Spring中HandlerAdapter接口源码解析
作者：立小研先森
这篇文章主要介绍了Spring中HandlerAdapter接口源码解析,HandlerAdapter是一个适配器接口类,适配器模式是指两个不兼容接口之间的桥梁,要想让一个接口使用另外一个接口的实现中间可以加一层适配器类,需要的朋友可以参考下
HandlerAdapter接口源码
HandlerAdapter是一个适配器接口类，适配器模式是指两个不兼容接口之间的桥梁，要想让一个接口使用另外一个接口的实现中间可以加一层适配器类；举个例子：笔记本没有网线接口，那我想连接网线接通网络如何实现呢？我可以买一个以太网转换器，网线插入转换器上，转换器插入笔记本上就实现了连接网络的功能，那这个转换器起到的就是一个适配器的作用；在接口访问控制器方法的时候是通过HandlerAdapter接口的实现类来进行的，本文以最常用的RequestMappingHandlerAdapter适配器类为主线索来讲解。
接口的源码如下：
public interface HandlerAdapter {
/**
* 判定是否支持传入的handler
*/
boolean supports(Object handler);
/**
* 使用给定的handler来处理当前request请求
*/
@Nullable
ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception;
/**
* 返回handler最后修改的时间
*/
long getLastModified(HttpServletRequest request, Object handler);
}HandlerAdapter的实现类有多个，我们以RequestMappingHandlerAdapter适配器类为主线索，而此类又是AbstractHandlerMethodAdapter抽象类的子类；
如下是RequestMappingHandlerAdapter适配器类的关系图
1.HandlerAdapter接口的初始化
容器加载时DispatcherServlet中的初始化方法initStrategies方法会被调用，里面的
/**
* 容器中HandlerAdapter接口实现类集合
**/
@Nullable
private List<HandlerAdapter> handlerAdapters;
/**
* 初始化handlerAdapters集合，如果在BeanFactory中没有HandlerAdapter，那么将使用默认
* 的SimpleControllerHandlerAdapter
*/
private void initHandlerAdapters(ApplicationContext context) {
this.handlerAdapters = null;
//判定是否检测所有的HandlerAdapter
if (this.detectAllHandlerAdapters) {
//查看容器中所有实现了HandlerAdapter的bean
Map<String, HandlerAdapter> 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.
}
}
// Ensure we have at least some HandlerAdapters, by registering
// default HandlerAdapters if no other adapters are found.
if (this.handlerAdapters == null) {
this.handlerAdapters = getDefaultStrategies(context, HandlerAdapter.class);
if (logger.isTraceEnabled()) {
logger.trace("No HandlerAdapters declared for servlet '" + getServletName() +
"': using default strategies from DispatcherServlet.properties");
}
}
}
上面的代码是从容器中获取HandlerAdapter接口实现类的bean集合
2.RequestMappingHandlerAdapter处理request请求
前端发送过来一个request请求首先进入DispatcherServlet的doService方法，再进入doDispatch方法，那我们看下doDispatch方法的源码：
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
HttpServletRequest processedRequest = request;
HandlerExecutionChain mappedHandler = null;
boolean multipartRequestParsed = false;
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
try {
ModelAndView mv = null;
Exception dispatchException = null;
try {
processedRequest = checkMultipart(request);
multipartRequestParsed = (processedRequest != request);
//通过request请求获取HandlerExecutionChain处理器执行程序链
//也即通过request获取匹配的HandlerMapping实现类，通过实现类的getHandler
//方法获取HandlerExecutionChain处理程序执行器链类，里面包含了请求对应的HandlerMethod
//及对应的所有拦截器
// Determine handler for the current request.
mappedHandler = getHandler(processedRequest);
if (mappedHandler == null) {
noHandlerFound(processedRequest, response);
return;
}
//根据上面获取到的HandlerMethod获取匹配到的适配器类
// Determine handler adapter for the current request.
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
// Process last-modified header, if supported by the handler.
String method = request.getMethod();
boolean isGet = "GET".equals(method);
if (isGet || "HEAD".equals(method)) {
long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
return;
}
}
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
//根据适配器对象调用具体的方法（如：RequestMappingHandlerAdapter）
// Actually invoke the handler.
