上篇文章走读了springboot中消息处理进入到servlet里了，这次，具体走读了请求消息在servlet里是怎么处理的。这里主要补充servlet和springmvc相关的知识。
servlet相关知识
servlet生命周期
servlet生命周期在servlet的代码里能很清楚的体现出来。代码为：
public interface Servlet {
//servlet 初始化，这里摘录了部分注释
/**
* The servlet container calls the init method exactly once
* after instantiating the servlet. The init method must
* complete successfully before the servlet can receive any requests.
*/
public void init(ServletConfig config) throws ServletException;
/**
*
* Returns a {@link ServletConfig} object, which contains initialization and
* startup parameters for this servlet. The ServletConfig
* object returned is the one passed to the init method.
*
*
* Implementations of this interface are responsible for storing the
* ServletConfig object so that this method can return it. The
* {@link GenericServlet} class, which implements this interface, already
* does this.
*
* @return the ServletConfig object that initializes this
* servlet
*
* @see #init
*/
public ServletConfig getServletConfig();
/**
* Called by the servlet container to allow the servlet to respond to a
* request.
*
*
* This method is only called after the servlet's init() method
* has completed successfully.
*
*
* The status code of the response always should be set for a servlet that
* throws or sends an error.
*/
//真正的处理请求
public void service(ServletRequest req, ServletResponse res)
throws ServletException, IOException;
/**
* Returns information about the servlet, such as author, version, and
* copyright.
*
*
* The string that this method returns should be plain text and not markup
* of any kind (such as HTML, XML, etc.).
*
* @return a String containing servlet information
*/
public String getServletInfo();
/**
* Called by the servlet container to indicate to a servlet that the servlet
* is being taken out of service. This method is only called once all
* threads within the servlet's service method have exited or
* after a timeout period has passed. After the servlet container calls this
* method, it will not call the service method again on this
* servlet.
*
*
* This method gives the servlet an opportunity to clean up any resources
* that are being held (for example, memory, file handles, threads) and make
* sure that any persistent state is synchronized with the servlet's current
* state in memory.
*/
public void destroy();
}
从代码中可以看出，servlet生命周期是init-->service-->destory;
具体过程
1、加载与实例化（new）
servlet在启动时或第一次接收到请求时，会到内存中去查询一下是否有servlet实例，有则取出来，没有则new一个出来。
2、初始化（init）
在创建servlet之后，会调用init方法，进行初始化，该步主要是为接收处理请求做一些必要的准备，只会执行一次。
3、提供服务（service）
servlet实例接收客户端的ServletRequest信息，通过request的信息，调用相应的doXXX()方法，并返回response。
4、销毁（destroy）
servlet容器在关闭时，销毁servlet实例。只会执行一次
后面以SpringMVC为例来具体说明servlet的生命周期。
SpringMVC相关知识
这里只简单的罗列一下SpringMVC中M，V，C 的关系。如图：
1、客户端发送request请求进入到分发器中，DispatcherServlet中。
2、分发器通过uri到控制器映射中去查询相应的处理器（HandlerMapping）。
3、分发器拿到对应的处理器之后，调用处理器响应的接口，返回数据及对应的视图。
4、分发器拿到处理器返回的modelAndView后，查找相应的视同解析器进行渲染。
5、视图将渲染好的结果返回给终端用户进行展示。
下面通过源码的方式看springboot中关于springMVC和servlet相关的实现。
请求消息在SpringMVC中的流向
servlet的创建过程（new）
源码阅读接上篇文章，现在到了servlet的处理了。在这之前，看servlet在springboot中是如何完成实例化及初始化的。
首先看servlet是如何new出来的。springboot中，使用的是dispatcherServlet，DispatcherServlet的类的继承关系图如下
该类使用自动装配的方式初始化一个beanName为
dispatcherServlet的bean。类名为DispatcherServletAutoConfiguration,具体代码如下:
@Bean(name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
public DispatcherServlet dispatcherServlet(WebMvcProperties webMvcProperties) {
DispatcherServlet dispatcherServlet = new DispatcherServlet();
dispatcherServlet.setDispatchOptionsRequest(webMvcProperties.isDispatchOptionsRequest());
dispatcherServlet.setDispatchTraceRequest(webMvcProperties.isDispatchTraceRequest());
dispatcherServlet.setThrowExceptionIfNoHandlerFound(webMvcProperties.isThrowExceptionIfNoHandlerFound());
