Spring auto configuration vs explicit @Enable* configuration declaration

Spring 4 provides a great feature with auto configuration along with @Conditional API. Spring also has many built-in @Enable*** configuration (such as @EnableWebMvc, @EnableCaching, @EnableScheduling...). But I am confused when I should use explicitly these @Enable** configuration or I just need Auto Configuration and define some custom beans to override is enough. Please explain me this issue.

@EnableWebMvc, @EnableCaching, @EnableScheduling are ways to enable different capabilities that spring provide through some of its module.

These are not part of springboot

. These features involves lot of heavy lifting to be done. And hence these are not activated by default.

For example even if you use @Scheduled, scheduler will not be enabled unless you enable scheduling capability using @EnableScheduling. This enables spring to do necesasry things required to support this feature. This may/may not include running several AutoConfiguration classes

AutoConfiguration classes provide a way to plugin configuration which needs to be done during startup. This is extendable. This means, you can write your own Autoconfiguration classes. And these Autoconfiguration classes are part of springboot

Spring boot is mainly opinionated, which means it does take a lot of decisions based on the dependecies it sees in the pom. For example when it sees mongo dependecies, it tries to connect to moongo database on localhost and port 27017. This is done through AutoConfiguration classes. Which is extendable, by ways of providing custom values through application.properties or provinding custom implementations

If you use Spring Boot then AutoConfiguration is automatically enabled and if you can handle those using application.properties file.

If you override/customize some Configuration then please check following code :

import java.util.concurrent.Executor;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.scheduling.annotation.EnableAsync;
import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor;

@Configuration
@EnableAsync
public class AsyncConfig 
{
	@Bean(name ="taskExecutor")
    public Executor taskExecutor()
	{
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setCorePoolSize(2);
        executor.setMaxPoolSize(2);
        executor.setQueueCapacity(100);
        executor.setThreadNamePrefix("Thread-");
        executor.initialize();
        return executor;
    }
}

Here we can custom configure Asynchronous functionality.