我们接着上一篇文章的容器处理来讲，当postParseRequest方法返回true时，则由容器继续处理，在service方法中有connector.getService().getContainer().getPipeline().getFirst().invoke(request, response)这一行：
-
Connector调用getService()返回StandardService；
-
StandardService调用getContainer返回StandardEngine；
-
StandardEngine调用getPipeline返回与其关联的StandardPipeline；
Engine处理请求
我们在前面的文章中讲过StandardEngine的构造函数为自己的Pipeline添加了基本阀StandardEngineValve，代码如下：
public StandardEngine() { super(); pipeline.setBasic(new StandardEngineValve()); try {
setJvmRoute(System.getProperty("jvmRoute"));
} catch(Exception ex) {
log.warn(sm.getString("standardEngine.jvmRouteFail"));
}
}
接下来我们看看StandardEngineValve的invoke()方法。该方法主要是选择合适的Host，然后调用Host中pipeline的第一个Valve的invoke()方法。
public final void invoke(Request request, Response response) throws IOException, ServletException { // Select the Host to be used for this Request Host host = request.getHost(); if (host == null) {
response.sendError
(HttpServletResponse.SC_BAD_REQUEST,
sm.getString("standardEngine.noHost",
request.getServerName())); return;
} if (request.isAsyncSupported()) {
request.setAsyncSupported(host.getPipeline().isAsyncSupported());
} // Ask this Host to process this request host.getPipeline().getFirst().invoke(request, response); }
该方法很简单，校验该Engline 容器是否含有Host容器，如果不存在，返回400错误，否则继续执行 host.getPipeline().getFirst().invoke(request, response)，可以看到 Host 容器先获取自己的管道，再获取第一个阀门，我们再看看该阀门的 invoke 方法。
Host处理请求
分析Host的时候，我们从Host的构造函数入手，该方法主要是设置基础阀门。
public StandardHost() { super();
pipeline.setBasic(new StandardHostValve());
}
StandardPipeline调用getFirst得到第一个阀去处理请求，由于基本阀是最后一个，所以最后会由基本阀去处理请求。
StandardHost的Pipeline里面一定有 ErrorReportValve 与 StandardHostValve两个Valve，ErrorReportValve主要是检测 Http 请求过程中是否出现过什么异常, 有异常的话, 直接拼装 html 页面, 输出到客户端。
我们看看ErrorReportValve的invoke方法：
public void invoke(Request request, Response response) throws IOException, ServletException { // Perform the request // 1. 先将 请求转发给下一个 Valve getNext().invoke(request, response); // 2. 这里的 isCommitted 表明, 请求是正常处理结束 if (response.isCommitted()) { return;
} // 3. 判断请求过程中是否有异常发生 Throwable throwable = (Throwable) request.getAttribute(RequestDispatcher.ERROR_EXCEPTION); if (request.isAsyncStarted() && ((response.getStatus() < 400 && throwable == null) || request.isAsyncDispatching())) { return;
} if (throwable != null) { // The response is an error response.setError(); // Reset the response (if possible) try { // 4. 重置 response 里面的数据(此时 Response 里面可能有些数据) response.reset();
} catch (IllegalStateException e) { // Ignore } // 5. 这就是我们常看到的 500 错误码 response.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
}
response.setSuspended(false); try { // 6. 这里就是将 异常的堆栈信息组合成 html 页面, 输出到前台 report(request, response, throwable);
} catch (Throwable tt) {
ExceptionUtils.handleThrowable(tt);
} if (request.isAsyncStarted()) { // 7. 若是异步请求的话, 设置对应的 complete (对应的是 异步 Servlet) request.getAsyncContext().complete();
}
}
该方法首先执行了下个阀门的 invoke 方法。然后根据返回的Request 属性设置一些错误信息。那么下个阀门是谁呢？其实就是基础阀门了：StandardHostValve，该阀门的 invoke 的方法是如何实现的呢？
@Override public final void invoke(Request request, Response response) throws IOException, ServletException { // Select the Context to be used for this Request Context context = request.getContext(); if (context == null) {
response.sendError
(HttpServletResponse.SC_INTERNAL_SERVER_ERROR,
sm.getString("standardHost.noContext")); return;
} // Bind the context CL to the current thread if( context.getLoader() != null ) { // Not started - it should check for availability first // This should eventually move to Engine, it's generic. if (Globals.IS_SECURITY_ENABLED) {
PrivilegedAction<Void> pa = new PrivilegedSetTccl(
context.getLoader().getClassLoader());
AccessController.doPrivileged(pa);
} else {
Thread.currentThread().setContextClassLoader