dispatcherServlet.setPublishEvents(webMvcProperties.isPublishRequestHandledEvents());
dispatcherServlet.setEnableLoggingRequestDetails(webMvcProperties.isLogRequestDetails());
return dispatcherServlet;
}
这里就是直接new出来一个servlet，并初始化相关的配置。
这个servlet对象是如何注册到tomcat容器里呢，这里就有下面一个名称为dispatcherServletRegistration的bean来做的事情了，具体代码为：
@Configuration(proxyBeanMethods = false)
@Conditional(DispatcherServletRegistrationCondition.class)
@ConditionalOnClass(ServletRegistration.class)
@EnableConfigurationProperties(WebMvcProperties.class)
@Import(DispatcherServletConfiguration.class)
protected static class DispatcherServletRegistrationConfiguration {
@Bean(name = DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME)
@ConditionalOnBean(value = DispatcherServlet.class, name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
public DispatcherServletRegistrationBean dispatcherServletRegistration(DispatcherServlet dispatcherServlet,
WebMvcProperties webMvcProperties, ObjectProvider multipartConfig) {
DispatcherServletRegistrationBean registration = new DispatcherServletRegistrationBean(dispatcherServlet,
webMvcProperties.getServlet().getPath());
registration.setName(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME);
registration.setLoadOnStartup(webMvcProperties.getServlet().getLoadOnStartup());
multipartConfig.ifAvailable(registration::setMultipartConfig);
return registration;
}
}
这里需要看一下DispatcherServletRegistrationBean类的继承关系图了。
从图中看出，
DispatcherServletRegistrationBean实现了接口ServletContextInitializer，SpringBoot内嵌tomcat代码走读（一）中，有对这个接口的调用代码。this.webServer = factory.getWebServer(getSelfInitializer());在获取webServer时，传入想改接口的调用。
接下来我们看DispatcherServletRegistrationBean的
OnStartup的实现,该方法实现在其父类RegistrationBean中。
@Override
public final void onStartup(ServletContext servletContext) throws ServletException {
String description = getDescription();
if (!isEnabled()) {
logger.info(StringUtils.capitalize(description) + " was not registered (disabled)");
return;
}
register(description, servletContext);
}
主要方法register的实现在其子类DynamicRegistrationBean中。
@Override
protected final void register(String description, ServletContext servletContext) {
D registration = addRegistration(description, servletContext);
if (registration == null) {
logger.info(StringUtils.capitalize(description) + " was not registered (possibly already registered?)");
return;
}
configure(registration);
}
其主要方法addRegistration在其子类ServletRegistrationBean中实现。
@Override
protected ServletRegistration.Dynamic addRegistration(String description, ServletContext servletContext) {
String name = getServletName();
return servletContext.addServlet(name, this.servlet);
}
servletContext为ApplicationContextFacade，addServlet代码为:
@Override
public ServletRegistration.Dynamic addServlet(String servletName,
Servlet servlet) {
if (SecurityUtil.isPackageProtectionEnabled()) {
return (ServletRegistration.Dynamic) doPrivileged("addServlet",
new Class[]{String.class, Servlet.class},
new Object[]{servletName, servlet});
} else {
return context.addServlet(servletName, servlet);
}
}
Tomcat的ApplicationContext里加入servlet。代码为:
private ServletRegistration.Dynamic addServlet(String servletName, String servletClass,
Servlet servlet, Map initParams) throws IllegalStateException {
if (servletName == null || servletName.equals("")) {
throw new IllegalArgumentException(sm.getString(
"applicationContext.invalidServletName", servletName));
}
if (!context.getState().equals(LifecycleState.STARTING_PREP)) {
//TODO Spec breaking enhancement to ignore this restriction
throw new IllegalStateException(
sm.getString("applicationContext.addServlet.ise",
getContextPath()));
}
Wrapper wrapper = (Wrapper) context.findChild(servletName);
// Assume a 'complete' ServletRegistration is one that has a class and
// a name
if (wrapper == null) {
wrapper = context.createWrapper();
