Struts1.1b3部分源代碼分析.
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Struts1.1部分源代碼分析
一：說明
本文針對Struts1.1b3做分析，主要希望通過對源代碼的分析闡述Struts1.1的工作方式。
本文不適合初學者參考，適合具有一定基于Struts開發的程序員參考。
下面的描述；里面將會對ActionServlet,RequestProcessor,ModuleConfig等幾個類做一些
說明。以注釋源代碼的方式，說明取工作流程。
特別申明：Struts1.1代碼版權屬于Apache遵循The Apache Software License, Version 1.1.
本文版權屬于孤魂一笑個人所有，任何個人或組織希望轉載，請與我聯系。并獲得我的授權
方可轉載。
二：ActionServlet分析
我們先來看一下使用Struts的配置文件。
action
org.apache.struts.action.ActionServlet
definitions-config
/WEB-INF/tiles-defs.xml,/WEB-INF/tiles-tests-defs.xml,/WEB-INF/tiles-tutorial-defs.xml,
/WEB-INF/tiles-examples-defs.xml
definitions-debug
0
definitions-parser-details
0
definitions-parser-validate
true
?
config
/WEB-INF/struts-config.xml
?
config/examples
/WEB-INF/struts-examples-config.xml
?
config/test
/WEB-INF/struts-tests-config.xml
?
config/tutorial
/WEB-INF/struts-tutorial-config.xml
validate
true
debug
2
detail
2
?
application
org.apache.struts.webapp.tiles.dev1-1.ApplicationResources
2
?
action
*.do
?
接下來我們來看一下ActionServlet的具體使用
javax.servlet.http.HttpServlet
|
|-->org.apache.struts.action.ActionServlet
所以本質上ActionServlet是一個普通的servlet，負責處理.do為后綴的Http請求.
servlet在執行doGet(),doPost(),之前先調用init(),
以下我們先分析一下init()方法
/**
* Initialize this servlet. Most of the processing has been factored into
* support methods so that you can override particular functionality at a
* fairly granular level.
* servlet初始化操作,注意初始化順序
* @exception ServletException if we cannot configure ourselves correctly
*/
public void init() throws ServletException {
//注意初始化的順序
//Initialize our internal MessageResources bundle
initInternal();
//Initialize other global characteristics of the controller servlet
//處理一些全局變量的設置如：debug，detail等
initOther();
//Initialize the servlet mapping under which our controller servlet
//is being accessed. This will be used in the &html:form>
//tag to generate correct destination URLs for form submissions
//主要是注冊DTD文件以及解析web.xml關于ActionServlet的配置。如后綴名等.
// Configure the processing rules that we need
// digester.addCallMethod("web-app/servlet-mapping",
// "addServletMapping", 2);
// digester.addCallParam("web-app/servlet-mapping/servlet-name", 0);
// digester.addCallParam("web-app/servlet-mapping/url-pattern", 1);
//initServlet()的上面一段將把Struts默認的后綴名從web.xml中解析得到
//也就是web.xml中的如下配置：
//
//action
//*.do
//默認以.do結尾的請求都將由Struts來處理，你可以自己修改
//
initServlet();
// Initialize modules as needed
//在Attribute中保存類實例
getServletContext().setAttribute(Globals.ACTION_SERVLET_KEY, this);
//根據配置文件生成ModuleConfig,這是很重要的一步.下面會專門分析
//在tiles的配置中先解析注釋為"Mark 0"的一個配置文件:/WEB-INF/struts-config.xml
//使用initModuleConfig方法解析XML文件.
//參數為prefix："",paths:"/WEB-INF/struts-config.xml"
ModuleConfig moduleConfig = initModuleConfig("", config);
//初始化Message
initModuleMessageResources(moduleConfig);
//初始化JDBC DataSource
initModuleDataSources(moduleConfig);
//初始化PlunIn
initModulePlugIns(moduleConfig);
moduleConfig.freeze();
//在Struts1.1以后可以使用多個配置文件,在解析完默認的配置文件也就是上面提到的
//注釋為"Mark 0"的一個配置文件:/WEB-INF/struts-config.xml后解析其他的配置文件
Enumeration names = getServletConfig().getInitParameterNames();
//依次解析注釋為"Mark 1"、"Mark 2"、"Mark 3"對應配置文件
while (names.hasMoreElements()) {
//每一個配置文件的文件名
String name = (String) names.nextElement();
if (!name.startsWith("config/")) {
continue;
}
//
String prefix = name.substring(6);
moduleConfig = initModuleConfig
(prefix, getServletConfig().getInitParameter(name));
initModuleMessageResources(moduleConfig);
initModuleDataSources(moduleConfig);
initModulePlugIns(moduleConfig);
moduleConfig.freeze();
}
destroyConfigDigester();
}
/**
* 此方法使用Digester解析XML,關于使用Digester的介紹參看我的另外一篇文章
*
Initialize the application configuration information for the
* specified module.
