這篇文章主要介紹了Struts1教學之ActionMapping,小編覺得挺不錯的,現在分享給大家,也給大家做個參考。一起跟著小編過來看看吧
首先斷點走出了processpath方法,
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這個方法是用來截取字串的,今天我們來看看怎麼獲得ActionMapping的方法---processMapping。
在此之前簡單說一下ActionMapping,它的原始程式碼中可以看出,其中最重要的屬性和我們的mvc小實例中的ActionMapping類似,都是有path、type還有forwardMap,主要是對應的struts-config設定檔而來,這個就是保存這個設定檔的資訊到記憶體中。
具體的mvc小實例的ActionMapping程式碼如下:
package com.cjq.servlet; import java.util.Map; public class ActionMapping { private String path; private Object type; private Map forwardMap; public String getPath() { return path; } public void setPath(String path) { this.path = path; } public Object getType() { return type; } public void setType(Object type) { this.type = type; } public Map getForwardMap() { return forwardMap; } public void setForwardMap(Map forwardMap) { this.forwardMap = forwardMap; } }
而Struts中的Actionconfig(因為ActionMapping是繼承這個ActionConfig的,所以我們來看ActionConfig比較直接)的程式碼如下:
從這兩部分程式碼來看,更印證了我在開篇寫的mvc小實例是一個struts框架的雛形。
講完ActionMapping的一些內容後,相信對ActionMapping有所了解,那麼系統是如何產生ActionMapping和如何找到ActionMapping的呢?這就是今天要說的整體:
我們看下web.xml中有一個
進入斷點偵錯,先在processMapping方法上設定斷點。
進入原始程式碼中:
/** * <p>Select the mapping used to process theselection path for this request * If no mapping can be identified, createan error response and return * <code>null</code>.</p> * * @param request The servlet request weare processing * @param response The servlet response weare creating * @param path The portion of the requestURI for selecting a mapping * * @exception IOException if an input/outputerror occurs */ protectedActionMapping processMapping(HttpServletRequestrequest, HttpServletResponse response, String path) throws IOException { // Is there a mapping for this path? ActionMapping mapping = (ActionMapping) moduleConfig.findActionConfig(path); // If a mapping is found, put it in the request and return it if (mapping != null) { request.setAttribute(Globals.MAPPING_KEY, mapping); return (mapping); } // Locate the mapping for unknown paths (if any) ActionConfig configs[] = moduleConfig.findActionConfigs(); for (int i = 0; i < configs.length; i++) { if (configs[i].getUnknown()) { mapping = (ActionMapping)configs[i]; request.setAttribute(Globals.MAPPING_KEY, mapping); return (mapping); } } // No mapping can be found to process this request String msg = getInternal().getMessage("processInvalid"); log.error(msg + " " + path); response.sendError(HttpServletResponse.SC_NOT_FOUND, msg); return null; }
首先我們傳入我們在上一步所截取的路徑,透過moduleConfig的findAction方法來找出ActionConfig,並且傳回ActionMapping。具體程式碼是:
ActionMapping mapping =(ActionMapping) moduleConfig.findActionConfig(path);
如果找到,那就講ActionMapping存放到request的context中。程式碼:
if (mapping != null) { request.setAttribute(Globals.MAPPING_KEY, mapping); return (mapping); }
如果沒有透過path找到mapping,則在Actionconfig中遍歷為未知路徑尋找mapping,如果找到則存放到request中,如果沒有找到,則回傳錯誤訊息,具體程式碼如下:
// Locate the mapping for unknownpaths (if any) ActionConfig configs[] = moduleConfigfindActionConfigs(); for (int i = 0; i < configslength; i++) { if (configs[i].getUnknown()) { mapping = (ActionMapping)configs[i]; request.setAttribute(Globals.MAPPING_KEY, mapping); return (mapping); } } // No mapping can be found to process this request String msg = getInternal().getMessage("processInvalid"); log.error(msg + " " + path); response.sendError(HttpServletResponse.SC_NOT_FOUND, msg); return null;
來看下ActionServlet中的一個方法processActionForm,當我們在截取字串,再根據字串在取得ActionMapping(這是前兩篇文章中介紹的)之後,我們就要用利用ActionMapping來建立ActionForm了,並且把ActionForm放到request或session中管理。
先來看看特定struts中processActionForm方法的具體實作:
