前一篇文章分析到了org.apache.catalina.deploy.WebXml类的configureContext方法，可以看到在这个方法中通过各种setXXX、addXXX方法的调用，使得每个应用中的web.xml文件的解析后将应用内部的表示Servlet、Listener、Filter的配置信息与表示一个web应用的Context对象关联起来。
这里列出configureContext方法中与Servlet、Listener、Filter的配置信息设置相关的调用代码：
for (FilterDef filter : filters.values()) {
if (filter.getAsyncSupported() == null) {
filter.setAsyncSupported("false");
}
context.addFilterDef(filter);
}
for (FilterMap filterMap : filterMaps) {
context.addFilterMap(filterMap);
}
这是设置Filter相关配置信息的。
for (String listener : listeners) {
context.addApplicationListener(
new ApplicationListener(listener, false));
}
这是给应用添加Listener的。
for (ServletDef servlet : servlets.values()) {
Wrapper wrapper = context.createWrapper();
// Description is ignored
// Display name is ignored
// Icons are ignored
// jsp-file gets passed to the JSP Servlet as an init-param
if (servlet.getLoadOnStartup() != null) {
wrapper.setLoadOnStartup(servlet.getLoadOnStartup().intValue());
}
if (servlet.getEnabled() != null) {
wrapper.setEnabled(servlet.getEnabled().booleanValue());
}
wrapper.setName(servlet.getServletName());
Map<String,String> params = servlet.getParameterMap();
for (Entry<String, String> entry : params.entrySet()) {
wrapper.addInitParameter(entry.getKey(), entry.getValue());
}
wrapper.setRunAs(servlet.getRunAs());
Set<SecurityRoleRef> roleRefs = servlet.getSecurityRoleRefs();
for (SecurityRoleRef roleRef : roleRefs) {
wrapper.addSecurityReference(
roleRef.getName(), roleRef.getLink());
}
wrapper.setServletClass(servlet.getServletClass());
MultipartDef multipartdef = servlet.getMultipartDef();
if (multipartdef != null) {
if (multipartdef.getMaxFileSize() != null &&
multipartdef.getMaxRequestSize()!= null &&
multipartdef.getFileSizeThreshold() != null) {
wrapper.setMultipartConfigElement(new MultipartConfigElement(
multipartdef.getLocation(),
Long.parseLong(multipartdef.getMaxFileSize()),
Long.parseLong(multipartdef.getMaxRequestSize()),
Integer.parseInt(
multipartdef.getFileSizeThreshold())));
} else {
wrapper.setMultipartConfigElement(new MultipartConfigElement(
multipartdef.getLocation()));
}
}
if (servlet.getAsyncSupported() != null) {
wrapper.setAsyncSupported(
servlet.getAsyncSupported().booleanValue());
}
wrapper.setOverridable(servlet.isOverridable());
context.addChild(wrapper);
}
for (Entry<String, String> entry : servletMappings.entrySet()) {
context.addServletMapping(entry.getKey(), entry.getValue());
}
这段代码是设置Servlet的相关配置信息的。
以上是在各个web应用的web.xml文件中（如果是servlet3，还会包括将这些配置信息放在类的注解中，所以解析web.xml文件之前可能会存在各个web.xml文件信息的合并步骤，这些动作的代码在前一篇文章中讲ContextConfig类的webConfig方法中）的相关配置信息的设置，但需要注意的是，这里仅仅是将这些配置信息保存到了StandardContext的相应实例变量中，真正在一次请求访问中用到的Servlet、Listener、Filter的实例并没有构造出来，以上方法调用仅构造了代表这些实例的封装类的实例，如StandardWrapper、ApplicationListener、FilterDef、FilterMap。
那么一个web应用中的Servlet、Listener、Filter的实例究竟在什么时候构造出来的呢？答案在org.apache.catalina.core.StandardContext类的startInternal方法中：
protected synchronized void startInternal() throws LifecycleException {
if(log.isDebugEnabled())
log.debug("Starting " + getBaseName());
// Send j2ee.state.starting notification
if (this.getObjectName() != null) {
Notification notification = new Notification("j2ee.state.starting",
this.getObjectName(), sequenceNumber.getAndIncrement());
broadcaster.sendNotification(notification);
}
setConfigured(false);
boolean ok = true;
// Currently this is effectively a NO-OP but needs to be called to
// ensure the NamingResources follows the correct lifecycle
if (namingResources != null) {
namingResources.start();
}
// Add missing components as necessary
if (webappResources == null) { // (1) Required by Loader
if (log.isDebugEnabled())