wrapper.setName(servletName);
context.addChild(wrapper);
} else {
if (wrapper.getName() != null &&
wrapper.getServletClass() != null) {
if (wrapper.isOverridable()) {
wrapper.setOverridable(false);
} else {
return null;
}
}
}
ServletSecurity annotation = null;
if (servlet == null) {
wrapper.setServletClass(servletClass);
Class clazz = Introspection.loadClass(context, servletClass);
if (clazz != null) {
annotation = clazz.getAnnotation(ServletSecurity.class);
}
} else {
wrapper.setServletClass(servlet.getClass().getName());
wrapper.setServlet(servlet);
if (context.wasCreatedDynamicServlet(servlet)) {
annotation = servlet.getClass().getAnnotation(ServletSecurity.class);
}
}
if (initParams != null) {
for (Map.Entry initParam: initParams.entrySet()) {
wrapper.addInitParameter(initParam.getKey(), initParam.getValue());
}
}
ServletRegistration.Dynamic registration =
new ApplicationServletRegistration(wrapper, context);
if (annotation != null) {
registration.setServletSecurity(new ServletSecurityElement(annotation));
}
return registration;
}
这里主要逻辑是向tomcat里添加servlet。前面我们知道tomcat的体系结构，为了提高扩展性，tomcat里分层定义了很多组件，在最内层组件为Wrapper，这里就是想warapper中添加servlet。这里用默认的wrapper，StandardWrapper，具体代码为：
@Override
public void setServlet(Servlet servlet) {
instance = servlet;
}
至此，tomcat的基本功能就有了，servlet也有了。但是，当前的servlet还不能用，因为从上面的servlet生命周期看，这只完成了第一步，还有init这一步没有完成。那么，init在什么时候呢。继续看代码。
从代码中可以知道，当第一个请求过来时，servlet才进行init操作。接上篇文章的请求流程图，这里看请求在servlet中的流向。这里流程图从StandardWrapperValue的invoke方法开始进行。
调用流程图如下：
按照流程图，我们走读一下代码，具体看看相关的处理逻辑。
首先看invoke方法里的代码逻辑。
public final void invoke(Request request, Response response)
throws IOException, ServletException {
// Initialize local variables we may need
boolean unavailable = false;
Throwable throwable = null;
// This should be a Request attribute...
long t1=System.currentTimeMillis();
requestCount.incrementAndGet();
StandardWrapper wrapper = (StandardWrapper) getContainer();
Servlet servlet = null;
Context context = (Context) wrapper.getParent();
//去掉一些与主流程关系不太大的代码
.......
// Allocate a servlet instance to process this request
try {
if (!unavailable) {
servlet = wrapper.allocate();
}
} catch (UnavailableException e) {
。。。。。。
MessageBytes requestPathMB = request.getRequestPathMB();
DispatcherType dispatcherType = DispatcherType.REQUEST;
if (request.getDispatcherType()==DispatcherType.ASYNC) dispatcherType = DispatcherType.ASYNC;
request.setAttribute(Globals.DISPATCHER_TYPE_ATTR,dispatcherType);
request.setAttribute(Globals.DISPATCHER_REQUEST_PATH_ATTR,
requestPathMB);
// Create the filter chain for this request
//获取一个ApplicationFilterChain
ApplicationFilterChain filterChain =
ApplicationFilterFactory.createFilterChain(request, wrapper, servlet);
// Call the filter chain for this request
// NOTE: This also calls the servlet's service() method
Container container = this.container;
try {
if ((servlet != null) && (filterChain != null)) {
。。。。。。
} else {
// 开始处理请求
if (request.isAsyncDispatching()) {
request.getAsyncContextInternal().doInternalDispatch();
} else {
// 开始处理请求
filterChain.doFilter
(request.getRequest(), response.getResponse());
}
}
}
} catch (ClientAbortException | CloseNowException e) {
。。。。。。
}
}
上面代码比较长，做了一下删减。主要的功能是初始化servlet（init）和具体调用servlet的service方法。
servlet的init方法在allocate()中调用。service方法在doFilter中调用。
servlet初始化过程（init）
具体看下allocate()的实现。
public Servlet allocate() throws ServletException {
// If we are currently unloading this servlet, throw an exception
if (unloading) {
throw new ServletException(sm.getString("standardWrapper.unloading", getName()));
}
boolean newInstance = false;
// If not SingleThreadedModel, return the same instance every time
//该处并不知道singleThreadModel的值，使用默认值，在loadServlet中会有确定的赋值，但SingleThreadedModel已经被废弃，这里也走不到该分支中，所以，springboot中的servlet是一个实例。
//当为SingleThreadedModel类型时，容器中会有多个servlet实例，默认最多20个。
