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前段時(shí)間準(zhǔn)備做一個(gè)小網(wǎng)站，但是又不想用Spring/Struts/WebWork這樣的大塊頭，因此決定自己寫(xiě)一個(gè)MVC框架?；?天左右時(shí)間完成，目前運(yùn)行良好，整個(gè)MVC框架僅21KB，感興趣的朋友可以從http://code.google.com/p/lightweight-mvc/downloads/list下載完整的源代碼和jar包。 設(shè)計(jì)目標(biāo)： 一個(gè)最簡(jiǎn)單最小巧的MVC框架，花哨的功能一個(gè)不要，越簡(jiǎn)潔越好，并且不使用XML配置文件，而是完全用Java 5注解配置。 功能列表： 組件必須用IoC配置； 處理HTTP請(qǐng)求的Action，類(lèi)似WebWork每個(gè)請(qǐng)求都生成一個(gè)新實(shí)例，并自動(dòng)填充屬性； 類(lèi)似Filter的Interceptor機(jī)制，但是在IoC容器中配置； 統(tǒng)一的異常處理； 多視圖支持。 由于組件需要用IoC容器配置，因此，第一步就是尋找小巧的IoC容器，Google Guice是一個(gè)很不錯(cuò)的選擇，并且完全用Java 5注解配置組件。這個(gè)MVC框架唯一依賴(lài)的也就是Guice和Commons Logging兩個(gè)jar包，如果使用Velocity作為視圖則還需要Velocity的jar包。 下一步，開(kāi)始設(shè)計(jì)各主要功能類(lèi)： 負(fù)責(zé)處理Http請(qǐng)求的Action類(lèi)必須實(shí)現(xiàn)的Action接口： package com.javaeedev.lightweight.mvc; public interface Action { ModelAndView execute() throws Exception; } 從WebWork抄過(guò)來(lái)，不過(guò)返回值由String改成了ModelAndView（從Spring抄過(guò)來(lái)的），好處是不必再次根據(jù)String查找視圖的絕對(duì)路徑，直接在ModelAndView中包含了。用Spring的MVC其實(shí)可以發(fā)現(xiàn)，ModelAndView同時(shí)包含一個(gè)Model（本質(zhì)是一個(gè)Map）和View的路徑，減少了Struts和WebWork需要的一個(gè)XML映射文件，而維護(hù)XML配置文件是一件相當(dāng)令人頭疼的問(wèn)題，往往改了代碼還要改配置，索性寫(xiě)死在代碼中得了，視圖路徑又不會(huì)經(jīng)常改變，沒(méi)必要為了額外的靈活性給自己搞一堆XML配置文件。 Action返回的ModelAndView： package com.javaeedev.lightweight.mvc; public final class ModelAndView { private String view;
private Map<string object> model;</string> /**
* Construct a View with empty model.
*
* @param view View's logic name.
*/
public ModelAndView(String view) {
this.view = view;
this.model = Collections.emptyMap();
} /**
* Construct a View with model.
*
* @param view View's logic name.
* @param model Model as a Map.
*/
public ModelAndView(String view, Map<string object> model) {<br> this.view = view;<br> this.model = model;<br> }</string> /**
* Return View.
*
* @return View's logic name.
*/
public String getView() {
return view;
} /**
* Return model.
*
* @return Model as a Map.
*/
public Map<string object> getModel() {<br> return model;<br> }</string> } 這個(gè)完全是從Spring MVC抄過(guò)來(lái)的，Map改成了泛型，View路徑可以以"redirect:"開(kāi)頭表示重定向，這個(gè)和Spring MVC一致。雖然直接調(diào)用HttpServletResponse也可以重定向，但是遇到事務(wù)處理起來(lái)會(huì)很麻煩，還是讓MVC框架自己來(lái)處理會(huì)好一些。 WebWork的Action設(shè)計(jì)的好處是大大簡(jiǎn)化了參數(shù)的綁定，不過(guò)很多時(shí)候也需要在Action中訪問(wèn)HttpSession等對(duì)象，因此還需要設(shè)計(jì)一個(gè)ActionContext類(lèi)，通過(guò)ThreadLocal讓Action對(duì)象能輕易地訪問(wèn)到這些對(duì)象： package com.javaeedev.lightweight.mvc; public final class ActionContext { private static ThreadLocal<actioncontext> contextThreadLocal = new ThreadLocal<actioncontext>();</actioncontext></actioncontext> /**
* Get current ActionContext.
*
* @return ActionContext.
*/
public static ActionContext getActionContext() {
return contextThreadLocal.get();
} private HttpServletRequest request;
private HttpServletResponse response;
private HttpSession session;
private ServletContext context; /**
* Initiate all servlet objects as thread local.
*
* @param request HttpServletRequest object.
