What is the difference between configuration and component?

Configuration defines how components should be created, configured, and linked together. A component is an instance of a class that represents a standalone functional block in the application, managed by Spring.

Using configuration (for example, a @Configuration class or XML), we declare beans (@Bean), specify their dependencies, and scope. The Spring container then uses this configuration to create and manage the lifecycle of these bean-components.

Example:

// src/main/java/com/example/app/config/AppConfig.java
package com.example.app.config;

import com.example.app.service.MyService;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration // This is a configuration class
public class AppConfig {

    @Bean // This declares a bean (component) MyService
    public MyService myService() {
        return new MyService(); // Create an instance of the component
    }
}

// src/main/java/com/example/app/service/MyService.java
package com.example.app.service;

// This is a component (bean) defined in the configuration
public class MyService {

    public void doSomething() {
        System.out.println("MyService is doing something.");
    }
}

In this example, AppConfig is the configuration, and the instance of the MyService class created by the myService() method is the component (bean). The configuration describes how to create and provide MyService.