if (!singleThreadModel) {
// Load and initialize our instance if necessary
//前文提到了instance在bean初始化时已经将instance赋值了，这里instance！=null,但instanceInitialized=false
if (instance == null || !instanceInitialized) {
synchronized (this) {
//该分支在该处不会走到。
if (instance == null) {
。。。。。。
}
if (!instanceInitialized) {
//init servlet
initServlet(instance);
}
}
}
if (singleThreadModel) {
if (newInstance) {
// Have to do this outside of the sync above to prevent a
// possible deadlock
synchronized (instancePool) {
instancePool.push(instance);
nInstances++;
}
}
} else {
if (log.isTraceEnabled()) {
log.trace(" Returning non-STM instance");
}
// For new instances, count will have been incremented at the
// time of creation
if (!newInstance) {
countAllocated.incrementAndGet();
}
return instance;
}
}
synchronized (instancePool) {
while (countAllocated.get() >= nInstances) {
// Allocate a new instance if possible, or else wait
if (nInstances < maxInstances) {
try {
instancePool.push(loadServlet());
nInstances++;
} catch (ServletException e) {
throw e;
} catch (Throwable e) {
ExceptionUtils.handleThrowable(e);
throw new ServletException(sm.getString("standardWrapper.allocate"), e);
}
} else {
try {
instancePool.wait();
} catch (InterruptedException e) {
// Ignore
}
}
}
if (log.isTraceEnabled()) {
log.trace(" Returning allocated STM instance");
}
countAllocated.incrementAndGet();
return instancePool.pop();
}
}
allocate方法中，instance ！=null，singleThreadModel 一直都为false，因为不会走到loadServlet中，singleThreadModel的值一直为false。容器中servlet实例只有一个。提一句：如果singleThreadModel类型为SingleThreadModel时，容器中可以有多个servlet实例，放在一个大小为20的栈中。SingleThreadModel已经被废弃掉了
@deprecated As of Java Servlet API 2.4, with no direct replacement.。
下面看initServlet()方法的处理逻辑。
private synchronized void initServlet(Servlet servlet)
throws ServletException {
if (instanceInitialized && !singleThreadModel) return;
// Call the initialization method of this servlet
try {
if( Globals.IS_SECURITY_ENABLED) {
boolean success = false;
try {
Object[] args = new Object[] { facade };
SecurityUtil.doAsPrivilege("init",
servlet,
classType,
args);
success = true;
} finally {
if (!success) {
// destroy() will not be called, thus clear the reference now
SecurityUtil.remove(servlet);
}
}
} else {
servlet.init(facade);
}
instanceInitialized = true;
} catch (UnavailableException f) {
unavailable(f);
throw f;
} catch (ServletException f) {
// If the servlet wanted to be unavailable it would have
// said so, so do not call unavailable(null).
throw f;
} catch (Throwable f) {
ExceptionUtils.handleThrowable(f);
getServletContext().log(sm.getString("standardWrapper.initException", getName()), f);
// If the servlet wanted to be unavailable it would have
// said so, so do not call unavailable(null).
throw new ServletException
(sm.getString("standardWrapper.initException", getName()), f);
}
}
这段代码很简单，就是调用servlet的init方法。
具体的init方法实现在其父类GenericServlet中。
@Override
public void init(ServletConfig config) throws ServletException {
this.config = config;
this.init();
}
这里的init方法在子类HttpServletBean中。
// Let subclasses do whatever initialization they like.
initServletBean();
}
initServletBean()方法在子类FrameworkServlet中。
@Override
protected final void initServletBean() throws ServletException {
long startTime = System.currentTimeMillis();
try {
this.webApplicationContext = initWebApplicationContext();
initFrameworkServlet();
}
catch (ServletException | RuntimeException ex) {
logger.error("Context initialization failed", ex);
throw ex;
}
}
initFrameworkServlet()是留给子类实现的一个扩展接口，默认为空实现，主要的逻辑在initWebApplicationContext()中，该方法主要是初始化一些策略，如文件解析器，国际化解析器，主题解析器，处理器映射器，处理器适配器，异常处理器，视图解析器等。具体的实现在子类DispatcherServlet中。
代码如下：
@Override
protected void onRefresh(ApplicationContext context) {
initStrategies(context);
}
/**
* Initialize the strategy objects that this servlet uses.
