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

// @since 第一版Spring MVC就有了  所以这个接口是非常古老的接口~~~也是Spring MVC最早期的实现方式
@FunctionalInterface
public interface Controller {
  @Nullable
  ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) throws Exception;
}

@org.springframework.stereotype.Controller("/democontroller") // 注意此处需要以/开头，表示使用BeanNameURLHandlerMapping的方式处理
public class DemoController implements Controller {
    @Override
    public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) throws Exception {
        System.out.println("this my demo controller~");
        return new ModelAndView("index");
    }
}

this my demo controller~

@org.springframework.stereotype.Controller("/democontroller") // 注意此处需要以/开头，表示使用BeanNameURLHandlerMapping的方式处理
public class DemoController implements Controller {
    @Override
    public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) throws Exception {
        System.out.println("this my demo controller~");
        response.getWriter().write("this my demo controller from body");
        return null; // 返回null告诉视图渲染  直接把body里面的内容输出浏览器即可
    }
}

// 关于WebContentGenerator  这里暂时略过
// AbstractController继承了org.springframework.web.servlet.support.WebContentGenerator抽象类。提供了针对http请求的设定
public abstract class AbstractController extends WebContentGenerator implements Controller {
  ...
  @Override
  @Nullable
  public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response)
      throws Exception {
    // 如果请求是OPTIONS请求  那就直接return null了  它一般用于跨域  所以设置上Allow这个请求头
    //getAllowHeader()方法在WebContentGenerator里
    if (HttpMethod.OPTIONS.matches(request.getMethod())) {
      response.setHeader("Allow", getAllowHeader());
      return null;
    }
    // 指定supportedMethods后，看看这个request是否合法
    checkRequest(request);
    // 处理response的cache缓存和缓存时间等等
    prepareResponse(response);
    // Execute handleRequestInternal in synchronized block if required.
    // 如果有需要，会给这个请求上锁~~~~在锁内执行
    if (this.synchronizeOnSession) {
      HttpSession session = request.getSession(false);
      if (session != null) {
        Object mutex = WebUtils.getSessionMutex(session);
        synchronized (mutex) {
          return handleRequestInternal(request, response);
        }
      }
    }
    return handleRequestInternal(request, response);
  } 
  // 子类实现这个抽象方法即可~~~~~
  @Nullable
  protected abstract ModelAndView handleRequestInternal(HttpServletRequest request, HttpServletResponse response)
      throws Exception;
}

// @since 1.1.1  实现了接口InitializingBean
public class ServletWrappingController extends AbstractController
    implements BeanNameAware, InitializingBean, DisposableBean {
  ...
  @Override
  public void afterPropertiesSet() throws Exception {
    // 必须制定它关联的是哪个Servlet
    if (this.servletClass == null) {
      throw new IllegalArgumentException("'servletClass' is required");
    }
    // 如果没有指定servlet的名字，就用beanName作为名字~
    if (this.servletName == null) {
      this.servletName = this.beanName;
    }
    // 对servlet进行init方法  初始化
    this.servletInstance = ReflectionUtils.accessibleConstructor(this.servletClass).newInstance();
    this.servletInstance.init(new DelegatingServletConfig());
  }
  // 最终请求是交给了这个servlet去真正处理的~~~~~
  @Override
  protected ModelAndView handleRequestInternal(HttpServletRequest request, HttpServletResponse response)
      throws Exception {
    Assert.state(this.servletInstance != null, "No Servlet instance");
    this.servletInstance.service(request, response);
    return null;
  }
}

rd.include(request, response);
rd.forward(request, response);

public class ParameterizableViewController extends AbstractController {
  // 由此课件，默认只支持get和Head方法
  public ParameterizableViewController() {
    super(false);
    setSupportedMethods(HttpMethod.GET.name(), HttpMethod.HEAD.name());
  }
  ...
  // 支持redirect:这样的前缀
  @Nullable
  public String getViewName() {
    if (this.view instanceof String) {
      String viewName = (String) this.view;
      if (getStatusCode() != null && getStatusCode().is3xxRedirection()) {
        return viewName.startsWith("redirect:") ? viewName : "redirect:" + viewName;
      } else {
        return viewName;
      }
    }
    return null;
  }
  ...
}

<bean name="/index.action" class="org.springframework.web.servlet.mvc.ParameterizableViewController">
     <property name="viewName" value="/index.jsp"/>
</bean>

<bean id="viewMappings" class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping" >
  <!-- 默认处理器 -->
  <property name="defaultHandler">  
            <bean name="index" class="org.springframework.web.servlet.mvc.UrlFilenameViewController" />  
     </property>   
</bean>

    @Bean("/*") //"/*"会把它注册为一个默认的handler~
    public UrlFilenameViewController urlFilenameViewController() {
        UrlFilenameViewController controller = new UrlFilenameViewController();
        controller.setPrefix("/api/v1/");
        controller.setSuffix(".do");
        return controller;
    }

// @since 2.0  它是Spring2.0后才出来的
// 用于处理HTTP请求的组件的纯处理程序接口，类似于`servlet`
@FunctionalInterface
public interface HttpRequestHandler {
  // Process the given request, generating a response
  // 处理这个request 生成一个response
  void handleRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException;
}

<mvc:default-servlet-handler />