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Tomcat源码分析 (九)----- HTTP请求处理过程(二)

发布时间:2023/10/11 综合教程 530 老码农
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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StandardEngineValveinvoke()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StandardWrapperValveinvoke()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。

  1. 关键点1:这儿调用Wrapper的allocate()方法分配一个Servlet实例
  2. 关键点2,创建过滤器链,类似于Pipeline的功能
  3. 关键点3,调用过滤器链的doFilter,最终会调用到Servlet的service方法
  4. 关键点4,释放掉过滤器链及其相关资源
  5. 关键点5,释放掉Servlet及相关资源
  6. 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:

  1. 卸载过程中,不能分配Servlet
  2. 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)
  3. 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
  4. 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:

  1. 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
  2. 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.ApplicationFilterFactorycreateFilterChain()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。

总结

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