首先我们要了解下SPI机制
Service Provider Interface ，即服务提供者接口的意思。它通过在ClassPath路径下的META-INF/services文件夹查找文件，自动加载文件里所定义的类
SpringMVC原理.jpg
就是我们启动的时候会自动加载这个类。
@Override
public void onStartup(@Nullable Set<Class<?>> webAppInitializerClasses, ServletContext servletContext)
throws ServletException {
List<WebApplicationInitializer> initializers = Collections.emptyList();
if (webAppInitializerClasses != null) {
initializers = new ArrayList<>(webAppInitializerClasses.size());
for (Class<?> waiClass : webAppInitializerClasses) {
// Be defensive: Some servlet containers provide us with invalid classes,
// no matter what @HandlesTypes says... 所有的非接口非抽象的WebApplicationInitializer实现类
if (!waiClass.isInterface() && !Modifier.isAbstract(waiClass.getModifiers()) &&
WebApplicationInitializer.class.isAssignableFrom(waiClass)) {
try {
initializers.add((WebApplicationInitializer) //集合负责保存满足上面条件的类
ReflectionUtils.accessibleConstructor(waiClass).newInstance());
}
catch (Throwable ex) {
throw new ServletException("Failed to instantiate WebApplicationInitializer class", ex);
}
}
}
}
if (initializers.isEmpty()) {
servletContext.log("No Spring WebApplicationInitializer types detected on classpath");
return;
}
//下面会遍历所有满足要求的WebApplicationInitializer，调用他们的onStartup
servletContext.log(initializers.size() + " Spring WebApplicationInitializers detected on classpath");
AnnotationAwareOrderComparator.sort(initializers);
for (WebApplicationInitializer initializer : initializers) {
initializer.onStartup(servletContext); //所有的 WebApplicationInitializer 的 onStartup
}
}
然后我们去看官方文档。https://docs.spring.io/spring-framework/docs/current/reference/html/web.html#mvc-servlet
public class AppStarter implements WebApplicationInitializer {
// @Override
public void onStartup(ServletContext servletContext) throws ServletException {
//1、创建ioc容器
AnnotationConfigWebApplicationContext context = new AnnotationConfigWebApplicationContext();
context.register(SpringConfig.class); //2、传入一个配置类
//以上截止，ioc容器都没有启动
//3、配置了 DispatcherServlet,利用Servlet的初始化机制
DispatcherServlet servlet = new DispatcherServlet(context);
ServletRegistration.Dynamic registration = servletContext.addServlet("app", servlet);
registration.setLoadOnStartup(1);
registration.addMapping("/"); //映射路径
//启动了容器？上面的Servlet添加到 servletContext 里面以后，Tomcat就会对 DispatcherServlet进行初始化
//<servlet></servlet>
// servletContext.addServlet("abc",XXXX.class)
}
}
通过继承这个WebApplicationInitializer让tomcat启动的时候就加载。
上面的Servlet添加到 servletContext 里面以后，Tomcat就会对 DispatcherServlet进行初始化
接下来是HttpServletBean的init方法
@Override
public final void init() throws ServletException {
// Set bean properties from init parameters.
PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
if (!pvs.isEmpty()) {
try {
BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
ResourceLoader resourceLoader = new ServletContextResourceLoader(getServletContext());
bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));
initBeanWrapper(bw);
bw.setPropertyValues(pvs, true);
}
catch (BeansException ex) {
if (logger.isErrorEnabled()) {
logger.error("Failed to set bean properties on servlet '" + getServletName() + "'", ex);
}
throw ex;
}
}
//模板方法模式。给子类留的喜欢干的事 Let subclasses do whatever initialization they like.
initServletBean();
}
然后是FrameworkServlet的initServletBean()
@Override
protected final void initServletBean() throws ServletException {
getServletContext().log("Initializing Spring " + getClass().getSimpleName() + " '" + getServletName() + "'");
if (logger.isInfoEnabled()) {
logger.info("Initializing Servlet '" + getServletName() + "'");
}
long startTime = System.currentTimeMillis();
try {
this.webApplicationContext = initWebApplicationContext(); //初始化WebIOC容器
initFrameworkServlet();
}
catch (ServletException | RuntimeException ex) {
logger.error("Context initialization failed", ex);
throw ex;
}
if (logger.isDebugEnabled()) {
String value = this.enableLoggingRequestDetails ?