(context.getLoader().getClassLoader());
}
} if (request.isAsyncSupported()) {
request.setAsyncSupported(context.getPipeline().isAsyncSupported());
} // Don't fire listeners during async processing // If a request init listener throws an exception, the request is // aborted boolean asyncAtStart = request.isAsync(); // An async error page may dispatch to another resource. This flag helps // ensure an infinite error handling loop is not entered boolean errorAtStart = response.isError(); if (asyncAtStart || context.fireRequestInitEvent(request)) { // Ask this Context to process this request try { context.getPipeline().getFirst().invoke(request, response); } catch (Throwable t) {
ExceptionUtils.handleThrowable(t); if (errorAtStart) {
container.getLogger().error("Exception Processing " + request.getRequestURI(), t);
} else {
request.setAttribute(RequestDispatcher.ERROR_EXCEPTION, t);
throwable(request, response, t);
}
} // If the request was async at the start and an error occurred then // the async error handling will kick-in and that will fire the // request destroyed event *after* the error handling has taken // place if (!(request.isAsync() || (asyncAtStart && request.getAttribute(
RequestDispatcher.ERROR_EXCEPTION) != null))) { // Protect against NPEs if context was destroyed during a // long running request. if (context.getState().isAvailable()) { if (!errorAtStart) { // Error page processing response.setSuspended(false);
Throwable t = (Throwable) request.getAttribute(
RequestDispatcher.ERROR_EXCEPTION); if (t != null) {
throwable(request, response, t);
} else {
status(request, response);
}
}
context.fireRequestDestroyEvent(request);
}
}
} // Access a session (if present) to update last accessed time, based on a // strict interpretation of the specification if (ACCESS_SESSION) {
request.getSession(false);
} // Restore the context classloader if (Globals.IS_SECURITY_ENABLED) {
PrivilegedAction<Void> pa = new PrivilegedSetTccl(
StandardHostValve.class.getClassLoader());
AccessController.doPrivileged(pa);
} else {
Thread.currentThread().setContextClassLoader
(StandardHostValve.class.getClassLoader());
}
}
首先校验了Request 是否存在 Context，其实在执行 CoyoteAdapter.postParseRequest 方法的时候就设置了，如果Context 不存在，就返回500，接着还是老套路：context.getPipeline().getFirst().invoke，该管道获取的是基础阀门：StandardContextValve，我们还是关注他的 invoke 方法。
Context处理请求
接着Context会去处理请求，同理，StandardContextValve的invoke方法会被调用：
@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); }
Wrapper处理请求
Wrapper是一个Servlet的包装，我们先来看看构造方法。主要作用就是设置基础阀门StandardWrapperValve。
public StandardWrapper() { super(); swValve=new StandardWrapperValve(); pipeline.setBasic(swValve); broadcaster = new NotificationBroadcasterSupport();
}
接下来我们看看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 { // 关键点1：这儿调用Wrapper的allocate()方法分配一个Servlet实例 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 // 关键点2，创建过滤器链，类似于Pipeline的功能 ApplicationFilterChain filterChain = ApplicationFilterFactory.createFilterChain(request, wrapper, servlet); // 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()) {
request.getAsyncContextInternal().doInternalDispatch();
} else { // 关键点3，调用过滤器链的doFilter，最终会调用到Servlet的service方法 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 { // 关键点3，调用过滤器链的doFilter，最终会调用到Servlet的service方法 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 // 关键点4，释放掉过滤器链及其相关资源 if (filterChain != null) {
filterChain.release();
} // 关键点5，释放掉Servlet及相关资源 // 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 // 关键点6，如果servlet被标记为永远不可达，则需要卸载掉它，并释放这个servlet实例 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;
}
通过阅读源码，我们发现了几个关键点。现罗列如下，后面我们会逐一分析这些关键点相关的源码。
-
关键点1：这儿调用Wrapper的allocate()方法分配一个Servlet实例
-
关键点2，创建过滤器链，类似于Pipeline的功能
-
