Tomcat 中的 Wrapper
Wrapper 定义
public interface Wrapper extends Container {
public static final String ADD_MAPPING_EVENT = "addMapping";
public static final String REMOVE_MAPPING_EVENT = "removeMapping";
public long getAvailable();
public void setAvailable(long available);
public int getLoadOnStartup();
public void setLoadOnStartup(int value);
public String getRunAs();
public void setRunAs(String runAs);
public String getServletClass();
public void setServletClass(String servletClass);
public String[] getServletMethods() throws ServletException;
public boolean isUnavailable();
public Servlet getServlet();
public void setServlet(Servlet servlet);
public void addInitParameter(String name, String value);
public void addMapping(String mapping);
public void addSecurityReference(String name, String link);
public Servlet allocate() throws ServletException;
public void deallocate(Servlet servlet) throws ServletException;
public String findInitParameter(String name);
public String[] findInitParameters();
public String[] findMappings();
public String findSecurityReference(String name);
public String[] findSecurityReferences();
public void incrementErrorCount();
public void load() throws ServletException;
public void removeInitParameter(String name);
public void removeMapping(String mapping);
public void removeSecurityReference(String name);
public void unavailable(UnavailableException unavailable);
public void unload() throws ServletException;
public MultipartConfigElement getMultipartConfigElement();
public void setMultipartConfigElement(
MultipartConfigElement multipartConfig);
public boolean isAsyncSupported();
public void setAsyncSupported(boolean asyncSupport);
public boolean isEnabled();
public void setEnabled(boolean enabled);
@Deprecated
public void setServletSecurityAnnotationScanRequired(boolean b);
@Deprecated
public void servletSecurityAnnotationScan() throws ServletException;
public boolean isOverridable();
public void setOverridable(boolean overridable);
}
从定义中可以看出
- Wrapper 接口继承了 Container 接口
- Wrapper 跟跟 Servlet 有关联
- Wrapper 的实现类是 StandardWrapper
StandardWrapper 的构造方法
public StandardWrapper() {
super();
//为 pipeline 添加基础阀 StandardWrapperValve
pipeline.setBasic(new StandardWrapperValve());
}
StandardWrapper 的 allocate 方法 -- 实例化Servlet
public Servlet allocate() throws ServletException {
if (debug >= 1)
log("Allocating an instance");
// If we are currently unloading this servlet, throw an exception
if (unloading)
throw new ServletException
(sm.getString("standardWrapper.unloading", getName()));
// If not SingleThreadedModel, return the same instance every time
if (!singleThreadModel) {
// Load and initialize our instance if necessary
if (instance == null) {
synchronized (this) {
if (instance == null) {
try {
//加载Servlet
instance = loadServlet();
} catch (ServletException e) {
throw e;
} catch (Throwable e) {
throw new ServletException
(sm.getString("standardWrapper.allocate"), e);
}
}
}
}
//如果不是 SingleThreadModel 只会存在一个实例，所以直接返回唯一的实例就行
//SingleThreadModel 表示同一个对象在同一时刻只能被一个线程访问，所以会创建多个对象来处理多线程。这里会用对象池来管理对象
if (!singleThreadModel) {
if (debug >= 2)
log(" Returning non-STM instance");
countAllocated++;
return (instance);
}
}
synchronized (instancePool) {
//活动数量大于实例数量，要一直创建新的 Servlet 对象
//注意这个活动数量不是 Servlet 的数量，应该是活动线程的数量
while (countAllocated >= nInstances) {
// Allocate a new instance if possible, or else wait
if (nInstances < maxInstances) {
//如果实例数量小于最大实例数量，创建新的 Servlet 对象
//注意这里最大数量默认 20
try {
instancePool.push(loadServlet());
nInstances++;
} catch (ServletException e) {
throw e;
} catch (Throwable e) {
throw new ServletException
(sm.getString("standardWrapper.allocate"), e);
}
} else {
//如果实例数量达到最大数量，等待其它 Servlet 结束
try {
instancePool.wait();
} catch (InterruptedException e) {
;
}
}
}
if (debug >= 2)
log(" Returning allocated STM instance");
//如果活动线程数量小于实例数量，表示有空闲的 Servlet 对象来处理活动线程
//这里直接返回空闲的 Servlet 对象
countAllocated++;
return (Servlet) instancePool.pop();
}
}
StandardWrapper 的 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;
SystemLogHandler.startCapture();
Servlet servlet = null;
try {
// If this "servlet" is really a JSP file, get the right class.
