BAEL-5449 Instantiating Multiple Beans of the Same Class with Spring Annotations (#12446)

* added multiple bean instantiation

* added module /spring-core-6 and formatting changes

* resolved formatting issues as suggested

* resolved formatting issues and changed package names

* formatting changes in XML files

* Reformatted XML files as per the instructions

* FIXED Example in Section 3 and some changes in Pom.xml

* changed xml config to Java config in solution 3

* Project updated to spring boot application

* Removed unwanted spring dependencies from pom.xml

* moved the project under new module spring-core-6

* added spring-core-6 module in parent's pom.xml

* resolved formatting issue in parent's pom.xml

* new module entry in parent's pom

* final commit

* Added spring-core-6 in parent's pom.xml 

* fixed some merging issues.

* added spring-core-6 module entry under jdk9-and-above profile in main pom

* removed App.java from multibeaninstantiation directory

pom.xml

@@ -1246,6 +1246,7 @@
                  <module>core-java-modules/core-java-networking-3</module>
                  <module>core-java-modules/core-java-strings</module>
                  <module>core-java-modules/core-java-httpclient</module>
+                 <module>spring-core-6</module>
                  <module>ddd-contexts</module>
                  <module>docker-modules</module>
                  <module>apache-httpclient-2</module>
@@ -1328,6 +1329,7 @@
                 <module>testing-modules/testing-assertions</module>
                 <module>persistence-modules/fauna</module>
                 <module>lightrun</module>
+                <module>spring-core-6</module>
             </modules>
         </profile>
     </profiles>
@@ -1400,4 +1402,4 @@
         <guava.version>31.0.1-jre</guava.version>
     </properties>
 
-</project>
+</project>

spring-core-6/pom.xml

@@ -0,0 +1,76 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <groupId>com.baeldung</groupId>
+    <artifactId>spring-core-6</artifactId>
+    <version>0.0.1-SNAPSHOT</version>
+    <name>spring-core-6</name>
+    <url>http://www.baeldung.com</url>
+
+    <properties>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+        <maven.compiler.source>11</maven.compiler.source>
+        <maven.compiler.target>11</maven.compiler.target>
+    </properties>
+
+    <dependencies>
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <version>4.11</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-web</artifactId>
+            <version>2.0.0.RELEASE</version>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <pluginManagement>
+            <plugins>
+                <plugin>
+                    <artifactId>maven-clean-plugin</artifactId>
+                    <version>3.1.0</version>
+                </plugin>
+                <plugin>
+                    <artifactId>maven-resources-plugin</artifactId>
+                    <version>3.0.2</version>
+                </plugin>
+                <plugin>
+                    <artifactId>maven-compiler-plugin</artifactId>
+                    <version>3.8.0</version>
+                </plugin>
+                <plugin>
+                    <artifactId>maven-surefire-plugin</artifactId>
+                    <version>2.22.1</version>
+                </plugin>
+                <plugin>
+                    <artifactId>maven-jar-plugin</artifactId>
+                    <version>3.0.2</version>
+                </plugin>
+                <plugin>
+                    <artifactId>maven-install-plugin</artifactId>
+                    <version>2.5.2</version>
+                </plugin>
+                <plugin>
+                    <artifactId>maven-deploy-plugin</artifactId>
+                    <version>2.8.2</version>
+                </plugin>
+
+                <plugin>
+                    <artifactId>maven-site-plugin</artifactId>
+                    <version>3.7.1</version>
+                </plugin>
+                <plugin>
+                    <artifactId>maven-project-info-reports-plugin</artifactId>
+                    <version>3.0.0</version>
+                </plugin>
+            </plugins>
+        </pluginManagement>
+    </build>
+</project>

spring-core-6/src/main/java/com/baeldung/multibeaninstantiation/solution1/Person.java

@@ -0,0 +1,17 @@
+package com.baeldung.multibeaninstantiation.solution1;
+
+public class Person {
+    private String firstName;
+    private String lastName;
+
+    public Person(String firstName, String secondName) {
+        super();
+        this.firstName = firstName;
+        this.lastName = secondName;
+    }
+
+    @Override
+    public String toString() {
+        return "Person [firstName=" + firstName + ", secondName=" + lastName + "]";
+    }
+}

spring-core-6/src/main/java/com/baeldung/multibeaninstantiation/solution1/PersonConfig.java

