Bean Components, Config and Main Class

Package: com.javajee.spring.service

JJWriter.java

package com.javajee.spring.service;

public interface JJWriter {

    public void write();

}

JJFileWriter.java

package com.javajee.spring.service;

public class JJFileWriter implements JJWriter {

    public void write() {
        System.out.println("Writing to File!!!");
    }
    
    @Override
    public String toString(){
        return "Writing to File!!!";
    }

}

JJDatabaseWriter.java

package com.javajee.spring.service;

public class JJDatabaseWriter implements JJWriter {

    public void write() {
        System.out.println("Writing to Database!!!");
    }
    
    @Override
    public String toString(){
        return "Writing to Database!!!";
    }
}

WriterFactory.java

package com.javajee.spring.service;

public class WriterFactory {

    public JJWriter getWriter(String str) {
        switch (str) {
        case "file":
            return new JJFileWriter();
        case "db":
            return new JJDatabaseWriter();
        default:
            return null;
        }
    }

}

Package: com.javajee.spring.controller

WriterController.java

package com.javajee.spring.controller;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;

import com.javajee.spring.service.JJWriter;

@Controller
public class WriterController {

    @Autowired
    JJWriter writer;
    
    public void write(){
        writer.write();
    }

}

Package: com.javajee.spring.config

DemoConfig.java

package com.javajee.spring.config;

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

import com.javajee.spring.service.JJWriter;
import com.javajee.spring.service.WriterFactory;

@Configuration
@ComponentScan(basePackages="com.javajee.spring")
@PropertySource("classpath:/application.properties")
public class DemoConfig {
    
    @Bean
    public WriterFactory getWriterFactory(){
        return new WriterFactory();
    }
    
    @Bean
    @Profile("fileprofile")
    public JJWriter getJJFIleWriter(WriterFactory factory)
    {
        return factory.getWriter("file");
    }
    
    @Bean
    @Profile({"default","dbprofile"})
    public JJWriter getJJDatabaseWriter(WriterFactory factory)
    {
        return factory.getWriter("db");
    }

}

Package: com.javajee.spring

Main class: JJWriterMain.java

package com.javajee.spring;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

import com.javajee.spring.config.DemoConfig;
import com.javajee.spring.controller.WriterController;
import com.javajee.spring.service.JJWriter;

public class JJWriterMain {
    
    @Autowired
    JJWriter writer;

    public static void main(String[] args) {
        
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(DemoConfig.class);

        WriterController writerController = context.getBean("writerController", WriterController.class);

        writerController.write();
        
        context.close();

    }

}

Note:

In this example, I have used annotations and Java configuration. However, factory implementation makes more sense in xml configuration due to some useful tag support provided by Spring xml configuration.

This example also makes use of many other annotations and concepts we have learned in this section like controller, componentscan, configuration, bean, profile, autowired etc. We will refactor the code into different packages and show the use of annotations like @Controller. Note that, technically you can use @Component or any other layer based annotations here. You can use @ComponentScan for all of these annotations. I have used the same application.properties file with a single line for activating the profile: spring.profiles.active=dbprofile. I have specified the file through @PropertySource annotation over my java configuration file.