struts原理及核心流程

这是Struts2官方站点提供的Struts 2 的整体结构。



　　一个请求在Struts2框架中的处理大概分为以下几个步骤：

客户端提起一个（HttpServletRequest）请求,如上文在浏览器中输入”http://localhost:8080/TestMvc/add.action”就是提起一个（HttpServletRequest）请求。
请求被提交到一系列（主要是三层）的过滤器（Filter），如（ActionContextCleanUp、其他过滤器（SiteMesh等）、 FilterDispatcher）。注意这里是有顺序的，先ActionContextCleanUp，再其他过滤器（SiteMesh等）、最后到FilterDispatcher。
FilterDispatcher是控制器的核心，就是mvc中c控制层的核心。下面粗略的分析下我理解的FilterDispatcher工作流程和原理：FilterDispatcher进行初始化并启用核心doFilter

其代码如下：

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

HttpServletRequest request = (HttpServletRequest) req;

HttpServletResponse response = (HttpServletResponse) res;

ServletContext servletContext = filterConfig.getServletContext();

// 在这里处理了HttpServletRequest和HttpServletResponse。

DispatcherUtils du = DispatcherUtils.getInstance();

du.prepare(request, response);//正如这个方法名字一样进行locale、encoding以及特殊request parameters设置

try ...{

request = du.wrapRequest(request, servletContext);//对request进行包装

} catch (IOException e) ...{

String message = "Could not wrap servlet request with MultipartRequestWrapper!";

LOG.error(message, e);

throw new ServletException(message, e);

}

ActionMapperIF mapper = ActionMapperFactory.getMapper();//得到action的mapper

ActionMapping mapping = mapper.getMapping(request);// 得到action 的 mapping

if (mapping == null) ...{

// there is no action in this request, should we look for a static resource?

String resourcePath = RequestUtils.getServletPath(request);

if ("".equals(resourcePath) && null != request.getPathInfo()) ...{

resourcePath = request.getPathInfo();

}

if ("true".equals(Configuration.get(WebWorkConstants.WEBWORK_SERVE_STATIC_CONTENT))

&& resourcePath.startsWith("/webwork")) ...{

String name = resourcePath.substring("/webwork".length());

findStaticResource(name, response);

} else ...{

// this is a normal request, let it pass through

chain.doFilter(request, response);

}

// WW did its job here

return;

}

Object o = null;

try ...{

//setupContainer(request);

o = beforeActionInvocation(request, servletContext);

//整个框架最最核心的方法，下面分析

du.serviceAction(request, response, servletContext, mapping);

} finally ...{

afterActionInvocation(request, servletContext, o);

ActionContext.setContext(null);

}

}

du.serviceAction(request, response, servletContext, mapping);

//这个方法询问ActionMapper是否需要调用某个Action来处理这个（request）请求，如果ActionMapper决定需要调用某个Action，FilterDispatcher把请求的处理交给ActionProxy

public void serviceAction(HttpServletRequest request, HttpServletResponse response, String namespace, String actionName, Map requestMap, Map parameterMap, Map sessionMap, Map applicationMap) ...{

HashMap extraContext = createContextMap(requestMap, parameterMap, sessionMap, applicationMap, request, response, getServletConfig()); //实例化Map请求 ，询问ActionMapper是否需要调用某个Action来处理这个（request）请求

extraContext.put(SERVLET_DISPATCHER, this);

OgnlValueStack stack = (OgnlValueStack) request.getAttribute(ServletActionContext.WEBWORK_VALUESTACK_KEY);

if (stack != null) ...{

extraContext.put(ActionContext.VALUE_STACK,new OgnlValueStack(stack));

}

try ...{

ActionProxy proxy = ActionProxyFactory.getFactory().createActionProxy(namespace, actionName, extraContext);

//这里actionName是通过两道getActionName解析出来的, FilterDispatcher把请求的处理交给ActionProxy，下面是ServletDispatcher的 TODO:

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

proxy.execute();

//通过代理模式执行ActionProxy

if (stack != null)...{

request.setAttribute(ServletActionContext.WEBWORK_VALUESTACK_KEY,stack);

}

} catch (ConfigurationException e) ...{

log.error("Could not find action", e);

sendError(request, response, HttpServletResponse.SC_NOT_FOUND, e);

} catch (Exception e) ...{

log.error("Could not execute action", e);

sendError(request, response, HttpServletResponse.SC_INTERNAL_SERVER_ERROR, e);

}

}

FilterDispatcher询问ActionMapper是否需要调用某个Action来处理这个（request）请求，如果ActionMapper决定需要调用某个Action，FilterDispatcher把请求的处理交给ActionProxy。
ActionProxy通过Configuration Manager（struts.xml）询问框架的配置文件，找到需要调用的Action类.