"shown which may lead to unsafe logging of potentially sensitive data" :
"masked to prevent unsafe logging of potentially sensitive data";
logger.debug("enableLoggingRequestDetails='" + this.enableLoggingRequestDetails +
"': request parameters and headers will be " + value);
}
if (logger.isInfoEnabled()) {
logger.info("Completed initialization in " + (System.currentTimeMillis() - startTime) + " ms");
}
}
初始化WebIOC容器
protected WebApplicationContext initWebApplicationContext() {
WebApplicationContext rootContext =
WebApplicationContextUtils.getWebApplicationContext(getServletContext()); //父容器
WebApplicationContext wac = null; //先会获取之前的 WebApplicationContext（构建父子容器）
if (this.webApplicationContext != null) {
// A context instance was injected at construction time -> use it
wac = this.webApplicationContext; //当前的web-ioc容器
if (wac instanceof ConfigurableWebApplicationContext) {
ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
if (!cwac.isActive()) {
// The context has not yet been refreshed -> provide services such as
// setting the parent context, setting the application context id, etc
if (cwac.getParent() == null) {
// The context instance was injected without an explicit parent -> set
// the root application context (if any; may be null) as the parent
cwac.setParent(rootContext); //父子容器的体现，
}
configureAndRefreshWebApplicationContext(cwac); //配置并且刷新容器
}
}
}
if (wac == null) {
// No context instance was injected at construction time -> see if one
// has been registered in the servlet context. If one exists, it is assumed
// that the parent context (if any) has already been set and that the
// user has performed any initialization such as setting the context id
wac = findWebApplicationContext();
}
if (wac == null) {
// No context instance is defined for this servlet -> create a local one
wac = createWebApplicationContext(rootContext);
}
if (!this.refreshEventReceived) {
// Either the context is not a ConfigurableApplicationContext with refresh
// support or the context injected at construction time had already been
// refreshed -> trigger initial onRefresh manually here.
synchronized (this.onRefreshMonitor) {
onRefresh(wac);
}
}
if (this.publishContext) {
// Publish the context as a servlet context attribute.
String attrName = getServletContextAttributeName();
getServletContext().setAttribute(attrName, wac);
}
return wac;
}
父子容器
这里有个父子容器的体现cwac.setParent(rootContext); //父子容器的体现，
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好了想要搞这个父子容器，我们要用一个新的启动类
/**
* 最快速的整合注解版SpringMVC和Spring的
*/
public class QuickAppStarter extends AbstractAnnotationConfigDispatcherServletInitializer {
@Override //根容器的配置（Spring的配置文件===Spring的配置类）
protected Class<?>[] getRootConfigClasses() {
return new Class<?>[]{SpringConfig.class};
}
@Override //web容器的配置（SpringMVC的配置文件===SpringMVC的配置类）
protected Class<?>[] getServletConfigClasses() {
return new Class<?>[]{SpringMVCConfig.class};
}
@Override //Servlet的映射，DispatcherServlet的映射路径
protected String[] getServletMappings() {
return new String[]{"/"};
}
@Override
protected void customizeRegistration(ServletRegistration.Dynamic registration) {
// super.customizeRegistration(registration);
// registration.addMapping("");//
}
}
@ComponentScan(value = "com.demo.web",excludeFilters = {
@ComponentScan.Filter(type= FilterType.ANNOTATION,value = Controller.class)
})
@Configuration
public class SpringConfig {
//Spring的父容器
}
@ComponentScan(value = "com.demo.web",includeFilters = {
@ComponentScan.Filter(type= FilterType.ANNOTATION,value = Controller.class)
},useDefaultFilters = false)
public class SpringMVCConfig {
//SpringMVC的子容器，能扫描的Spring容器中的组件
}
我们现在从新启动断点重新从onStartup进来进入AbstractDispatcherServletInitializer的onStartup
@Override
public void onStartup(ServletContext servletContext) throws ServletException {
super.onStartup(servletContext);
registerDispatcherServlet(servletContext);
}
- super.onStartup(servletContext);
- registerDispatcherServlet(servletContext);
首先 super.onStartup(servletContext); 中启动方法中调用的是父类的方法
@Override //注册ContextLoaderListener；contextInitialized
public void onStartup(ServletContext servletContext) throws ServletException {
registerContextLoaderListener(servletContext);
}
/**
* Register a {@link ContextLoaderListener} against the given servlet context. The
* {@code ContextLoaderListener} is initialized with the application context returned
* from the {@link #createRootApplicationContext()} template method.