*
* @param prefix Module prefix for this module
* @param paths Comma-separated list of context-relative resource path(s)
* for this modules's configuration resource(s)
*
* @exception ServletException if initialization cannot be performed
* @since Struts 1.1
*/
protected ModuleConfig initModuleConfig
(String prefix, String paths) throws ServletException {
if (log.isDebugEnabled()) {
log.debug("Initializing module path '" + prefix +
"' configuration from '" + paths + "'");
}
// Parse the configuration for this module
ModuleConfig config = null;
InputStream input = null;
String mapping = null;
try {
//工廠方法創建ModuleConfig標記為：prefix
ModuleConfigFactory factoryObject =
ModuleConfigFactory.createFactory();
config = factoryObject.createModuleConfig(prefix);
// Support for module-wide ActionMapping type override
mapping = getServletConfig().getInitParameter("mapping");
if (mapping != null) {
config.setActionMappingClass(mapping);
}
// Configure the Digester instance we will use
//得到解析XML的digester
Digester digester = initConfigDigester();
// Process each specified resource path
while (paths.length() > 0) {
//開始解析指定路徑文件名的文件
digester.push(config);
String path = null;
//文件是否為多個并且使用","分割
int comma = paths.indexOf(',');
//存在多個配置文件
if (comma >= 0) {
//先解析第一個
path = paths.substring(0, comma).trim();
//paths存放剩余的文件名下次再處理
paths = paths.substring(comma + 1);
} else {
//當前只存在一個
path = paths.trim();
//沒有剩余,下次循環根據上面一句將會在唯一的循環退出點"point break"
//退出循環
paths = "";
}
//全部解析完成跳出循環
//point break
if (path.length() < 1) {
break;
}
//根據文件名取文件
URL url = getServletContext().getResource(path);
InputSource is = new InputSource(url.toExternalForm());
input = getServletContext().getResourceAsStream(path);
is.setByteStream(input);
digester.parse(is);
//全局變量的形式把解析生成的ModuleConfig實例保存起來
//如"Mark 1"處標記的"config/examples",
//key為："org.apache.struts.action.MODULEexamples"
//Globals.MODULE_KEY值為:org.apache.struts.action.MODULE
getServletContext().setAttribute
(Globals.MODULE_KEY + prefix, config);
input.close();
}
} catch (Throwable t) {
log.error(internal.getMessage("configParse", paths), t);
throw new UnavailableException
(internal.getMessage("configParse", paths));
} finally {
if (input != null) {
try {
input.close();
} catch (IOException e) {
;
}
}
}
// Force creation and registration of DynaActionFormClass instances
// for all dynamic form beans we wil be using
//根據ModuleConfig實例得到配置的FormBean的配置
//注意：因為在Struts整個運行當中FormBean的實例要在Action的實例創建之前先創建
//因為Action執行perform(1.1以前)，execute（1.1）需要使用到FormBean
FormBeanConfig fbs[] = config.findFormBeanConfigs();
for (int i = 0; i < fbs.length; i++) {
if (fbs[i].getDynamic()) {
DynaActionFormClass.createDynaActionFormClass(fbs[i]);
}
}
// Special handling for the default module (for
// backwards compatibility only, will be removed later)
//下面是生成一些實例
if (prefix.length() < 1) {
defaultControllerConfig(config);
defaultMessageResourcesConfig(config);
defaultFormBeansConfig(config);
defaultForwardsConfig(config);
defaultMappingsConfig(config);
}
// Return the completed configuration object
//config.freeze(); // Now done after plugins init
return (config);
}
到此初始化工作基本結束，下面將處理具體的Http請求。在Servlet協議中所有的post方法將調用
以下方法來處理
public void doPost(HttpServletRequest request,
HttpServletResponse response)
throws IOException, ServletException {}
get方法也調用類似的方法來處理
在Struts中post,get方法都調用同一個方法
process(request, response);來處理具體的請求
如下：
/**
* 對每一個提交過來的Action進行處理
* Perform the standard request processing for this request, and create
* the corresponding response.