* May be overridden in subclasses in order to initialize further strategy objects.
*/
protected void initStrategies(ApplicationContext context) {
//文件解析器，没有，返回为空。
initMultipartResolver(context);
//国际化解析，没有，返回默认值，AcceptHeaderLocaleResolver
initLocaleResolver(context);
//主题解析，没有返回默认值FixedThemeResolver
initThemeResolver(context);
//处理器映射，若没有，返回默认值BeanNameUrlHandlerMapping，RequestMappingHandlerMapping，RouterFunctionMapping
initHandlerMappings(context);
//处理器适配器，若没有，返回默认值HttpRequestHandlerAdapter，SimpleControllerHandlerAdapter，RequestMappingHandlerAdapter，HandlerFunctionAdapter
initHandlerAdapters(context);
//异常解析，若没有，返回默认值ExceptionHandlerExceptionResolver，ResponseStatusExceptionResolver，DefaultHandlerExceptionResolver
initHandlerExceptionResolvers(context);
//异常后，没有返回视图时的默认处理DefaultRequestToViewNameTranslator
initRequestToViewNameTranslator(context);
//视图解析，没有返回InternalResourceViewResolver
initViewResolvers(context);
//默认值SessionFlashMapManager
initFlashMapManager(context);
}
后面通过看具体的请求处理来看上面的处理器如何工作的。
到此，servlet的init方法正式处理完成，就可以提供服务了。
servlet提供服务过程（service）
下面，看service如何处理。
从前文中的代码中可以知道，在调用service之前，需要获取一个ApplicationFilterChain，先来看看ApplicationFilterFactory中createFilterChain里做了哪些事情。从类名中可以猜到，这里主要是添加一些Filter相关的信息。具体代码为：
public static ApplicationFilterChain createFilterChain(ServletRequest request,
Wrapper wrapper, Servlet servlet) {
// Create and initialize a filter chain object
ApplicationFilterChain filterChain = null;
if (request instanceof Request) {
Request req = (Request) request;
if (Globals.IS_SECURITY_ENABLED) {
// Security: Do not recycle
filterChain = new ApplicationFilterChain();
} else {
filterChain = (ApplicationFilterChain) req.getFilterChain();
if (filterChain == null) {
filterChain = new ApplicationFilterChain();
req.setFilterChain(filterChain);
}
}
} else {
// Request dispatcher in use
filterChain = new ApplicationFilterChain();
}
filterChain.setServlet(servlet);
filterChain.setServletSupportsAsync(wrapper.isAsyncSupported());
// Acquire the filter mappings for this Context
StandardContext context = (StandardContext) wrapper.getParent();
//获取Filter列表
FilterMap filterMaps[] = context.findFilterMaps();
// If there are no filter mappings, we are done
if ((filterMaps == null) || (filterMaps.length == 0))
return filterChain;
// Acquire the information we will need to match filter mappings
DispatcherType dispatcher =
(DispatcherType) request.getAttribute(Globals.DISPATCHER_TYPE_ATTR);
String requestPath = null;
Object attribute = request.getAttribute(Globals.DISPATCHER_REQUEST_PATH_ATTR);
if (attribute != null){
requestPath = attribute.toString();
}
String servletName = wrapper.getName();
// Add the relevant path-mapped filters to this filter chain
for (FilterMap filterMap : filterMaps) {
if (!matchDispatcher(filterMap, dispatcher)) {
continue;
}
if (!matchFiltersURL(filterMap, requestPath))
continue;
ApplicationFilterConfig filterConfig = (ApplicationFilterConfig)
context.findFilterConfig(filterMap.getFilterName());
if (filterConfig == null) {
// FIXME - log configuration problem
continue;
}
filterChain.addFilter(filterConfig);
}
// Add filters that match on servlet name second
for (FilterMap filterMap : filterMaps) {
if (!matchDispatcher(filterMap, dispatcher)) {
continue;
}
if (!matchFiltersServlet(filterMap, servletName))
continue;
ApplicationFilterConfig filterConfig = (ApplicationFilterConfig)
context.findFilterConfig(filterMap.getFilterName());
if (filterConfig == null) {
// FIXME - log configuration problem
continue;
}
filterChain.addFilter(filterConfig);
}
// Return the completed filter chain
return filterChain;
}
其中比较重要的一行代码FilterMap filterMaps[] = context.findFilterMaps();，获取过滤器列表。
@Override
public FilterMap[] findFilterMaps() {
return filterMaps.asArray();
}
这里filterMaps是在什么时候进行赋值的呢？此处又会回到ServletContextInitializer这个接口的onStartup方法里了。
前文里提到过，在createWebServer时，有个方法引用getSelfInitializer。这里同样走到这段代码里。
Filter相关的准备工作
我们在通常在springboot里定义过滤器时，可以使用如下代码：
