第20讲 - RequestMappingHandlerMapping 与 RequestMappingHandlerAdapter

DispatcherServlet初始化时机

public class A20Application {
    public static void main(String[] args) {
        AnnotationConfigServletWebServerApplicationContext context =
                new AnnotationConfigServletWebServerApplicationContext(WebConfig.class);
    }
}

@Configuration
@ComponentScan
public class WebConfig {

    @Bean
    public TomcatServletWebServerFactory tomcatServletWebServerFactory() {
        return new TomcatServletWebServerFactory();
    }

    @Bean
    public DispatcherServlet dispatcherServlet() {
        return new DispatcherServlet();
    }

    @Bean
    public DispatcherServletRegistrationBean dispatcherServletRegistrationBean(DispatcherServlet dispatcherServlet) {
        return new DispatcherServletRegistrationBean(dispatcherServlet, "/");
    }

}

程序运行打印日志

并没有打印DispatcherServlet初始化信息，浏览器访问一次后打印日志如下：

也就是说明默认DispatcherServlet初始化默认是在首次访问Tomcat容器的时候 

可通过配置改变此时机

    @Bean
    public DispatcherServletRegistrationBean dispatcherServletRegistrationBean(DispatcherServlet dispatcherServlet) {
        DispatcherServletRegistrationBean registrationBean = new DispatcherServletRegistrationBean(dispatcherServlet, "/");
        registrationBean.setLoadOnStartup(1); // 大于0则为Tomcat启动时初始化
        return registrationBean;
    }

初始化时都做了哪些事

    // 每一个方法都是初始化一类组件
    protected void initStrategies(ApplicationContext context) {
        this.initMultipartResolver(context);
        this.initLocaleResolver(context);
        this.initThemeResolver(context);
        this.initHandlerMappings(context);
        this.initHandlerAdapters(context);
        this.initHandlerExceptionResolvers(context);
        this.initRequestToViewNameTranslator(context);
        this.initViewResolvers(context);
        this.initFlashMapManager(context);
    }

RequestMappingHandlerMapping 的作用

@Controller
public class Controller1 {

    private static final Logger log = LoggerFactory.getLogger(Controller1.class);

    @GetMapping("/test1")
    public ModelAndView test1() throws Exception {
        log.debug("test1()");
        return null;
    }

    @PostMapping("/test2")
    public ModelAndView test2(@RequestParam("name") String name) {
        log.debug("test2({})", name);
        return null;
    }

    @PutMapping("/test3")
    public ModelAndView test3(@Token String token) {
        log.debug("test3({})", token);
        return null;
    }

    @RequestMapping("/test4")
    public User test4() {
        log.debug("test4");
    }

}

public class A20Application {
    public static void main(String[] args) {
        AnnotationConfigServletWebServerApplicationContext context =
                new AnnotationConfigServletWebServerApplicationContext(WebConfig.class);

        // 解析 @RequestMapping 以及派生注解，生成路径与控制器方法的映射关系, 在初始化时就生成
        RequestMappingHandlerMapping handlerMapping = context.getBean(RequestMappingHandlerMapping.class);
        // 获取映射结果
        Map handlerMethods = handlerMapping.getHandlerMethods();
        handlerMethods.forEach((k, v) -> {
            System.out.println(k + " => " + v);
        });
    }
}

MyRequestMappingHandlerAdapter 的作用

public class MyRequestMappingHandlerAdapter extends RequestMappingHandlerAdapter {
    @Override
    public ModelAndView invokeHandlerMethod(HttpServletRequest request, HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
        return super.invokeHandlerMethod(request, response, handlerMethod);
    }
}

public class A20Application {
    public static void main(String[] args) throws Exception {
        AnnotationConfigServletWebServerApplicationContext context =
                new AnnotationConfigServletWebServerApplicationContext(WebConfig.class);
        context.registerBean(MyRequestMappingHandlerAdapter.class);
        // 解析 @RequestMapping 以及派生注解，生成路径与控制器方法的映射关系, 在初始化时就生成
        RequestMappingHandlerMapping handlerMapping = context.getBean(RequestMappingHandlerMapping.class);
        // 获取映射结果
        Map handlerMethods = handlerMapping.getHandlerMethods();
        handlerMethods.forEach((k, v) -> {
            System.out.println(k + " => " + v);
        });

        MockHttpServletRequest request = new MockHttpServletRequest("GET", "/test1");
        MockHttpServletResponse response = new MockHttpServletResponse();
        HandlerExecutionChain chain = handlerMapping.getHandler(request);
        System.out.println(chain);
        // 调用控制器方法
        MyRequestMappingHandlerAdapter handlerAdapter = context.getBean(MyRequestMappingHandlerAdapter.class);
        handlerAdapter.invokeHandlerMethod(request, response, (HandlerMethod) chain.getHandler());
    }
}