Spring 注解学习手札(二) 控制层梳理.docx

言归正传，研究一下注解下的控制层。我习惯于使用JSTL展示页面，因此需要在原lib基础上增加jstl.jar和standard.jar，详细lib依赖如下：引用aopalliance-1.0.jarcommons-logging-1.1.1.jarlog4j-1.2.15.jarspring-beans-2.5.6.jarspring-context-2.5.6.jarspring-context-support-2.5.6.jarspring-core-2.5.6.jarspring-tx-2.5.6.jarspring-web-2.5.6.jarspring-webmvc-2.5.6.jarstandard.jarjstl.jar上一篇文中，我们定义了控制器AccountController：AccountController.javaJava代码1. /*2. *2010-1-233. */4. packageorg.zlex.spring.controller;5. 6. importjavax.servlet.http.HttpServletRequest;7. importjavax.servlet.http.HttpServletResponse;8. 9. importorg.springframework.beans.factory.annotation.Autowired;10. importorg.springframework.stereotype.Controller;11. importorg.springframework.web.bind.ServletRequestUtils;12. importorg.springframework.web.bind.annotation.RequestMapping;13. importorg.springframework.web.bind.annotation.RequestMethod;14. importorg.zlex.spring.service.AccountService;15. 16. /*17. *18. *author梁栋19. *version1.020. *since1.021. */22. Controller23. RequestMapping(/account.do)24. publicclassAccountController25. 26. Autowired27. privateAccountServiceaccountService;28. 29. RequestMapping(method=RequestMethod.GET)30. publicvoidhello(HttpServletRequestrequest,HttpServletResponseresponse)31. throwsException32. 33. Stringusername=ServletRequestUtils.getRequiredStringParameter(34. request,username);35. Stringpassword=ServletRequestUtils.getRequiredStringParameter(36. request,password);37. System.out.println(accountService.verify(username,password);38. 39. 先说注解RequestMapping这里使用注解RequestMapping(method = RequestMethod.GET)指定这个方法为get请求时调用。同样，我们可以使用注解RequestMapping(method = RequestMethod.POST)指定该方法接受post请求。Java代码1. Controller2. RequestMapping(/account.do)3. publicclassAccountController4. 5. RequestMapping(method=RequestMethod.GET)6. publicvoidget()7. 8. 9. RequestMapping(method=RequestMethod.POST)10. publicvoidpost()11. 12. 这与我们久别的Servlet很相像，类似于doGet()和doPost()方法！我们也可以将其改造为多动作控制器，如下代码所示：Java代码1. Controller2. RequestMapping(/account.do)3. publicclassAccountController4. 5. RequestMapping(params=method=login)6. publicvoidlogin()7. 8. 9. RequestMapping(params=method=logout)10. publicvoidlogout()11. 这样，我们可以通过参数“method”指定不同的参数值从而通过请求（/account.do?method=login和/account.do?method=logout）调用不同的方法！注意：使用多动作控制器必须在配置文件中加入注解支持！Xml代码1. 当然，我们也可以将注解RequestMapping指定到某一个方法上，如：Java代码1. Controller2. publicclassAccountController3. 4. RequestMapping(/a.do)5. publicvoida()6. 7. RequestMapping(/b.do)8. publicvoidb()9. 这样，请求“a.do”和“b.do”将对应不同的方法a() 和b()。这使得一个控制器可以同时承载多个请求！RequestMapping(/account.do)是RequestMapping(value=/account.do)的简写！再说输入参数！这里的方法名可以随意定义，但是参数和返回值却又要求！为什么？直接看源代码，我们就能找到答案！AnnotationMethodHandlerAdapter.java部分源代码有关参数部分：Java代码1. Override2. protectedObjectresolveStandardArgument(ClassparameterType,NativeWebRequestwebRequest)3. throwsException4. 5. HttpServletRequestrequest=(HttpServletRequest)webRequest.getNativeRequest();6. HttpServletResponseresponse=(HttpServletResponse)webRequest.getNativeResponse();7. 8. if(ServletRequest.class.isAssignableFrom(parameterType)9. returnrequest;10. 11. elseif(ServletResponse.class.isAssignableFrom(parameterType)12. this.responseArgumentUsed=true;13. returnresponse;14. 15. elseif(HttpSession.class.isAssignableFrom(parameterType)16. returnrequest.getSession();17. 18. elseif(Principal.class.isAssignableFrom(parameterType)19. returnrequest.getUserPrincipal();20. 21. elseif(Locale.class.equals(parameterType)22. returnRequestContextUtils.getLocale(request);23. 24. elseif(InputStream.class.isAssignableFrom(parameterType)25. returnrequest.getInputStream();26. 27. elseif(Reader.class.isAssignableFrom(parameterType)28. returnrequest.getReader();29. 30. elseif(OutputStream.class.isAssignableFrom(parameterType)31. this.responseArgumentUsed=true;32. returnresponse.getOutputStream();33. 34. elseif(Writer.class.isAssignableFrom(parameterType)35. this.responseArgumentUsed=true;36. returnresponse.getWriter();37. 38. returnsuper.resolveStandardArgument(parameterType,webRequest);39. 也就是说，如果我们想要在自定义的方法中获得一些个“标准”输入参数，参数类型必须包含在以下类型中：引用ServletRequestServletResponseHttpSessionPrincipalLocaleInputStreamOutputStreamReaderWriter当然，上述接口其实都是对于HttpServletRequest和HttpServletResponse的扩展。此外，我们还可以定义自己的参数。注意：自定义参数必须是实现类，绝非接口！Spring容器将帮你完成对象初始化工作！比如说上文中，我们需要参数username和password。我们可以这么写：Java代码1. RequestMapping(method=RequestMethod.GET)2. publicvoidhello(Stringusername,Stringpassword)3. System.out.println(accountService.verify(username,password);4. 