Tomcat学习笔记（四）
LiuYang 2021/6/3 JavaTomcat
# 热加载
tomcat通过一个后台线程的不断判断，不断执行周期性任务来判断，是否需要执行热加载。 在StandardEngine的初始化方法中，启动了这个周期性的后台任务。间隔60s。
// Start our thread
if (backgroundProcessorDelay > 0) {
monitorFuture = Container.getService(ContainerBase.this).getServer()
.getUtilityExecutor().scheduleWithFixedDelay(
new ContainerBackgroundProcessorMonitor(), 0, 60, TimeUnit.SECONDS);
}
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# ContainerBackgroundProcessorMonitor
protected class ContainerBackgroundProcessorMonitor implements Runnable {
@Override
public void run() {
if (getState().isAvailable()) {
threadStart();
}
}
}
protected void threadStart() {
if (backgroundProcessorDelay > 0
&& (getState().isAvailable() || LifecycleState.STARTING_PREP.equals(getState()))
&& (backgroundProcessorFuture == null || backgroundProcessorFuture.isDone())) {
if (backgroundProcessorFuture != null && backgroundProcessorFuture.isDone()) {
// There was an error executing the scheduled task, get it and log it
try {
backgroundProcessorFuture.get();
} catch (InterruptedException | ExecutionException e) {
log.error(sm.getString("containerBase.backgroundProcess.error"), e);
}
}
backgroundProcessorFuture = Container.getService(this).getServer().getUtilityExecutor()
.scheduleWithFixedDelay(new ContainerBackgroundProcessor(),
backgroundProcessorDelay, backgroundProcessorDelay,
TimeUnit.SECONDS);
}
}
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# ContainerBackgroundProcessor
看的出来，ContainerBackgroundProcessorMonitor，启动了线程，这回轮到了ContainerBackgroundProcessor来执行任务，间隔时间也变成了我们设置的时间。
/**
* Private runnable class to invoke the backgroundProcess method
* of this container and its children after a fixed delay.
*/
protected class ContainerBackgroundProcessor implements Runnable {
@Override
public void run() {
processChildren(ContainerBase.this);
}
protected void processChildren(Container container) {
ClassLoader originalClassLoader = null;
try {
if (container instanceof Context) {
Loader loader = ((Context) container).getLoader();
// Loader will be null for FailedContext instances
if (loader == null) {
return;
}
// Ensure background processing for Contexts and Wrappers
// is performed under the web app's class loader
originalClassLoader = ((Context) container).bind(false, null);
}
container.backgroundProcess();
Container[] children = container.findChildren();
for (Container child : children) {
if (child.getBackgroundProcessorDelay() <= 0) {
processChildren(child);
}
}
} catch (Throwable t) {
ExceptionUtils.handleThrowable(t);
log.error(sm.getString("containerBase.backgroundProcess.error"), t);
} finally {
if (container instanceof Context) {
((Context) container).unbind(false, originalClassLoader);
}
}
}
}
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上面的代码我们可以知道，在这个后台线程的run方法里，我们显示执行了当前容器的backgroundProcess方法，然后又循环了所有自容器的backgroundProcess方法。 backgroundProcess方法中，通过fireLifecycleEvent来出发监听器，
fireLifecycleEvent(Lifecycle.PERIODIC_EVENT, null);
protected void fireLifecycleEvent(String type, Object data) {
LifecycleEvent event = new LifecycleEvent(this, type, data);
for (LifecycleListener listener : lifecycleListeners) {
listener.lifecycleEvent(event);
}
}
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# 热加载
对待Context容器，执行下列方法。
@Override
public void backgroundProcess() {
if (!getState().isAvailable())
return;
Loader loader = getLoader();
if (loader != null) {
try {
loader.backgroundProcess();
} catch (Exception e) {
log.warn(sm.getString(
"standardContext.backgroundProcess.loader", loader), e);
}
}
Manager manager = getManager();
if (manager != null) {
try {
manager.backgroundProcess();