// HOLD YOUR NOSE - this is a kludge that avoids having to do special
// case Catalina-specific code in Jasper - it also requires that the
// servlet path be replaced by the <jsp-file> element content in
// order to be completely effective
//获取servlet类的全路径
String actualClass = servletClass;
if ((actualClass == null) && (jspFile != null)) {
Wrapper jspWrapper = (Wrapper)
((Context) getParent()).findChild(Constants.JSP_SERVLET_NAME);
if (jspWrapper != null)
actualClass = jspWrapper.getServletClass();
}
// Complain if no servlet class has been specified
if (actualClass == null) {
unavailable(null);
throw new ServletException
(sm.getString("standardWrapper.notClass", getName()));
}
// Acquire an instance of the class loader to be used
//获取加载器
Loader loader = getLoader();
if (loader == null) {
unavailable(null);
throw new ServletException
(sm.getString("standardWrapper.missingLoader", getName()));
}
//获取类加载器
ClassLoader classLoader = loader.getClassLoader();
// Special case class loader for a container provided servlet
if (isContainerProvidedServlet(actualClass)) {
classLoader = this.getClass().getClassLoader();
log(sm.getString
("standardWrapper.containerServlet", getName()));
}
// Load the specified servlet class from the appropriate class loader
Class classClass = null;
try {
//加载 Servlet 对象的类到jvm
if (classLoader != null) {
System.out.println("Using classLoader.loadClass");
classClass = classLoader.loadClass(actualClass);
} else {
System.out.println("Using forName");
classClass = Class.forName(actualClass);
}
} catch (ClassNotFoundException e) {
unavailable(null);
throw new ServletException
(sm.getString("standardWrapper.missingClass", actualClass),
e);
}
if (classClass == null) {
unavailable(null);
throw new ServletException
(sm.getString("standardWrapper.missingClass", actualClass));
}
// Instantiate and initialize an instance of the servlet class itself
try {
//通过反射实例化 Servlet 对象
servlet = (Servlet) classClass.newInstance();
} catch (ClassCastException e) {
unavailable(null);
// Restore the context ClassLoader
throw new ServletException
(sm.getString("standardWrapper.notServlet", actualClass), e);
} catch (Throwable e) {
unavailable(null);
// Restore the context ClassLoader
throw new ServletException
(sm.getString("standardWrapper.instantiate", actualClass), e);
}
// Check if loading the servlet in this web application should be
// allowed
if (!isServletAllowed(servlet)) {
throw new SecurityException
(sm.getString("standardWrapper.privilegedServlet",
actualClass));
}
// Special handling for ContainerServlet instances
if ((servlet instanceof ContainerServlet) &&
isContainerProvidedServlet(actualClass)) {
System.out.println("calling setWrapper");
((ContainerServlet) servlet).setWrapper(this);
System.out.println("after calling setWrapper");
}
// Call the initialization method of this servlet
try {
//发送事件
instanceSupport.fireInstanceEvent(InstanceEvent.BEFORE_INIT_EVENT,
servlet);
//调用 Servlet 的init方法
servlet.init(facade);
// Invoke jspInit on JSP pages
if ((loadOnStartup > 0) && (jspFile != null)) {
// Invoking jspInit
HttpRequestBase req = new HttpRequestBase();
HttpResponseBase res = new HttpResponseBase();
req.setServletPath(jspFile);
req.setQueryString("jsp_precompile=true");
servlet.service(req, res);
}
instanceSupport.fireInstanceEvent(InstanceEvent.AFTER_INIT_EVENT,
servlet);
} catch (UnavailableException f) {
instanceSupport.fireInstanceEvent(InstanceEvent.AFTER_INIT_EVENT,
servlet, f);
unavailable(f);
throw f;
} catch (ServletException f) {
instanceSupport.fireInstanceEvent(InstanceEvent.AFTER_INIT_EVENT,
servlet, f);
// If the servlet wanted to be unavailable it would have
// said so, so do not call unavailable(null).
throw f;
} catch (Throwable f) {
instanceSupport.fireInstanceEvent(InstanceEvent.AFTER_INIT_EVENT,
servlet, f);
// If the servlet wanted to be unavailable it would have
// said so, so do not call unavailable(null).