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
applyDefaultViewName(processedRequest, mv);
mappedHandler.applyPostHandle(processedRequest, response, mv);
}
catch (Exception ex) {
dispatchException = ex;
}
catch (Throwable err) {
// As of 4.3, we're processing Errors thrown from handler methods as well,
// making them available for @ExceptionHandler methods and other scenarios.
dispatchException = new NestedServletException("Handler dispatch failed", err);
}
processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
}
catch (Exception ex) {
triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
}
catch (Throwable err) {
triggerAfterCompletion(processedRequest, response, mappedHandler,
new NestedServletException("Handler processing failed", err));
}
finally {
if (asyncManager.isConcurrentHandlingStarted()) {
// Instead of postHandle and afterCompletion
if (mappedHandler != null) {
mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
}
}
else {
// Clean up any resources used by a multipart request.
if (multipartRequestParsed) {
cleanupMultipart(processedRequest);
}
}
}
}
跳出本文分析的正文流程，来分析下AbstractHandlerMethodAdapter适配器类；
Abstract base class for {@link HandlerAdapter} implementations that support
handlers of type {@link HandlerMethod}.
源码注解说明类抽象类的实现support方法判定是否支持HandlerMethod;
/**
* 判定适配器类是否支持HandlerMethod
**/
@Override
public final boolean supports(Object handler) {
return (handler instanceof HandlerMethod && supportsInternal((HandlerMethod) handler));
}
getHandlerAdapter方法实现源码：
/**
* 获取可以处理handler的HandlerAdapter适配器类
*/
protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
if (this.handlerAdapters != null) {
for (HandlerAdapter adapter : this.handlerAdapters) {
//判定适配器类是否支持HandlerMethod
if (adapter.supports(handler)) {
return adapter;
}
}
}
throw new ServletException("No adapter for handler [" + handler +
"]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler");
}
ha.handle(processedRequest, response, mappedHandler.getHandler());方法会调用AbstractHandlerMethodAdapter适配器类的handle方法：
@Override
@Nullable
public final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
throws Exception {
return handleInternal(request, response, (HandlerMethod) handler);
}
而handleInternal方法最终会调用RequestMappingHandlerAdapter类的handlerInternal方法：
@Override
protected ModelAndView handleInternal(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
ModelAndView mav;
checkRequest(request);
// Execute invokeHandlerMethod in synchronized block if required.
if (this.synchronizeOnSession) {
HttpSession session = request.getSession(false);
if (session != null) {
Object mutex = WebUtils.getSessionMutex(session);
synchronized (mutex) {
mav = invokeHandlerMethod(request, response, handlerMethod);
}
}
else {
// No HttpSession available -> no mutex necessary
mav = invokeHandlerMethod(request, response, handlerMethod);
}
}
else {
// No synchronization on session demanded at all...
mav = invokeHandlerMethod(request, response, handlerMethod);
}
if (!response.containsHeader(HEADER_CACHE_CONTROL)) {
if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {
applyCacheSeconds(response, this.cacheSecondsForSessionAttributeHandlers);
}
else {
prepareResponse(response);
}
}
return mav;
}
handleInternal方法又会调用invokeHandlerMethod方法：
@Nullable
protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
ServletWebRequest webRequest = new ServletWebRequest(request, response);
try {
WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);
//创建HandlerMethod的子类ServletInvocableHandlerMethod的实例对象
ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
if (this.argumentResolvers != null) {
//设置参数解析器
invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
}
if (this.returnValueHandlers != null) {
//设置返回值处理程序
invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);
}
invocableMethod.setDataBinderFactory(binderFactory);
invocableMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer);
ModelAndViewContainer mavContainer = new ModelAndViewContainer();
mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));
modelFactory.initModel(webRequest, mavContainer, invocableMethod);
mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);
AsyncWebRequest asyncWebRequest = WebAsyncUtils.createAsyncWebRequest(request, response);
asyncWebRequest.setTimeout(this.asyncRequestTimeout);
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
asyncManager.setTaskExecutor(this.taskExecutor);
