request的生命历程

When the request leaves the browser ?, it carries information about what the user is asking for. At the least, the request will be carrying the requested URL. But it may also carry additional data, such as the information submitted in a form by the user.

The first stop in the request’s travels is at Spring’s DispatcherServlet. Like most Javabased web frameworks, Spring MVC funnels requests through a single front controller servlet. A front controller is a common web application pattern where a single servlet delegates responsibility for a request to other components of an application to perform actual processing. In the case of Spring MVC, DispatcherServlet is the front controller.

The DispatcherServlet’s job is to send the request on to a Spring MVC controller. A controller is a Spring component that processes the request. But a typical application may have several controllers, and DispatcherServlet needs some help deciding which controller to send the request to. So the DispatcherServlet consults one or more handler mappings ? to figure out where the request’s next stop will be. The handler mapping pays particular attention to the URL carried by the request when making its decision.

Once an appropriate controller has been chosen, DispatcherServlet sends the request on its merry way to the chosen controller ?. At the controller, the request drops off its payload (the information submitted by the user) and patiently waits while the controller processes that information. (Actually, a well-designed controller performs little or no processing itself and instead delegates responsibility for the business Wlogic to one or more service objects.)

The logic performed by a controller often results in some information that needs to be carried back to the user and displayed in the browser. This information is referred to as the model. But sending raw information back to the user isn’t sufficient—it needs to be formatted in a user-friendly format, typically HTML. For that, the information needs to be given to a view, typically a JavaServer Page (JSP).

One of the last things a controller does is package up the model data and identify the name of a view that should render the output. It then sends the request, along with the model and view name, back to the DispatcherServlet ?.

So that the controller doesn’t get coupled to a particular view, the view name passed back to DispatcherServlet doesn’t directly identify a specific JSP. It doesn’t even necessarily suggest that the view is a JSP. Instead, it only carries a logical name that will be used to look up the actual view that will produce the result. The DispatcherServlet consults a view resolver ? to map the logical view name to a specific view implementation, which may or may not be a JSP.

Now that DispatcherServlet knows which view will render the result, the request’s job is almost over. Its final stop is at the view implementation ?, typically a JSP, where it delivers the model data. The request’s job is finally done. The view will use the model data to render output that will be carried back to the client by the (notso-hardworking) response object ?.

搭建Spring MVC

• 配置DISPATCHERSERVLET

  • 　　getServletMappings()　　：identifies one or more paths that DispatcherServlet will be mapped to. In this case, it’s mapped to /, indicating that it will be the application’s default servlet. It will handle all requests coming into the application。
  •      getRootConfigClasses()　　：will be used to configure the application context created by ContextLoaderListener.
  • 　　getRootConfigClasses()　　：will define beans for DispatcherServlet’s application context 。

package spittr.config;

import org.springframework.web.servlet.support.AbstractAnnotationConfigDispatcherServletInitializer;

import spittr.web.WebConfig;

public class SpitterWebInitializer 
    extends AbstractAnnotationConfigDispatcherServletInitializer{

    @Override
    protected Class<?>[] getRootConfigClasses() {
        return new Class<?>[] { RootConfig.class };
    }

    @Override
    protected Class<?>[] getServletConfigClasses() {
        return new Class<?>[] { WebConfig.class };
    }

    @Override
    protected String[] getServletMappings() {
        return new String[] { "/" }; //Map DispatcherServlet to /
    }

}

附上AbstractAnnotationConfigDispatcherServletInitializer源码：

package org.springframework.web.servlet.support;

import org.springframework.util.ObjectUtils;
import org.springframework.web.context.WebApplicationContext;
import org.springframework.web.context.support.AnnotationConfigWebApplicationContext;

/**
 * Base class for {@link org.springframework.web.WebApplicationInitializer}
 * implementations that register a
 * {@link org.springframework.web.servlet.DispatcherServlet DispatcherServlet}
 * configured with annotated classes, e.g. Spring‘s
 * {@link org.springframework.context.annotation.Configuration @Configuration} classes.
 *
 * <p>Concrete implementations are required to implement {@link #getRootConfigClasses()}
 * and {@link #getServletConfigClasses()} as well as {@link #getServletMappings()}.
 * Further template and customization methods are provided by
 * {@link AbstractDispatcherServletInitializer}.
 *
 * <p>This is the preferred approach for applications that use Java-based
 * Spring configuration.
 *
 * @author Arjen Poutsma
 * @author Chris Beams
 * @since 3.2
 */
public abstract class AbstractAnnotationConfigDispatcherServletInitializer
        extends AbstractDispatcherServletInitializer {

