struts2处理请求的过程分析

和struts2启动一样，它也有一个入口，那就是org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter的doFilter方法。

public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {

        HttpServletRequest request = (HttpServletRequest) req;
        HttpServletResponse response = (HttpServletResponse) res;

        try {
            prepare.setEncodingAndLocale(request, response);
            prepare.createActionContext(request, response);
            prepare.assignDispatcherToThread();
			if ( excludedPatterns != null && prepare.isUrlExcluded(request, excludedPatterns)) {
				chain.doFilter(request, response);
			} else {
				request = prepare.wrapRequest(request);
				ActionMapping mapping = prepare.findActionMapping(request, response, true);
				if (mapping == null) {
					boolean handled = execute.executeStaticResourceRequest(request, response);
					if (!handled) {
						chain.doFilter(request, response);
					}
				} else {
					execute.executeAction(request, response, mapping);
				}
			}
        } finally {
            prepare.cleanupRequest(request);
        }
    }

这部分包括设置编码，创建actioncontext，并把这个Distance变量设置到此线程的本地副本instance中

private static ThreadLocal<Dispatcher> instance = new ThreadLocal<Dispatcher>();

接下来是获得actionmapping。这个actionmapping是根据我们的request的uri来和配置文件中的设置匹配，得到相应的action。

public ActionMapping findActionMapping(HttpServletRequest request, HttpServletResponse response, boolean forceLookup) {
        ActionMapping mapping = (ActionMapping) request.getAttribute(STRUTS_ACTION_MAPPING_KEY);
        if (mapping == null || forceLookup) {
            try {
                mapping = dispatcher.getContainer().getInstance(ActionMapper.class).getMapping(request, dispatcher.getConfigurationManager());
                if (mapping != null) {
                    request.setAttribute(STRUTS_ACTION_MAPPING_KEY, mapping);
                }
            } catch (Exception ex) {
                dispatcher.sendError(request, response, servletContext, HttpServletResponse.SC_INTERNAL_SERVER_ERROR, ex);
            }
        }

        return mapping;
    }

还记得dispatcher.getContainer().getInstance(ActionMapper.class)的原理吗？从我们上篇文章中，这个已经说过，在struts2的初始化中，container已经创建成功了，而且这个容器中有factories的这个map，每项都是一个name和type组成的Key和它对应的对象工厂的Value组成的。我们看看getMapping是怎么实现的。

public ActionMapping getMapping(HttpServletRequest request,
                                    ConfigurationManager configManager) {
        ActionMapping mapping = new ActionMapping();
        String uri = getUri(request);

        int indexOfSemicolon = uri.indexOf(";");
        uri = (indexOfSemicolon > -1) ? uri.substring(0, indexOfSemicolon) : uri;

        uri = dropExtension(uri, mapping);
        if (uri == null) {
            return null;
        }

        parseNameAndNamespace(uri, mapping, configManager);

        handleSpecialParameters(request, mapping);

        if (mapping.getName() == null) {
            return null;
        }

        parseActionName(mapping);

        return mapping;
    }

    protected ActionMapping parseActionName(ActionMapping mapping) {
        if (mapping.getName() == null) {
            return mapping;
        }
        if (allowDynamicMethodCalls) {
            // handle "name!method" convention.
            String name = mapping.getName();
            int exclamation = name.lastIndexOf("!");
            if (exclamation != -1) {
                mapping.setName(name.substring(0, exclamation));

                mapping.setMethod(name.substring(exclamation + 1));
            }
        }
        return mapping;
    }

protected void parseNameAndNamespace(String uri, ActionMapping mapping,
                                         ConfigurationManager configManager) {
        String namespace, name;
        int lastSlash = uri.lastIndexOf("/");
        if (lastSlash == -1) {
            namespace = "";
            name = uri;
        } else if (lastSlash == 0) {
            // ww-1046, assume it is the root namespace, it will fallback to
            // default
            // namespace anyway if not found in root namespace.
            namespace = "/";
            name = uri.substring(lastSlash + 1);
        } else if (alwaysSelectFullNamespace) {
            // Simply select the namespace as everything before the last slash
            namespace = uri.substring(0, lastSlash);
            name = uri.substring(lastSlash + 1);
        } else {
            // Try to find the namespace in those defined, defaulting to ""
            Configuration config = configManager.getConfiguration();
            String prefix = uri.substring(0, lastSlash);
            namespace = "";
            boolean rootAvailable = false;
            // Find the longest matching namespace, defaulting to the default
            for (Object cfg : config.getPackageConfigs().values()) {
                String ns = ((PackageConfig) cfg).getNamespace();
                if (ns != null && prefix.startsWith(ns) && (prefix.length() == ns.length() || prefix.charAt(ns.length()) == '/')) {
                    if (ns.length() > namespace.length()) {
                        namespace = ns;
                    }
                }
                if ("/".equals(ns)) {
                    rootAvailable = true;
                }
            }

            name = uri.substring(namespace.length() + 1);

            // Still none found, use root namespace if found
            if (rootAvailable && "".equals(namespace)) {
                namespace = "/";
            }
        }

        if (!allowSlashesInActionNames && name != null) {
            int pos = name.lastIndexOf('/');
            if (pos > -1 && pos < name.length() - 1) {
                name = name.substring(pos + 1);
            }
        }

        mapping.setNamespace(namespace);
        mapping.setName(name);
    }

这段代码应该很简单吧。无非就是解析request的uri，获得它的namespace，name，method等，设置到actionmapping中。当获得了actionmapping后，就开始真正处理请求了。

execute.executeAction(request, response, mapping);

public void executeAction(HttpServletRequest request, HttpServletResponse response, ActionMapping mapping) throws ServletException {
        dispatcher.serviceAction(request, response, servletContext, mapping);
    }

public void serviceAction(HttpServletRequest request, HttpServletResponse response, ServletContext context,
                              ActionMapping mapping) throws ServletException {