@@ -0,0 +1,17 @@
+package com.baeldung.multibeaninstantiation.solution1;
+
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+
+@Configuration
+public class PersonConfig {
+    @Bean
+    public Person personOne() {
+        return new Person("Harold", "Finch");
+    }
+
+    @Bean
+    public Person personTwo() {
+        return new Person("John", "Reese");
+    }
+}

spring-core-6/src/main/java/com/baeldung/multibeaninstantiation/solution1/SpringApp1.java

@@ -0,0 +1,11 @@
+package com.baeldung.multibeaninstantiation.solution1;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication
+public class SpringApp1 {
+    public static void main(String[] args) {
+        SpringApplication.run(SpringApp1.class, args);
+    }
+}

spring-core-6/src/main/java/com/baeldung/multibeaninstantiation/solution2/Person.java

@@ -0,0 +1,17 @@
+package com.baeldung.multibeaninstantiation.solution2;
+
+public class Person {
+    private String firstName;
+    private String lastName;
+
+    public Person(String firstName, String secondName) {
+        super();
+        this.firstName = firstName;
+        this.lastName = secondName;
+    }
+
+    @Override
+    public String toString() {
+        return "Person [firstName=" + firstName + ", secondName=" + lastName + "]";
+    }
+}

spring-core-6/src/main/java/com/baeldung/multibeaninstantiation/solution2/PersonConfig.java

@@ -0,0 +1,10 @@
+package com.baeldung.multibeaninstantiation.solution2;
+
+import org.springframework.context.annotation.ComponentScan;
+import org.springframework.context.annotation.Configuration;
+
+@Configuration
+@ComponentScan("com.baeldung.multibeaninstantiation.solution2")
+public class PersonConfig {
+
+}

spring-core-6/src/main/java/com/baeldung/multibeaninstantiation/solution2/PersonOne.java

@@ -0,0 +1,13 @@
+package com.baeldung.multibeaninstantiation.solution2;
+
+import org.springframework.stereotype.Component;
+
+import com.baeldung.multibeaninstantiation.solution2.Person;
+
+@Component
+public class PersonOne extends Person {
+
+    public PersonOne() {
+        super("Harold", "Finch");
+    }
+}

spring-core-6/src/main/java/com/baeldung/multibeaninstantiation/solution2/PersonTwo.java

@@ -0,0 +1,13 @@
+package com.baeldung.multibeaninstantiation.solution2;
+
+import org.springframework.stereotype.Component;
+
+import com.baeldung.multibeaninstantiation.solution2.Person;
+
+@Component
+public class PersonTwo extends Person {
+
+    public PersonTwo() {
+        super("John", "Reese");
+    }
+}

spring-core-6/src/main/java/com/baeldung/multibeaninstantiation/solution2/SpringApp2.java

@@ -0,0 +1,11 @@
+package com.baeldung.multibeaninstantiation.solution2;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication
+public class SpringApp2 {
+    public static void main(String[] args) {
+        SpringApplication.run(SpringApp2.class, args);
+    }
+}

spring-core-6/src/main/java/com/baeldung/multibeaninstantiation/solution3/Human.java

@@ -0,0 +1,33 @@
+package com.baeldung.multibeaninstantiation.solution3;
+
+import org.springframework.beans.factory.InitializingBean;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.util.Assert;
+
+public class Human implements InitializingBean {
+
+    private Person personOne;
+
+    private Person personTwo;
+
+    @Override
+    public void afterPropertiesSet() throws Exception {
+        Assert.notNull(personOne, "Harold is alive!");
+        Assert.notNull(personTwo, "John is alive!");
+    }
+
+    /* Setter injection */
+    @Autowired
+    public void setPersonOne(Person personOne) {
+        this.personOne = personOne;
+        this.personOne.setFirstName("Harold");
+        this.personOne.setSecondName("Finch");
+    }
+
+    @Autowired
+    public void setPersonTwo(Person personTwo) {
+        this.personTwo = personTwo;
+        this.personTwo.setFirstName("John");
+        this.personTwo.setSecondName("Reese");
+    }
+}

spring-core-6/src/main/java/com/baeldung/multibeaninstantiation/solution3/MultiBeanFactory.java

