官方文档：
@RestController is a stereotype annotation that combines @ResponseBody and @Controller.
意思是： @RestController注解相当于@ResponseBody ＋ @Controller合在一起的作用。
1 如果只是使用@RestController注解Controller
Controller中的方法无法返回jsp页面，或者html，配置的视图解析器 InternalResourceViewResolver不起作用，返回的内容就是Return 里的内容（String/JSON）。
2 如果只是使用@Controller注解Controller若需要返回到指定页面，则需要用 @Controller配合视图解析器InternalResourceViewResolver才行。
若需要返回JSON，XML或自定义mediaType内容到页面，则需要在对应的方法上加上@ResponseBody注解。
3、实例：
1）使用@Controller 注解Controller
若返回到指定页面，在对应的方法上，视图解析器可以解析return 的jsp,html页面，并且跳转到相应页面。即返回 login.jsp 到页面。
@Controller
public class LogincController {
@RequestMapping(value="/login",method = RequestMethod.GET)
public String login() {
return "login";
}
}若返回 json 等内容到页面，则需要加@ResponseBody注解。即返回 login 到页面
@Controller
public class LogincController {
@ResponseBody
@RequestMapping(value="/login",method = RequestMethod.GET)
public String login() {
return "login";
}
}2）使用@RestController注解Controller
相当于@Controller+@ResponseBody两个注解的结合，返回json数据不需要在方法前面加@ResponseBody注解了，但使用@RestController这个注解，就不能返回jsp,html页面，视图解析器无法解析jsp,html页面。即返回 login 到页面
@RestController
public class LogincController {
@RequestMapping(value="/login",method = RequestMethod.GET)
public String login() {
return "login";
}
}如果想返回指定页面，通过 ModelAndView 返回，亲测有效（不推荐）
@RestController
public class LogincController {
@RequestMapping(value="/login",method = RequestMethod.GET)
public ModelAndView login() {
ModelAndView mv = new ModelAndView();
mv.setViewName("login");
return mv;
}
}
最后贴上 Spring5.x 的 @RestController 和 @Controller 源码，加深学习和理解。
Controller源码：
/*
* 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
*
* http://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).
*
* 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 "";
}
RestController源码：
/*
* 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
*
* http://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}.
*
* Types that carry this annotation are treated as controllers where
* {@link RequestMapping @RequestMapping} methods assume
* {@link ResponseBody @ResponseBody} semantics by default.
*
*
NOTE: {@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 "";
}
ResponseBody源码：
@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface ResponseBody {
}end ~