@Bean
public FilterRegistrationBean xxxFilter() {
FilterRegistrationBean registrationBean = new FilterRegistrationBean();
XxxFilter xxxFilter = new XxxFilter();
registrationBean.addUrlPatterns("/*");
registrationBean.setFilter(xxxFilter);
return registrationBean;
}
看下FilterRegistrationBean的类图：
FilterRegistrationBean同样实现了ServletContextInitializer接口。
同时，我们还可以进行如下方式定义过滤器。
@Service
public class TestFilter implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
}
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
throws IOException, ServletException {
chain.doFilter(request, response);
}
@Override
public void destroy() {
}
}
这种方式没有显式的定义成一个FilterRegistrationBean，在代码中事实上也封装成一个FilterRegistrationBean。接下来看具体的代码实现。
首先看ServletContextInitializer的onStartup的调用处代码。
private void selfInitialize(ServletContext servletContext) throws ServletException {
prepareWebApplicationContext(servletContext);
registerApplicationScope(servletContext);
WebApplicationContextUtils.registerEnvironmentBeans(getBeanFactory(), servletContext);
for (ServletContextInitializer beans : getServletContextInitializerBeans()) {
beans.onStartup(servletContext);
}
}
getServletContextInitializerBeans()里从bean工厂里获取ServletContextInitializer类型的bean，调用onStartup方法。
protected Collection getServletContextInitializerBeans() {
return new ServletContextInitializerBeans(getBeanFactory());
}
public ServletContextInitializerBeans(ListableBeanFactory beanFactory,
Class... initializerTypes) {
this.initializers = new LinkedMultiValueMap<>();
this.initializerTypes = (initializerTypes.length != 0) ? Arrays.asList(initializerTypes)
: Collections.singletonList(ServletContextInitializer.class);
//显式定义为ServletContextInitializer的bean
addServletContextInitializerBeans(beanFactory);
//未显式定义为ServletContextInitializer的bean
addAdaptableBeans(beanFactory);
List sortedInitializers = this.initializers.values().stream()
.flatMap((value) -> value.stream().sorted(AnnotationAwareOrderComparator.INSTANCE))
.collect(Collectors.toList());
this.sortedList = Collections.unmodifiableList(sortedInitializers);
logMappings(this.initializers);
}
显式定义为ServletContextInitializer的bean的处理方法：
private void addServletContextInitializerBeans(ListableBeanFactory beanFactory) {
for (Class initializerType : this.initializerTypes) {
for (Entry initializerBean : getOrderedBeansOfType(beanFactory,
initializerType)) {
addServletContextInitializerBean(initializerBean.getKey(), initializerBean.getValue(), beanFactory);
}
}
}
private void addServletContextInitializerBean(String beanName, ServletContextInitializer initializer,
ListableBeanFactory beanFactory) {
if (initializer instanceof ServletRegistrationBean) {
Servlet source = ((ServletRegistrationBean) initializer).getServlet();
addServletContextInitializerBean(Servlet.class, beanName, initializer, beanFactory, source);
}
else if (initializer instanceof FilterRegistrationBean) {
Filter source = ((FilterRegistrationBean) initializer).getFilter();
addServletContextInitializerBean(Filter.class, beanName, initializer, beanFactory, source);
}
else if (initializer instanceof DelegatingFilterProxyRegistrationBean) {
String source = ((DelegatingFilterProxyRegistrationBean) initializer).getTargetBeanName();
addServletContextInitializerBean(Filter.class, beanName, initializer, beanFactory, source);
}
else if (initializer instanceof ServletListenerRegistrationBean) {
EventListener source = ((ServletListenerRegistrationBean) initializer).getListener();
addServletContextInitializerBean(EventListener.class, beanName, initializer, beanFactory, source);
}
else {
addServletContextInitializerBean(ServletContextInitializer.class, beanName, initializer, beanFactory,
initializer);
}
}
private void addServletContextInitializerBean(Class type, String beanName, ServletContextInitializer initializer,
ListableBeanFactory beanFactory, Object source) {
this.initializers.add(type, initializer);
if (source != null) {
