Spring auto wire bean using java based annotation

Question

I am trying to make a new simple Spring boot application to demo dependency injection. I would like to import beans using @Autowired annotation.

Here is my sample piece of code

----Example.class----

package com.example.project;


import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.*;
import org.springframework.boot.autoconfigure.*;
import org.springframework.web.bind.annotation.*;

@RestController
@EnableAutoConfiguration
public class Example {


    @Autowired
    public myBean first;

    @RequestMapping("/")
    String home() {
        return "Hello World!";
    }

    public static void main(String[] args) throws Exception {
        SpringApplication.run(Example.class, args);
    }

}

----myBean.class----

package com.example.project;

public class myBean {

    myBean()
    {
        System.out.println("Hi myBean Constructed");
    }
}

---BeanConfiguration.class---

package com.example.project;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.ComponentScan;

@Configuration
@ComponentScan(basePackages = "com.example.project")
public class BeanConfigurationClass {

    @Bean
    public myBean getBean()
    {
        return new myBean();

    }
}

--pom.xml---

<?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>example</groupId>
    <artifactId>1</artifactId>
    <version>1.0-SNAPSHOT</version>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.4.2.RELEASE</version>
    </parent>
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <version>1.2.5.RELEASE</version>
                <executions>
                    <execution>
                        <goals>
                            <goal>repackage</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
    </dependencies>
</project>

However when i try to run the application it is unable to find the bean and gives the following error Field first in com.example.project.Example required a bean of type 'com.example.project.myBean' that could not be found.

I also tried using xml based configuration but faced the same error. Is there something fundamentally wrong going over here.

Thanking you in anticipation.

Answer 1

You should try to do following,

Move @EnableAutoConfiguration from controller to your main application class i.e. BeanConfigurationClass. This is because BeanConfigurationClass is your configuration file and all configurations related annotations should placed on this.

Also rename your myBean to MyBean and annotate that with @Component annotation.

EDIT : Remove following annotations from your BeanConfigurationClass and add only this one @SpringBootApplication it will take care of all those removed.

@Configuration
@ComponentScan
@EnableAutoConfiguration

Add as ,

@SpringBootApplication
BeanConfigurationClass

Answer 2

Name of the classes must starts with CAPITAL letter ! Must be 'My Bean' ..

Answer 3

1. Move @EnableAutoConfiguration from controller to your main application class.
2. Get rid of BeanConfigurationClass

3. Add one of spring DI class annotations on myBean class:

   @Component
   public class myBean {
   
       myBean(){
           System.out.println("Hi myBean Constructed");
       }
   }