public void init(FilterConfig filterConfig) throws ServletException {
        InitOperations init = new InitOperations();
        Dispatcher dispatcher = null;
        try {
            //封裝filterConfig，其中有個主要方法getInitParameterNames將參數(shù)名字以String格式存儲在List中
            FilterHostConfig config = new FilterHostConfig(filterConfig);
            //初始化struts內(nèi)部日志
            init.initLogging(config);
            //創(chuàng)建dispatcher ，并初始化
            dispatcher = init.initDispatcher(config);
            init.initStaticContentLoader(config, dispatcher);
            //初始化類屬性：prepare 、execute
            prepare = new PrepareOperations(filterConfig.getServletContext(), dispatcher);
            execute = new ExecuteOperations(filterConfig.getServletContext(), dispatcher);
            this.excludedPatterns = init.buildExcludedPatternsList(dispatcher);
            //回調(diào)空的postInit方法
            postInit(dispatcher, filterConfig);
        } finally {
            if (dispatcher != null) {
                dispatcher.cleanUpAfterInit();
            }
            init.cleanup();
        }
    }

public class FilterHostConfig implements HostConfig {

    private FilterConfig config;
    //構(gòu)造方法
    public FilterHostConfig(FilterConfig config) {
        this.config = config;
    }
    //根據(jù)init-param配置的param-name獲取param-value的值
    public String getInitParameter(String key) {
        return config.getInitParameter(key);
    }
    //返回初始化參數(shù)名的迭代器
    public Iterator<String> getInitParameterNames() {
        return MakeIterator.convert(config.getInitParameterNames());
    }
    //返回Servlet上下文
    public ServletContext getServletContext() {
        return config.getServletContext();
    }
}

public Dispatcher initDispatcher( HostConfig filterConfig ) {
  Dispatcher dispatcher = createDispatcher(filterConfig);
  dispatcher.init();
  return dispatcher;
}

private Dispatcher createDispatcher( HostConfig filterConfig ) {
        //存放參數(shù)的Map
        Map<String, String> params = new HashMap<String, String>();
        //將參數(shù)存放到Map
        for ( Iterator e = filterConfig.getInitParameterNames(); e.hasNext(); ) {
            String name = (String) e.next();
            String value = filterConfig.getInitParameter(name);
            params.put(name, value);
        }
        //根據(jù)servlet上下文和參數(shù)Map構(gòu)造Dispatcher
        return new Dispatcher(filterConfig.getServletContext(), params);
    }

public void init() {

        if (configurationManager == null) {
            configurationManager = createConfigurationManager(BeanSelectionProvider.DEFAULT_BEAN_NAME);
        }

        try {
            init_FileManager();
            //加載org/apache/struts2/default.properties
            init_DefaultProperties(); // [1]
            //加載struts-default.xml,struts-plugin.xml,struts.xml
            init_TraditionalXmlConfigurations(); // [2]
            init_LegacyStrutsProperties(); // [3]
            //用戶自己實(shí)現(xiàn)的ConfigurationProviders類
            init_CustomConfigurationProviders(); // [5]
            //Filter的初始化參數(shù)
            init_FilterInitParameters() ; // [6]
            init_AliasStandardObjects() ; // [7]

            Container container = init_PreloadConfiguration();
            container.inject(this);
            init_CheckWebLogicWorkaround(container);

            if (!dispatcherListeners.isEmpty()) {
                for (DispatcherListener l : dispatcherListeners) {
                    l.dispatcherInitialized(this);
                }
            }
        } catch (Exception ex) {
            if (LOG.isErrorEnabled())
                LOG.error("Dispatcher initialization failed", ex);
            throw new StrutsException(ex);
        }
    }

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

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

        try {
            //設(shè)置編碼和國際化
            prepare.setEncodingAndLocale(request, response);
            //創(chuàng)建action上下文
            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);
                //如果mapping為空，則認(rèn)為不是調(diào)用action,會調(diào)用下一個過濾器鏈，直到獲取到mapping才調(diào)用action
                if (mapping == null) {
                    boolean handled = execute.executeStaticResourceRequest(request, response);
                    if (!handled) {
                        chain.doFilter(request, response);
                    }
                } else {
                    //執(zhí)行action
                    execute.executeAction(request, response, mapping);
                }
            }
        } finally {
            prepare.cleanupRequest(request);
        }
    }

public void setEncodingAndLocale(HttpServletRequest request, HttpServletResponse response) {
    dispatcher.prepare(request, response);
}

public void prepare(HttpServletRequest request, HttpServletResponse response) {
        String encoding = null;
        if (defaultEncoding != null) {
            encoding = defaultEncoding;
        }
        // check for Ajax request to use UTF-8 encoding strictly http://www.w3.org/TR/XMLHttpRequest/#the-send-method
        if ("XMLHttpRequest".equals(request.getHeader("X-Requested-With"))) {
            encoding = "UTF-8";
        }