如果参数名不能与这里的变量名保持一致，那么我们可以使用注解RequestParam进行强制绑定，代码如下所示：Java代码1. RequestMapping(method=RequestMethod.GET)2. publicvoidhello(RequestParam(username)Stringu,3. RequestParam(password)Stringp)4. System.out.println(accountService.verify(u,p);5. 这比起我们之前写的代码有所简洁：Java代码1. RequestMapping(method=RequestMethod.GET)2. publicvoidhello(HttpServletRequestrequest,HttpServletResponseresponse)3. throwsException4. 5. Stringusername=ServletRequestUtils.getRequiredStringParameter(6. request,username);7. Stringpassword=ServletRequestUtils.getRequiredStringParameter(8. request,password);9. System.out.println(accountService.verify(username,password);10. ServletRequestUtils类的工作已经由Spring底层实现了，我们只需要把参数名定义一致即可，其内部取参无需关心！除了传入参数，我们还可以定义即将传出的参数，如加入ModelMap参数：Java代码1. SuppressWarnings(unchecked)2. RequestMapping(method=RequestMethod.GET)3. publicMaphello(Stringusername,Stringpassword,ModelMapmodel)4. 5. System.out.println(accountService.verify(username,password);6. 7. model.put(msg,username);8. 9. returnmodel;10. 这时，我们没有定义页面名称，Spring容器将根据请求名指定同名view，即如果是jap页面，则account.do-account.jsp！不得不承认，这样写起来的确减少了代码量！接着说输出参数！通过ModelMap，我们可以绑定输出到的页面的参数，但最终我们将要返回到何种页面呢？再次查看AnnotationMethodHandlerAdapter源代码！AnnotationMethodHandlerAdapter.java部分源代码有关返回值部分：Java代码1. SuppressWarnings(unchecked)2. publicModelAndViewgetModelAndView(MethodhandlerMethod,ClasshandlerType,ObjectreturnValue,3. ExtendedModelMapimplicitModel,ServletWebRequestwebRequest)4. 5. if(returnValueinstanceofModelAndView)6. ModelAndViewmav=(ModelAndView)returnValue;7. mav.getModelMap().mergeAttributes(implicitModel);8. returnmav;9. 10. elseif(returnValueinstanceofModel)11. returnnewModelAndView().addAllObjects(implicitModel).addAllObjects(Model)returnValue).asMap();12. 13. elseif(returnValueinstanceofMap)14. returnnewModelAndView().addAllObjects(implicitModel).addAllObjects(Map)returnValue);15. 16. elseif(returnValueinstanceofView)17. returnnewModelAndView(View)returnValue).addAllObjects(implicitModel);18. 19. elseif(returnValueinstanceofString)20. returnnewModelAndView(String)returnValue).addAllObjects(implicitModel);21. 22. elseif(returnValue=null)23. /Eitherreturnednullorwasvoidreturn.24. if(this.responseArgumentUsed|webRequest.isNotModified()25. returnnull;26. 27. else28. /Assumingviewnametranslation.29. returnnewModelAndView().addAllObjects(implicitModel);30. 31. 32. elseif(!BeanUtils.isSimpleProperty(returnValue.getClass()33. /Assumeasinglemodelattribute.34. ModelAttributeattr=AnnotationUtils.findAnnotation(handlerMethod,ModelAttribute.class);35. StringattrName=(attr!=null?attr.value():);36. ModelAndViewmav=newModelAndView().addAllObjects(implicitModel);37. if(.equals(attrName)38. ClassresolvedType=GenericTypeResolver.resolveReturnType(handlerMethod,handlerType);39. attrName=Conventions.getVariableNameForReturnType(handlerMethod,resolvedType,returnValue);40. 41. returnmav.addObject(attrName,returnValue);42. 43. else44. thrownewIllegalArgumentException(Invalidhandlermethodreturnvalue:+returnValue);45. 46. 返回值的定义十分庞大，或者说可怕的if-else多少有点让我觉得厌恶！我们可以定义以下类型的返回值：引用ModelAndViewModelViewMapStringnullModelAndView、Model和View都是Spring之前版本所特有的元素，Map对应于传入参数ModelMap，String定义页面名称，null即对应void类型方法！最常用的实现方式如下：Java代码1. SuppressWarnings(unchecked)2. RequestMapping(method=RequestMethod.GET)3. publicStringhello(Stringusername,Stringpassword,ModelMapmodel)4. 5. System.out.println(accountService.verify(username,password);6. 7. model.put(msg,username);8. 9. returnaccount;10. 当然，对于我来说在返回值中写入这么一个字符串多少有点不能接受，于是我还是乐于使用输入参数ModelMap+输出参数Map的方式。给出一个完整的AccountController实现：AccountController.javaJava代码1. /*2. *2010-1-233. */4. packageorg.zlex.spring.controller;5. 6. importjava.util.Map;7. 8. importorg.springframework.beans.factory.annotation.Autowired;9. importorg.springframework.stereotype.Controller;10. importorg.springframework.ui.ModelMap;11. importorg.springframework.web.bind.annotation.RequestMapping;12. importorg.springframework.web.bind.annotation.RequestMethod;13. importorg.zlex.spring.service.AccountService;14. 15. /*16. *17. *author梁栋18. *version1.019. *since1.020. */21. Controller22. RequestMapping(/account.do)23. publicclassAccountController24. 25. Autowired26. privateAccountServiceaccountService;27. 28. SuppressWarnings(unchecked)29. RequestMapping(method=RequestMethod.GET)30. publicMaphello(Stringusername,Stringpassword,ModelMapmodel)31. 32. System.o