} catch (Exception e) {
log.warn(sm.getString(
"standardContext.backgroundProcess.manager", manager),
e);
}
}
WebResourceRoot resources = getResources();
if (resources != null) {
try {
resources.backgroundProcess();
} catch (Exception e) {
log.warn(sm.getString(
"standardContext.backgroundProcess.resources",
resources), e);
}
}
InstanceManager instanceManager = getInstanceManager();
if (instanceManager != null) {
try {
instanceManager.backgroundProcess();
} catch (Exception e) {
log.warn(sm.getString(
"standardContext.backgroundProcess.instanceManager",
resources), e);
}
}
super.backgroundProcess();
}
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- WebappLoader:检查 WEB-INF/classes 和 WEB-INF/lib 目录下的类文件
- Manager：检查session
- WebResourceRoot：检查静态资源
在WebappLoader的backgroundProcess方法里，调用了reload()方法。这里面分别将context的声明中期从先停止，再开始。实现了重新加载。
@Override
public void backgroundProcess() {
if (reloadable && modified()) {
try {
Thread.currentThread().setContextClassLoader
(WebappLoader.class.getClassLoader());
if (context != null) {
context.reload();
}
} finally {
if (context != null && context.getLoader() != null) {
Thread.currentThread().setContextClassLoader
(context.getLoader().getClassLoader());
}
}
}
}
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# tomcat加载器
 我们都知道为了实现tomcat部署多个工程，tomcat打破了java的类加载机制--双亲委派机制。
# java的双亲委派
public abstract class ClassLoader {
// 每个类加载器都有个父加载器
private final ClassLoader parent;
public Class<?> loadClass(String name) {
// 查找一下这个类是不是已经加载过了
Class<?> c = findLoadedClass(name);
// 如果没有加载过
if( c == null ){
// 先委托给父加载器去加载，注意这是个递归调用
if (parent != null) {
c = parent.loadClass(name);
}else {
// 如果父加载器为空，查找 Bootstrap 加载器是不是加载过了
c = findBootstrapClassOrNull(name);
}
}
// 如果父加载器没加载成功，调用自己的 findClass 去加载
if (c == null) {
c = findClass(name);
}
return c；
}
protected Class<?> findClass(String name){
//1. 根据传入的类名 name，到在特定目录下去寻找类文件，把.class 文件读入内存
...
//2. 调用 defineClass 将字节数组转成 Class 对象
return defineClass(buf, off, len)；
}
// 将字节码数组解析成一个 Class 对象，用 native 方法实现
protected final Class<?> defineClass(byte[] b, int off, int len){
...
}
}
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我们之前已经在JVM的笔记中记录了，
- BootstrapClassLoader引导类加载器:负责加载支撑JVM运行的位于JRE的lib目录下的核心类库，比如 rt.jar、charsets.jar等
- ExtClassLoader扩展类加载器:负责加载支撑JVM运行的位于JRE的lib目录下的ext扩展目录中的JAR类包
- AppClassLoader应用程序类加载器:负责加载ClassPath路径下的类包，主要就是加载你自己写的那些类
- 自定义加载器:负责加载用户自定义路径下的类包
# WebappClassLoader打破双亲委派
自定义的WebappClassLoader，为每个web应用创建一个。所以每个context容器只维护一个WebAppClassLoader。 因为不同的类加载器实例加载的类会被认为是不同的类。等于在jvm虚拟机内部为每个web应用创建了隔离空间。
# find方法
public Class<?> findClass(String name) throws ClassNotFoundException {
if (log.isDebugEnabled())
log.debug(" findClass(" + name + ")");
checkStateForClassLoading(name);
// (1) Permission to define this class when using a SecurityManager
if (securityManager != null) {
int i = name.lastIndexOf('.');
if (i >= 0) {
try {
if (log.isTraceEnabled())
log.trace(" securityManager.checkPackageDefinition");
securityManager.checkPackageDefinition(name.substring(0,i));
} catch (Exception se) {
if (log.isTraceEnabled())
log.trace(" -->Exception-->ClassNotFoundException", se);
throw new ClassNotFoundException(name, se);
}
}
}
// Ask our superclass to locate this class, if possible
// (throws ClassNotFoundException if it is not found)
Class<?> clazz = null;
try {
if (log.isTraceEnabled())
log.trace(" findClassInternal(" + name + ")");
try {
if (securityManager != null) {
PrivilegedAction<Class<?>> dp =
new PrivilegedFindClassByName(name);
clazz = AccessController.doPrivileged(dp);
} else {
clazz = findClassInternal(name);
}
} catch(AccessControlException ace) {