        Locale locale = null;
        if (defaultLocale != null) {
            locale = LocalizedTextUtil.localeFromString(defaultLocale, request.getLocale());
        }

        if (encoding != null) {
            applyEncoding(request, encoding);
        }

        if (locale != null) {
            response.setLocale(locale);
        }

        if (paramsWorkaroundEnabled) {
            request.getParameter("foo"); // simply read any parameter (existing or not) to "prime" the request
        }
    }

static ThreadLocal<ActionContext> actionContext = new ThreadLocal<ActionContext>();

/**
     * Creates the action context and initializes the thread local
     */
    public ActionContext createActionContext(HttpServletRequest request, HttpServletResponse response) {
        ActionContext ctx;
        Integer counter = 1;
        Integer oldCounter = (Integer) request.getAttribute(CLEANUP_RECURSION_COUNTER);
        if (oldCounter != null) {
            counter = oldCounter + 1;
        }
        //此處是從ThreadLocal中獲取此ActionContext變量
        ActionContext oldContext = ActionContext.getContext();
        if (oldContext != null) {
            // detected existing context, so we are probably in a forward
            ctx = new ActionContext(new HashMap<String, Object>(oldContext.getContextMap()));
        } else {
            ValueStack stack = dispatcher.getContainer().getInstance(ValueStackFactory.class).createValueStack();
            stack.getContext().putAll(dispatcher.createContextMap(request, response, null, servletContext));
            //stack.getContext()返回的是一個Map<String，Object>，根據(jù)此Map構(gòu)造一個ActionContext
            ctx = new ActionContext(stack.getContext());
        }
        request.setAttribute(CLEANUP_RECURSION_COUNTER, counter);
        //將ActionContext存到ThreadLocal
        ActionContext.setContext(ctx);
        return ctx;
    }

public Map<String,Object> createContextMap(HttpServletRequest request, HttpServletResponse response,
            ActionMapping mapping, ServletContext context) {

        // request map wrapping the http request objects
        Map requestMap = new RequestMap(request);

        // parameters map wrapping the http parameters.  ActionMapping parameters are now handled and applied separately
        Map params = new HashMap(request.getParameterMap());

        // session map wrapping the http session
        Map session = new SessionMap(request);

        // application map wrapping the ServletContext
        Map application = new ApplicationMap(context);
        //requestMap、params、session等Map封裝成為一個上下文Map
        Map<String,Object> extraContext = createContextMap(requestMap, params, session, application, request, response, context);

        if (mapping != null) {
            extraContext.put(ServletActionContext.ACTION_MAPPING, mapping);
        }
        return extraContext;
    }

public HttpServletRequest wrapRequest(HttpServletRequest oldRequest) throws ServletException {
        HttpServletRequest request = oldRequest;
        try {
            // Wrap request first, just in case it is multipart/form-data
            // parameters might not be accessible through before encoding (ww-1278)
            request = dispatcher.wrapRequest(request, servletContext);
        } catch (IOException e) {
            throw new ServletException("Could not wrap servlet request with MultipartRequestWrapper!", e);
        }
        return request;
    }

public HttpServletRequest wrapRequest(HttpServletRequest request, ServletContext servletContext) throws IOException {
        // don't wrap more than once
        if (request instanceof StrutsRequestWrapper) {
            return request;
        }

        String content_type = request.getContentType();
        //如果content_type是multipart/form-data類型，則將request包裝成MultiPartRequestWrapper對象，否則包裝成StrutsRequestWrapper對象
        if (content_type != null && content_type.contains("multipart/form-data")) {
            MultiPartRequest mpr = getMultiPartRequest();
            LocaleProvider provider = getContainer().getInstance(LocaleProvider.class);
            request = new MultiPartRequestWrapper(mpr, request, getSaveDir(servletContext), provider);
        } else {
            request = new StrutsRequestWrapper(request, disableRequestAttributeValueStackLookup);
        }

        return request;
    }

public ActionMapping findActionMapping(HttpServletRequest request, HttpServletResponse response, boolean forceLookup) {
        //首先從request對象中取mapping對象，看是否存在
        ActionMapping mapping = (ActionMapping) request.getAttribute(STRUTS_ACTION_MAPPING_KEY);
        //不存在就創(chuàng)建一個
        if (mapping == null || forceLookup) {
            try {
                //首先創(chuàng)建ActionMapper對象，通過ActionMapper對象創(chuàng)建mapping對象
                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;
    }

