引用一張Struts2調用的時序圖:
1.用戶發送請求;這個請求被交給你在web.xml文件配置的過濾器(Filter)struts2的過濾器(StrutsPrepareAndExecuteFilter)一般都是在最後一個。調用其doFilter方法。
<filter-mapping>
<filter-name>userLoginFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<!-- 配置struts2的核心攔截器,官方推出用StrutsPreparedAndExcuteFilter代替FilterDispatcher -->
<filter>
<filter-name>struts2</filter-name>
<filter-class>org.apache.struts2.dispatcher.filter.StrutsPrepareAndExecuteFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>struts2</filter-name>
<url-pattern>*.action</url-pattern>
</filter-mapping>
StrutsPrepareAndExecuteFilter的doFiler方法:
public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {
HttpServletRequest request = (HttpServletRequest) req;
HttpServletResponse response = (HttpServletResponse) res;
try {
String uri = RequestUtils.getUri(request);
if (excludedPatterns != null && prepare.isUrlExcluded(request, excludedPatterns)) {
LOG.trace("Request {} is excluded from handling by Struts, passing request to other filters", uri);
chain.doFilter(request, response);
} else {
LOG.trace("Checking if {} is a static resource", uri);
boolean handled = execute.executeStaticResourceRequest(request, response);
if (!handled) {
LOG.trace("Assuming uri {} as a normal action", uri);
prepare.setEncodingAndLocale(request, response);
prepare.createActionContext(request, response);
prepare.assignDispatcherToThread();
request = prepare.wrapRequest(request);
ActionMapping mapping = prepare.findActionMapping(request, response, true);
if (mapping == null) {
LOG.trace("Cannot find mapping for {}, passing to other filters", uri);
chain.doFilter(request, response);
} else {
LOG.trace("Found mapping {} for {}", mapping, uri);
execute.executeAction(request, response, mapping);
}
}
}
} finally {
prepare.cleanupRequest(request);
}
}
2. 調用PrepareOperations的findActionMapping(request, response, true),以便確定這個請求是否有對應的action調用。 返回一個描述action調用的ActionMapping對象 。具體實現類是org.apache.struts2.dispatcher.mapper.DefaultActionMapper的getMapping方法。
public ActionMapping getMapping(HttpServletRequest request, ConfigurationManager configManager) {
ActionMapping mapping = new ActionMapping();
String uri = RequestUtils.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);
return parseActionName(mapping);
}
3. ExecuteOperations調用executeAction處理Action。其實質是調用Dispatcher類的serviceAction方法得到一個ActionProxy實例。該方法根據ActionMapping這個對象中的屬性以及configurationManager來生成一個ActionProxy。具體實現類是DefaultActionProxyFactory。
ActionProxy proxy = 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();
}
4. ActionProxy設置ActionInvocation對象的執行上下文,然後調用其invoke方法。從攔截器映射中查找尚未執行的攔截器,調用他的intercept(invocation)方法,並將自身對象引用作爲參數傳遞給攔截器。
5. 攔截器完成某些預處理工作後,反過來調用ActionInvocation的invoke方法,ActionInvocation維護者自己的狀態,所以他知道哪些攔截器已經被執行,如果還沒有執行的攔截器,就繼續執行他的intercept(invocation)方法。 至所有的攔截器都已經執行過了,就調用action實例的execute方法 。
6. ActionInvocation根據action執行返回的結果碼,查找對應的Result,調用Result的execute(invocation)方法,將結果頁面呈現給用戶。 ActionInvocation的invoke方法將控制權返回給攔截器映射中的最後一個攔截器,該攔截器完成所有必須的後期處理工作,然後從intercept(invocation)方法返回,允許前一個攔截器執行他自己的後處理工作。如此循環到所有的攔截器都成功返回。
7. ActionInvocation的invoke方法執行完畢後,想ActionProxy返回一個String類型的結果碼,最後,ActionProxy清理狀態並返回。
ps:關於ActionContext是何時創建的,可以參考下文:
https://blog.csdn.net/u011496144/article/details/74931136