log.warn(sm.getString("webappClassLoader.securityException", name,
ace.getMessage()), ace);
throw new ClassNotFoundException(name, ace);
} catch (RuntimeException e) {
if (log.isTraceEnabled())
log.trace(" -->RuntimeException Rethrown", e);
throw e;
}
if ((clazz == null) && hasExternalRepositories) {
try {
clazz = super.findClass(name);
} catch(AccessControlException ace) {
log.warn(sm.getString("webappClassLoader.securityException", name,
ace.getMessage()), ace);
throw new ClassNotFoundException(name, ace);
} catch (RuntimeException e) {
if (log.isTraceEnabled())
log.trace(" -->RuntimeException Rethrown", e);
throw e;
}
}
if (clazz == null) {
if (log.isDebugEnabled())
log.debug(" --> Returning ClassNotFoundException");
throw new ClassNotFoundException(name);
}
} catch (ClassNotFoundException e) {
if (log.isTraceEnabled())
log.trace(" --> Passing on ClassNotFoundException");
throw e;
}
// Return the class we have located
if (log.isTraceEnabled())
log.debug(" Returning class " + clazz);
if (log.isTraceEnabled()) {
ClassLoader cl;
if (Globals.IS_SECURITY_ENABLED){
cl = AccessController.doPrivileged(
new PrivilegedGetClassLoader(clazz));
} else {
cl = clazz.getClassLoader();
}
log.debug(" Loaded by " + cl.toString());
}
return clazz;
}
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- fclazz = findClassInternal(name); 方法先尝试加载本地目录
- clazz = super.findClass(name); 本地目录加载不到的情况下交给父类加载
- 再没有就抛出异常
# load方法
public Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException {
synchronized (JreCompat.isGraalAvailable() ? this : getClassLoadingLock(name)) {
if (log.isDebugEnabled())
log.debug("loadClass(" + name + ", " + resolve + ")");
Class<?> clazz = null;
// Log access to stopped class loader
checkStateForClassLoading(name);
// (0) Check our previously loaded local class cache
clazz = findLoadedClass0(name);
if (clazz != null) {
if (log.isDebugEnabled())
log.debug(" Returning class from cache");
if (resolve)
resolveClass(clazz);
return clazz;
}
// (0.1) Check our previously loaded class cache
clazz = JreCompat.isGraalAvailable() ? null : findLoadedClass(name);
if (clazz != null) {
if (log.isDebugEnabled())
log.debug(" Returning class from cache");
if (resolve)
resolveClass(clazz);
return clazz;
}
// (0.2) Try loading the class with the system class loader, to prevent
// the webapp from overriding Java SE classes. This implements
// SRV.10.7.2
String resourceName = binaryNameToPath(name, false);
ClassLoader javaseLoader = getJavaseClassLoader();
boolean tryLoadingFromJavaseLoader;
try {
// Use getResource as it won't trigger an expensive
// ClassNotFoundException if the resource is not available from
// the Java SE class loader. However (see
// https://bz.apache.org/bugzilla/show_bug.cgi?id=58125 for
// details) when running under a security manager in rare cases
// this call may trigger a ClassCircularityError.
// See https://bz.apache.org/bugzilla/show_bug.cgi?id=61424 for
// details of how this may trigger a StackOverflowError
// Given these reported errors, catch Throwable to ensure any
// other edge cases are also caught
URL url;
if (securityManager != null) {
PrivilegedAction<URL> dp = new PrivilegedJavaseGetResource(resourceName);
url = AccessController.doPrivileged(dp);
} else {
url = javaseLoader.getResource(resourceName);
}
tryLoadingFromJavaseLoader = (url != null);
} catch (Throwable t) {
// Swallow all exceptions apart from those that must be re-thrown
ExceptionUtils.handleThrowable(t);
// The getResource() trick won't work for this class. We have to
// try loading it directly and accept that we might get a
// ClassNotFoundException.
