BAEL-3832: Difference between BeanFactory and ApplicationContext completed

spring-core-3/pom.xml

@@ -67,6 +67,12 @@
             <version>${junit-jupiter.version}</version>
             <scope>test</scope>
         </dependency>
+        
+        <dependency>
+		    <groupId>log4j</groupId>
+		    <artifactId>log4j</artifactId>
+		    <version>${log4j.version}</version>
+		</dependency>
     </dependencies>
 
     <build>
@@ -83,6 +89,7 @@
         <maven.surefire.version>2.22.1</maven.surefire.version>
         <annotation-api.version>1.3.2</annotation-api.version>
         <spring.boot.version>2.2.2.RELEASE</spring.boot.version>
+        <log4j.version>1.2.17</log4j.version>
     </properties>
 
 </project>

spring-core-3/src/main/java/com/baeldung/ioccontainer/bean/CustomBeanFactoryPostProcessor.java

@@ -0,0 +1,16 @@
+package com.baeldung.ioccontainer.bean;
+
+import org.apache.log4j.LogManager;
+import org.apache.log4j.Logger;
+import org.springframework.beans.BeansException;
+import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
+import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
+
+public class CustomBeanFactoryPostProcessor implements BeanFactoryPostProcessor {
+    static final Logger LOGGER = LogManager.getLogger(CustomBeanPostProcessor.class.getName());
+
+    @Override
+    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
+        LOGGER.info("BeanFactoryPostProcessor is Registered");
+    }
+}

spring-core-3/src/main/java/com/baeldung/ioccontainer/bean/CustomBeanPostProcessor.java

@@ -0,0 +1,17 @@
+package com.baeldung.ioccontainer.bean;
+
+import org.apache.log4j.LogManager;
+import org.apache.log4j.Logger;
+import org.springframework.beans.BeansException;
+import org.springframework.beans.factory.config.BeanPostProcessor;
+
+public class CustomBeanPostProcessor implements BeanPostProcessor {
+
+    static final Logger LOGGER = LogManager.getLogger(CustomBeanPostProcessor.class.getName());
+
+    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
+        LOGGER.info("BeanPostProcessor is Registered Before Initialization");
+        return bean;
+    }
+
+}

spring-core-3/src/main/java/com/baeldung/ioccontainer/bean/Student.java

@@ -0,0 +1,12 @@
+package com.baeldung.ioccontainer.bean;
+
+import org.apache.log4j.LogManager;
+import org.apache.log4j.Logger;
+
+public class Student {
+    static final Logger LOGGER = LogManager.getLogger(Student.class.getName());
+
+    public void postConstruct() {
+        LOGGER.info("Student Bean is initialized");
+    }
+}

