替换配置servlet
servlet 容器启动的时候,会先加载指定路径下的文件里的类。
也就是加载所有实现了 javax.servlet.ServletContainerInitializer 的类。调用它的 onStartup 方法。
@HandlesTypes(LoadServlet.class)
public class MyServletContainerInitializer implements ServletContainerInitializer {
//tomcat启动会调用
@Override //set里面是所有LoadServlet的实例
public void onStartup(Set<Class<?>> set, ServletContext servletContext) throws ServletException {
Iterator var4;
if (set != null) {
var4 = set.iterator();
while (var4.hasNext()) {
Class<?> clazz = (Class<?>) var4.next();
if (!clazz.isInterface() && !Modifier.isAbstract(clazz.getModifiers()) && LoadServlet.class.isAssignableFrom(clazz)) {
try {
((LoadServlet) clazz.newInstance()).loadOnstarp(servletContext);
} catch (Exception e) {
e.printStackTrace();
}
}
}
}
}
}
自定义接口 LoadServlet
public interface LoadServlet {
void loadOnstarp(ServletContext servletContext);
}
自己实现一个 LoadServlet:
public class LoadServletImpl implements LoadServlet {
@Override
public void loadOnstarp(ServletContext servletContext) {
//在这里加入自己写的servlet
ServletRegistration.Dynamic initServlet = servletContext.addServlet("initServlet", "com.xiangxue.jack.servlet.InitServlet");
//<load-on-startup>值大于等于0可以随着tomcat启动而加载
initServlet.setLoadOnStartup(1);
//拦截url路径
initServlet.addMapping("/init");
}
}
通过这一步可以实现配置 servlet 的功能
替换配置ContextLoaderListener和DispatcherServlet
LoadServlet 的作用和 spring 里的 WebApplicationInitializer 类似
public interface WebApplicationInitializer {
void onStartup(ServletContext servletContext) throws ServletException;
}
@HandlesTypes(WebApplicationInitializer.class)
public class SpringServletContainerInitializer implements ServletContainerInitializer {
@Override
public void onStartup(@Nullable Set<Class<?>> webAppInitializerClasses, ServletContext servletContext)
throws ServletException {
List<WebApplicationInitializer> initializers = new LinkedList<>();
if (webAppInitializerClasses != null) {
for (Class<?> waiClass : webAppInitializerClasses) {
// Be defensive: Some servlet containers provide us with invalid classes,
// no matter what @HandlesTypes says...
if (!waiClass.isInterface() && !Modifier.isAbstract(waiClass.getModifiers()) &&
WebApplicationInitializer.class.isAssignableFrom(waiClass)) {
try {
initializers.add((WebApplicationInitializer)
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;
}
servletContext.log(initializers.size() + " Spring WebApplicationInitializers detected on classpath");
AnnotationAwareOrderComparator.sort(initializers);
for (WebApplicationInitializer initializer : initializers) {
initializer.onStartup(servletContext);
}
}
}
跟 onStartup:
类 WebApplicationInitializer
@Override
public void onStartup(ServletContext servletContext) throws ServletException {
super.onStartup(servletContext);
//注册DispatcherServlet
registerDispatcherServlet(servletContext);
}
ContextLoaderListener
跟 onStartup:
类 AbstractContextLoaderInitializer
@Override
public void onStartup(ServletContext servletContext) throws ServletException {
registerContextLoaderListener(servletContext);
}
跟 registerContextLoaderListener:
protected void registerContextLoaderListener(ServletContext servletContext) {
//创建spring上下文,注册了SpringContainer
WebApplicationContext rootAppContext = createRootApplicationContext();
if (rootAppContext != null) {
//创建监听器
/*
形如这种配置
* <listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
<!--<listener-class>org.springframework.web.context.request.RequestContextListener</listener-class>-->
</listener>
*
* */
ContextLoaderListener listener = new ContextLoaderListener(rootAppContext);
listener.setContextInitializers(getRootApplicationContextInitializers());
servletContext.addListener(listener);
}
else {
logger.debug("No ContextLoaderListener registered, as " +
"createRootApplicationContext() did not return an application context");
}
}
跟 createRootApplicationContext:
@Override
@Nullable
protected WebApplicationContext createRootApplicationContext() {
Class<?>[] configClasses = getRootConfigClasses();
if (!ObjectUtils.isEmpty(configClasses)) {
AnnotationConfigWebApplicationContext context = new AnnotationConfigWebApplicationContext();
context.register(configClasses);
return context;
}
else {
return null;
}
}
跟 getRootConfigClasses:
自己定义一个子类
public class WebAppInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {
//父容器
@Override
protected Class<?>[] getRootConfigClasses() {
return new Class<?>[]{SpringContainer.class};
}
//SpringMVC配置子容器
@Override
protected Class<?>[] getServletConfigClasses() {
return new Class<?>[]{MvcContainer.class};
}
//获取DispatcherServlet的映射信息
@Override
protected String[] getServletMappings() {
return new String[]{"/"};
}
@Override
protected Filter[] getServletFilters() {
return super.getServletFilters();