tryLoadingFromJavaseLoader = true;
}
if (tryLoadingFromJavaseLoader) {
try {
clazz = javaseLoader.loadClass(name);
if (clazz != null) {
if (resolve)
resolveClass(clazz);
return clazz;
}
} catch (ClassNotFoundException e) {
// Ignore
}
}
// (0.5) Permission to access this class when using a SecurityManager
if (securityManager != null) {
int i = name.lastIndexOf('.');
if (i >= 0) {
try {
securityManager.checkPackageAccess(name.substring(0,i));
} catch (SecurityException se) {
String error = sm.getString("webappClassLoader.restrictedPackage", name);
log.info(error, se);
throw new ClassNotFoundException(error, se);
}
}
}
boolean delegateLoad = delegate || filter(name, true);
// (1) Delegate to our parent if requested
if (delegateLoad) {
if (log.isDebugEnabled())
log.debug(" Delegating to parent classloader1 " + parent);
try {
clazz = Class.forName(name, false, parent);
if (clazz != null) {
if (log.isDebugEnabled())
log.debug(" Loading class from parent");
if (resolve)
resolveClass(clazz);
return clazz;
}
} catch (ClassNotFoundException e) {
// Ignore
}
}
// (2) Search local repositories
if (log.isDebugEnabled())
log.debug(" Searching local repositories");
try {
clazz = findClass(name);
if (clazz != null) {
if (log.isDebugEnabled())
log.debug(" Loading class from local repository");
if (resolve)
resolveClass(clazz);
return clazz;
}
} catch (ClassNotFoundException e) {
// Ignore
}
// (3) Delegate to parent unconditionally
if (!delegateLoad) {
if (log.isDebugEnabled())
log.debug(" Delegating to parent classloader at end: " + parent);
try {
clazz = Class.forName(name, false, parent);
if (clazz != null) {
if (log.isDebugEnabled())
log.debug(" Loading class from parent");
if (resolve)
resolveClass(clazz);
return clazz;
}
} catch (ClassNotFoundException e) {
// Ignore
}
}
}
throw new ClassNotFoundException(name);
}
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- clazz = findLoadedClass0(name); 查看本地缓存是否已经加载（等于说tomcat的类加载器是否加载）
protected Class<?> findLoadedClass0(String name) {
String path = binaryNameToPath(name, true);
ResourceEntry entry = resourceEntries.get(path);
if (entry != null) {
return entry.loadedClass;
}
return null;
}
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- findLoadedClass(name); 判断系统的类加载器是否加载过
- clazz = javaseLoader.loadClass(name); 让ExtClassLoader去加载这个类，防止自己应用的类去覆盖jre的核心类。
- clazz = findClass(name); 如果没有加载到，说明这个类不属于jre核心类，就在该应用的目录下去加载。
- clazz = Class.forName(name, false, parent);Web 应用是通过Class.forName调用交给系统类加载器的，因为Class.forName的默认加载器就是系统类加载器。
- 如都加载失败，抛出异常。
# SharedClassLoader
负责两个 Web 应用之间怎么共享库类，如果我们多个web应用需要加载共同的类，就需要在这个类加载器的下指定目录。
# CatalinaClassloader
tomcat本身也是一个java应用程序，CatalinaClassloader专门负责加载tomcat自身的类。来隔离 Tomcat 本身的类和 Web 应用的类。
# CommonClassLoader
这个类作为SharedClassLoader和CatalinaClassloader的父类，也就是说，可以共享加载tomcat和应用之间的类。
# contextClassLoader
如果我们有一些共同的类需要在各个应用中共享，但由于JVM机制，如果一个类由类加载器 A 加载，那么这个类的依赖类也是由相同的类加载器加载。例如Spring的类和业务类。 会把业务类也通过SharedClassLoader来进行加载，上下文加载器保存在线程私有数据里，只要是同一个线程，一旦设置了线程上下文加载器，在线程后续执行过程中就能把这个类加载器取出来用。 所以当Spring启动，需要加载业务类的时候，就会在私有线程里把业务类取出来并去WebappClassLoader指定的路径来加载。
# Servlet管理
# servlet调用
StandardContextValve的invoke方法，Context 容器的 BasicValve 会调用 Wrapper 容器中 Pipeline 中的第一个 Valve，然后会调用到 StandardWrapperValve的invoke方法。
@Override
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();
// Check for the application being marked unavailable
if (!context.getState().isAvailable()) {
response.sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE,
sm.getString("standardContext.isUnavailable"));
unavailable = true;
}
// Check for the servlet being marked unavailable
if (!unavailable && wrapper.isUnavailable()) {
container.getLogger().info(sm.getString("standardWrapper.isUnavailable",
wrapper.getName()));
long available = wrapper.getAvailable();
if ((available > 0L) && (available < Long.MAX_VALUE)) {
response.setDateHeader("Retry-After", available);
response.sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE,
sm.getString("standardWrapper.isUnavailable",
wrapper.getName()));