* @param response HttpServletResponse object.
* @param session HttpSession object.
* @param context ServletContext object.
*/
static void setActionContext(HttpServletRequest request, HttpServletResponse response, HttpSession session, ServletContext context) {
ActionContext actionContext = new ActionContext();
actionContext.setRequest(request);
actionContext.setResponse(response);
actionContext.setSession(session);
actionContext.setServletContext(context);
contextThreadLocal.set(actionContext);
} /**
* Remove all servlet objects from thread local.
*/
static void remove() {
contextThreadLocal.remove();
} /**
* Get HttpServletRequest object.
*
* @return HttpServletRequest object.
*/
public HttpServletRequest getRequest() {
return request;
} /**
* Set HttpServletRequest object.
*
* @param request HttpServletRequest object.
*/
void setRequest(HttpServletRequest request) {
this.request = request;
} /**
* Get HttpServletResponse object.
*
* @return HttpServletResponse object.
*/
public HttpServletResponse getResponse() {
return response;
} /**
* Set HttpServletResponse object.
*
* @param response HttpServletResponse object.
*/
void setResponse(HttpServletResponse response) {
this.response = response;
} /**
* Get HttpSession object.
*
* @return HttpSession object.
*/
public HttpSession getSession() {
return session;
} /**
* Set HttpSession object.
*
* @param session HttpSession object.
*/
void setSession(HttpSession session) {
this.session = session;
} /**
* Get ServletContext object.
*
* @return ServletContext object.
*/
public ServletContext getServletContext() {
return context;
} /**
* Set ServletContext object.
*
* @param context ServletContext object.
*/
void setServletContext(ServletContext context) {
this.context = context;
} } 接下來(lái)是定義類(lèi)似Filter功能的Interceptor接口： package com.javaeedev.lightweight.mvc; /**
* Intercept action's execution like servlet Filter, but interceptors are
* configured and managed by IoC container. Another difference from Filter
* is that Interceptor is executed around Action's execution, but before
* rendering view.
*
* @author Xuefeng
*/
public interface Interceptor { /**
* Do intercept and invoke chain.doInterceptor() to process next interceptor.
* NOTE that process will not continue if chain.doInterceptor() method is not
* invoked.
*
* @param action Action instance to handle http request.
* @param chain Interceptor chain.
* @throws Exception If any exception is thrown, process will not continued.
*/
void intercept(Action action, InterceptorChain chain) throws Exception; } InterceptorChain對(duì)象和FilterChain是一樣的，它允許一個(gè)攔截器是否將請(qǐng)求繼續(xù)交給下一攔截器處理，還是中斷當(dāng)前請(qǐng)求的處理： package com.javaeedev.lightweight.mvc; /**
* Holds all interceptors as a chain.
*
* @author Xuefeng
*/
public interface InterceptorChain { /**
* Apply next interceptor around the execution of Action.
*
* @param action Target Action to execute.
* @throws Exception Any exception if error occured.
*/
void doInterceptor(Action action) throws Exception; } 最后是支持多種View的ViewResolver，這個(gè)也抄自Spring MVC： package com.javaeedev.lightweight.mvc; import java.io.IOException;
import java.util.Map; import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse; /**
* To resolve and render a view.
*
* @author Xuefeng
*/
public interface ViewResolver { /**
* Init this ViewResolver.
*
* @param context ServletContext object that holds information of current
* web application.
* @throws ServletException If init failed.
*/
void init(ServletContext context) throws ServletException; /**
* To resolve view's name and render view if necessary.
*
* @param view View's logic name.
* @param model Model represent as a generic Map.
* @param request HttpServletRequest object.
* @param response HttpServletResponse object.
* @throws ServletException If any ServletException occur.
* @throws IOException If any IOException occur.
*/
void resolveView(String view, Map<string object> model, HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException;</string> } 第一個(gè)版本支持JSP和Velocity兩種View，其實(shí)支持其他的View完全是可擴(kuò)展的，只需要參考現(xiàn)有的兩種ViewResolver的實(shí)現(xiàn)再寫(xiě)一個(gè)實(shí)現(xiàn)即可，例如支持FreeMarker的ViewResolver。 到此為止，提供給客戶(hù)端的API準(zhǔn)備完畢。下一步是如何實(shí)現(xiàn)這些API。雖然概念和結(jié)構(gòu)都來(lái)自WebWork和Spring，但是其具體實(shí)現(xiàn)卻沒(méi)有參考他們的源代碼，因?yàn)樽x大塊頭的源碼本身就是一件非常費(fèi)力的事情，還不如自己身體力行，寫(xiě)代碼往往比讀懂代碼更快。 后面我們會(huì)講述如何實(shí)現(xiàn)該MVC框架。
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