*
* @param request The servlet request we are processing
* @param response The servlet response we are creating
*
* @exception IOException if an input/output error occurs
* @exception ServletException if a servlet exception is thrown
*/
protected void process(HttpServletRequest request,
HttpServletResponse response)
throws IOException, ServletException {
//設置或刪除Attribute
RequestUtils.selectModule(request, getServletContext());
//具體的處理交給RequestProcessor去處理HttpRequest,HttpResponse
//這是一個很典型的設計模式
//下面我們將詳細來分析RequestProcessor，很容易理解Struts的運行方式
getRequestProcessor(getModuleConfig(request)).process(request, response);
}
三:RequestProcessor分析
通過前面的分析我們知道Struts中對HttpRequest,HttpResponse的處理都交給RequestProcessor
的process（）方法來處理。下面我們來看看process方法
/**
*
Process an HttpServletRequest and create the
* corresponding HttpServletResponse.
*
* @param request The servlet request we are processing
* @param response The servlet response we are creating
*
* @exception IOException if an input/output error occurs
* @exception ServletException if a processing exception occurs
*/
public void process(HttpServletRequest request,
HttpServletResponse response)
throws IOException, ServletException {
// Wrap multipart requests with a special wrapper
//如果是upload,返回一個MultipartRequestWrapper()
request = processMultipart(request);
// Identify the path component we will use to select a mapping
//對request進行分析得到提交過來的Form Action
String path = processPath(request, response);
if (path == null) {
return;
}
if (log.isInfoEnabled()) {
log.info("Processing a '" + request.getMethod() +
"' for path '" + path + "'");
}
// Select a Locale for the current user if requested
//本地化處理
processLocale(request, response);
// Set the content type and no-caching headers if requested
processContent(request, response);
//設置Cache不保存
processNoCache(request, response);
// General purpose preprocessing hook
if (!processPreprocess(request, response)) {
return;
}
// Identify the mapping for this request
//得到path以后，根據配置文件(struts-config.xml)的相關配置來得到一個
//ActionMapping的實例
//ActionMapping繼承ActionConfig
//仔細看一下ActionMapping的代碼就能發現：
//下面的一段將解析影射一個ActionMapping的實例
//在ActionServlet在初始化的時候實際上已經把所有的ActionMapping的實例
//都已經創建好了。processMapping方法實際上是從Attribute中去得到已經
//保存好的ActionMapping的實例，可以理解為在Tomcat啟動的時候已經
//把所有的ActionMapping保存在Attribute里面。所以在Tomcat啟動的時候
//比較慢，如果Struts-config.xml有問題啟動就會出錯。
/***
type="org.apache.struts.webapp.tiles.test.TestActionTileAction">
?
**/
//****注意得到創建實例的順序
//ActionMapping實例已經創建好了，現在從Atribute中取到
ActionMapping mapping = processMapping(request, response, path);
if (mapping == null) {
return;
}
// Check for any role required to perform this action
if (!processRoles(request, response, mapping)) {
return;
}
// Process any ActionForm bean related to this request
//根據mapping得到ActionForm的實例。
//同名ActionForm在系統中只會創建一次。
ActionForm form = processActionForm(request, response, mapping);
//壓棧
processPopulate(request, response, form, mapping);
//處理校驗,調用ActionForm的validate方法
//假如出錯將會返回到前一頁面
//也就是說在Action還沒有創建之前就將做校驗
if (!processValidate(request, response, form, mapping)) {
return;
}
// Process a forward or include specified by this mapping
if (!processForward(request, response, mapping)) {
return;
}
if (!processInclude(request, response, mapping)) {
return;
}
// Create or acquire the Action instance to process this request
//在得到ActionMapping、ActionForm的實例后接下來得到Action實例
//實例如果已經創建從Map里面去取如果沒有創建一個并保存在Map里面
//對保存Action實例的Map 實現線程同步
Action action = processActionCreate(request, response, mapping);
if (action == null) {
return;
}
// Call the Action instance itself
//在ActionMapping、ActionForm、Action實例創建好以后
//調用Action的execute()方法得到一個ActionForward
//因為所有的可執行Action都必須有override Action的execute()/perform()方法
ActionForward forward =
processActionPerform(request, response,
action, form, mapping);
// Process the returned ActionForward instance
//Action已經正常執行，執行結束后將返回到另外一個頁面
processActionForward(request, response, forward);
}
仔細閱讀上面的代碼，要特別注意ActionMapping、ActionForm、Action的實例是依次創建的。
創建完以后才去執行Action的execute()方法。為什么要依次創建ActionMapping、ActionForm
、Action??????