} else if (available == Long.MAX_VALUE) {
response.sendError(HttpServletResponse.SC_NOT_FOUND,
sm.getString("standardWrapper.notFound",
wrapper.getName()));
}
unavailable = true;
}
// Allocate a servlet instance to process this request
try {
if (!unavailable) {
servlet = wrapper.allocate();
}
} catch (UnavailableException e) {
container.getLogger().error(
sm.getString("standardWrapper.allocateException",
wrapper.getName()), e);
long available = wrapper.getAvailable();
if ((available > 0L) && (available < Long.MAX_VALUE)) {
response.setDateHeader("Retry-After", available);
response.sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE,
sm.getString("standardWrapper.isUnavailable",
wrapper.getName()));
} else if (available == Long.MAX_VALUE) {
response.sendError(HttpServletResponse.SC_NOT_FOUND,
sm.getString("standardWrapper.notFound",
wrapper.getName()));
}
} catch (ServletException e) {
container.getLogger().error(sm.getString("standardWrapper.allocateException",
wrapper.getName()), StandardWrapper.getRootCause(e));
throwable = e;
exception(request, response, e);
} catch (Throwable e) {
ExceptionUtils.handleThrowable(e);
container.getLogger().error(sm.getString("standardWrapper.allocateException",
wrapper.getName()), e);
throwable = e;
exception(request, response, e);
servlet = null;
}
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
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)) {
// Swallow output if needed
if (context.getSwallowOutput()) {
try {
SystemLogHandler.startCapture();
if (request.isAsyncDispatching()) {
request.getAsyncContextInternal().doInternalDispatch();
} else {
filterChain.doFilter(request.getRequest(),
response.getResponse());
}
} finally {
String log = SystemLogHandler.stopCapture();
if (log != null && log.length() > 0) {
context.getLogger().info(log);
}
}
} else {
if (request.isAsyncDispatching()) {
request.getAsyncContextInternal().doInternalDispatch();
} else {
filterChain.doFilter
(request.getRequest(), response.getResponse());
}
}
}
} catch (ClientAbortException | CloseNowException e) {
if (container.getLogger().isDebugEnabled()) {
container.getLogger().debug(sm.getString(
"standardWrapper.serviceException", wrapper.getName(),
context.getName()), e);
}
throwable = e;
exception(request, response, e);
} catch (IOException e) {
container.getLogger().error(sm.getString(
"standardWrapper.serviceException", wrapper.getName(),
context.getName()), e);
throwable = e;
exception(request, response, e);
} catch (UnavailableException e) {
container.getLogger().error(sm.getString(
"standardWrapper.serviceException", wrapper.getName(),
context.getName()), e);
// throwable = e;
// exception(request, response, e);
wrapper.unavailable(e);
long available = wrapper.getAvailable();
if ((available > 0L) && (available < Long.MAX_VALUE)) {
response.setDateHeader("Retry-After", available);
response.sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE,
sm.getString("standardWrapper.isUnavailable",
wrapper.getName()));
} else if (available == Long.MAX_VALUE) {
response.sendError(HttpServletResponse.SC_NOT_FOUND,
sm.getString("standardWrapper.notFound",
wrapper.getName()));
}
// Do not save exception in 'throwable', because we
// do not want to do exception(request, response, e) processing
} catch (ServletException e) {
Throwable rootCause = StandardWrapper.getRootCause(e);
if (!(rootCause instanceof ClientAbortException)) {
container.getLogger().error(sm.getString(
"standardWrapper.serviceExceptionRoot",
wrapper.getName(), context.getName(), e.getMessage()),
rootCause);
}
throwable = e;
exception(request, response, e);
} catch (Throwable e) {
ExceptionUtils.handleThrowable(e);
container.getLogger().error(sm.getString(
"standardWrapper.serviceException", wrapper.getName(),
context.getName()), e);
throwable = e;
exception(request, response, e);
} finally {
// Release the filter chain (if any) for this request
if (filterChain != null) {
filterChain.release();
}
// Deallocate the allocated servlet instance