    /**
     * {@inheritDoc}
     * <p>This implementation creates an {@link AnnotationConfigWebApplicationContext},
     * providing it the annotated classes returned by {@link #getRootConfigClasses()}.
     * Returns {@code null} if {@link #getRootConfigClasses()} returns {@code null}.
     */
    @Override
    protected WebApplicationContext createRootApplicationContext() {
        Class<?>[] configClasses = getRootConfigClasses();
        if (!ObjectUtils.isEmpty(configClasses)) {
            AnnotationConfigWebApplicationContext rootAppContext = new AnnotationConfigWebApplicationContext();
            rootAppContext.register(configClasses);
            return rootAppContext;
        }
        else {
            return null;
        }
    }

    /**
     * {@inheritDoc}
     * <p>This implementation creates an {@link AnnotationConfigWebApplicationContext},
     * providing it the annotated classes returned by {@link #getServletConfigClasses()}.
     */
    @Override
    protected WebApplicationContext createServletApplicationContext() {
        AnnotationConfigWebApplicationContext servletAppContext = new AnnotationConfigWebApplicationContext();
        Class<?>[] configClasses = getServletConfigClasses();
        if (!ObjectUtils.isEmpty(configClasses)) {
            servletAppContext.register(configClasses);
        }
        return servletAppContext;
    }

    /**
     * Specify {@link org.springframework.context.annotation.Configuration @Configuration}
     * and/or {@link org.springframework.stereotype.Component @Component} classes to be
     * provided to the {@linkplain #createRootApplicationContext() root application context}.
     * @return the configuration classes for the root application context, or {@code null}
     * if creation and registration of a root context is not desired
     */
    protected abstract Class<?>[] getRootConfigClasses();

    /**
     * Specify {@link org.springframework.context.annotation.Configuration @Configuration}
     * and/or {@link org.springframework.stereotype.Component @Component} classes to be
     * provided to the {@linkplain #createServletApplicationContext() dispatcher servlet
     * application context}.
     * @return the configuration classes for the dispatcher servlet application context or
     * {@code null} if all configuration is specified through root config classes.
     */
    protected abstract Class<?>[] getServletConfigClasses();

}

• ENABLING SPRING MVC
  

  • package spittr.web;
    
    import org.springframework.context.annotation.Bean;
    import org.springframework.context.annotation.ComponentScan;
    import org.springframework.context.annotation.Configuration;
    import org.springframework.web.servlet.ViewResolver;
    import org.springframework.web.servlet.config.annotation.DefaultServletHandlerConfigurer;
    import org.springframework.web.servlet.config.annotation.EnableWebMvc;
    import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;
    import org.springframework.web.servlet.view.InternalResourceViewResolver;
    
    @Configuration
    @EnableWebMvc
    @ComponentScan("spittr.web")
    public class WebConfig extends WebMvcConfigurerAdapter {
    
      @Bean
      public ViewResolver viewResolver() {
        InternalResourceViewResolver resolver = new InternalResourceViewResolver();
        resolver.setPrefix("/WEB-INF/views/");
        resolver.setSuffix(".jsp");
        return resolver;
      }
      
      @Override
      public void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) {
        configurer.enable();
      }
    }

    注解 @EnableWebMvc 使得Spring MVC生效
    

  • 注解@ComponentScan("spittr.web") Enable component-scanning
  • 方法 ViewResolver viewResolver()：配置了一个viewResolver
  • 方法configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer)：Configure static content handling 。By calling enable() on the given DefaultServletHandlerConfigurer, you’re asking DispatcherServlet to forward requests for static resources to the servlet container’s default servlet and not to try to handle them itself。

• 　　rootConfig:

@Configuration
@ComponentScan(basePackages={"spitter"},
excludeFilters={
@Filter(type=FilterType.ANNOTATION, value=http://www.mamicode.com/EnableWebMvc.class)
})
public class RootConfig {
}

• Writing a simple controller

package spittr.web;

import static org.springframework.web.bind.annotation.RequestMethod.GET;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;

@Controller
@RequestMapping("/home")
public class HomeController {

  @RequestMapping(method = GET)
  public String home() {
    return "home";
  }

}

views/home.jsp

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@ page session="false" %>
<html>
  <head>
    <title>Spitter</title>
    <link rel="stylesheet" 
          type="text/css" 
          href="<c:url value="http://www.mamicode.com//resources/style.css" />" >
  </head>
  <body>
    <h1>Welcome to Spitter</h1>

    <a href="<c:url value="http://www.mamicode.com//spittles" />">Spittles</a> | 
    <a href="<c:url value="http://www.mamicode.com//spitter/register" />">Register</a>
  </body>
</html>

• 运行结果

实验过程中遇到的问题：

　　注解配置spring mvc的前提之一就是servlet 3 以及使用高版本的tomcat(tomcat 7或以上)以及JDK的版本问题。

　　实验所用的tomcat版本为tomcat8,编译版本jdk为1.8，servlet版本为3.0.1版本。

spring in action 第五章基于注解搭建SpringMvc环境