// Mark the underlying source as seen in case it wraps an existing bean
this.seen.add(source);
}
if (logger.isTraceEnabled()) {
String resourceDescription = getResourceDescription(beanName, beanFactory);
int order = getOrder(initializer);
logger.trace("Added existing " + type.getSimpleName() + " initializer bean '" + beanName + "'; order="
+ order + ", resource=" + resourceDescription);
}
}
未显式定义为ServletContextInitializer的bean
protected void addAdaptableBeans(ListableBeanFactory beanFactory) {
MultipartConfigElement multipartConfig = getMultipartConfig(beanFactory);
addAsRegistrationBean(beanFactory, Servlet.class, new ServletRegistrationBeanAdapter(multipartConfig));
addAsRegistrationBean(beanFactory, Filter.class, new FilterRegistrationBeanAdapter());
for (Class listenerType : ServletListenerRegistrationBean.getSupportedTypes()) {
addAsRegistrationBean(beanFactory, EventListener.class, (Class) listenerType,
new ServletListenerRegistrationBeanAdapter());
}
}
private void addAsRegistrationBean(ListableBeanFactory beanFactory, Class type,
Class beanType, RegistrationBeanAdapter adapter) {
List> entries = getOrderedBeansOfType(beanFactory, beanType, this.seen);
for (Entry entry : entries) {
String beanName = entry.getKey();
B bean = entry.getValue();
if (this.seen.add(bean)) {
// One that we haven't already seen
//通过适配器模式，进行处理。
RegistrationBean registration = adapter.createRegistrationBean(beanName, bean, entries.size());
int order = getOrder(bean);
registration.setOrder(order);
this.initializers.add(type, registration);
if (logger.isTraceEnabled()) {
logger.trace("Created " + type.getSimpleName() + " initializer for bean '" + beanName + "'; order="
+ order + ", resource=" + getResourceDescription(beanName, beanFactory));
}
}
}
}
private static class FilterRegistrationBeanAdapter implements RegistrationBeanAdapter {
@Override
public RegistrationBean createRegistrationBean(String name, Filter source, int totalNumberOfSourceBeans) {
FilterRegistrationBean bean = new FilterRegistrationBean<>(source);
bean.setName(name);
return bean;
}
}
代码比较简单，这里只做代码的罗列，不做详细说明。
接下来看FilterRegistrationBean里onStartup方法的处理逻辑，该方法的实现在其父类RegistrationBean中。
@Override
public final void onStartup(ServletContext servletContext) throws ServletException {
String description = getDescription();
if (!isEnabled()) {
logger.info(StringUtils.capitalize(description) + " was not registered (disabled)");
return;
}
register(description, servletContext);
}
register方法在RegistrationBean子类DynamicRegistrationBean中。
@Override
protected final void register(String description, ServletContext servletContext) {
D registration = addRegistration(description, servletContext);
if (registration == null) {
logger.info(StringUtils.capitalize(description) + " was not registered (possibly already registered?)");
return;
}
configure(registration);
}
addRegistration在其子类AbstractFilterRegistrationBean中实现。
@Override
protected Dynamic addRegistration(String description, ServletContext servletContext) {
Filter filter = getFilter();
return servletContext.addFilter(getOrDeduceName(filter), filter);
}
addFilter代码走到ApplicationContextFacade中。
@Override
public FilterRegistration.Dynamic addFilter(String filterName,
Filter filter) {
if (SecurityUtil.isPackageProtectionEnabled()) {
return (FilterRegistration.Dynamic) doPrivileged("addFilter",
new Class[]{String.class, Filter.class},
new Object[]{filterName, filter});
} else {
return context.addFilter(filterName, filter);
}
}
最后走到ApplicationContext中。
private FilterRegistration.Dynamic addFilter(String filterName,
String filterClass, Filter filter) throws IllegalStateException {
FilterDef filterDef = context.findFilterDef(filterName);
if (filterDef == null) {
filterDef = new FilterDef();
filterDef.setFilterName(filterName);
context.addFilterDef(filterDef);
} else {
if (filterDef.getFilterName() != null &&
filterDef.getFilterClass() != null) {
return null;
}
}
......
