How do I inject a logger into a field in the sample spring boot application?

Solution using @Bean:

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import org.springframework.beans.factory.InjectionPoint;
import org.springframework.beans.factory.config.ConfigurableBeanFactory;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Scope;

@Configuration
public class LoggerConfiguration {

    @Bean
    @Scope(ConfigurableBeanFactory.SCOPE_PROTOTYPE)
    public Logger logger(InjectionPoint injectionPoint){
        return LoggerFactory.getLogger(injectionPoint.getMethodParameter().getContainingClass());
    }

}

After that, just inject the Logger using Constructor Injection (field injection will not work):

@Service
class SomeService {

    private Logger logger;

    public SomeService(Logger logger;) {
        this.logger = logger;
    }

    public void someMethod() {
        logger.error("Some log");
    }  
}

Although it is not the usual way you can add a logger bean directly in your context reproducing the classic bind:

private final Logger logger = LoggerFactory.getLogger(MainController.class);

simply inserting in the spring context:

<bean id="logger" scope="prototype" class="org.slf4j.LoggerFactory" factory-method="getLogger">
    <constructor-arg name="name" value="youLoggerName" />
</bean>

then you can simply inject your logger:

@Autowired
private Logger logger;

If the objective here is code reduction then try Project Lombok. You then don't even need to declare the logger - just add an annotation and use log instead of logger

So your above code will now look like this:

import javax.servlet.http.HttpServletResponse;

import org.slf4j.Logger;
// import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;

import lombok.extern.slf4j.Slf4j;

@Slf4j
@Controller
public class MainController {

    @RequestMapping("/")
    public String enterSite(HttpServletResponse response) {
        log.info("site entered");
        return "welcome";
    }
}