throw new ServletException
(sm.getString("standardWrapper.initException", getName()), f);
}
// Register our newly initialized instance
//如果当前 Servlet 实现了 SingleThreadModel 接口，加入对象池中
singleThreadModel = servlet instanceof SingleThreadModel;
if (singleThreadModel) {
if (instancePool == null)
instancePool = new Stack();
}
fireContainerEvent("load", this);
} finally {
String log = SystemLogHandler.stopCapture();
if (log != null && log.length() > 0) {
if (getServletContext() != null) {
getServletContext().log(log);
} else {
out.println(log);
}
}
}
//返回创建的 Servlet 对象
return servlet;
}
StandardWrapper 的基础阀 -- StandardWrapperValve
public void invoke(Request request, Response response,
ValveContext valveContext)
throws IOException, ServletException {
// Initialize local variables we may need
boolean unavailable = false;
Throwable throwable = null;
//获取 Wrapper 对象，要通过这个对象实例化 Servlet，获取 Servlet
StandardWrapper wrapper = (StandardWrapper) getContainer();
//获取请求体对象
ServletRequest sreq = request.getRequest();
//获取返回体对象
ServletResponse sres = response.getResponse();
Servlet servlet = null;
HttpServletRequest hreq = null;
//强转
if (sreq instanceof HttpServletRequest)
hreq = (HttpServletRequest) sreq;
HttpServletResponse hres = null;
if (sres instanceof HttpServletResponse)
hres = (HttpServletResponse) sres;
// Check for the application being marked unavailable
if (!((Context) wrapper.getParent()).getAvailable()) {
hres.sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE,
sm.getString("standardContext.isUnavailable"));
unavailable = true;
}
// Check for the servlet being marked unavailable
if (!unavailable && wrapper.isUnavailable()) {
log(sm.getString("standardWrapper.isUnavailable",
wrapper.getName()));
if (hres == null) {
; // NOTE - Not much we can do generically
} else {
long available = wrapper.getAvailable();
if ((available > 0L) && (available < Long.MAX_VALUE))
hres.setDateHeader("Retry-After", available);
hres.sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE,
sm.getString("standardWrapper.isUnavailable",
wrapper.getName()));
}
unavailable = true;
}
// Allocate a servlet instance to process this request
try {
if (!unavailable) {
//调用 Wrapper 的 allocate 方法创建并获取 Servlet 对象
servlet = wrapper.allocate();
}
} catch (ServletException e) {
log(sm.getString("standardWrapper.allocateException",
wrapper.getName()), e);
throwable = e;
exception(request, response, e);
servlet = null;
} catch (Throwable e) {
log(sm.getString("standardWrapper.allocateException",
wrapper.getName()), e);
throwable = e;
exception(request, response, e);
servlet = null;
}
// Acknowlege the request
try {
//握手，返回Ack
response.sendAcknowledgement();
} catch (IOException e) {
sreq.removeAttribute(Globals.JSP_FILE_ATTR);
log(sm.getString("standardWrapper.acknowledgeException",
wrapper.getName()), e);
throwable = e;
exception(request, response, e);
} catch (Throwable e) {
log(sm.getString("standardWrapper.acknowledgeException",
wrapper.getName()), e);
throwable = e;
exception(request, response, e);
servlet = null;
}
// Create the filter chain for this request
//创建请求过滤链
ApplicationFilterChain filterChain =
createFilterChain(request, servlet);
// Call the filter chain for this request
// NOTE: This also calls the servlet's service() method
try {
String jspFile = wrapper.getJspFile();
if (jspFile != null)
sreq.setAttribute(Globals.JSP_FILE_ATTR, jspFile);
else
sreq.removeAttribute(Globals.JSP_FILE_ATTR);
if ((servlet != null) && (filterChain != null)) {
//Servlet 的 service 方法在这调用
//这里调用的是 ApplicationFilterChain 的 doFilter 方法
filterChain.doFilter(sreq, sres);
}
sreq.removeAttribute(Globals.JSP_FILE_ATTR);
} catch (IOException e) {
sreq.removeAttribute(Globals.JSP_FILE_ATTR);
log(sm.getString("standardWrapper.serviceException",
wrapper.getName()), e);
throwable = e;
exception(request, response, e);
} catch (UnavailableException e) {
sreq.removeAttribute(Globals.JSP_FILE_ATTR);
log(sm.getString("standardWrapper.serviceException",
wrapper.getName()), e);
// throwable = e;
// exception(request, response, e);
wrapper.unavailable(e);
long available = wrapper.getAvailable();
if ((available > 0L) && (available < Long.MAX_VALUE))
hres.setDateHeader("Retry-After", available);
hres.sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE,
sm.getString("standardWrapper.isUnavailable",
wrapper.getName()));