关键点3，调用过滤器链的doFilter，最终会调用到Servlet的service方法
-
关键点4，释放掉过滤器链及其相关资源
-
关键点5，释放掉Servlet及相关资源
-
关键点6，如果servlet被标记为永远不可达，则需要卸载掉它，并释放这个servlet实例
关键点1 - Wrapper分配Servlet实例
我们来分析一下Wrapper.allocate()方法
@Override public Servlet allocate() throws ServletException { // If we are currently unloading this servlet, throw an exception // 卸载过程中，不能分配Servlet if (unloading) { throw new ServletException(sm.getString("standardWrapper.unloading", getName()));
} boolean newInstance = false; // If not SingleThreadedModel, return the same instance every time // 如果Wrapper没有实现SingleThreadedModel，则每次都会返回同一个Servlet if (!singleThreadModel) { // Load and initialize our instance if necessary // 实例为null或者实例还未初始化，使用synchronized来保证并发时的原子性 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. // 加载Servlet 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);
}
} // 初始化Servlet 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++;
}
}
} // 非单线程模型，直接返回已经创建的Servlet，也就是说，这种情况下只会创建一个Servlet else { 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;
}
} // 如果是单线程模式，则使用servlet对象池技术来加载多个Servlet synchronized (instancePool) { while (countAllocated.get() >= nInstances) { // Allocate a new instance if possible, or else wait 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 { try {
instancePool.wait();
} catch (InterruptedException e) { // Ignore }
}
} if (log.isTraceEnabled()) {
log.trace(" Returning allocated STM instance");
}
countAllocated.incrementAndGet(); return instancePool.pop();
}
}
总结下来，注意以下几点即可：
-
卸载过程中，不能分配Servlet
-
如果不是单线程模式，则每次都会返回同一个Servlet（默认Servlet实现方式）
-
Servlet实例为null或者Servlet实例还未初始化，使用synchronized来保证并发时的原子性
-
如果是单线程模式，则使用servlet对象池技术来加载多个Servlet
接下来我们看看loadServlet()方法
public synchronized Servlet loadServlet() throws ServletException { // 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()));
} // 关键的地方，就是通过实例管理器，创建Servlet实例，而实例管理器是通过特殊的类加载器来加载给定的类 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: // https://bz.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);
}
} // Special handling for ContainerServlet instances // Note: The InstanceManager checks if the application is permitted // to load ContainerServlets if (servlet instanceof ContainerServlet) {
((ContainerServlet) servlet).setWrapper(this);
}
classLoadTime=(int) (System.currentTimeMillis() -t1); if (servlet instanceof SingleThreadModel) { if (instancePool == null) {
instancePool = new Stack<>();
}
singleThreadModel = true;
} // 调用Servlet的init方法 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;
}
关键的地方有两个：
-
通过实例管理器，创建Servlet实例，而实例管理器是通过特殊的类加载器来加载给定的类
-
调用Servlet的init方法
关键点2 - 创建过滤器链
创建过滤器链是调用的org.apache.catalina.core.ApplicationFilterFactory的createFilterChain()方法。我们来分析一下这个方法。该方法需要注意的地方已经在代码的comments里面说明了。
public static ApplicationFilterChain createFilterChain(ServletRequest request,
Wrapper wrapper, Servlet servlet) { // If there is no servlet to execute, return null if (servlet == null) return null; // Create and initialize a filter chain object // 1. 如果加密打开了，则可能会多次调用这个方法 // 2. 为了避免重复生成filterChain对象，所以会将filterChain对象放在Request里面进行缓存 ApplicationFilterChain filterChain = null; if (request instanceof Request) {
Request req = (Request) request; if (Globals.IS_SECURITY_ENABLED) { // Security: Do not recycle filterChain = new ApplicationFilterChain();
} else {
filterChain = (ApplicationFilterChain) req.getFilterChain(); if (filterChain == null) {
filterChain = new ApplicationFilterChain();
req.setFilterChain(filterChain);
}
}
} else { // Request dispatcher in use filterChain = new ApplicationFilterChain();
}
filterChain.setServlet(servlet);