四:ModuleConfig分析
現在我們很有必要了解一下ModuleConfig這個類，因為太多地方用到了。
實際上ModuleConfig是一個接口有一個實現。org.apache.struts.config.impl.ModuleConfigImpl
具體實現我就沒有不要去分析了。我們來看看這個接口。
package org.apache.struts.config;
/**
*
The collection of static configuration information that describes a
* Struts-based module. Multiple modules are identified by
* a prefix at the beginning of the context
* relative portion of the request URI. If no module prefix can be
* matched, the default configuration (with a prefix equal to a zero-length
* string) is selected, which is elegantly backwards compatible with the
* previous Struts behavior that only supported one module.
*
* @author Rob Leland
* @version $Revision: 1.2 $ $Date: 2002/12/22 05:31:14 $
* @since Struts 1.1
*/
public interface ModuleConfig {
/**
* Has this module been completely configured yet. Once this flag
* has been set, any attempt to modify the configuration will return an
* IllegalStateException.
*/
boolean getConfigured();
/**
* The controller configuration object for this module.
*/
ControllerConfig getControllerConfig();
/**
* The controller configuration object for this module.
* @param cc The controller configuration object for this module.
*/
void setControllerConfig(ControllerConfig cc);
/**
* The prefix of the context-relative portion of the request URI, used to
* select this configuration versus others supported by the controller
* servlet. A configuration with a prefix of a zero-length String is the
* default configuration for this web module.
*/
String getPrefix();
/**
* The prefix of the context-relative portion of the request URI, used to
* select this configuration versus others supported by the controller
* servlet. A configuration with a prefix of a zero-length String is the
* default configuration for this web module.
*/
public void setPrefix(String prefix);
/**
* The default class name to be used when creating action mapping
* instances.
*/
String getActionMappingClass();
/**
* The default class name to be used when creating action mapping
* instances.
* @param actionMappingClass default class name to be used when creating action mapping
* instances.
*/
void setActionMappingClass(String actionMappingClass);
/**
* Add a new ActionConfig instance to the set associated
* with this module.
*
* @param config The new configuration instance to be added
*
* @exception java.lang.IllegalStateException if this module configuration
* has been frozen
*/
void addActionConfig(ActionConfig config);
/**
* Add a new DataSourceConfig instance to the set associated
* with this module.
*
* @param config The new configuration instance to be added
*
* @exception java.lang.IllegalStateException if this module configuration
* has been frozen
*/
void addDataSourceConfig(DataSourceConfig config);
/**
* Add a new ExceptionConfig instance to the set associated
* with this module.
*
* @param config The new configuration instance to be added
*
* @exception java.lang.IllegalStateException if this module configuration
* has been frozen
*/
void addExceptionConfig(ExceptionConfig config);
/**
* Add a new FormBeanConfig instance to the set associated
* with this module.
*
* @param config The new configuration instance to be added
*
* @exception java.lang.IllegalStateException if this module configuration
* has been frozen
*/
void addFormBeanConfig(FormBeanConfig config);
/**
* Add a new ForwardConfig instance to the set of global
* forwards associated with this module.
*
* @param config The new configuration instance to be added
*
* @exception java.lang.IllegalStateException if this module configuration
* has been frozen
*/
void addForwardConfig(ForwardConfig config);
/**
* Add a new MessageResourcesConfig instance to the set
* associated with this module.
*
* @param config The new configuration instance to be added
*
* @exception IllegalStateException if this module configuration
* has been frozen
*/
void addMessageResourcesConfig(MessageResourcesConfig config);
/**
* Add a newly configured {@link org.apache.struts.config.PlugInConfig} instance to the set of
* plug-in Actions for this module.
*
* @param plugInConfig The new configuration instance to be added
*/
void addPlugInConfig(PlugInConfig plugInConfig);
/**
* Return the action configuration for the specified path, if any;
* otherwise return null.
*
* @param path Path of the action configuration to return
*/
ActionConfig findActionConfig(String path);
/**
* Return the action configurations for this module. If there are
* none, a zero-length array is returned.
*/
ActionConfig[] findActionConfigs();
/**
* Return the data source configuration for the specified key, if any;
* otherwise return null.