// Do not save exception in 'throwable', because we
// do not want to do exception(request, response, e) processing
} catch (ServletException e) {
sreq.removeAttribute(Globals.JSP_FILE_ATTR);
log(sm.getString("standardWrapper.serviceException",
wrapper.getName()), e);
throwable = e;
exception(request, response, e);
} catch (Throwable e) {
sreq.removeAttribute(Globals.JSP_FILE_ATTR);
log(sm.getString("standardWrapper.serviceException",
wrapper.getName()), e);
throwable = e;
exception(request, response, e);
}
// Release the filter chain (if any) for this request
try {
if (filterChain != null)
filterChain.release();
} catch (Throwable e) {
log(sm.getString("standardWrapper.releaseFilters",
wrapper.getName()), e);
if (throwable == null) {
throwable = e;
exception(request, response, e);
}
}
// Deallocate the allocated servlet instance
try {
if (servlet != null) {
//释放 Servlet 对象
wrapper.deallocate(servlet);
}
} catch (Throwable e) {
log(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) {
log(sm.getString("standardWrapper.unloadException",
wrapper.getName()), e);
if (throwable == null) {
throwable = e;
exception(request, response, e);
}
}
}
ApplicationFilterChain 的 doFilter 方法
public void doFilter(ServletRequest request, ServletResponse response)
throws IOException, ServletException {
if( System.getSecurityManager() != null ) {
final ServletRequest req = request;
final ServletResponse res = response;
try {
java.security.AccessController.doPrivileged(
new java.security.PrivilegedExceptionAction()
{
public Object run() throws ServletException, IOException {
//这里最重要，会调用Servlet的service方法
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 的 internalDoFilter方法
private void internalDoFilter(ServletRequest request, ServletResponse response)
throws IOException, ServletException {
// Construct an iterator the first time this method is called
if (this.iterator == null)
this.iterator = filters.iterator();
// Call the next filter if there is one
if (this.iterator.hasNext()) {
ApplicationFilterConfig filterConfig =
(ApplicationFilterConfig) iterator.next();
Filter filter = null;
try {
filter = filterConfig.getFilter();
support.fireInstanceEvent(InstanceEvent.BEFORE_FILTER_EVENT,
filter, request, response);
//调用过滤器的 doFilter 方法
filter.doFilter(request, response, this);
support.fireInstanceEvent(InstanceEvent.AFTER_FILTER_EVENT,
filter, request, response);
} catch (IOException e) {
if (filter != null)
support.fireInstanceEvent(InstanceEvent.AFTER_FILTER_EVENT,
filter, request, response, e);
throw e;
} catch (ServletException e) {
if (filter != null)
support.fireInstanceEvent(InstanceEvent.AFTER_FILTER_EVENT,
filter, request, response, e);
throw e;
} catch (RuntimeException e) {
if (filter != null)
support.fireInstanceEvent(InstanceEvent.AFTER_FILTER_EVENT,
filter, request, response, e);
throw e;
} catch (Throwable e) {
if (filter != null)
support.fireInstanceEvent(InstanceEvent.AFTER_FILTER_EVENT,
filter, request, response, e);
throw new ServletException
(sm.getString("filterChain.filter"), e);
}
return;
}
// We fell off the end of the chain -- call the servlet instance
try {
support.fireInstanceEvent(InstanceEvent.BEFORE_SERVICE_EVENT,
servlet, request, response);
//Servlet 的 service 方法在这调用
if ((request instanceof HttpServletRequest) &&
(response instanceof HttpServletResponse)) {
servlet.service((HttpServletRequest) request,
(HttpServletResponse) response);
} else {
servlet.service(request, response);
}
support.fireInstanceEvent(InstanceEvent.AFTER_SERVICE_EVENT,
servlet, request, response);
} catch (IOException e) {
support.fireInstanceEvent(InstanceEvent.AFTER_SERVICE_EVENT,
servlet, request, response, e);
throw e;
} catch (ServletException e) {
support.fireInstanceEvent(InstanceEvent.AFTER_SERVICE_EVENT,
servlet, request, response, e);
throw e;
} catch (RuntimeException e) {
support.fireInstanceEvent(InstanceEvent.AFTER_SERVICE_EVENT,
servlet, request, response, e);
throw e;
} catch (Throwable e) {
support.fireInstanceEvent(InstanceEvent.AFTER_SERVICE_EVENT,
servlet, request, response, e);
throw new ServletException
(sm.getString("filterChain.servlet"), e);
}
}
小结
- Wrapper 中的 allocate 方法会通过反射实例化 Servlet 对象，注意这个方法在基础阀中调用
- 基础阀会在请求到来后通过最顶层容器通过 invoke 方法来调用，基础阀是pipeline的最后一个valve
- 基础阀会调用子容器的 pipeline 的 invoke 方法，在最底层容器Wrapper的基础阀中会实例化Servlet对象，并调用 Servlet 的 service 方法
