spring core proxy : bean post processor

spring-core/proxy/src/test/java/com/example/proxy/postprocessor/BasicTest.java

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+package com.example.proxy.postprocessor;
+
+import lombok.extern.slf4j.Slf4j;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.NoSuchBeanDefinitionException;
+import org.springframework.context.ApplicationContext;
+import org.springframework.context.annotation.AnnotationConfigApplicationContext;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+
+public class BasicTest {
+
+    @Test
+    void basicConfig() {
+        ApplicationContext applicationContext = new AnnotationConfigApplicationContext(BasicConfig.class);
+
+        A a = applicationContext.getBean("beanA", A.class);
+        a.helloA();
+
+        Assertions.assertThrows(NoSuchBeanDefinitionException.class, () -> applicationContext.getBean(B.class));
+    }
+
+    @Slf4j
+    @Configuration
+    static class BasicConfig {
+        @Bean(name = "beanA")
+        public A a() {
+            return new A();
+        }
+    }
+
+    @Slf4j
+    static class A {
+        public void helloA() {
+            log.info("hello A");
+        }
+    }
+
+    @Slf4j
+    static class B {
+        public void helloA() {
+            log.info("hello B");
+        }
+    }
+}

spring-core/proxy/src/test/java/com/example/proxy/postprocessor/BeanPostProcessorTest.java

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+package com.example.proxy.postprocessor;
+
+import lombok.extern.slf4j.Slf4j;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.BeansException;
+import org.springframework.beans.factory.NoSuchBeanDefinitionException;
+import org.springframework.beans.factory.config.BeanPostProcessor;
+import org.springframework.context.ApplicationContext;
+import org.springframework.context.annotation.AnnotationConfigApplicationContext;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+
+public class BeanPostProcessorTest {
+
+    @Test
+    void basicConfig() {
+        ApplicationContext applicationContext = new AnnotationConfigApplicationContext(BeanPostProcessorConfig.class);
+
+        B b = applicationContext.getBean("beanA", B.class);
+        b.helloB();
+
+        Assertions.assertThrows(NoSuchBeanDefinitionException.class, () -> applicationContext.getBean(BasicTest.A.class));
+    }
+
+    @Slf4j
+    @Configuration
+    static class BeanPostProcessorConfig {
+        @Bean(name = "beanA")
+        public A a() {
+            return new A();
+        }
+
+        @Bean
+        public AToBPostProcessor aToBPostProcessor() {
+            return new AToBPostProcessor();
+        }
+    }
+
+    @Slf4j
+    static class A {
+        public void helloA() {
+            log.info("hello A");
+        }
+    }
+
+    @Slf4j
+    static class B {
+        public void helloB() {
+            log.info("hello B");
+        }
+    }
+
+    @Slf4j
+    static class AToBPostProcessor implements BeanPostProcessor {
+        @Override
+        public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
+            log.info("beanName={} bean={}", beanName, bean);
+            if (bean instanceof A) {
+                return new B();
+            }
+            return bean;
+        }
+    }
+}