try {
if (servlet != null) {
wrapper.deallocate(servlet);
}
} catch (Throwable e) {
ExceptionUtils.handleThrowable(e);
container.getLogger().error(sm.getString("standardWrapper.deallocateException",
wrapper.getName()), e);
if (throwable == null) {
throwable = e;
exception(request, response, e);
}
}
// If this servlet has been marked permanently unavailable,
// unload it and release this instance
try {
if ((servlet != null) &&
(wrapper.getAvailable() == Long.MAX_VALUE)) {
wrapper.unload();
}
} catch (Throwable e) {
ExceptionUtils.handleThrowable(e);
container.getLogger().error(sm.getString("standardWrapper.unloadException",
wrapper.getName()), e);
if (throwable == null) {
exception(request, response, e);
}
}
long t2=System.currentTimeMillis();
long time=t2-t1;
processingTime += time;
if( time > maxTime) maxTime=time;
if( time < minTime) minTime=time;
}
}
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- servlet = wrapper.allocate(); 创建了servlet实例。
- ApplicationFilterChain filterChain = ApplicationFilterFactory.createFilterChain(request, wrapper, servlet); 为当前的请求建立了一个filter链。
- filterChain.doFilter(request.getRequest(),response.getResponse()); 调用这个 Filter 链。这个filter链中的最后一个负责调用servlet。
# Filter
- filter是在Context 容器用 Map 集合来保存 Filter。
- filter链对应每一个请求，
private void internalDoFilter(ServletRequest request,
ServletResponse response)
throws IOException, ServletException {
// Call the next filter if there is one
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);
}
if( Globals.IS_SECURITY_ENABLED ) {
final ServletRequest req = request;
final ServletResponse res = response;
Principal principal =
((HttpServletRequest) req).getUserPrincipal();
Object[] args = new Object[]{req, res, this};
SecurityUtil.doAsPrivilege ("doFilter", filter, classType, args, principal);
} else {
filter.doFilter(request, response, this);
}
} catch (IOException | ServletException | RuntimeException e) {
throw e;
} catch (Throwable e) {
e = ExceptionUtils.unwrapInvocationTargetException(e);
ExceptionUtils.handleThrowable(e);
throw new ServletException(sm.getString("filterChain.filter"), e);
}
return;
}
// We fell off the end of the chain -- call the servlet instance
try {
if (ApplicationDispatcher.WRAP_SAME_OBJECT) {
lastServicedRequest.set(request);
lastServicedResponse.set(response);
}
if (request.isAsyncSupported() && !servletSupportsAsync) {
request.setAttribute(Globals.ASYNC_SUPPORTED_ATTR,
Boolean.FALSE);
}
// Use potentially wrapped request from this point
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);
}
} catch (IOException | ServletException | RuntimeException e) {
throw e;
} catch (Throwable e) {
e = ExceptionUtils.unwrapInvocationTargetException(e);
ExceptionUtils.handleThrowable(e);
throw new ServletException(sm.getString("filterChain.servlet"), e);
} finally {
if (ApplicationDispatcher.WRAP_SAME_OBJECT) {
lastServicedRequest.set(null);
lastServicedResponse.set(null);
}
}
}
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- private ApplicationFilterConfig[] filters = new ApplicationFilterConfig[0]; Filter 链中存有filter数组，并且通过pos来储存当且filter被调用的位置信息。
- 通过pos < n 判断是否都调到了最后一个，开始顺序调用filter。其中filters[pos++]来实现filter链的顺序调用。这么做的原因是因为，每次调用的doFilter方法都是再执行chain.doFilter方法。
- servlet.service(request, response); filter链的最后就调用这个sevlet的service方法。
# Listener
和filter一样，Context 容器也通过数组和list来管理监听器。但是分成了2类。
- 生命周期相关的监听器
- 属性的变化的监听器
// 监听属性值变化的监听器
private List<Object> applicationEventListenersList = new CopyOnWriteArrayList<>();
// 监听生命事件的监听器
private Object applicationLifecycleListenersObjects[] = new Object[0];
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监听器的触发，以ServletContextListener为例子，在Context的启动方法中，其中代用了一个listenerStart方法，其中调用了listener的方法，这里的 ServletContextListener 接口是一种留给用户的扩展机制，用户可以实现这个接口来定义自己的监听器，监听 Context 容器的启停事件。比如可以自定义加载缓存等等。
ServletContextListener lr = (ServletContextListener) instances[i];
lr.contextInitialized(event);
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最后关于Spring与Tomcat的整合部分，找到一篇比较好的文章作为参考。