* @param servletContext the servlet context to register the listener against
*/
protected void registerContextLoaderListener(ServletContext servletContext) {
WebApplicationContext rootAppContext = createRootApplicationContext(); //创建一个根容器
if (rootAppContext != null) {
ContextLoaderListener listener = new ContextLoaderListener(rootAppContext);
listener.setContextInitializers(getRootApplicationContextInitializers());
servletContext.addListener(listener);//注册监听器
}
else {
logger.debug("No ContextLoaderListener registered, as " +
"createRootApplicationContext() did not return an application context");
}
}
WebApplicationContext rootAppContext = createRootApplicationContext(); //创建一个根容器
这边是模版方法给我们注册父组件配置
@Override
@Nullable //重写了爷爷类的创建根容器方法
protected WebApplicationContext createRootApplicationContext() {
Class<?>[] configClasses = getRootConfigClasses(); //获取根配置
if (!ObjectUtils.isEmpty(configClasses)) {
AnnotationConfigWebApplicationContext context = new AnnotationConfigWebApplicationContext();
context.register(configClasses); //创建了一个IOC容器并把配置类注册进来
return context;
}
else {
return null;
}
}
接下来再次回到 registerDispatcherServlet(servletContext);
protected void registerDispatcherServlet(ServletContext servletContext) {
String servletName = getServletName();
Assert.hasLength(servletName, "getServletName() must not return null or empty");
WebApplicationContext servletAppContext = createServletApplicationContext(); //创建Servlet容器
Assert.notNull(servletAppContext, "createServletApplicationContext() must not return null");
FrameworkServlet dispatcherServlet = createDispatcherServlet(servletAppContext);
Assert.notNull(dispatcherServlet, "createDispatcherServlet(WebApplicationContext) must not return null");
dispatcherServlet.setContextInitializers(getServletApplicationContextInitializers());
ServletRegistration.Dynamic registration = servletContext.addServlet(servletName, dispatcherServlet);
if (registration == null) {
throw new IllegalStateException("Failed to register servlet with name '" + servletName + "'. " +
"Check if there is another servlet registered under the same name.");
}
registration.setLoadOnStartup(1);
registration.addMapping(getServletMappings()); //根据我们指定的DispatcherServlet的路径进行注册
registration.setAsyncSupported(isAsyncSupported());
Filter[] filters = getServletFilters();
if (!ObjectUtils.isEmpty(filters)) {
for (Filter filter : filters) {
registerServletFilter(servletContext, filter);
}
}
customizeRegistration(registration);
}
WebApplicationContext servletAppContext = createServletApplicationContext(); //创建Servlet容器
@Override
protected WebApplicationContext createServletApplicationContext() {
AnnotationConfigWebApplicationContext context = new AnnotationConfigWebApplicationContext(); //这里又创建了一个容器
Class<?>[] configClasses = getServletConfigClasses(); //获取web应用的配置
if (!ObjectUtils.isEmpty(configClasses)) {
context.register(configClasses);
}
return context;
}
registration.addMapping(getServletMappings()); //根据我们指定的DispatcherServlet的路径进行注册
到此为止创建好了2个父子容器，那什么时候初始化。
父容器初始化
我们在做父容器的时候有注册过一个监听器，监听器在tomcat启动后会回调。
ContextLoaderListener下的
@Override
public void contextInitialized(ServletContextEvent event) { //根容器初始化
initWebApplicationContext(event.getServletContext()); //初始化webioc容器
}
public WebApplicationContext initWebApplicationContext(ServletContext servletContext) {
if (servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE) != null) {
throw new IllegalStateException(
"Cannot initialize context because there is already a root application context present - " +
"check whether you have multiple ContextLoader* definitions in your web.xml!");
}
servletContext.log("Initializing Spring root WebApplicationContext");
Log logger = LogFactory.getLog(ContextLoader.class);
if (logger.isInfoEnabled()) {
logger.info("Root WebApplicationContext: initialization started");
}
long startTime = System.currentTimeMillis();
try {
// Store context in local instance variable, to guarantee that
// it is available on ServletContext shutdown.
if (this.context == null) {
this.context = createWebApplicationContext(servletContext);
}
if (this.context instanceof ConfigurableWebApplicationContext) {
ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) this.context;
if (!cwac.isActive()) {
// The context has not yet been refreshed -> provide services such as
// setting the parent context, setting the application context id, etc
if (cwac.getParent() == null) {
// The context instance was injected without an explicit parent ->
// determine parent for root web application context, if any.
