
        }
    }
}