return new ApplicationFilterRegistration(filterDef, context);
}
最后将FilterDef加入到StandradContext的filterDefs中。
回过头来，看DynamicRegistrationBean中register的第二个主要调用的方法configure()
对于过滤器来说，实现方法在AbstractFilterRegistrationBean中。
@Override
protected void configure(FilterRegistration.Dynamic registration) {
super.configure(registration);
EnumSet dispatcherTypes = this.dispatcherTypes;
if (dispatcherTypes == null) {
T filter = getFilter();
if (ClassUtils.isPresent("org.springframework.web.filter.OncePerRequestFilter",
filter.getClass().getClassLoader()) && filter instanceof OncePerRequestFilter) {
dispatcherTypes = EnumSet.allOf(DispatcherType.class);
}
else {
dispatcherTypes = EnumSet.of(DispatcherType.REQUEST);
}
}
Set servletNames = new LinkedHashSet<>();
for (ServletRegistrationBean servletRegistrationBean : this.servletRegistrationBeans) {
servletNames.add(servletRegistrationBean.getServletName());
}
servletNames.addAll(this.servletNames);
if (servletNames.isEmpty() && this.urlPatterns.isEmpty()) {
registration.addMappingForUrlPatterns(dispatcherTypes, this.matchAfter, DEFAULT_URL_MAPPINGS);
}
else {
if (!servletNames.isEmpty()) {
registration.addMappingForServletNames(dispatcherTypes, this.matchAfter,
StringUtils.toStringArray(servletNames));
}
if (!this.urlPatterns.isEmpty()) {
registration.addMappingForUrlPatterns(dispatcherTypes, this.matchAfter,
StringUtils.toStringArray(this.urlPatterns));
}
}
}
registration.addMappingForUrlPatterns(dispatcherTypes, this.matchAfter, DEFAULT_URL_MAPPINGS);这里的方法将每个filter通过StandardContext的addFilterMapBefore方式，塞到filterMap中的arrays中。通过findFilterMaps就能得到所有的filter了。
到此，Filter相关的准备工作完成。
需要补充上面流程的流程图。
回到service
回到前文的ApplicationFilterChain的获取上。ApplicationFilterFactory里通过context.findFilterMaps();获取所有的过滤器，放入filterChain中。
StandardWrapperValue中代码继续往下走，调用了ApplicationFilterChain的doFilter方法。
private void internalDoFilter(ServletRequest request,
ServletResponse response)
throws IOException, ServletException {
// 遍历所有的filter，这里就是为啥我们在定义Filter时，为了让chain能顺利的走完需要调用chain.doFilter()的原因。
if (pos < n) {
ApplicationFilterConfig filterConfig = filters[pos++];
try {
Filter filter = filterConfig.getFilter();
if (request.isAsyncSupported() && "false".equalsIgnoreCase(
filterConfig.getFilterDef().getAsyncSupported())) {
request.setAttribute(Globals.ASYNC_SUPPORTED_ATTR, Boolean.FALSE);
}
。。。。。。
} else {
filter.doFilter(request, response, this);
}
}
。。。。。。
}
return;
}
// We fell off the end of the chain -- call the servlet instance
try {
。。。。。。
if ((request instanceof HttpServletRequest) &&
(response instanceof HttpServletResponse) &&
Globals.IS_SECURITY_ENABLED ) {
final ServletRequest req = request;
final ServletResponse res = response;
Principal principal =
((HttpServletRequest) req).getUserPrincipal();
Object[] args = new Object[]{req, res};
SecurityUtil.doAsPrivilege("service",
servlet,
classTypeUsedInService,
args,
principal);
} else {
servlet.service(request, response);
}
} 。。。。。。
。。。。。。
}
}
以上代码就进入到了servlet的另外一个生命周期了，提供service服务了。
下篇文章，我们具体看下service接口里的逻辑。