深入理解Tomcat系列之五:Context容器和Wrapper容器
前言
Context容器是一個Web項目的代表,主要管理Servlet實例,在Tomcat中Servlet實例是以Wrapper出現的。如今問題是怎樣才幹通過Context容器找到詳細的Servlet呢?在解決問題之前。Context容器須要先啟動,啟動的過程就是載入個類資源文件以及打開子容器以及Pipeline管道的過程。啟動Context容器後。就能夠處理詳細的請求了,詳細是通過Request對象,從代碼清單4-3的Wrapper wrapper = request.getWrapper()
就能夠看出來。
那麽Context調用invoke方法後又發生什麽了呢?詳細運行的是org.apache.catalina.core.StandardContextValve的invoke方法。相當於進入了Context管道中,要開始通過管道中一個個閘門了。
StandardContext的處理流程能夠用以下的圖簡化:
代碼清單4-3:
/** * Select the appropriate child Wrapper to process this request, * based on the specified request URI. If no matching Wrapper can * be found, return an appropriate HTTP error. * * @param request Request to be processed * @param response Response to be produced * * @exception IOException if an input/output error occurred * @exception ServletException if a servlet error occurred */ @Override public final void invoke(Request request, Response response) throws IOException, ServletException { // Disallow any direct access to resources under WEB-INF or META-INF MessageBytes requestPathMB = request.getRequestPathMB(); if ((requestPathMB.startsWithIgnoreCase("/META-INF/", 0)) || (requestPathMB.equalsIgnoreCase("/META-INF")) || (requestPathMB.startsWithIgnoreCase("/WEB-INF/", 0)) || (requestPathMB.equalsIgnoreCase("/WEB-INF"))) { response.sendError(HttpServletResponse.SC_NOT_FOUND); return; } // Select the Wrapper to be used for this Request Wrapper wrapper = request.getWrapper(); if (wrapper == null || wrapper.isUnavailable()) { response.sendError(HttpServletResponse.SC_NOT_FOUND); return; } // Acknowledge the request try { response.sendAcknowledgement(); } catch (IOException ioe) { container.getLogger().error(sm.getString( "standardContextValve.acknowledgeException"), ioe); request.setAttribute(RequestDispatcher.ERROR_EXCEPTION, ioe); response.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR); return; } if (request.isAsyncSupported()) { request.setAsyncSupported(wrapper.getPipeline().isAsyncSupported()); } wrapper.getPipeline().getFirst().invoke(request, response); }
- 禁止直接訪問WEB-INF或者META-INF文件夾下的資源
- 選擇詳細的Wrapper處理請求
- 返回一個確認響應
- 調用Wrapper容器的invoke方法,把處理請求交給StandardWrapperValve處理
Wrapper容器
Wrapper容器負責管理一個Servlet,包含Servlet的裝載、初始化、資源回收。Wrapper是最底層的容器,其不能在加入子容器了。Wrapper是一個接口。其標準實現類是StandardWrapper,以下是這兩個類的結構:
上面的圖都僅僅是類的一部分。因為Wrapper與Servlet息息相關。當中的loadServlet方法負責裝載Servlet,其源代碼例如以下:
代碼清單4-4:
/**
* Load and initialize an instance of this servlet, if there is not already
* at least one initialized instance. This can be used, for example, to
* load servlets that are marked in the deployment descriptor to be loaded
* at server startup time.
*/
public synchronized Servlet loadServlet() throws ServletException {
if (unloading) {
throw new ServletException(
sm.getString("standardWrapper.unloading", getName()));
}
// Nothing to do if we already have an instance or an instance pool
if (!singleThreadModel && (instance != null))
return instance;
PrintStream out = System.out;
if (swallowOutput) {
SystemLogHandler.startCapture();
}
Servlet servlet;
try {
long t1=System.currentTimeMillis();
// Complain if no servlet class has been specified
if (servletClass == null) {
unavailable(null);
throw new ServletException
(sm.getString("standardWrapper.notClass", getName()));
}
InstanceManager instanceManager = ((StandardContext)getParent()).getInstanceManager();
try {
servlet = (Servlet) instanceManager.newInstance(servletClass);
} catch (ClassCastException e) {
unavailable(null);
// Restore the context ClassLoader
throw new ServletException
(sm.getString("standardWrapper.notServlet", servletClass), e);
} catch (Throwable e) {
e = ExceptionUtils.unwrapInvocationTargetException(e);
ExceptionUtils.handleThrowable(e);
unavailable(null);
// Added extra log statement for Bugzilla 36630:
// http://issues.apache.org/bugzilla/show_bug.cgi?id=36630
if(log.isDebugEnabled()) {
log.debug(sm.getString("standardWrapper.instantiate", servletClass), e);
}
// Restore the context ClassLoader
throw new ServletException
(sm.getString("standardWrapper.instantiate", servletClass), e);
}
if (multipartConfigElement == null) {
MultipartConfig annotation =
servlet.getClass().getAnnotation(MultipartConfig.class);
if (annotation != null) {
multipartConfigElement =
new MultipartConfigElement(annotation);
}
}
processServletSecurityAnnotation(servlet.getClass());
// Special handling for ContainerServlet instances
if ((servlet instanceof ContainerServlet) &&
(isContainerProvidedServlet(servletClass) ||
((Context) getParent()).getPrivileged() )) {
((ContainerServlet) servlet).setWrapper(this);
}
classLoadTime=(int) (System.currentTimeMillis() -t1);
if (servlet instanceof SingleThreadModel) {
if (instancePool == null) {
instancePool = new Stack<Servlet>();
}
singleThreadModel = true;
}
//init servlet instance
initServlet(servlet);
fireContainerEvent("load", this);
loadTime=System.currentTimeMillis() -t1;
} finally {
if (swallowOutput) {
String log = SystemLogHandler.stopCapture();
if (log != null && log.length() > 0) {
if (getServletContext() != null) {
getServletContext().log(log);
} else {
out.println(log);
}
}
}
}
return servlet;
}
該類主要負責初始化一個Servlet實例,並調用該實例的init方法,然後通知感興趣的事件監聽程序。代碼清單4-3中調用了Wrapper的invoke方法,這種方法完畢什麽呢?
代碼清單4-5:
/**
* Invoke the servlet we are managing, respecting the rules regarding
* servlet lifecycle and SingleThreadModel support.
*
* @param request Request to be processed
* @param response Response to be produced
*
* @exception IOException if an input/output error occurred
* @exception ServletException if a servlet error occurred
*/
@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++;
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);
}
}
}
- 初始化一些本地變量
- 推斷當前應用是否可用。就是推斷是否確實有這個項目
- 分配一個Servlet實例
- 為請求創建一個過濾器鏈
- 過濾器過濾請求
- 關閉過濾器
- 又一次委派原來委派的Servlet實例
- 釋放資源
這種方法與上面的loadServlet關系例如以下:
能夠看出在調用loadServlet的allocate方法的時候調用了StandardWrapperValve的invoke方法,在Wrapper容器獲得請求後,通過allocate方法從實例池棧中彈出一個servlet實例來處理這個請求,servlet實例被封裝成filterChain對象,緊接著通過一系列的過濾器過濾到達servlet.service()方法。這個過程能夠例如以下:
深入理解Tomcat系列之五:Context容器和Wrapper容器