filterChain.setServletSupportsAsync(wrapper.isAsyncSupported()); // Acquire the filter mappings for this Context StandardContext context = (StandardContext) wrapper.getParent(); // 从这儿看出过滤器链对象里面的元素是根据Context里面的filterMaps来生成的 FilterMap filterMaps[] = context.findFilterMaps(); // If there are no filter mappings, we are done if ((filterMaps == null) || (filterMaps.length == 0)) return (filterChain); // Acquire the information we will need to match filter mappings DispatcherType dispatcher = (DispatcherType) request.getAttribute(Globals.DISPATCHER_TYPE_ATTR);
String requestPath = null;
Object attribute = request.getAttribute(Globals.DISPATCHER_REQUEST_PATH_ATTR); if (attribute != null){
requestPath = attribute.toString();
}
String servletName = wrapper.getName(); // Add the relevant path-mapped filters to this filter chain // 类型和路径都匹配的情况下，将context.filterConfig放到过滤器链里面 for (int i = 0; i < filterMaps.length; i++) { if (!matchDispatcher(filterMaps[i] ,dispatcher)) { continue;
} if (!matchFiltersURL(filterMaps[i], requestPath)) continue;
ApplicationFilterConfig filterConfig = (ApplicationFilterConfig)
context.findFilterConfig(filterMaps[i].getFilterName()); if (filterConfig == null) { // FIXME - log configuration problem continue;
}
filterChain.addFilter(filterConfig);
} // Add filters that match on servlet name second // 类型和servlet名称都匹配的情况下，将context.filterConfig放到过滤器链里面 for (int i = 0; i < filterMaps.length; i++) { if (!matchDispatcher(filterMaps[i] ,dispatcher)) { continue;
} if (!matchFiltersServlet(filterMaps[i], servletName)) continue;
ApplicationFilterConfig filterConfig = (ApplicationFilterConfig)
context.findFilterConfig(filterMaps[i].getFilterName()); if (filterConfig == null) { // FIXME - log configuration problem continue;
}
filterChain.addFilter(filterConfig);
} // Return the completed filter chain return filterChain;
}
关键点3 - 调用过滤器链的doFilter
ApplicationFilterChain类的doFilter函数代码如下,它会将处理委托给internalDoFilter函数。
@Override 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);
}
}
ApplicationFilterChain类的internalDoFilter函数代码如下：
// 1. `internalDoFilter`方法通过pos和n来调用过滤器链里面的每个过滤器。pos表示当前的过滤器下标，n表示总的过滤器数量 // 2. `internalDoFilter`方法最终会调用servlet.service()方法 private void internalDoFilter(ServletRequest request,
ServletResponse response) throws IOException, ServletException { // Call the next filter if there is one // 1. 当pos小于n时, 则执行Filter if (pos < n) { // 2. 得到 过滤器 Filter，执行一次post++ 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 { // 4. 这里的 filter 的执行 有点递归的感觉, 通过 pos 来控制从 filterChain 里面拿出那个 filter 来进行操作 // 这里把this（filterChain）传到自定义filter里面，我们自定义的filter，会重写doFilter，在这里会被调用，doFilter里面会执行业务逻辑，如果执行业务逻辑成功，则会调用 filterChain.doFilter(servletRequest, servletResponse); ，filterChain就是这里传过去的this；如果业务逻辑执行失败，则return，filterChain终止，后面的servlet.service(request, response)也不会执行了 // 所以在 Filter 里面所调用 return, 则会终止 Filter 的调用, 而下面的 Servlet.service 更本就没有调用到 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 { //当pos等于n时，过滤器都执行完毕，终于执行了熟悉的servlet.service(request, response)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) {
lastServicedRequest.set(null);
lastServicedResponse.set(null);
}
}
}
自定义Filter
@WebFilter(urlPatterns = "/*", filterName = "myfilter") public class FileterController implements Filter {
@Override public void init(FilterConfig filterConfig) throws ServletException {
System.out.println("Filter初始化中");
}
@Override public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
System.out.println("登录逻辑"); if("登录失败"){
response.getWriter().write("登录失败"); //后面的拦截器和servlet都不会执行了 return;
} //登录成功，执行下一个过滤器 filterChain.doFilter(servletRequest, servletResponse);
}
@Override public void destroy() {
System.out.println("Filter销毁中");
}
}
-
pos和n是ApplicationFilterChain的成员变量，分别表示过滤器链的当前位置和过滤器总数，所以当pos小于n时，会不断执行ApplicationFilterChain的doFilter方法；
-
当pos等于n时，过滤器都执行完毕，终于执行了熟悉的servlet.service(request, response)方法。
如果您觉得本文的内容对您的学习有所帮助：
关键字：
Tomcat源码分析