*
* @param key Key of the data source configuration to return
*/
DataSourceConfig findDataSourceConfig(String key);
/**
* Return the data source configurations for this module. If there
* are none, a zero-length array is returned.
*/
DataSourceConfig[] findDataSourceConfigs();
/**
* Return the exception configuration for the specified type, if any;
* otherwise return null.
*
* @param type Exception class name to find a configuration for
*/
ExceptionConfig findExceptionConfig(String type);
/**
* Return the exception configurations for this module. If there
* are none, a zero-length array is returned.
*/
ExceptionConfig[] findExceptionConfigs();
/**
* Return the form bean configuration for the specified key, if any;
* otherwise return null.
*
* @param name Name of the form bean configuration to return
*/
FormBeanConfig findFormBeanConfig(String name);
/**
* Return the form bean configurations for this module. If there
* are none, a zero-length array is returned.
*/
FormBeanConfig[] findFormBeanConfigs();
/**
* Return the forward configuration for the specified key, if any;
* otherwise return null.
*
* @param name Name of the forward configuration to return
*/
ForwardConfig findForwardConfig(String name);
/**
* Return the form bean configurations for this module. If there
* are none, a zero-length array is returned.
*/
ForwardConfig[] findForwardConfigs();
/**
* Return the message resources configuration for the specified key,
* if any; otherwise return null.
*
* @param key Key of the data source configuration to return
*/
MessageResourcesConfig findMessageResourcesConfig(String key);
/**
* Return the message resources configurations for this module.
* If there are none, a zero-length array is returned.
*/
MessageResourcesConfig[] findMessageResourcesConfigs();
/**
* Return the configured plug-in actions for this module. If there
* are none, a zero-length array is returned.
*/
PlugInConfig[] findPlugInConfigs();
/**
* Freeze the configuration of this module. After this method
* returns, any attempt to modify the configuration will return
* an IllegalStateException.
*/
void freeze();
/**
* Remove the specified action configuration instance.
*
* @param config ActionConfig instance to be removed
*
* @exception java.lang.IllegalStateException if this module configuration
* has been frozen
*/
void removeActionConfig(ActionConfig config);
/**
* Remove the specified exception configuration instance.
*
* @param config ActionConfig instance to be removed
*
* @exception java.lang.IllegalStateException if this module configuration
* has been frozen
*/
void removeExceptionConfig(ExceptionConfig config);
/**
* Remove the specified data source configuration instance.
*
* @param config DataSourceConfig instance to be removed
*
* @exception java.lang.IllegalStateException if this module configuration
* has been frozen
*/
void removeDataSourceConfig(DataSourceConfig config);
/**
* Remove the specified form bean configuration instance.
*
* @param config FormBeanConfig instance to be removed
*
* @exception java.lang.IllegalStateException if this module configuration
* has been frozen
*/
void removeFormBeanConfig(FormBeanConfig config);
/**
* Remove the specified forward configuration instance.
*
* @param config ForwardConfig instance to be removed
*
* @exception java.lang.IllegalStateException if this module configuration
* has been frozen
*/
void removeForwardConfig(ForwardConfig config);
/**
* Remove the specified message resources configuration instance.
*
* @param config MessageResourcesConfig instance to be removed
*
* @exception java.lang.IllegalStateException if this module configuration
* has been frozen
*/
void removeMessageResourcesConfig(MessageResourcesConfig config);
}
上面的注釋已經非常清晰了。我就不去浪費大家的時間了，再想仔細看就去看他的實現。
其實主要是對HashMap()的處理。
五：ActionMapping分析
最后我們實現很有必要看一下ActionMapping,因為你如果想清楚的了解Struts-config.xml
這個配置文件的作用，你應該要知道ActionMapping
前面已經說過ActionMapping繼承ActionConfig
以下就是ActionMapping加的四個方法。
/**
*
Find and return the ExceptionConfig instance defining
* how exceptions of the specified type should be handled. This is
* performed by checking local and then global configurations for the
* specified exception's class, and then looking up the superclass chain
* (again checking local and then global configurations). If no handler
* configuration can be found, return null.
*
* @param type Exception class for which to find a handler
* @since Struts 1.1
*/
public ExceptionConfig findException(Class type) {
}
/**
*
Find and return the ForwardConfig instance defining
* how forwarding to the specified logical name should be handled. This is
* performed by checking local and then global configurations for the
* specified forwarding configuration. If no forwarding configuration
* can be found, return null.