@@ -0,0 +1,9 @@
+package com.baeldung.multibeaninstantiation.solution3;
+
+import java.util.List;
+
+public interface MultiBeanFactory<T> {
+    List<T> getObject(String name) throws Exception;
+
+    Class<?> getObjectType();
+}

spring-core-6/src/main/java/com/baeldung/multibeaninstantiation/solution3/Person.java

@@ -0,0 +1,49 @@
+package com.baeldung.multibeaninstantiation.solution3;
+
+import org.springframework.beans.factory.FactoryBean;
+import org.springframework.beans.factory.annotation.Qualifier;
+
+@Qualifier(value = "personOne, personTwo")
+public class Person implements FactoryBean<Object> {
+    private String firstName;
+    private String secondName;
+
+    public Person() {
+        // initialization code (optional)
+    }
+
+    @Override
+    public Class<Person> getObjectType() {
+        return Person.class;
+    }
+
+    @Override
+    public Object getObject() throws Exception {
+        return new Person();
+    }
+
+    public boolean isSingleton() {
+        return true;
+    }
+
+    public String getFirstName() {
+        return firstName;
+    }
+
+    public void setFirstName(String firstName) {
+        this.firstName = firstName;
+    }
+
+    public String getSecondName() {
+        return secondName;
+    }
+
+    public void setSecondName(String secondName) {
+        this.secondName = secondName;
+    }
+
+    @Override
+    public String toString() {
+        return "Person [firstName=" + firstName + ", secondName=" + secondName + "]";
+    }
+}

spring-core-6/src/main/java/com/baeldung/multibeaninstantiation/solution3/PersonConfig.java

@@ -0,0 +1,22 @@
+package com.baeldung.multibeaninstantiation.solution3;
+
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+
+@Configuration
+public class PersonConfig {
+    @Bean
+    public PersonFactoryPostProcessor PersonFactoryPostProcessor() {
+        return new PersonFactoryPostProcessor();
+    }
+
+    @Bean
+    public Person person() {
+        return new Person();
+    }
+
+    @Bean
+    public Human human() {
+        return new Human();
+    }
+}

spring-core-6/src/main/java/com/baeldung/multibeaninstantiation/solution3/PersonFactoryPostProcessor.java

@@ -0,0 +1,33 @@
+package com.baeldung.multibeaninstantiation.solution3;
+
+import java.util.Map;
+
+import org.springframework.beans.BeansException;
+import org.springframework.beans.factory.annotation.Qualifier;
+import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
+import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
+
+public class PersonFactoryPostProcessor implements BeanFactoryPostProcessor {
+
+    @Override
+    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
+        Map<String, Object> map = beanFactory.getBeansWithAnnotation(Qualifier.class);
+        for (Map.Entry<String, Object> entry : map.entrySet()) {
+            createInstances(beanFactory, entry.getKey(), entry.getValue());
+        }
+    }
+
+    private void createInstances(ConfigurableListableBeanFactory beanFactory, String beanName, Object bean) {
+        Qualifier qualifier = bean.getClass()
+            .getAnnotation(Qualifier.class);
+        for (String name : extractNames(qualifier)) {
+            Object newBean = beanFactory.getBean(beanName);
+            beanFactory.registerSingleton(name.trim(), newBean);
+        }
+    }
+
+    private String[] extractNames(Qualifier qualifier) {
+        return qualifier.value()
+            .split(",");
+    }
+}

spring-core-6/src/main/java/com/baeldung/multibeaninstantiation/solution3/SpringApp3.java

@@ -0,0 +1,11 @@
+package com.baeldung.multibeaninstantiation.solution3;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication
+public class SpringApp3 {
+    public static void main(String[] args) {
+        SpringApplication.run(SpringApp3.class, args);
+    }
+}