StandardWrapperValve分析-tomcat6.x源码阅读
2013-11-10
StandardWrapperValve是StandardWrapper容器的BasicValve，tomcat使用容器的BasicValve来控制处理请求，StandardWrapperValve的作用是负责为请求选择Wrapper,调用Servlet处理请求,控制请求处理流程。寄生于StandardWrapper中，StandardWrapperValve作为BasicValve是如何完成即可功能的呢。
StandardWrapperValve在方法invoke(Request, Response)中完成即可功能,在StandardCOntextValve的invoke(Request, Response)方法中调用。invoke(Request, Response)中做了很多逻辑操作，方法被标记为final，不允许更改方法。
invoke(Request, Response)
负责选择Wrapper过滤Filter，调用servlet处理请求，在方法中有很多逻辑操作，详细如下:
- 验证Wrapper和Context的可用性
- 通过wrapper的allocate()方法来获取servlet
- 判断是否为Comet
- 调用response.sendAcknowledgement();发送"HTTP/1.1 100 Continue” + CRLF + CRLF
- 获取在该Servlet上面注册的所有Filter，组成FilterChain
- 如果为JSP，设置属性
- 在Servlet上面调用FilterChain过滤，在FilterChain链完成对Servlet方法的调用，处理请求
- 重置FilterChain链
- 调用wrapper.deallocate(servlet);归还Wrapper
- 判断Servlet还是否可以用，如果不可用，调用wrapper.unload();卸载Servlet
/**
* Process a Comet event. The main differences here are to not use sendError
* (the response is committed), to avoid creating a new filter chain (which
* would work but be pointless), and a few very minor tweaks.
*
* @param request
* The servlet request to be processed
* @param response
* The servlet response to be created
*
* @exception IOException
* if an input/output error occurs, or is thrown by a
* subsequently invoked Valve, Filter, or Servlet
* @exception ServletException
* if a servlet error occurs, or is thrown by a subsequently
* invoked Valve, Filter, or Servlet
*/
public void event(Request request, Response response, CometEvent event)
throws IOException, ServletException {
// Initialize local variables we may need
Throwable throwable = null;
// This should be a Request attribute...
long t1 = System.currentTimeMillis();
// FIXME: Add a flag to count the total amount of events processed ?
// requestCount++;
StandardWrapper wrapper = (StandardWrapper) getContainer();
Servlet servlet = null;
Context context = (Context) wrapper.getParent();
// Check for the application being marked unavailable
boolean unavailable = !context.getAvailable()
|| wrapper.isUnavailable();
// Allocate a servlet instance to process this request
try {
if (!unavailable) {
servlet = wrapper.allocate();
}
} catch (UnavailableException e) {
// The response is already committed, so it's not possible to do
// anything
} catch (ServletException e) {
container
.getLogger()
.error(sm.getString("standardWrapper.allocateException",
wrapper.getName()), StandardWrapper.getRootCause(e));
throwable = e;
exception(request, response, e);
servlet = null;
} catch (Throwable e) {
container.getLogger().error(
sm.getString("standardWrapper.allocateException",
wrapper.getName()), e);
throwable = e;
exception(request, response, e);
servlet = null;
}
MessageBytes requestPathMB = null;
if (request != null) {
requestPathMB = request.getRequestPathMB();
}
request.setAttribute(ApplicationFilterFactory.DISPATCHER_TYPE_ATTR,
ApplicationFilterFactory.REQUEST_INTEGER);
request.setAttribute(
ApplicationFilterFactory.DISPATCHER_REQUEST_PATH_ATTR,
requestPathMB);
// Get the current (unchanged) filter chain for this request
ApplicationFilterChain filterChain = (ApplicationFilterChain) request
.getFilterChain();
// Call the filter chain for this request
// NOTE: This also calls the servlet's event() method
try {
String jspFile = wrapper.getJspFile();
if (jspFile != null)
request.setAttribute(Globals.JSP_FILE_ATTR, jspFile);
else
request.removeAttribute(Globals.JSP_FILE_ATTR);
if ((servlet != null) && (filterChain != null)) {
// Swallow output if needed
if (context.getSwallowOutput()) {
try {
SystemLogHandler.startCapture();
filterChain.doFilterEvent(request.getEvent());
} finally {
String log = SystemLogHandler.stopCapture();
if (log != null && log.length() > 0) {
context.getLogger().info(log);
}
}
} else {
filterChain.doFilterEvent(request.getEvent());
}
}
request.removeAttribute(Globals.JSP_FILE_ATTR);
} catch (ClientAbortException e) {
request.removeAttribute(Globals.JSP_FILE_ATTR);
throwable = e;
exception(request, response, e);
} catch (IOException e) {
request.removeAttribute(Globals.JSP_FILE_ATTR);
container.getLogger().error(
sm.getString("standardWrapper.serviceException",
wrapper.getName()), e);
throwable = e;
exception(request, response, e);
} catch (UnavailableException e) {
request.removeAttribute(Globals.JSP_FILE_ATTR);
container.getLogger().error(
sm.getString("standardWrapper.serviceException",
wrapper.getName()), e);
// Do not save exception in 'throwable', because we
// do not want to do exception(request, response, e) processing
} catch (ServletException e) {
request.removeAttribute(Globals.JSP_FILE_ATTR);
Throwable rootCause = StandardWrapper.getRootCause(e);
if (!(rootCause instanceof ClientAbortException)) {
container.getLogger().error(
sm.getString("standardWrapper.serviceException",
wrapper.getName()), rootCause);
}
throwable = e;
exception(request, response, e);
} catch (Throwable e) {
request.removeAttribute(Globals.JSP_FILE_ATTR);
container.getLogger().error(
sm.getString("standardWrapper.serviceException",
wrapper.getName()), e);
throwable = e;
exception(request, response, e);
}
// Release the filter chain (if any) for this request
if (filterChain != null) {
filterChain.reuse();
}
// Deallocate the allocated servlet instance
try {
if (servlet != null) {
wrapper.deallocate(servlet);
}
} catch (Throwable 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) {
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;
}
以上是invoke(Request,Response)方法的源码，代码中发现有很多的异常处理逻辑，针对不同的异常处理逻辑，响应给请求的内容页不一样。从上面可以看出invoke方法控制了请求的传递过程，在方法并没有直接调用servlet的方法，而是将调用servlet中的方法放到FilterChain中。
再坚持