*
* @param name Logical name of the forwarding instance to be returned
*/
public ActionForward findForward(String name) {
}
/**
*
Return the logical names of all locally defined forwards for this
* mapping. If there are no such forwards, a zero-length array
* is returned.
*/
public String[] findForwards() {
}
/**
*
Create (if necessary) and return an {@link ActionForward} that
* corresponds to the input property of this Action.
*
* @since Struts 1.1b2
*/
public ActionForward getInputForward() {
}
還是看以下他的基類ActionConfig吧
public class ActionConfig implements Serializable {
/**
* Has configuration of this component been completed?
*/
protected boolean configured = false;
/**
* The set of exception handling configurations for this
* action, if any, keyed by the type property.
*/
protected HashMap exceptions = new HashMap();
/**
* The set of local forward configurations for this action, if any,
* keyed by the name property.
*/
protected HashMap forwards = new HashMap();
/**
* The module configuration with which we are associated.
*/
protected ModuleConfig moduleConfig = null;
/**
* The request-scope or session-scope attribute name under which our
* form bean is accessed, if it is different from the form bean's
* specified name.
*/
protected String attribute = null;
/**
* Context-relative path of the web application resource that will process
* this request via RequestDispatcher.forward(), instead of instantiating
* and calling the Action class specified by "type".
* Exactly one of forward, include, or
* type must be specified.
*/
protected String forward = null;
/**
* Context-relative path of the web application resource that will process
* this request via RequestDispatcher.include(), instead of instantiating
* and calling the Action class specified by "type".
* Exactly one of forward, include, or
* type must be specified.
*/
protected String include = null;
/**
* Context-relative path of the input form to which control should be
* returned if a validation error is encountered. Required if "name"
* is specified and the input bean returns validation errors.
*/
protected String input = null;
/**
* Fully qualified Java class name of the
* MultipartRequestHandler implementation class used to
* process multi-part request data for this Action.
*/
protected String multipartClass = null;
/**
* Name of the form bean, if any, associated with this Action.
*/
protected String name = null;
/**
* General purpose configuration parameter that can be used to pass
* extra iunformation to the Action instance selected by this Action.
* Struts does not itself use this value in any way.
*/
protected String parameter = null;
/**
* Context-relative path of the submitted request, starting with a
* slash ("/") character, and omitting any filename extension if
* extension mapping is being used.
*/
protected String path = null;
/**
* Prefix used to match request parameter names to form ben property
* names, if any.
*/
protected String prefix = null;
/**
* Comma-delimited list of security role names allowed to request
* this Action.
*/
protected String roles = null;
/**
* Identifier of the scope ("request" or "session") within which
* our form bean is accessed, if any.
*/
protected String scope = "session";
/**
* Suffix used to match request parameter names to form bean property
* names, if any.
*/
protected String suffix = null;
/**
* Fully qualified Java class name of the Action class
* to be used to process requests for this mapping if the
* forward and include properties are not set.
* Exactly one of forward, include, or
* type must be specified.
*/
protected String type = null;
/**
* Should the validate() method of the form bean associated
* with this action be called?
*/
protected boolean validate = true;
}
其實ActionConfig是一個很典型的ValueObject.所以其他的get/set方法我就不寫出來了。
看這個代碼一定要和struts-config.xml一起來看，根據struts-config.xml去找找
每一段配置文件最終要生成一個ActionConfig,他們之間的對應關系。
如果你想擴展Struts,ActionMapping估計你一定要修改。還有ActionServlet你也要修改。
六：結束語
分析了一些代碼下面做一些概述。先來整體的了解一下Struts的工作流程.
在實現一個基于Struts的運用之前我們首先是做環境設置，Struts正常工作需要至少兩個
配置文件web.xml,struts-config.xml.
web.xml告訴App Server所有以.do結尾的請求最終提交給ActionServlet去處理。
2就規定ActionServlet是在App Server啟動的時候
創建的并且一直存在。
ActionServlet在創建的時候會做如下的工作：
保存一些后面需要使用的實例在Attribute(內存)里面。
根據web.xml的配置解析struts-config.xml文件。
根據struts-config.xml的配置生成ActionMapping實例并且保存。
ActionServlet在生命周期就一直等待Http 請求
每一個.do結尾的Http 請求都由ActionServlet先截獲然后根據請求路徑得到具體調用那
一個Action去處理，在這之前生成、處理ActionForm。具體知道那一個Action去處理請求
后調用Action的execute()/perform()處理完成，返回。
?