log.debug("Configuring default Resources");
try {
if ((getDocBase() != null) && (getDocBase().endsWith(".war")) &&
(!(new File(getBasePath())).isDirectory()))
setResources(new WARDirContext());
else
setResources(new FileDirContext());
} catch (IllegalArgumentException e) {
log.error("Error initializing resources: " + e.getMessage());
ok = false;
}
}
if (ok) {
if (!resourcesStart()) {
log.error( "Error in resourceStart()");
ok = false;
}
}
if (getLoader() == null) {
WebappLoader webappLoader = new WebappLoader(getParentClassLoader());
webappLoader.setDelegate(getDelegate());
setLoader(webappLoader);
}
// Initialize character set mapper
getCharsetMapper();
// Post work directory
postWorkDirectory();
// Validate required extensions
boolean dependencyCheck = true;
try {
dependencyCheck = ExtensionValidator.validateApplication
(getResources(), this);
} catch (IOException ioe) {
log.error("Error in dependencyCheck", ioe);
dependencyCheck = false;
}
if (!dependencyCheck) {
// do not make application available if depency check fails
ok = false;
}
// Reading the "catalina.useNaming" environment variable
String useNamingProperty = System.getProperty("catalina.useNaming");
if ((useNamingProperty != null)
&& (useNamingProperty.equals("false"))) {
useNaming = false;
}
if (ok && isUseNaming()) {
if (getNamingContextListener() == null) {
NamingContextListener ncl = new NamingContextListener();
ncl.setName(getNamingContextName());
ncl.setExceptionOnFailedWrite(getJndiExceptionOnFailedWrite());
addLifecycleListener(ncl);
setNamingContextListener(ncl);
}
}
// Standard container startup
if (log.isDebugEnabled())
log.debug("Processing standard container startup");
// Binding thread
ClassLoader oldCCL = bindThread();
try {
if (ok) {
// Start our subordinate components, if any
if ((loader != null) && (loader instanceof Lifecycle))
((Lifecycle) loader).start();
// since the loader just started, the webapp classloader is now
// created.
// By calling unbindThread and bindThread in a row, we setup the
// current Thread CCL to be the webapp classloader
unbindThread(oldCCL);
oldCCL = bindThread();
// Initialize logger again. Other components might have used it
// too early, so it should be reset.
logger = null;
getLogger();
if ((cluster != null) && (cluster instanceof Lifecycle))
((Lifecycle) cluster).start();
Realm realm = getRealmInternal();
if ((realm != null) && (realm instanceof Lifecycle))
((Lifecycle) realm).start();
if ((resources != null) && (resources instanceof Lifecycle))
((Lifecycle) resources).start();
// Notify our interested LifecycleListeners
fireLifecycleEvent(Lifecycle.CONFIGURE_START_EVENT, null);
// Start our child containers, if not already started
for (Container child : findChildren()) {
if (!child.getState().isAvailable()) {
child.start();
}
}
// Start the Valves in our pipeline (including the basic),
// if any
if (pipeline instanceof Lifecycle) {
((Lifecycle) pipeline).start();
}
// Acquire clustered manager
Manager contextManager = null;
if (manager == null) {
if (log.isDebugEnabled()) {
log.debug(sm.getString("standardContext.cluster.noManager",
Boolean.valueOf((getCluster() != null)),
Boolean.valueOf(distributable)));
}
if ( (getCluster() != null) && distributable) {
try {
contextManager = getCluster().createManager(getName());
} catch (Exception ex) {
log.error("standardContext.clusterFail", ex);
ok = false;
}
} else {
contextManager = new StandardManager();
}
}
// Configure default manager if none was specified
if (contextManager != null) {
if (log.isDebugEnabled()) {
log.debug(sm.getString("standardContext.manager",
contextManager.getClass().getName()));
}
setManager(contextManager);
}
if (manager!=null && (getCluster() != null) && distributable) {
//let the cluster know that there is a context that is distributable
//and that it has its own manager
getCluster().registerManager(manager);
}
}
} finally {
// Unbinding thread
unbindThread(oldCCL);
}
if (!getConfigured()) {
log.error( "Error getConfigured");
ok = false;
}
// We put the resources into the servlet context
if (ok)
getServletContext().setAttribute
(Globals.RESOURCES_ATTR, getResources());
// Initialize associated mapper
mapper.setContext(getPath(), welcomeFiles, resources);
// Binding thread
oldCCL = bindThread();
if (ok ) {
if (getInstanceManager() == null) {
javax.naming.Context context = null;
if (isUseNaming() && getNamingContextListener() != null) {
context = getNamingContextListener().getEnvContext();
}
Map<String, Map<String, String>> injectionMap = buildInjectionMap(
getIgnoreAnnotations() ? new NamingResources(): getNamingResources());
setInstanceManager(new DefaultInstanceManager(context,
injectionMap, this, this.getClass().getClassLoader()));
getServletContext().setAttribute(
InstanceManager.class.getName(), getInstanceManager());
}
}
try {
// Create context attributes that will be required
if (ok) {
getServletContext().setAttribute(
JarScanner.class.getName(), getJarScanner());
}
// Set up the context init params
mergeParameters();
// Call ServletContainerInitializers
for (Map.Entry<ServletContainerInitializer, Set<Class<?>>> entry :
initializers.entrySet()) {
try {
entry.getKey().onStartup(entry.getValue(),
getServletContext());
} catch (ServletException e) {
log.error(sm.getString("standardContext.sciFail"), e);
ok = false;
break;
}
}
// Configure and call application event listeners
if (ok) {
if (!listenerStart()) {
log.error( "Error listenerStart");
ok = false;
}
}
try {
// Start manager
if ((manager != null) && (manager instanceof Lifecycle)) {
((Lifecycle) getManager()).start();
}
} catch(Exception e) {
log.error("Error manager.start()", e);
ok = false;
}
// Configure and call application filters
if (ok) {
if (!filterStart()) {
log.error("Error filterStart");
ok = false;
}
}
// Load and initialize all "load on startup" servlets
if (ok) {
loadOnStartup(findChildren());
}
// Start ContainerBackgroundProcessor thread
super.threadStart();
} finally {
// Unbinding thread
unbindThread(oldCCL);
}
// Set available status depending upon startup success
if (ok) {
if (log.isDebugEnabled())
log.debug("Starting completed");
} else {
log.error(sm.getString("standardContext.startFailed", getName()));
}
startTime=System.currentTimeMillis();
// Send j2ee.state.running notification
if (ok && (this.getObjectName() != null)) {
Notification notification =
new Notification("j2ee.state.running", this.getObjectName(),
sequenceNumber.getAndIncrement());
broadcaster.sendNotification(notification);
}
// Close all JARs right away to avoid always opening a peak number
// of files on startup
if (getLoader() instanceof WebappLoader) {
((WebappLoader) getLoader()).closeJARs(true);
}
// Reinitializing if something went wrong
if (!ok) {
setState(LifecycleState.FAILED);
} else {
setState(LifecycleState.STARTING);
}
}
这303行可以讲的东西有很多，为了不偏离本文主题只抽出与现在要讨论的问题相关的代码来分析。
第125行会发布一个CONFIGURE_START_EVENT事件，按前一篇博文所述，这里即会触发对web.xml的解析。第205、206行设置实例管理器为DefaultInstanceManager（这个类在后面谈实例构造时会用到）。第237行会调用listenerStart方法，第255行调用了filterStart方法，第263行调用了loadOnStartup方法，这三处调用即触发Listener、Filter、Servlet真正对象的构造，下面逐个分析这些方法。
listenerStart方法的完整代码较长，这里仅列出与Listenner对象构造相关的代码：
// Instantiate the required listeners
ApplicationListener listeners[] = applicationListeners;
Object results[] = new Object[listeners.length];
boolean ok = true;
Set<Object> noPluggabilityListeners = new HashSet<Object>();
for (int i = 0; i < results.length; i++) {
if (getLogger().isDebugEnabled())
getLogger().debug(" Configuring event listener class '" +
listeners[i] + "'");
try {
ApplicationListener listener = listeners[i];
results[i] = instanceManager.newInstance(
listener.getClassName());
if (listener.isPluggabilityBlocked()) {
noPluggabilityListeners.add(results[i]);
}
} catch (Throwable t) {
t = ExceptionUtils.unwrapInvocationTargetException(t);
ExceptionUtils.handleThrowable(t);
getLogger().error
(sm.getString("standardContext.applicationListener",
listeners[i]), t);
ok = false;
}
}
先从Context对象中取出实例变量applicationListeners（该变量的值在web.xml解析时设置），第12行通过调用instanceManager.newInstance(listener.getClassName())，前面在看StandardContext的startInternal方法第205行时看到instanceManager被设置为DefaultInstanceManager对象，所以这里实际会执行DefaultInstanceManager类的newInstance方法：
public Object newInstance(String className) throws IllegalAccessException, InvocationTargetException, NamingException, InstantiationException, ClassNotFoundException {
Class<?> clazz = loadClassMaybePrivileged(className, classLoader);
return newInstance(clazz.newInstance(), clazz);
}
所以instanceManager.newInstance(listener.getClassName())这段代码的作用是取出web.xml中配置的Listener的class配置信息，从而构造实际配置的Listener对象。
看下filterStart方法：
public boolean filterStart() {
if (getLogger().isDebugEnabled())
getLogger().debug("Starting filters");
// Instantiate and record a FilterConfig for each defined filter
boolean ok = true;
synchronized (filterConfigs) {
filterConfigs.clear();
Iterator<String> names = filterDefs.keySet().iterator();
while (names.hasNext()) {
String name = names.next();
if (getLogger().isDebugEnabled())
getLogger().debug(" Starting filter '" + name + "'");
ApplicationFilterConfig filterConfig = null;
try {
filterConfig =
new ApplicationFilterConfig(this, filterDefs.get(name));
filterConfigs.put(name, filterConfig);
} catch (Throwable t) {
t = ExceptionUtils.unwrapInvocationTargetException(t);
ExceptionUtils.handleThrowable(t);
getLogger().error
(sm.getString("standardContext.filterStart", name), t);
ok = false;
}
}
}
return (ok);
}
这段代码看起来很简单，取出web.xml解析时读到的filter配置信息，在第17行调用ApplicationFilterConfig了构造方法：
ApplicationFilterConfig(Context context, FilterDef filterDef)
throws ClassCastException, ClassNotFoundException,
IllegalAccessException, InstantiationException,
ServletException, InvocationTargetException, NamingException {
super();
this.context = context;
this.filterDef = filterDef;
// Allocate a new filter instance if necessary
if (filterDef.getFilter() == null) {
getFilter();
} else {
this.filter = filterDef.getFilter();
getInstanceManager().newInstance(filter);
initFilter();
}
}
默认情况下filterDef中是没有Filter对象的，所以会调用第12行getFilter方法：
Filter getFilter() throws ClassCastException, ClassNotFoundException,
IllegalAccessException, InstantiationException, ServletException,
InvocationTargetException, NamingException {
// Return the existing filter instance, if any
if (this.filter != null)
return (this.filter);
// Identify the class loader we will be using
String filterClass = filterDef.getFilterClass();
this.filter = (Filter) getInstanceManager().newInstance(filterClass);
initFilter();
return (this.filter);
}
与Listener的对象构造类似，都是通过调用getInstanceManager().newInstance方法。当然，按照Servlet规范，第13行还会调用Filter的init方法。
看下loadOnStartup方法：
public void loadOnStartup(Container children[]) {
// Collect "load on startup" servlets that need to be initialized
TreeMap<Integer, ArrayList<Wrapper>> map =
new TreeMap<Integer, ArrayList<Wrapper>>();
for (int i = 0; i < children.length; i++) {
Wrapper wrapper = (Wrapper) children[i];
int loadOnStartup = wrapper.getLoadOnStartup();
if (loadOnStartup < 0)
continue;
Integer key = Integer.valueOf(loadOnStartup);
ArrayList<Wrapper> list = map.get(key);
if (list == null) {
list = new ArrayList<Wrapper>();
map.put(key, list);
}
list.add(wrapper);
}
// Load the collected "load on startup" servlets
for (ArrayList<Wrapper> list : map.values()) {
for (Wrapper wrapper : list) {
try {
wrapper.load();
} catch (ServletException e) {
getLogger().error(sm.getString("standardWrapper.loadException",
getName()), StandardWrapper.getRootCause(e));
// NOTE: load errors (including a servlet that throws
// UnavailableException from tht init() method) are NOT
// fatal to application startup
}
}
}
}
在web应用启动时将会加载配置了load-on-startup属性的Servlet。第24行，调用了StandardWrapper类的load方法：
public synchronized void load() throws ServletException {
instance = loadServlet();
if (!instanceInitialized) {
initServlet(instance);
}
if (isJspServlet) {
StringBuilder oname =
new StringBuilder(MBeanUtils.getDomain(getParent()));
oname.append(":type=JspMonitor,name=");
oname.append(getName());
oname.append(getWebModuleKeyProperties());
try {
jspMonitorON = new ObjectName(oname.toString());
Registry.getRegistry(null, null)
.registerComponent(instance, jspMonitorON, null);
} catch( Exception ex ) {
log.info("Error registering JSP monitoring with jmx " +
instance);
}
}
}
在第2行loadServlet方法中与上面的Listener和Filter对象构造一样调用instanceManager.newInstance来构造Servlet对象，与Filter类似在第5行调用Servlet的init方法。
当然，这种加载只是针对配置了load-on-startup属性的Servlet而言，其它一般Servlet的加载和初始化会推迟到真正请求访问web应用而第一次调用该Servlet时，下面会看到这种情况下代码分析。
以上分析的web应用启动后这些对象的加载情况，接下来分析一下一次请求访问时，相关的Filter、Servlet对象的调用。
在本博前面的《Tomcat7中一次请求处理的前世今生》系列文章中曾经分析了一次请求如何与容器中的Engine、Host、Context、Wrapper各级组件匹配，并在这些容器组件内部的管道中流转的。在该系列第四篇文章最后提到，一次请求最终会执行与它最适配的一个StandardWrapper的基础阀org.apache.catalina.core.StandardWrapperValve的invoke方法。当时限于篇幅没继续往下分析，这里接着这段来看看请求的流转。看下invoke方法的代码：
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++;
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;
}
// Identify if the request is Comet related now that the servlet has been allocated
boolean comet = false;
if (servlet instanceof CometProcessor && request.getAttribute(
Globals.COMET_SUPPORTED_ATTR) == Boolean.TRUE) {
comet = true;
request.setComet(true);
}
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
ApplicationFilterFactory factory =
ApplicationFilterFactory.getInstance();
ApplicationFilterChain filterChain =
factory.createFilterChain(request, wrapper, servlet);
// Reset comet flag value after creating the filter chain
request.setComet(false);
// Call the filter chain for this request
// NOTE: This also calls the servlet's service() method
try {
if ((servlet != null) && (filterChain != null)) {
// Swallow output if needed
if (context.getSwallowOutput()) {
try {
SystemLogHandler.startCapture();
if (request.isAsyncDispatching()) {
//TODO SERVLET3 - async
((AsyncContextImpl)request.getAsyncContext()).doInternalDispatch();
} else if (comet) {
filterChain.doFilterEvent(request.getEvent());
request.setComet(true);
} 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()) {
//TODO SERVLET3 - async
((AsyncContextImpl)request.getAsyncContext()).doInternalDispatch();
} else if (comet) {
request.setComet(true);
filterChain.doFilterEvent(request.getEvent());
} else {
filterChain.doFilter
(request.getRequest(), response.getResponse());
}
}
}
} catch (ClientAbortException 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);
}
// Release the filter chain (if any) for this request
if (filterChain != null) {
if (request.isComet()) {
// If this is a Comet request, then the same chain will be used for the
// processing of all subsequent events.
filterChain.reuse();
} else {
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) {
throwable = e;
exception(request, response, e);
}
}
long t2=System.currentTimeMillis();
long time=t2-t1;
processingTime += time;
if( time > maxTime) maxTime=time;
if( time < minTime) minTime=time;
}
因为要支持Servlet3的新特性及各种异常处理，这段代码显得比较长。关注重点第42行，这里会调用StandardWrapper的allocate方法，不再贴出这个方法的代码，需要提醒的是在allocate方法中可能会调用loadServlet()方法，这就是上一段提到的请求访问web应用而第一次调用该Servlet时再加载并初始化Servlet。
第87到91行会构造一个过滤器链（filterChain）用于执行这一次请求所经过的相应Filter，第111和第128行会调用该filterChain的doFilter方法：
public void doFilter(ServletRequest request, ServletResponse response)
throws IOException, ServletException {
if( Globals.IS_SECURITY_ENABLED ) {
final ServletRequest req = request;
final ServletResponse res = response;
try {
java.security.AccessController.doPrivileged(
new java.security.PrivilegedExceptionAction<Void>() {
@Override
public Void run()
throws ServletException, IOException {
internalDoFilter(req,res);
return null;
}
}
);
} catch( PrivilegedActionException pe) {
Exception e = pe.getException();
if (e instanceof ServletException)
throw (ServletException) e;
else if (e instanceof IOException)
throw (IOException) e;
else if (e instanceof RuntimeException)
throw (RuntimeException) e;
else
throw new ServletException(e.getMessage(), e);
}
} else {
internalDoFilter(request,response);
}
}
在该方法最后调用了internalDoFilter方法：
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++];
Filter filter = null;
try {
filter = filterConfig.getFilter();
support.fireInstanceEvent(InstanceEvent.BEFORE_FILTER_EVENT,
filter, request, response);
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);
}
support.fireInstanceEvent(InstanceEvent.AFTER_FILTER_EVENT,
filter, request, response);
} catch (IOException e) {
if (filter != null)
support.fireInstanceEvent(InstanceEvent.AFTER_FILTER_EVENT,
filter, request, response, e);
throw e;
} catch (ServletException e) {
if (filter != null)
support.fireInstanceEvent(InstanceEvent.AFTER_FILTER_EVENT,
filter, request, response, e);
throw e;
} catch (RuntimeException e) {
if (filter != null)
support.fireInstanceEvent(InstanceEvent.AFTER_FILTER_EVENT,
filter, request, response, e);
throw e;
} catch (Throwable e) {
e = ExceptionUtils.unwrapInvocationTargetException(e);
ExceptionUtils.handleThrowable(e);
if (filter != null)
support.fireInstanceEvent(InstanceEvent.AFTER_FILTER_EVENT,
filter, request, response, 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);
}
support.fireInstanceEvent(InstanceEvent.BEFORE_SERVICE_EVENT,
servlet, request, response);
if (request.isAsyncSupported()
&& !support.getWrapper().isAsyncSupported()) {
request.setAttribute(Globals.ASYNC_SUPPORTED_ATTR,
Boolean.FALSE);
}
// Use potentially wrapped request from this point
if ((request instanceof HttpServletRequest) &&
(response instanceof HttpServletResponse)) {
if( 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);
}
} else {
servlet.service(request, response);
}
support.fireInstanceEvent(InstanceEvent.AFTER_SERVICE_EVENT,
servlet, request, response);
} catch (IOException e) {
support.fireInstanceEvent(InstanceEvent.AFTER_SERVICE_EVENT,
servlet, request, response, e);
throw e;
} catch (ServletException e) {
support.fireInstanceEvent(InstanceEvent.AFTER_SERVICE_EVENT,
servlet, request, response, e);
throw e;
} catch (RuntimeException e) {
support.fireInstanceEvent(InstanceEvent.AFTER_SERVICE_EVENT,
servlet, request, response, e);
throw e;
} catch (Throwable e) {
ExceptionUtils.handleThrowable(e);
support.fireInstanceEvent(InstanceEvent.AFTER_SERVICE_EVENT,
servlet, request, response, e);
throw new ServletException
(sm.getString("filterChain.servlet"), e);
} finally {
if (ApplicationDispatcher.WRAP_SAME_OBJECT) {
lastServicedRequest.set(null);
lastServicedResponse.set(null);
}
}
}
概述一下这段代码，第6到60行是执行过滤器链中的各个过滤器的doFilter方法，实例变量n表示过滤器链中所有的过滤器，pos表示当前要执行的过滤器。其中第7行取出当前要执行的Filter，之后将pos加1，接着第30行执行Filter的doFilter方法。一般的过滤器实现中在最后都会有这一句：
FilterChain.doFilter(request, response);
这样就又回到了filterChain的doFilter方法，形成了一个递归调用。要注意的是，filterChain对象内部的pos是不断加的，所以假如过滤器链中的各个Filter的doFilter方法都执行完之后将会执行到第63行，在接下来的第92行、第95行即调用Servlet的service方法。
相关推荐
Web服务器中的三大组件，即Servlet、Filter和Listener，是构建动态Web应用程序的关键元素。这些组件都是基于Java的，主要用于增强和扩展Web服务器的功能。 Servlet是Java中用于处理HTTP请求的核心组件，它是动态...
在web.xml文件中，你可以通过`<listener>`元素定义监听器，当Web应用启动时，Tomcat会实例化这些监听器并调用相应的初始化方法。 ```xml <listener> <listener-class>org.springframework.web.context....
7. **过滤器（Filter）和监听器（Listener）**：演示如何实现请求过滤和监听用户登录、注销等事件。 8. **部署与运行**：介绍如何在Tomcat服务器上部署Web应用，包括WAR文件的打包和发布。 9. **异常处理**：使用`...
在Java Web开发中，Servlet、Filter和Listener是三个核心组件，它们构成了Web应用程序的基础架构，用于处理HTTP请求、实现业务逻辑以及管理应用的生命周期。现在，让我们深入探讨这些概念及其在实际开发中的应用。 ...
7. **Pluggable Servlet上下文**：开发者可以通过实现`javax.servlet.ServletContextListener`来创建自定义的Servlet上下文，从而更灵活地控制Web应用程序的启动和停止过程。 8. **过滤器链的改进**：Servlet 3.0...
Servlet中的Filter是Java Web开发中的一个重要组件，它主要用于在Servlet处理请求之前或之后对请求和响应进行拦截和处理。Filter不直接处理用户请求，而是通过Filter链的方式串联多个Filter，形成一个处理流程。 1....
压缩包中的`servletapi`可能包含了Servlet API的完整JAR文件，通常在Java Web开发中，这个JAR会被添加到Web应用的类路径中，以便Web容器（如Tomcat、Jetty等）能够识别并调用Servlet API提供的功能。 综上所述，...
Servlet容器（如Tomcat）会在第一次请求时加载Servlet并调用init()方法，之后每次请求都会调用service()方法，最后在容器关闭或Servlet不再需要时调用destroy()方法。 5. **Servlet配置**：Servlet的配置通常在web....
通过源码，我们可以理解这些安全机制是如何集成到Servlet API中的，以及如何在实际应用中启用和配置它们。 七、异步处理与WebSocket支持 Servlet 4.0引入了异步处理能力，使得服务器可以在不阻塞线程的情况下处理长...
在Web.xml文件中，配置元素的物理顺序并不影响加载顺序，例如，监听器（Listener）、过滤器（Filter）和Servlet的加载顺序是固定的：`context-param` -> `listener` -> `filter` -> `servlet`。尽管`filter`和`...
总结，Servlet是Java Web开发的重要组成部分，理解其工作原理和使用方式对于开发高效、健壮的Web应用至关重要。通过学习和实践，开发者可以更好地驾驭Java Web世界，构建出满足各种需求的Web应用程序。
在本“Servlet中文帮助”中，我们将深入探讨Servlet的基本概念、工作原理以及如何在实际项目中应用。 一、Servlet基本概念 Servlet是一种Java类，遵循Java Servlet API规范，它被设计用来接收和响应HTTP请求。...
本文将深入探讨这个主题，重点关注Web容器如何处理配置文件`web.xml`，以及不同组件（如`context-param`、`listener`、`filter`和`servlet`）的加载顺序。 首先，当一个Web项目启动时，Web容器（如Tomcat、Jetty等...
最重要的是，Tomcat 7完全支持Servlet 3.0规范，这意味着开发者可以使用注解来配置Servlet、Filter和Listener，减少了web.xml文件的维护工作。此外，Servlet 3.0引入了异步Servlet，允许在后台处理请求，提高响应...
Tomcat作为一款广泛使用的开源Java Servlet容器，它的性能和可扩展性使得它在Web应用部署中占据重要地位。源码分析对于理解其运行原理、优化性能和解决潜在问题具有重要意义。 【描述】：虽然描述为空，但我们可以...
Servlet是Java Web开发中的核心组件，它用于处理...掌握这些概念有助于理解Web应用的工作原理，以及如何在实际项目中有效地使用Servlet和容器提供的功能。通过深入学习和实践，开发者可以构建出高效、可靠的Web服务。
当你在浏览器中访问一个Web应用时，请求会被发送到Web服务器，服务器上的Servlet容器（如Tomcat、Jetty等）会识别出请求并调用相应的Servlet来处理。Servlet通过实现javax.servlet.Servlet接口或其子接口，如javax....
4. **加载Web应用**: Tomcat解析`WEB-INF/web.xml`文件，这是Web应用的部署描述符，包含了Servlet、Filter和Listener的配置。 5. **Servlet容器与Web应用交互**: 当收到HTTP请求时，Tomcat会根据请求的URL找到对应...