ApplicationContext parent = loadParentContext(servletContext);
cwac.setParent(parent);
}
configureAndRefreshWebApplicationContext(cwac, servletContext);//配置和刷新容器
}
}
servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context);
ClassLoader ccl = Thread.currentThread().getContextClassLoader();
if (ccl == ContextLoader.class.getClassLoader()) {
currentContext = this.context;
}
else if (ccl != null) {
currentContextPerThread.put(ccl, this.context);
}
if (logger.isInfoEnabled()) {
long elapsedTime = System.currentTimeMillis() - startTime;
logger.info("Root WebApplicationContext initialized in " + elapsedTime + " ms");
}
return this.context;
}
catch (RuntimeException | Error ex) {
logger.error("Context initialization failed", ex);
servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, ex);
throw ex;
}
}
configureAndRefreshWebApplicationContext(cwac, servletContext);//配置和刷新容器
protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac, ServletContext sc) {
if (ObjectUtils.identityToString(wac).equals(wac.getId())) {
// The application context id is still set to its original default value
// -> assign a more useful id based on available information
String idParam = sc.getInitParameter(CONTEXT_ID_PARAM);
if (idParam != null) {
wac.setId(idParam);
}
else {
// Generate default id...
wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +
ObjectUtils.getDisplayString(sc.getContextPath()));
}
}
wac.setServletContext(sc);
String configLocationParam = sc.getInitParameter(CONFIG_LOCATION_PARAM);
if (configLocationParam != null) {
wac.setConfigLocation(configLocationParam);
}
// The wac environment's #initPropertySources will be called in any case when the context
// is refreshed; do it eagerly here to ensure servlet property sources are in place for
// use in any post-processing or initialization that occurs below prior to #refresh
ConfigurableEnvironment env = wac.getEnvironment();
if (env instanceof ConfigurableWebEnvironment) {
((ConfigurableWebEnvironment) env).initPropertySources(sc, null);
}
customizeContext(sc, wac);
wac.refresh(); //容器初始化
}
wac.refresh(); //容器初始化这里就是我们最熟悉的容器刷新12大步了。
到这边我们的父容器AOP，事务，IOC，自动装配组件功能都装载进来了。
子容器初始化
我们在创建子容器的时候我们有创建了一个DispatcherServlet，在tomcat启动后会调用init方法。这样又回到我们最最开始的流程。
protected WebApplicationContext initWebApplicationContext() {
WebApplicationContext rootContext =
WebApplicationContextUtils.getWebApplicationContext(getServletContext()); //父容器
WebApplicationContext wac = null; //先会获取之前的 WebApplicationContext（构建父子容器）
if (this.webApplicationContext != null) {
// A context instance was injected at construction time -> use it
wac = this.webApplicationContext; //当前的web-ioc容器
if (wac instanceof ConfigurableWebApplicationContext) {
ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
if (!cwac.isActive()) {
// The context has not yet been refreshed -> provide services such as
// setting the parent context, setting the application context id, etc
if (cwac.getParent() == null) {
// The context instance was injected without an explicit parent -> set
// the root application context (if any; may be null) as the parent
cwac.setParent(rootContext); //父子容器的体现，
}
configureAndRefreshWebApplicationContext(cwac); //配置并且刷新容器
}
}
}
if (wac == null) {
// No context instance was injected at construction time -> see if one
// has been registered in the servlet context. If one exists, it is assumed
// that the parent context (if any) has already been set and that the
// user has performed any initialization such as setting the context id
wac = findWebApplicationContext();
}
if (wac == null) {
// No context instance is defined for this servlet -> create a local one
wac = createWebApplicationContext(rootContext);
}
if (!this.refreshEventReceived) {
// Either the context is not a ConfigurableApplicationContext with refresh
// support or the context injected at construction time had already been
// refreshed -> trigger initial onRefresh manually here.
synchronized (this.onRefreshMonitor) {
onRefresh(wac); //容器刷新
}
}
if (this.publishContext) {
// Publish the context as a servlet context attribute.
String attrName = getServletContextAttributeName();
getServletContext().setAttribute(attrName, wac);
}
return wac;
}
获取父容器的时候就能找到父容器。
onRefresh(wac); //容器刷新 然后后面也执行了容器刷新
到这里就是把MVC的原理源码梳理了一遍，这里挖个坑.现在我们知道一个controller被注册到容器中了。那我们一个请求进来/test/a. 他是怎么找到对应的接口呢。
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