/** * <p>Retrieve and return the <code>ActionForm</code> associatedwith * this mapping, creating and retaining oneif necessary. If there is no * <code>ActionForm</code> associated with this mapping,return * <code>null</code>.</p> * * @param request The servlet request weare processing * @param response The servlet response weare creating * @param mapping The mapping we are using */ protectedActionForm processActionForm(HttpServletRequestrequest, HttpServletResponse response, ActionMapping mapping) { // Create (if necessary) a form bean to use ActionForm instance = RequestUtilscreateActionForm (request, mapping, moduleConfig, servlet); if (instance == null) { return (null); } // Store the new instance in the appropriate scope if (log.isDebugEnabled()) { log.debug(" Storing ActionForm bean instance in scope '" + mapping.getScope() + "' under attribute key '" + mapping.getAttribute() + "'"); } if ("request".equals(mapping.getScope())) { request.setAttribute(mapping.getAttribute(), instance); } else { HttpSession session =requestgetSession(); session.setAttribute(mapping.getAttribute(), instance); } return (instance); }
這個方法的大體流程是:根據ActionMapping中的name名稱查找ActionForm,如果配置了ActionForm,那麼就到request或session中查找,如果在request或session中存在已經建立的ActionForm,那麼將會回傳。如果不存在那麼會根據ActionForm的完成路徑採用反射進行創建,再將創建好的ActionForm放到request或session中,之後再傳回ActionForm。
#具體我們可以跟隨斷點偵錯來看看這個方法是如何運作的。
先設定斷點,之後再進入processActionForm方法。
第一個步驟就是建立ActionForm:
// Create (if necessary) a formbean to use ActionForm instance = RequestUtils.createActionForm (request, mapping, moduleConfig, servlet); if (instance == null) { return (null); }
透過呼叫RequestUtils.createActionForm的方法把ActionMapping中的ActionForm字串產生對象,並且返回。進入這段程式碼:
publicstaticActionForm createActionForm( HttpServletRequest request, ActionMapping mapping, ModuleConfig moduleConfig, ActionServlet servlet) { // Is there a form bean associated with this mapping? String attribute = mappinggetAttribute(); if (attribute == null) { return (null); } // Look up the form bean configuration information to use String name = mapping.getName(); FormBeanConfig config =moduleConfigfindFormBeanConfig(name); if (config == null) { log.warn("No FormBeanConfig found under '"+ name + "'"); return (null); } ActionForm instance = lookupActionForm(request,attribute, mappinggetScope()); // Can we recycle the existing form bean instance (if there is one)? try { if (instance != null && canReuseActionForm(instance,config)) { return (instance); } } catch(ClassNotFoundException e) { log.error(servlet.getInternal().getMessage("formBean",config.getType()), e); return (null); } return createActionForm(config,servlet); }
方法先定義變數name,並且從mapping取得值,String name = mapping.getName();也就是我們實例中的LoginForm字串。之後透過呼叫FormBeanConfig config =moduleConfig.findFormBeanConfig(name);這句話把對應的LoginForm字串產生對應的物件。
這裡要說明的是我們在struts-config設定檔中,配置過這樣一個標籤資訊:
<form-beans> <form-bean name="loginForm" type=".struts.LoginActionForm"/> </form-beans>
这个标签在服务器一启动的时候就会利用digester读取这里的配置信息,并且放在FormBeanConfig类中,这样我们可以通过上面那一句话就可以把LoginForm字符串生成相应的对象。
之后调用了ActionForm instance = lookupActionForm(request,attribute, mapping.getScope());这个方法,这个方法主要是查找scope属性中有没有存在ActionForm。具体实现:
if ("request".equals(scope)){ instance = (ActionForm)request.getAttribute(attribute); } else { session = request.getSession(); instance = (ActionForm)session.getAttribute(attribute); }
这里判断scope属性值是否为request,如果是则从request中读出ActionForm,如果不是则从session中读出。程序如果是第一次执行,那么ActionForm会是为空的。因为这里的ActionForm为空,所以就进入了if判断语句中,最后通过调用return createActionForm(config, servlet);创建ActionForm并且返回。
之后processActionForm就会把返回来的ActionForm放入request或者session中。具体实现就是:
if ("request".equals(mapping.getScope())){ request.setAttribute(mapping.getAttribute(), instance); } else { HttpSession session =request.getSession(); session.setAttribute(mapping.getAttribute(), instance); }
到此为止,ActionForm就创建完成,当ActionForm创建完成之后,就要用其他的方法来往ActionForm中赋值了
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