从DispatcherServlet说自定义访问处理-白红宇

从DispatcherServlet说自定义访问处理

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发布时间：2019-05-25

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从DispatcherServlet说自定义访问处理

DispatcherServlet是springMvc处理请求的核心逻辑,简单描述一下处理流程,

首先需要在web.xml中配置该Servlet的服务路径,默认是/*所有路径,这样web请求就从Servlet

容器把控制权流转到DispatcherServlet,看一下DispatcherServlet的核心方法:

protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {	//...省略部分代码,看到这里把请求委托给doDispatch	try {		doDispatch(request, response);	}	//...省略部分代码}

继续看一下doDispatch:

//省略部分代码,根据用户的请求,查找对应得handlermappedHandler = getHandler(processedRequest);//根据handler查找对应得适配器HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

再来看一下:

protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {	//遍历handlerMappings查找符合的类	if (this.handlerMappings != null) {		for (HandlerMapping mapping : this.handlerMappings) {			HandlerExecutionChain handler = mapping.getHandler(request);			if (handler != null) {				return handler;			}		}	}	return null;}

再看一下handler适配器种类:

HandlerAdapter (org.springframework.web.servlet)	HttpRequestHandlerAdapter (org.springframework.web.servlet.mvc)	SimpleServletHandlerAdapter (org.springframework.web.servlet.handler)	AbstractHandlerMethodAdapter (org.springframework.web.servlet.mvc.method)		RequestMappingHandlerAdapter (org.springframework.web.servlet.mvc.method.annotation)	SimpleControllerHandlerAdapter (org.springframework.web.servlet.mvc)

适配HttpRequestHandler,Servlet,Controller,@RequestMapping

接下来看一下如何把HandlerMapping和HandlerAdapter配置到spring中:

private void initHandlerMappings(ApplicationContext context) {	this.handlerMappings = null;	if (this.detectAllHandlerMappings) {		//查找子父容器中所有类型是HandlerMapping的类		Map
   
     matchingBeans =				BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);		if (!matchingBeans.isEmpty()) {			this.handlerMappings = new ArrayList<>(matchingBeans.values());			// We keep HandlerMappings in sorted order.			AnnotationAwareOrderComparator.sort(this.handlerMappings);		}	}	else {		try {			HandlerMapping hm = context.getBean(HANDLER_MAPPING_BEAN_NAME, HandlerMapping.class);			//保存到字段中			this.handlerMappings = Collections.singletonList(hm);		}		catch (NoSuchBeanDefinitionException ex) {			// Ignore, we'll add a default HandlerMapping later.		}	}	//省略部分代码}

初始化HandlerAdapter和上面类似:

private void initHandlerAdapters(ApplicationContext context) {	this.handlerAdapters = null;	if (this.detectAllHandlerAdapters) {		// Find all HandlerAdapters in the ApplicationContext, including ancestor contexts.		Map
   
     matchingBeans =				BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerAdapter.class, true, false);		if (!matchingBeans.isEmpty()) {			this.handlerAdapters = new ArrayList<>(matchingBeans.values());			// We keep HandlerAdapters in sorted order.			AnnotationAwareOrderComparator.sort(this.handlerAdapters);		}	}	else {		try {			HandlerAdapter ha = context.getBean(HANDLER_ADAPTER_BEAN_NAME, HandlerAdapter.class);			this.handlerAdapters = Collections.singletonList(ha);		}		catch (NoSuchBeanDefinitionException ex) {			// Ignore, we'll add a default HandlerAdapter later.		}	}	//省略部分代码}

来实践一下:

自定义一个类:

public class MyController implements HttpRequestHandler {    @Override    public void handleRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        response.setHeader(HttpHeaders.CONTENT_TYPE, MimeTypeUtils.TEXT_PLAIN_VALUE);        ServletOutputStream os = response.getOutputStream();        BufferedOutputStream bos = new BufferedOutputStream(os);        bos.write("my controller...".getBytes());        bos.flush();    }}

适配器配置:

@Configurationpublic class MyMappingConfig {    @Bean    public HandlerMapping handlerMapping(){        SimpleUrlHandlerMapping mapping = new SimpleUrlHandlerMapping();        Map
   
     map = new HashMap<>();        map.put("/test/test.html", new MyController());        mapping.setUrlMap(map);        mapping.setOrder(Ordered.HIGHEST_PRECEDENCE + 100);        return mapping;    }}

结果展示: