servlet容器怎么调用init，service，destroy方法，怎么调用Filter的过程
tomcat容器调用的最后一步就是StandardWrapperValve.invoke方法
一、tomcat调用servlet
@Override
public final void invoke(Request request, Response response)
throws IOException, ServletException {
boolean unavailable = false;
Throwable throwable = null;
// This should be a Request attribute...
long t1=System.currentTimeMillis();
requestCount.incrementAndGet();
//获取tomcat容器
StandardWrapper wrapper = (StandardWrapper) getContainer();
Servlet servlet = null;
Context context = (Context) wrapper.getParent();
//验证tomcat容器是否有效
if (!context.getState().isAvailable()) {
response.sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE,
sm.getString("standardContext.isUnavailable"));
unavailable = true;
}
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) {
//获取servlet容器
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);
// 创建Filter链路信息，绑定到当前request信息
ApplicationFilterChain filterChain =
ApplicationFilterFactory.createFilterChain(request, wrapper, servlet);
try {
//如果容器和Fliter链路都存在
if ((servlet != null) && (filterChain != null)) {
// Swallow output if needed
if (context.getSwallowOutput()) {
try {
SystemLogHandler.startCapture();
//是否异步
if (request.isAsyncDispatching()) {
request.getAsyncContextInternal().doInternalDispatch();
} else {
//调用Filter的doFilter方法，默认冲索引0开始，每调用一次+1，索引等于filter数组长度，不在执行doFilter方法，此方法最后通过servlet.sevice(request,response)调用
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);
}
// Release the filter chain (if any) for this request
if (filterChain != null) {
//释放filter链路
filterChain.release();
}
// Deallocate the allocated servlet instance
try {
if (servlet != null) {
//回收servlet容器
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);
}
}
try {
//如果servlet存在，容器不可用，就是关闭了，需要回收servlet
if ((servlet != null) &&
(wrapper.getAvailable() == Long.MAX_VALUE)) {
//回收容器池，并调用servlet的destory方法
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;
}二、申请servlet容器
@Override
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;
// 判断servlet容器是否是单例线程池模型，如果不是，每次都是获取一个新的servlet实例，使用完就会销毁
if (!singleThreadModel) {
// Load and initialize our instance if necessary
if (instance == null || !instanceInitialized) {
synchronized (this) {
if (instance == null) {
try {
if (log.isDebugEnabled()) {
log.debug("Allocating non-STM instance");
}
// Note: We don't know if the Servlet implements
// SingleThreadModel until we have loaded it.
instance = loadServlet();
newInstance = true;
if (!singleThreadModel) {
// For non-STM, increment here to prevent a race
// condition with unload. Bug 43683, test case
// #3
countAllocated.incrementAndGet();
}
} catch (ServletException e) {
throw e;
} catch (Throwable e) {
ExceptionUtils.handleThrowable(e);
throw new ServletException(sm.getString("standardWrapper.allocate"), e);
}
}
if (!instanceInitialized) {
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 {
//初始通过CAS自旋获取实例信息
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;
}
}
//锁定容器池
synchronized (instancePool) {
//如果获取的值大于容器池阈值，直接通过CAS自旋取一个servlet容器
while (countAllocated.get() >= nInstances) {
// 如果值小于阈值，用loadservlet()创建一个servlet放入容器池中，容器池总量++，loadservlet通过反射创建了servlet容器对象之后，会顺带执行它的init方法
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 {
//如果值大于等于阈值，先暂停
try {
instancePool.wait();
} catch (InterruptedException e) {
// Ignore
}
}
}
if (log.isTraceEnabled()) {
log.trace(" Returning allocated STM instance");
}
countAllocated.incrementAndGet();
获取servlet容器，并出栈
return instancePool.pop();
}
}三、调用doFilter，每个实现了Filter的类的doFilter方法最后又需要调用此方法，声明一个final的request和response，用于保证一次Http调用使用的request和response都是同一个对象
@Override
public void doFilter(ServletRequest request, ServletResponse response)
throws IOException, ServletException {
if( Globals.IS_SECURITY_ENABLED ) {
//声明request和response为final，保证servlet的service方法调用的request，和response为线程安全的对象。
final ServletRequest req = request;
final ServletResponse res = response;
try {
java.security.AccessController.doPrivileged(
new java.security.PrivilegedExceptionAction() {
@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);
}
} 四、执行doFilter和servlet容器的service方法
private void internalDoFilter(ServletRequest request,
ServletResponse response)
throws IOException, ServletException {
// Call the next filter if there is one
if (pos < n) {
//pos默认值为0，n为Filter数组大小，每次都++
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 {
//调用Filter实现的doFilter方法，并把当前链路传过去
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 {
//调用servlet的service方法
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) {
//释放request，response
lastServicedRequest.set(null);
lastServicedResponse.set(null);
}
}
}五、回收servlet容器
@Override
public void deallocate(Servlet servlet) throws ServletException {
// 如果不是servlet线程池模型，直接销毁
if (!singleThreadModel) {
countAllocated.decrementAndGet();
return;
}
// 放回容器线程池，唤醒展厅的线程池对象，前面申请不到容器的对象就可以申请了
synchronized (instancePool) {
countAllocated.decrementAndGet();
instancePool.push(servlet);
instancePool.notify();
}
}六、销毁tomcat容器和servlet容器（调用所有servlet的destroy方法）
@Override
public synchronized void unload() throws ServletException {
// Nothing to do if we have never loaded the instance
if (!singleThreadModel && (instance == null))
return;
unloading = true;
// Loaf a while if the current instance is allocated
// (possibly more than once if non-STM)
if (countAllocated.get() > 0) {
int nRetries = 0;
long delay = unloadDelay / 20;
while ((nRetries < 21) && (countAllocated.get() > 0)) {
if ((nRetries % 10) == 0) {
log.info(sm.getString("standardWrapper.waiting",
countAllocated.toString(),
getName()));
}
try {
Thread.sleep(delay);
} catch (InterruptedException e) {
// Ignore
}
nRetries++;
}
}
if (instanceInitialized) {
PrintStream out = System.out;
if (swallowOutput) {
SystemLogHandler.startCapture();
}
// Call the servlet destroy() method
try {
if( Globals.IS_SECURITY_ENABLED) {
try {
SecurityUtil.doAsPrivilege("destroy", instance);
} finally {
SecurityUtil.remove(instance);
}
} else {
//调用servlet的destroy方法
instance.destroy();
}
} catch (Throwable t) {
t = ExceptionUtils.unwrapInvocationTargetException(t);
ExceptionUtils.handleThrowable(t);
instance = null;
instancePool = null;
nInstances = 0;
fireContainerEvent("unload", this);
unloading = false;
throw new ServletException
(sm.getString("standardWrapper.destroyException", getName()),
t);
} finally {
// Annotation processing
if (!((Context) getParent()).getIgnoreAnnotations()) {
try {
((Context)getParent()).getInstanceManager().destroyInstance(instance);
} catch (Throwable t) {
ExceptionUtils.handleThrowable(t);
log.error(sm.getString("standardWrapper.destroyInstance", getName()), t);
}
}
// Write captured output
if (swallowOutput) {
String log = SystemLogHandler.stopCapture();
if (log != null && log.length() > 0) {
if (getServletContext() != null) {
getServletContext().log(log);
} else {
out.println(log);
}
}
}
}
}
// Deregister the destroyed instance
instance = null;
instanceInitialized = false;
if (isJspServlet && jspMonitorON != null ) {
Registry.getRegistry(null, null).unregisterComponent(jspMonitorON);
}
if (singleThreadModel && (instancePool != null)) {
try {
while (!instancePool.isEmpty()) {
Servlet s = instancePool.pop();
if (Globals.IS_SECURITY_ENABLED) {
try {
SecurityUtil.doAsPrivilege("destroy", s);
} finally {
SecurityUtil.remove(s);
}
} else {
s.destroy();
}
// Annotation processing
if (!((Context) getParent()).getIgnoreAnnotations()) {
((StandardContext)getParent()).getInstanceManager().destroyInstance(s);
}
}
} catch (Throwable t) {
t = ExceptionUtils.unwrapInvocationTargetException(t);
ExceptionUtils.handleThrowable(t);
instancePool = null;
nInstances = 0;
unloading = false;
fireContainerEvent("unload", this);
throw new ServletException
(sm.getString("standardWrapper.destroyException",
getName()), t);
}
instancePool = null;
nInstances = 0;
}
singleThreadModel = false;
unloading = false;
fireContainerEvent("unload", this);
}