struts2 實現原理解析
(2010-07-27 14:49:36)
標籤:
filterdispatcherthreadlocalactionproxy雜談 |
分類: java和數據庫 |
<filter> <filter-name>struts2</filter-name> <filter-class>org.apache.struts2.dispatcher.FilterDispatcher</filter-class> </filter> <filter-mapping> <filter-name>struts2</filter-name> <url-pattern>/*</url-pattern> </filter-mapping> |
<filter-class>
org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter
</filter-class>
而這個Filter FilterDispatcher 實際做了下列工作
public class FilterDispatcher implements StrutsStatics, Filter
- 1.filter的init()方法建立一個Dispatcher對象
init()方法將參數FilterConfig對象傳給Dispatcher對象,實際就是將ServletContext對象傳遞給Dispatcher對象
而ServletContext包含了各種基本Servlet的運行環境,比如ServletContext提供了getAttribute(), setAttribute() 等方法
所以,實際是Dispatcher對象接管了基本Servlet的一切功能
public void init(FilterConfig filterConfig) throws ServletException { dispatcher = createDispatcher(filterConfig); ... } |
protected Dispatcher createDispatcher(FilterConfig filterConfig) { ... return new Dispatcher(filterConfig.getServletContext(), params); } |
- 2.filter的doFilter()方法繼續操作前面init()方法建立的作Dispatcher對象,將HttpServletRequest對象和HttpServletResponse對象傳入Dispatcher中
public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException { HttpServletRequest request = (HttpServletRequest) req; HttpServletResponse response = (HttpServletResponse) res; ServletContext servletContext = getServletContext(); .... dispatcher.serviceAction(request, response, servletContext, mapping); } |
Dispatcher對象是Struts2的核心操作對象,它主要實現實現了下面的工作
- 1.它是線程安全的,即Dispatcher對象支持多線程,且每線程一副本
public class Dispatcher { private static ThreadLocal<Dispatcher> instance = new ThreadLocal<Dispatcher>(); //Store the dispatcher instance for this thread. public static void setInstance(Dispatcher instance) { Dispatcher.instance.set(instance); // Tie the ObjectFactory threadlocal instance to this Dispatcher instance if (instance != null) { Container cont = instance.getContainer(); if (cont != null) { ObjectFactory.setObjectFactory(cont.getInstance(ObjectFactory.class)); } else { LOG.warn("This dispatcher instance doesn't have a container, so the object factory won't be set."); } } else { ObjectFactory.setObjectFactory(null); } } //Provide the dispatcher instance for the current thread. public static Dispatcher getInstance() { return instance.get(); } |
- 2.上邊說了,Dispatcher對象的建立/構造,是接受了參數FilterDispatcher過濾器的FilterConfig傳來的ServletContext,這樣才接管了基本Servlet的一切功能
private ServletContext servletContext; private Map<String, String> initParams; public Dispatcher(ServletContext servletContext, Map<String, String> initParams) { this.servletContext = servletContext; this.initParams = initParams; } |
- 3. 上邊說了,FilterDispatcher過濾器的doFilter()方法,調用了Dispatcher對象的serviceAction()方法,並把HttpServletRequest對象和HttpServletResponse對象傳入
serviceAction內部完成了多項功能:
配置文件加載,配置初始化
調用ActionProxy對象實現對Action類的執行
ActionProxy對象又會按照Struts2的Stack結構依次執行Inteceptor,action,method
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); if (stack != null) { extraContext.put(ActionContext.VALUE_STACK, ValueStackFactory.getFactory().createValueStack(stack)); } try { 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, extraContext, true, false); proxy.setMethod(method); 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(); } // If there was a previous value stack then set it back onto the request if (stack != null) { request.setAttribute(ServletActionContext.STRUTS_VALUESTACK_KEY, stack); } |