}
}
//不扫描有@Controller注解的类
@ComponentScan(value = "com.xiangxue.jack",excludeFilters = {
@ComponentScan.Filter(type = FilterType.ANNOTATION,classes = {Controller.class})
})
public class SpringContainer {
}
Spring 上下文的 refresh() 在哪里
类 ContextLoaderListener 里有这么一个方法,会由 tomcat 去调:
@Override
public void contextInitialized(ServletContextEvent event) {
initWebApplicationContext(event.getServletContext());
}
跟 initWebApplicationContext:
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);
}
}
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;
}
}
跟 configureAndRefreshWebApplicationContext:
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);
//这里
wac.refresh();
}
DispatcherServlet
类 AbstractDispatcherServletInitializer
protected void registerDispatcherServlet(ServletContext servletContext) {
String servletName = getServletName();
Assert.hasLength(servletName, "getServletName() must not return null or empty");
//创建springmvc的上下文,注册了MvcContainer类
WebApplicationContext servletAppContext = createServletApplicationContext();
Assert.notNull(servletAppContext, "createServletApplicationContext() must not return null");
//创建DispatcherServlet
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.");
}
/*
* 如果该元素的值为负数或者没有设置,则容器会当Servlet被请求时再加载。
如果值为正整数或者0时,表示容器在应用启动时就加载并初始化这个servlet,
值越小,servlet的优先级越高,就越先被加载
* */
registration.setLoadOnStartup(1);
//骨架
registration.addMapping(getServletMappings());
registration.setAsyncSupported(isAsyncSupported());
//骨架
Filter[] filters = getServletFilters();
if (!ObjectUtils.isEmpty(filters)) {
for (Filter filter : filters) {
registerServletFilter(servletContext, filter);
}
}
customizeRegistration(registration);
}
跟 createServletApplicationContext:
@Override
protected WebApplicationContext createServletApplicationContext() {
AnnotationConfigWebApplicationContext context = new AnnotationConfigWebApplicationContext();
//骨架
Class<?>[] configClasses = getServletConfigClasses();
if (!ObjectUtils.isEmpty(configClasses)) {
context.register(configClasses);
}
return context;
}
跟 getServletConfigClasses:
类 AbstractAnnotationConfigDispatcherServletInitializer
又是前面出现过的自己定义的类
public class WebAppInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {
//父容器
@Override
protected Class<?>[] getRootConfigClasses() {
return new Class<?>[]{SpringContainer.class};
}
//SpringMVC配置子容器
@Override
protected Class<?>[] getServletConfigClasses() {
return new Class<?>[]{MvcContainer.class};
}
//获取DispatcherServlet的映射信息
@Override
protected String[] getServletMappings() {
return new String[]{"/"};
}
@Override
protected Filter[] getServletFilters() {
return super.getServletFilters();
}
}
这次跟 MvcContainer:
@ComponentScan(value = "com.xiangxue.jack",includeFilters = {
@ComponentScan.Filter(type = FilterType.ANNOTATION,classes = {Controller.class})
},useDefaultFilters = false)
public class MvcContainer {
}
SpringMVC 上下文的 refresh() 在哪里
容器启动的时候,tomcat 会调 DispatcherServlet 的 init 方法,这个方法在它的父类 HttpServletBean 里:
@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;
}
}
// Let subclasses do whatever initialization they like.
initServletBean();
}
跟 initServletBean:
类 FrameworkServlet
@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();
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");
}
}
跟 initWebApplicationContext:
protected WebApplicationContext initWebApplicationContext() {
//这里会从servletContext中获取到父容器,就是通过监听器加载的容器
WebApplicationContext rootContext =
WebApplicationContextUtils.getWebApplicationContext(getServletContext());
WebApplicationContext wac = null;
if (this.webApplicationContext != null) {
// A context instance was injected at construction time -> use it
wac = this.webApplicationContext;
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);
}
//容器加载
configureAndRefreshWebApplicationContext(cwac);
}
}
}
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;
}
跟 configureAndRefreshWebApplicationContext:
protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac) {
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
if (this.contextId != null) {
wac.setId(this.contextId);
}
else {
// Generate default id...
wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +
ObjectUtils.getDisplayString(getServletContext().getContextPath()) + '/' + getServletName());
}
}
wac.setServletContext(getServletContext());
wac.setServletConfig(getServletConfig());
wac.setNamespace(getNamespace());
wac.addApplicationListener(new SourceFilteringListener(wac, new ContextRefreshListener()));
// 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(getServletContext(), getServletConfig());
}
postProcessWebApplicationContext(wac);
applyInitializers(wac);
//这里
wac.refresh();
}
Spring 上下文是 SpringMVC上下文的父上下文。