        Map<String, Object> extraContext = createContextMap(request, response, mapping, context);

        // If there was a previous value stack, then create a new copy and pass it in to be used by the new Action
        ValueStack stack = (ValueStack) request.getAttribute(ServletActionContext.STRUTS_VALUESTACK_KEY);
        boolean nullStack = stack == null;
        if (nullStack) {
            ActionContext ctx = ActionContext.getContext();
            if (ctx != null) {
                stack = ctx.getValueStack();
            }
        }
        if (stack != null) {
            extraContext.put(ActionContext.VALUE_STACK, valueStackFactory.createValueStack(stack));
        }

        String timerKey = "Handling request from Dispatcher";
        try {
            UtilTimerStack.push(timerKey);
            String namespace = mapping.getNamespace();
            String name = mapping.getName();
            String method = mapping.getMethod();

            Configuration config = configurationManager.getConfiguration();
            ActionProxy proxy = config.getContainer().getInstance(ActionProxyFactory.class).createActionProxy(
                    namespace, name, method, extraContext, true, false);

            request.setAttribute(ServletActionContext.STRUTS_VALUESTACK_KEY, proxy.getInvocation().getStack());

            // if the ActionMapping says to go straight to a result, do it!
            if (mapping.getResult() != null) {
                Result result = mapping.getResult();
                result.execute(proxy.getInvocation());
            } else {
                proxy.execute();
            }

           //................
    }

前面一段是处理actioncontext和valuestack的内容。在createContextMap中根据原生的request，response等进行封装封装成map类型，再调用一个createContextMap的一个重载方法，把这些原生request,session等和封装后的map类型的request,session等放入到一个大的map中。如果你要在action中获得这些对象，也是可以的。

比如：Map<String, String> request=(Map<String, String>) ActionContext.getContext().get("request");对于Map类型的request用的字符串是"request"，如果你想获得原生request也是可以的，但是不是"request"，而是StrutsStatics.HTTP_REQUEST：

httprequest=(HttpServletRequest) ActionContext.getContext().get(StrutsStatics.HTTP_REQUEST);在map中就是以StrutsStatics.HTTP_REQUEST为键。

但是你可能会问：为什么session可以这样获得呢？Map<String, Object> session=ActionContext.getContext().getSession();而request却要通过get方法呢？

这是因为在ActionContext中并没有提供getRequest方法，也不知道为什么不提供，其实getSession()也是通过get方法实现的。

接下来是获得mapping的命名空间，action的名字，action的方法名。我们执行action,不就是要知道这些么。然后获得一个action的代理：ActionProxy proxy。

public ActionProxy createActionProxy(String namespace, String actionName, String methodName, Map<String, Object> extraContext, boolean executeResult, boolean cleanupContext) {
        
        ActionInvocation inv = new DefaultActionInvocation(extraContext, true);
        container.inject(inv);
        return createActionProxy(inv, namespace, actionName, methodName, executeResult, cleanupContext);
    }

创建actioninvocation。通过container的IOC机制进行注入。

public ActionProxy createActionProxy(ActionInvocation inv, String namespace, String actionName, String methodName, boolean executeResult, boolean cleanupContext) {
        
        StrutsActionProxy proxy = new StrutsActionProxy(inv, namespace, actionName, methodName, executeResult, cleanupContext);
        container.inject(proxy);
        proxy.prepare();
        return proxy;
    }

此时才创建action的代理对象，以后就通过该代理对象去执行。

protected void prepare() {
        String profileKey = "create DefaultActionProxy: ";
        try {
            UtilTimerStack.push(profileKey);
            config = configuration.getRuntimeConfiguration().getActionConfig(namespace, actionName);

            //.........

            resolveMethod();

            if (!config.isAllowedMethod(method)) {
                throw new ConfigurationException("Invalid method: " + method + " for action " + actionName);
            }

            invocation.init(this);

        } 
	//.........
    }

public void init(ActionProxy proxy) {
        this.proxy = proxy;
        Map<String, Object> contextMap = createContextMap();

        // Setting this so that other classes, like object factories, can use the ActionProxy and other
        // contextual information to operate
        ActionContext actionContext = ActionContext.getContext();

        if (actionContext != null) {
            actionContext.setActionInvocation(this);
        }

        createAction(contextMap);

        if (pushAction) {
            stack.push(action);
            contextMap.put("action", action);
        }

        invocationContext = new ActionContext(contextMap);
        invocationContext.setName(proxy.getActionName());

        // get a new List so we don't get problems with the iterator if someone changes the list
        List<InterceptorMapping> interceptorList = new ArrayList<InterceptorMapping>(proxy.getConfig().getInterceptors());
        interceptors = interceptorList.iterator();
    }

前面也是对context进行一些设置等，我就不分析了。

这里对actioninvocation进行了初始化操作，我们通过actioninvocation以后要执行一系列的interceptor和真正的action，所以这些东西都要在初始化中。

再回到serviceAction。因为我们已经得到了actionmapping和actionproxy。接下来就可以去执行拦截器interceptor和action了。

他们的执行就是如果还有interceptor就执行下一个interceptor，如果没有就执行真正的action了，采用一种责任链模式，这部分很简单，我也不分析。当action执行完后，又依次返回各个interceptor，再经过web服务器的各个容器中的各个valve（比如StandardContext容器的StandardContextValve）。这样就完成了整个的处理过程了。