spring-core-3/src/test/java/com/baeldung/ioccontainer/IOCContainerAppTest.java

@@ -0,0 +1,137 @@
+package com.baeldung.ioccontainer;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.apache.log4j.AppenderSkeleton;
+import org.apache.log4j.Logger;
+import org.apache.log4j.spi.LoggingEvent;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.BeanFactory;
+import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
+import org.springframework.beans.factory.xml.XmlBeanFactory;
+import org.springframework.context.ApplicationContext;
+import org.springframework.context.support.ClassPathXmlApplicationContext;
+import org.springframework.core.io.ClassPathResource;
+import org.springframework.core.io.Resource;
+
+import com.baeldung.ioccontainer.bean.CustomBeanFactoryPostProcessor;
+import com.baeldung.ioccontainer.bean.CustomBeanPostProcessor;
+import com.baeldung.ioccontainer.bean.Student;
+
+public class IOCContainerAppTest {
+
+    private LogAppender logAppender;
+    private List<LoggingEvent> loggingEvents;
+
+    @BeforeEach
+    public void initializeLogAppender() {
+        logAppender = new LogAppender();
+        Logger.getRootLogger()
+            .addAppender(logAppender);
+        loggingEvents = logAppender.events;
+    }
+
+    @AfterEach
+    public void removeLogAppender() {
+        Logger.getRootLogger()
+            .removeAppender(logAppender);
+    }
+
+    @Test
+    public void whenBFInitialized_thenNoStudentLogPrinted() {
+        Resource res = new ClassPathResource("ioc-container-difference-example.xml");
+        BeanFactory factory = new XmlBeanFactory(res);
+
+        String expected = "Student Bean is initialized";
+        assertFalse(checkWhetherLoggerContains(expected));
+    }
+
+    @Test
+    public void whenBFInitialized_thenStudentLogPrinted() {
+
+        Resource res = new ClassPathResource("ioc-container-difference-example.xml");
+        BeanFactory factory = new XmlBeanFactory(res);
+        Student student = (Student) factory.getBean("student");
+
+        String expected = "Student Bean is initialized";
+        assertTrue(checkWhetherLoggerContains(expected));
+    }
+
+    @Test
+    public void whenAppContInitialized_thenStudentObjInitialized() {
+        ApplicationContext context = new ClassPathXmlApplicationContext("ioc-container-difference-example.xml");
+
+        String expected = "Student Bean is initialized";
+        assertTrue(checkWhetherLoggerContains(expected));
+    }
+
+    @Test
+    public void whenBFInitialized_thenBFPProcessorAndBPProcessorNotRegAutomatically() {
+        Resource res = new ClassPathResource("ioc-container-difference-example.xml");
+        ConfigurableListableBeanFactory factory = new XmlBeanFactory(res);
+
+        String beanFactoryPostProcessorExpectedLog = "BeanFactoryPostProcessor is Registered";
+        assertFalse(checkWhetherLoggerContains(beanFactoryPostProcessorExpectedLog));
+
+        String beanPostProcessorExpectedLog = "BeanPostProcessor is Registered Before Initialization";
+        assertFalse(checkWhetherLoggerContains(beanPostProcessorExpectedLog));
+    }
+
+    @Test
+    public void whenAppContInitialized_thenBFPostProcessorAndBPostProcessorRegisteredAutomatically() {
+        ApplicationContext context = new ClassPathXmlApplicationContext("ioc-container-difference-example.xml");
+
+        String beanFactoryPostProcessorExpectedLog = "BeanFactoryPostProcessor is Registered";
+        assertTrue(checkWhetherLoggerContains(beanFactoryPostProcessorExpectedLog));
+
+        String beanPostProcessorExpectedLog = "BeanPostProcessor is Registered Before Initialization";
+        assertTrue(checkWhetherLoggerContains(beanPostProcessorExpectedLog));
+    }
+
+    @Test
+    public void whenBFPostProcessorAndBPProcessorRegisteredManually_thenReturnTrue() {
+        Resource res = new ClassPathResource("ioc-container-difference-example.xml");
+        ConfigurableListableBeanFactory factory = new XmlBeanFactory(res);
+
+        CustomBeanFactoryPostProcessor beanFactoryPostProcessor = new CustomBeanFactoryPostProcessor();
+        beanFactoryPostProcessor.postProcessBeanFactory(factory);
+        String beanFactoryPostProcessorExpectedLog = "BeanFactoryPostProcessor is Registered";
+        assertTrue(checkWhetherLoggerContains(beanFactoryPostProcessorExpectedLog));
+
+        CustomBeanPostProcessor beanPostProcessor = new CustomBeanPostProcessor();
+        factory.addBeanPostProcessor(beanPostProcessor);
+        Student student = (Student) factory.getBean("student");
+        String beanPostProcessorExpectedLog = "BeanPostProcessor is Registered Before Initialization";
+        assertTrue(checkWhetherLoggerContains(beanPostProcessorExpectedLog));
+    }
+
+    private boolean checkWhetherLoggerContains(String expectedLogMessge) {
+        boolean isLogExist = loggingEvents.stream()
+            .anyMatch(logEvent -> logEvent.getMessage()
+                .equals(expectedLogMessge));
+        return isLogExist;
+    }
+
+    public static class LogAppender extends AppenderSkeleton {
+        public List<LoggingEvent> events = new ArrayList<LoggingEvent>();
+
+        public void close() {
+        }
+
+        public boolean requiresLayout() {
+            return false;
+        }
+
+        @Override
+        protected void append(LoggingEvent event) {
+            events.add(event);
+        }
+
+    }
+}

spring-core-3/src/test/resources/ioc-container-difference-example.xml

@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<beans xmlns="http://www.springframework.org/schema/beans"
+       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xsi:schemaLocation="http://www.springframework.org/schema/beans
+    http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">
+
+	<bean id="student" class="com.baeldung.ioccontainer.bean.Student" init-method="postConstruct"/>
+	
+    <bean id="customBeanPostProcessor" class="com.baeldung.ioccontainer.bean.CustomBeanPostProcessor" />
+	<bean id="customBeanFactoryPostProcessor" class="com.baeldung.ioccontainer.bean.CustomBeanFactoryPostProcessor" />
+</beans>