struts2處理請求的過程分析

和struts2啟動一樣，它也有一個入口，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);
        }
    }

這部分包括設置編碼，創建actioncontext，並把這個Distance變量設置到此線程的本地副本instance中

private static ThreadLocal instance = new ThreadLocal();

接下來是獲得actionmapping。這個actionmapping是根據我們的request的uri來和配置文件中的設置匹配，得到相應的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;
    }

還記得dispatcher.getContainer().getInstance(ActionMapper.class)的原理嗎？從我們上篇文章中，這個已經說過，在struts2的初始化中，container已經創建成功了，而且這個容器中有factories的這個map，每項都是一個name和type組成的Key和它對應的對象工廠的Value組成的。我們看看getMapping是怎麼實現的。

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);
    }

這段代碼應該很簡單吧。無非就是解析request的uri，獲得它的namespace，name，method等，設置到actionmapping中。當獲得了actionmapping後，就開始真正處理請求了。

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 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();
            }

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

前面一段是處理actioncontext和valuestack的內容。在createContextMap中根據原生的request，response等進行封裝封裝成map類型，再調用一個createContextMap的一個重載方法，把這些原生request,session等和封裝後的map類型的request,session等放入到一個大的map中。如果你要在action中獲得這些對象，也是可以的。

比如：Map request=(Map) ActionContext.getContext().get("request");對於Map類型的request用的字符串是"request"，如果你想獲得原生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為鍵。

但是你可能會問：為什麼session可以這樣獲得呢？Map session=ActionContext.getContext().getSession();而request卻要通過get方法呢？

這是因為在ActionContext中並沒有提供getRequest方法，也不知道為什麼不提供，其實getSession()也是通過get方法實現的。

接下來是獲得mapping的命名空間，action的名字，action的方法名。我們執行action,不就是要知道這些麼。然後獲得一個action的代理：ActionProxy proxy。

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

創建actioninvocation。通過container的IOC機制進行注入。

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;
    }

此時才創建action的代理對象，以後就通過該代理對象去執行。

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 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 interceptorList = new ArrayList(proxy.getConfig().getInterceptors());
        interceptors = interceptorList.iterator();
    }

前面也是對context進行一些設置等，我就不分析了。

這裡對actioninvocation進行了初始化操作，我們通過actioninvocation以後要執行一系列的interceptor和真正的action，所以這些東西都要在初始化中。

再回到serviceAction。因為我們已經得到了actionmapping和actionproxy。接下來就可以去執行攔截器interceptor和action了。

他們的執行就是如果還有interceptor就執行下一個interceptor，如果沒有就執行真正的action了，采用一種責任鏈模式，這部分很簡單，我也不分析。當action執行完後，又依次返回各個interceptor，再經過web服務器的各個容器中的各個valve（比如StandardContext容器的StandardContextValve）。這樣就完成了整個的處理過程了。