asyncManager.setAsyncWebRequest(asyncWebRequest);
asyncManager.registerCallableInterceptors(this.callableInterceptors);
asyncManager.registerDeferredResultInterceptors(this.deferredResultInterceptors);
if (asyncManager.hasConcurrentResult()) {
Object result = asyncManager.getConcurrentResult();
mavContainer = (ModelAndViewContainer) asyncManager.getConcurrentResultContext()[0];
asyncManager.clearConcurrentResult();
LogFormatUtils.traceDebug(logger, traceOn -> {
String formatted = LogFormatUtils.formatValue(result, !traceOn);
return "Resume with async result [" + formatted + "]";
});
invocableMethod = invocableMethod.wrapConcurrentResult(result);
}
//调用ServletInvocableHandlerMethod类的invokeAndHandle方法
invocableMethod.invokeAndHandle(webRequest, mavContainer);
if (asyncManager.isConcurrentHandlingStarted()) {
return null;
}
return getModelAndView(mavContainer, modelFactory, webRequest);
}
finally {
webRequest.requestCompleted();
}
}
上面的方法会涉及到参数解析器的初始化、返回值处理程序的初始化，那这些返回值处理程序和参数解析程序如何初始化的呢？RequestMappingHandlerAdapter类实现了InitializingBean接口，该类加载后会调用afterPropertiesSet方法，会对这些处理程序进行初始化；
@Override
public void afterPropertiesSet() {
// Do this first, it may add ResponseBody advice beans
initControllerAdviceCache();
//参数解析器初始化
if (this.argumentResolvers == null) {
List<HandlerMethodArgumentResolver> resolvers = getDefaultArgumentResolvers();
this.argumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
}
//InitBinder的参数解析器初始化
if (this.initBinderArgumentResolvers == null) {
List<HandlerMethodArgumentResolver> resolvers = getDefaultInitBinderArgumentResolvers();
this.initBinderArgumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
}
//返回值处理程序初始化
if (this.returnValueHandlers == null) {
List<HandlerMethodReturnValueHandler> handlers = getDefaultReturnValueHandlers();
this.returnValueHandlers = new HandlerMethodReturnValueHandlerComposite().addHandlers(handlers);
}
}
调用ServletInvocableHandlerMethod.invokeAndHandle方法源码如下：
public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer,
Object... providedArgs) throws Exception {
//调用控制器方法，获取返回值
Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);
setResponseStatus(webRequest);
if (returnValue == null) {
if (isRequestNotModified(webRequest) || getResponseStatus() != null || mavContainer.isRequestHandled()) {
disableContentCachingIfNecessary(webRequest);
mavContainer.setRequestHandled(true);
return;
}
}
else if (StringUtils.hasText(getResponseStatusReason())) {
mavContainer.setRequestHandled(true);
return;
}
mavContainer.setRequestHandled(false);
Assert.state(this.returnValueHandlers != null, "No return value handlers");
try {
//将返回值交给HandlerMethodReturnValueHandlerComposite返回值代理类
//选择合适的HandlerMethodReturnValueHandler实现类处理返回值
this.returnValueHandlers.handleReturnValue(
returnValue, getReturnValueType(returnValue), mavContainer, webRequest);
}
catch (Exception ex) {
if (logger.isTraceEnabled()) {
logger.trace(formatErrorForReturnValue(returnValue), ex);
}
throw ex;
}
}
调用InvocableHandlerMethod.invokeForRequest方法源码：
/**
* 获取request请求参数，调用控制器方法
**/
@Nullable
public Object invokeForRequest(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
Object... providedArgs) throws Exception {
//获取request请求方法的参数
Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);
if (logger.isTraceEnabled()) {
logger.trace("Arguments: " + Arrays.toString(args));
}
return doInvoke(args);
}
调用InvocableHandlerMethod.doInvoke(Object… args)方法源码：
/**
* 使用给定的参数调用控制器方法
**/
@Nullable
protected Object doInvoke(Object... args) throws Exception {
ReflectionUtils.makeAccessible(getBridgedMethod());
try {
//调用真实最终的控制器方法，并返回执行后的结果
return getBridgedMethod().invoke(getBean(), args);
}
catch (IllegalArgumentException ex) {
assertTargetBean(getBridgedMethod(), getBean(), args);
String text = (ex.getMessage() != null ? ex.getMessage() : "Illegal argument");
throw new IllegalStateException(formatInvokeError(text, args), ex);
}
catch (InvocationTargetException ex) {
// Unwrap for HandlerExceptionResolvers ...
Throwable targetException = ex.getTargetException();
if (targetException instanceof RuntimeException) {
throw (RuntimeException) targetException;
}
else if (targetException instanceof Error) {
throw (Error) targetException;
}
else if (targetException instanceof Exception) {
throw (Exception) targetException;
}
else {
throw new IllegalStateException(formatInvokeError("Invocation failure", args), targetException);
}
}
}
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