【小家Spring】Spring MVC控制器中Handler的四种实现方式：Controller、HttpRequestHandler、Servlet、@RequestMapping(中)

@Configuration
@EnableWebMvc
public class WebMvcConfig extends WebMvcConfigurerAdapter {
    // 注册 一个默认的servlet处理器  让它处理静态资源
    @Override
    public void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) {
        DefaultServletHandlerConfigurer handlerConfigurer = new DefaultServletHandlerConfigurer(servletContext);
        // 这个Configurer只有一个enable方法，内部会 new DefaultServletHttpRequestHandler();
        handlerConfigurer.enable("default"); //默认值的servlet名字就是default
        super.configureDefaultServletHandling(configurer);
    }
}

  protected SimpleUrlHandlerMapping buildHandlerMapping() {
    if (this.handler == null) {
      return null;
    }
    SimpleUrlHandlerMapping handlerMapping = new SimpleUrlHandlerMapping();
    handlerMapping.setUrlMap(Collections.singletonMap("/**", this.handler));
    handlerMapping.setOrder(Integer.MAX_VALUE);
    return handlerMapping;
  }

// @since 3.0.4  可见它是一个HttpRequestHandler
public class DefaultServletHttpRequestHandler implements HttpRequestHandler, ServletContextAware {
}

<!-- 一次性可以写多个路径，里面都可议放置静态资源文件~   location表示资源文件的位置  mapping：表示请求URL-->
<mvc:resources location="/,classpath:/META-INF/publicResources/" mapping="/resources/**"/>
// 当然我们也可以写成多个,类似这样子
<mvc:resources location="/img/" mapping="/img/**"/>
<mvc:resources location="/js/" mapping="/js/**"/>
<mvc:resources location="/css/" mapping="/css/**"/>

@Configuration
@EnableWebMvc
public class WebMvcConfig extends WebMvcConfigurerAdapter {
    @Override
    public void addResourceHandlers(ResourceHandlerRegistry registry) {
        registry.addResourceHandler("/resource/**").addResourceLocations("/WEB-INF/static/"); // 支持Ant风格的路径匹配
    }
}

  Map<String, HttpRequestHandler> urlMap = new LinkedHashMap<>();
// 这个HttpRequestHandler是这么生成的
// 使用的ResourceHttpRequestHandler  因为我们无法指定locationValues  所以这里是[] 空集合
// 个人感觉这是Spring的一个问题，后面有时间回去社区里反馈此问题~~~（我使用的Spring版本为5.1.x）
  protected ResourceHttpRequestHandler getRequestHandler() {
    ResourceHttpRequestHandler handler = new ResourceHttpRequestHandler();
    // 给设置好ResourceResolvers
    if (this.resourceChainRegistration != null) {
      handler.setResourceResolvers(this.resourceChainRegistration.getResourceResolvers());
      handler.setResourceTransformers(this.resourceChainRegistration.getResourceTransformers());
    }
    // location们  可以发现每个mapping相当于对应着所有的location的
    handler.setLocationValues(this.locationValues);
    // 设置浏览器cache相关内容 
    if (this.cacheControl != null) {
      handler.setCacheControl(this.cacheControl);
    }
    else if (this.cachePeriod != null) {
      handler.setCacheSeconds(this.cachePeriod);
    }
    return handler;
  }

// @since 3.0.4 可以看到它实现的接口很多  是非常多的强大的一个资源处理器
// EmbeddedValueResolverAware:它能处理占位符~~~~
// 它的afterPropertiesSet()方法里做了非常多的事~~~~
public class ResourceHttpRequestHandler extends WebContentGenerator
    implements HttpRequestHandler, EmbeddedValueResolverAware, InitializingBean, CorsConfigurationSource {
    ...
}

@Configuration
@EnableWebMvc
public class WebMvcConfig extends WebMvcConfigurerAdapter {
    // 服务端：把HelloService暴露出去  服务端对接口必须有具体的实现~
    @Bean("/helloService") // 注意这里的BeanName请使用/路径的形式  （推荐使用这种方式，简单明了~~~）
    public HttpInvokerServiceExporter helloServiceExporter(HelloService helloService) {
        HttpInvokerServiceExporter exporter = new HttpInvokerServiceExporter();
        exporter.setService(helloService); // 真正的实现类  这个对服务端来说是必须的
        exporter.setServiceInterface(HelloService.class); // 必须设置一个接口~~~~
        return exporter;
    }
}

    //@Autowired
    //private ServletContext servletContext;
    // 需要注意的是：在Spring的config里面，是不允许通过servletContext再向web容器内添加servlet的~~~~
    // 注册一个HttpRequestHandlerServlet 来专门处理client端的请求
    // 要求：此servletName必须是上面对应的Bean的BeanName~~~~
    //servletContext.addServlet("helloServiceExporter", new HttpRequestHandlerServlet()).addMapping("/helloService");
// 这里在SPI里完成Servlet的注册~~~
public class MyWebAppInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {
    @Override
    protected void registerDispatcherServlet(ServletContext servletContext) {
        super.registerDispatcherServlet(servletContext);
        // 注册我们自己的Servlet 因为这个servlet在jar包里面  所以这里只能通过编程的方式注册~~~~
        // 请保证这个servlet的名字和BeanName相同~~  helloServiceExporter：为Bean的名字~~~
        servletContext.addServlet("helloServiceExporter", new HttpRequestHandlerServlet()).addMapping("/helloService");
        servletContext.addServlet("helloServiceExporter", new HttpRequestHandlerServlet()).addMapping("/helloService");
    }
}

@Configuration
public class RootConfig {
    @Bean("helloServiceFactoryBean")
    public HttpInvokerProxyFactoryBean helloServiceFactoryBean() {
        HttpInvokerProxyFactoryBean factoryBean = new HttpInvokerProxyFactoryBean();
        factoryBean.setServiceInterface(HelloService.class);
        factoryBean.setServiceUrl("http://localhost:8080/demo_war_war/helloService");
        return factoryBean;
    }
}

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(classes = {RootConfig.class, AsyncConfig.class})
public class TestSpringBean {
    @Autowired
    private HelloService helloService;
    @Test
    public void test1() {
        System.out.println(helloService); // HTTP invoker proxy for service URL [http://localhost:8080/demo_war_war/helloService]
        System.out.println(helloService.getClass()); //class com.sun.proxy.$Proxy30
        System.out.println(helloService.hello()); //service hello
        System.out.println("结束~");
    }
}

@HandlesTypes(value={XXX.class})
public class MyServletContainerInitializer implements ServletContainerInitializer {
  @Override
  public void onStartup(Set<Class<?>> arg0, ServletContext sc) throws ServletException {
    // 在这里里面完成所有的注册工作~~~~
  }
}

@Controller("/demoHttpRequestHandler")
public class DemoHttpRequestHandler implements HttpRequestHandler {
    @Override
    public void handleRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("this my DemoHttpRequestHandler");
        response.getWriter().write("this my DemoHttpRequestHandler");
    }
}

@WebServlet("/myServlet")
public class MyServlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        super.service(req, resp);
    }
}