Controller

김창모·2023년 5월 26일

SpringBoot

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4/19

Controller 만들기

localhost:8080 으로 접속했을시

Whitelabel Error Page
This application has no explicit mapping for /error, so you are seeing this as a fallback.

Sat May 27 06:30:50 KST 2023
There was an unexpected error (type=Not Found, status=404).

라는 메세지를 보았었다.
해석해보면

이 응용 프로그램에는 /error에 대한 명시적 매핑이 없으므로 대체 항목으로 표시됩니다.
기본 url 인 "/" 에 mapping 된 값이 없어 error 페이지가 나온것이다.

package com.hello.hello.controller;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class HelloController {

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

    @GetMapping("/hello")
    public String hello() {
        return "Hello";
    }
}

controller directory 를 만들고 HelloController 클래스를 만들었다.
"/" 으로 접속시 "Hello World!" 를 반환
"/hello" 으로 접속시 "Hello" 를 반환하려고 한다.

@RestController

/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.bind.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

import org.springframework.core.annotation.AliasFor;
import org.springframework.stereotype.Controller;

/**
 * A convenience annotation that is itself annotated with
 * {@link Controller @Controller} and {@link ResponseBody @ResponseBody}.
 * <p>
 * Types that carry this annotation are treated as controllers where
 * {@link RequestMapping @RequestMapping} methods assume
 * {@link ResponseBody @ResponseBody} semantics by default.
 *
 * <p><b>NOTE:</b> {@code @RestController} is processed if an appropriate
 * {@code HandlerMapping}-{@code HandlerAdapter} pair is configured such as the
 * {@code RequestMappingHandlerMapping}-{@code RequestMappingHandlerAdapter}
 * pair which are the default in the MVC Java config and the MVC namespace.
 *
 * @author Rossen Stoyanchev
 * @author Sam Brannen
 * @since 4.0
 */
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Controller
@ResponseBody
public @interface RestController {

	/**
	 * The value may indicate a suggestion for a logical component name,
	 * to be turned into a Spring bean in case of an autodetected component.
	 * @return the suggested component name, if any (or empty String otherwise)
	 * @since 4.0.1
	 */
	@AliasFor(annotation = Controller.class)
	String value() default "";

}

@RestController 어노테이션 을 살펴보자
@Controller 어노테이션과 @ResponseBody 어노테이션이 붙어있다.
컨트롤러 이면서 클라이언트 요청에 의해 반환될 Model 이 Body 에 직접 보여진다는 의미이다.

Controller

/*
 * Copyright 2002-2022 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.stereotype;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

import org.springframework.core.annotation.AliasFor;

/**
 * Indicates that an annotated class is a "Controller" (e.g. a web controller).
 *
 * <p>This annotation serves as a specialization of {@link Component @Component},
 * allowing for implementation classes to be autodetected through classpath scanning.
 * It is typically used in combination with annotated handler methods based on the
 * {@link org.springframework.web.bind.annotation.RequestMapping} annotation.
 *
 * @author Arjen Poutsma
 * @author Juergen Hoeller
 * @since 2.5
 * @see Component
 * @see org.springframework.web.bind.annotation.RequestMapping
 * @see org.springframework.context.annotation.ClassPathBeanDefinitionScanner
 */
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component
public @interface Controller {

	/**
	 * The value may indicate a suggestion for a logical component name,
	 * to be turned into a Spring bean in case of an autodetected component.
	 * @return the suggested component name, if any (or empty String otherwise)
	 */
	@AliasFor(annotation = Component.class)
	String value() default "";

}

@Component

@Controller 에는 @Component 어노테이션이 포함되어있으며

@Component 어노테이션은 스프링 컨테이너에 빈 등록하는법 에서 알아봤듯이 스프링 컨테이너에 빈을 등록해준다.

정리해보면 @Component 를 포함하는 @Controller 를 포함하는 @RestController 는 스프링 컨테이너에 빈으로 등록되었다.