如上文的struts.xml配置

<?xml version="1.0" encoding="GBK"?>

<!DOCTYPE struts PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 2.0//EN" "http://struts.apache.org/dtds/struts-2.0.dtd">

<struts>

<include file="struts-default.xml"/>

<package name="struts2" extends="struts-default">

<action name="add"

class="edisundong.AddAction" >

<result>add.jsp</result>

</action>

</package>

</struts>

如果提交请求的是add.action，那么找到的Action类就是edisundong.AddAction。
ActionProxy创建一个ActionInvocation的实例，同时ActionInvocation通过代理模式调用Action。但在调用之前ActionInvocation会根据配置加载Action相关的所有Interceptor。（Interceptor是struts2另一个核心级的概念）

下面我们来看看ActionInvocation是如何工作的：

ActionInvocation 是Xworks 中Action 调度的核心。而对Interceptor 的调度，也正是由ActionInvocation负责。ActionInvocation 是一个接口， 而DefaultActionInvocation 则是Webwork 对ActionInvocation的默认实现。

Interceptor 的调度流程大致如下：

1. ActionInvocation初始化时，根据配置，加载Action相关的所有Interceptor。

2. 通过ActionInvocation.invoke方法调用Action实现时，执行Interceptor。

Interceptor将很多功能从我们的Action中独立出来，大量减少了我们Action的代码，独立出来的行为具有很好的重用性。XWork、WebWork的许多功能都是有Interceptor实现，可以在配置文件中组装Action用到的Interceptor，它会按照你指定的顺序，在Action执行前后运行。

那么什么是拦截器。

拦截器就是AOP（Aspect-Oriented Programming）的一种实现。（AOP是指用于在某个方法或字段被访问之前，进行拦截然后在之前或之后加入某些操作。）

拦截器的例子这里就不展开了。

struts-default.xml文件摘取的内容：

< interceptor name ="alias" class ="com.opensymphony.xwork2.interceptor.AliasInterceptor" />

< interceptor name ="autowiring" class ="com.opensymphony.xwork2.spring.interceptor.ActionAutowiringInterceptor" />

< interceptor name ="chain" class ="com.opensymphony.xwork2.interceptor.ChainingInterceptor" />

< interceptor name ="conversionError" class ="org.apache.struts2.interceptor.StrutsConversionErrorInterceptor" />

< interceptor name ="createSession" class ="org.apache.struts2.interceptor.CreateSessionInterceptor" />

< interceptor name ="debugging" class ="org.apache.struts2.interceptor.debugging.DebuggingInterceptor" />

< interceptor name ="external-ref" class ="com.opensymphony.xwork2.interceptor.ExternalReferencesInterceptor" />

< interceptor name ="execAndWait" class ="org.apache.struts2.interceptor.ExecuteAndWaitInterceptor" />

< interceptor name ="exception" class ="com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor" />

< interceptor name ="fileUpload" class ="org.apache.struts2.interceptor.FileUploadInterceptor" />

< interceptor name ="i18n" class ="com.opensymphony.xwork2.interceptor.I18nInterceptor" />

< interceptor name ="logger" class ="com.opensymphony.xwork2.interceptor.LoggingInterceptor" />

< interceptor name ="model-driven" class ="com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor" />

< interceptor name ="scoped-model-driven" class ="com.opensymphony.xwork2.interceptor.ScopedModelDrivenInterceptor" />

< interceptor name ="params" class ="com.opensymphony.xwork2.interceptor.ParametersInterceptor" />

< interceptor name ="prepare" class ="com.opensymphony.xwork2.interceptor.PrepareInterceptor" />

< interceptor name ="static-params" class ="com.opensymphony.xwork2.interceptor.StaticParametersInterceptor" />

< interceptor name ="scope" class ="org.apache.struts2.interceptor.ScopeInterceptor" />

< interceptor name ="servlet-config" class ="org.apache.struts2.interceptor.ServletConfigInterceptor" />

< interceptor name ="sessionAutowiring" class ="org.apache.struts2.spring.interceptor.SessionContextAutowiringInterceptor" />

< interceptor name ="timer" class ="com.opensymphony.xwork2.interceptor.TimerInterceptor" />

< interceptor name ="token" class ="org.apache.struts2.interceptor.TokenInterceptor" />

< interceptor name ="token-session" class ="org.apache.struts2.interceptor.TokenSessionStoreInterceptor" />

< interceptor name ="validation" class ="com.opensymphony.xwork2.validator.ValidationInterceptor" />

< interceptor name ="workflow" class ="com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor" />

< interceptor name ="store" class ="org.apache.struts2.interceptor.MessageStoreInterceptor" />

< interceptor name ="checkbox" class ="org.apache.struts2.interceptor.CheckboxInterceptor" />

< interceptor name ="profiling" class ="org.apache.struts2.interceptor.ProfilingActivationInterceptor" />

一旦Action执行完毕，ActionInvocation负责根据struts.xml中的配置找到对应的返回结果。如上文中将结构返回“add.jsp”，但大部分时候都是返回另外一个action，那么流程又得走一遍………
转自:http://blog.csdn.net/ichsonx/article/details/2954397