public ActionMapping getMapping(HttpServletRequest request, ConfigurationManager configManager) {
        ActionMapping mapping = new ActionMapping();
        //獲得請求的uri，即請求路徑URL中工程名以后的部分，如/userAction.action
        String uri = getUri(request);
        //修正url的帶;jsessionid 時找不到的bug
        int indexOfSemicolon = uri.indexOf(";");
        uri = (indexOfSemicolon > -1) ? uri.substring(0, indexOfSemicolon) : uri;
        //刪除擴(kuò)展名，如.action或者.do
        uri = dropExtension(uri, mapping);
        if (uri == null) {
            return null;
        }
        //從uri中分離得到請求的action名、命名空間。
        parseNameAndNamespace(uri, mapping, configManager);
        //處理特殊的請求參數(shù)
        handleSpecialParameters(request, mapping);
        //如果允許動態(tài)方法調(diào)用，即形如/userAction!getAll.action的請求，分離action名和方法名
        return parseActionName(mapping);
    }

protected void parseNameAndNamespace(String uri, ActionMapping mapping, ConfigurationManager configManager) {
        String namespace, name;
        int lastSlash = uri.lastIndexOf("/"); //最后的斜桿的位置
        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);
        //允許采用完整的命名空間,即設(shè)置命名空間是否必須進(jìn)行精確匹配
        } 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); //臨時的命名空間，將會用來進(jìn)行匹配
            namespace = "";//將命名空間暫時設(shè)為""
            boolean rootAvailable = false;//rootAvailable作用是判斷配置文件中是否配置了命名空間"/"
            // Find the longest matching namespace, defaulting to the default
            for (Object cfg : config.getPackageConfigs().values()) { //循環(huán)遍歷配置文件中的package標(biāo)簽
                String ns = ((PackageConfig) cfg).getNamespace();    //獲取每個package標(biāo)簽的namespace屬性
                //進(jìn)行匹配
                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) {
            int pos = name.lastIndexOf('/');
            if (pos > -1 && pos < name.length() - 1) {
                name = name.substring(pos + 1);
            }
        }
        //將分離后的acion名和命名空間保存到mapping對象
        mapping.setNamespace(namespace);
        mapping.setName(cleanupActionName(name));
    }

if (ns != null && prefix.startsWith(ns) && (prefix.length() == ns.length() || prefix.charAt(ns.length()) == '/')) {
    if (ns.length() > namespace.length()) {
        namespace = ns;
    }
}

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

protected ActionMapping parseActionName(ActionMapping mapping) {
        if (mapping.getName() == null) {
            return null;
        }
        //如果允許動態(tài)方法調(diào)用
        if (allowDynamicMethodCalls) {
            // handle "name!method" convention.
            String name = mapping.getName();
            int exclamation = name.lastIndexOf("!");
            //如果包含"!"就進(jìn)行分離
            if (exclamation != -1) {
                //分離出action名
                mapping.setName(name.substring(0, exclamation));
                //分離出方法名
                mapping.setMethod(name.substring(exclamation + 1));
            }
        }
        return mapping;
    }

//如果mapping為空，則認(rèn)為不是調(diào)用action,會調(diào)用下一個過濾器鏈，直到獲取到mapping才調(diào)用action
                if (mapping == null) {
                    boolean handled = execute.executeStaticResourceRequest(request, response);
                    if (!handled) {
                        chain.doFilter(request, response);
                    }
                } else {
                    //執(zhí)行action
                    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 {
        //封轉(zhuǎn)上下文環(huán)境，主要將requestMap、params、session等Map封裝成為一個上下文Map
        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();//從mapping對象獲取命名空間
            String name = mapping.getName();          //獲取請求的action名
            String method = mapping.getMethod();      //獲取請求方法
            //得到配置對象
            Configuration config = configurationManager.getConfiguration();
            //根據(jù)執(zhí)行上下文參數(shù)，命名空間，名稱等創(chuàng)建用戶自定義Action的代理對象
            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!
            //如果配置文件中執(zhí)行的這個action配置了result，就直接轉(zhuǎn)到result
            if (mapping.getResult() != null) {
                Result result = mapping.getResult();
                result.execute(proxy.getInvocation());
            } else {
                proxy.execute();
            }

            // If there was a previous value stack then set it back onto the request
            if (!nullStack) {
                request.setAttribute(ServletActionContext.STRUTS_VALUESTACK_KEY, stack);
            }
        } catch (ConfigurationException e) {
            // WW-2874 Only log error if in devMode
            if (devMode) {
                String reqStr = request.getRequestURI();
                if (request.getQueryString() != null) {
                    reqStr = reqStr + "?" + request.getQueryString();
                }
                LOG.error("Could not find action or result\n" + reqStr, e);
            } else {
                if (LOG.isWarnEnabled()) {
                    LOG.warn("Could not find action or result", e);
                }
            }
            sendError(request, response, context, HttpServletResponse.SC_NOT_FOUND, e);
        } catch (Exception e) {
            if (handleException || devMode) {
                sendError(request, response, context, HttpServletResponse.SC_INTERNAL_SERVER_ERROR, e);
            } else {
                throw new ServletException(e);
            }
        } finally {
            UtilTimerStack.pop(timerKey);
        }
    }