接上一篇文章,對@RequestMapping進行地址映射講解以後,該篇主要講解request 數據到handler method 參數數據的綁定所用到的註解和什麼情形下使用;html
handler method 參數綁定經常使用的註解,咱們根據他們處理的Request的不一樣內容部分分爲四類:(主要講解經常使用類型)java
A、處理requet uri 部分(這裏指uri template中variable,不含queryString部分)的註解: @PathVariable;web
B、處理request header部分的註解: @RequestHeader, @CookieValue;spring
C、處理request body部分的註解:@RequestParam, @RequestBody;json
D、處理attribute類型是註解: @SessionAttributes, @ModelAttribute;api
當使用@RequestMapping URI template 樣式映射時, 即 someUrl/{paramId}, 這時的paramId可經過 @Pathvariable註解綁定它傳過來的值到方法的參數上。cookie
示例代碼:session
@Controller @RequestMapping("/owners/{ownerId}") public class RelativePathUriTemplateController { @RequestMapping("/pets/{petId}") public void findPet(@PathVariable String ownerId, @PathVariable String petId, Model model) { // implementation omitted } }
上面代碼把URI template 中變量 ownerId的值和petId的值,綁定到方法的參數上。若方法參數名稱和須要綁定的uri template中變量名稱不一致,須要在@PathVariable("name")指定uri template中的名稱。
mvc
@RequestHeader 註解,能夠把Request請求header部分的值綁定到方法的參數上。app
示例代碼:
這是一個Request 的header部分:
Host localhost:8080 Accept text/html,application/xhtml+xml,application/xml;q=0.9 Accept-Language fr,en-gb;q=0.7,en;q=0.3 Accept-Encoding gzip,deflate Accept-Charset ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive 300
@RequestMapping("/displayHeaderInfo.do") public void displayHeaderInfo(@RequestHeader("Accept-Encoding") String encoding, @RequestHeader("Keep-Alive") long keepAlive) { //... }
上面的代碼,把request header部分的 Accept-Encoding的值,綁定到參數encoding上了, Keep-Alive header的值綁定到參數keepAlive上。
@CookieValue 能夠把Request header中關於cookie的值綁定到方法的參數上。
例若有以下Cookie值:
JSESSIONID=415A4AC178C59DACE0B2C9CA727CDD84
參數綁定的代碼:
@RequestMapping("/displayHeaderInfo.do") public void displayHeaderInfo(@CookieValue("JSESSIONID") String cookie) { //... }
即把JSESSIONID的值綁定到參數cookie上。
@RequestParam
A) 常用來處理簡單類型的綁定,經過Request.getParameter() 獲取的String可直接轉換爲簡單類型的狀況( String--> 簡單類型的轉換操做由ConversionService配置的轉換器來完成);由於使用request.getParameter()方式獲取參數,因此能夠處理get 方式中queryString的值,也能夠處理post方式中 body data的值;
B)用來處理Content-Type: 爲 application/x-www-form-urlencoded
編碼的內容,提交方式GET、POST;
C) 該註解有兩個屬性: value、required; value用來指定要傳入值的id名稱,required用來指示參數是否必須綁定;
示例代碼:
@Controller @RequestMapping("/pets") @SessionAttributes("pet") public class EditPetForm { // ... @RequestMapping(method = RequestMethod.GET) public String setupForm(@RequestParam("petId") int petId, ModelMap model) { Pet pet = this.clinic.loadPet(petId); model.addAttribute("pet", pet); return "petForm"; } // ...
@RequestBody
該註解經常使用來處理Content-Type: 不是application/x-www-form-urlencoded
編碼的內容,例如application/json, application/xml等;
它是經過使用HandlerAdapter 配置的HttpMessageConverters
來解析post data body,而後綁定到相應的bean上的。
由於配置有FormHttpMessageConverter,因此也能夠用來處理 application/x-www-form-urlencoded
的內容,處理完的結果放在一個MultiValueMap<String, String>裏,這種狀況在某些特殊需求下使用,詳情查看FormHttpMessageConverter api;
示例代碼:
@RequestMapping(value = "/something", method = RequestMethod.PUT) public void handle(@RequestBody String body, Writer writer) throws IOException { writer.write(body); }
@SessionAttributes:
該註解用來綁定HttpSession中的attribute對象的值,便於在方法中的參數裏使用。
該註解有value、types兩個屬性,能夠經過名字和類型指定要使用的attribute 對象;
示例代碼:
@Controller @RequestMapping("/editPet.do") @SessionAttributes("pet") public class EditPetForm { // ... }
@ModelAttribute
該註解有兩個用法,一個是用於方法上,一個是用於參數上;
用於方法上時: 一般用來在處理@RequestMapping以前,爲請求綁定須要從後臺查詢的model;
用於參數上時: 用來經過名稱對應,把相應名稱的值綁定到註解的參數bean上;要綁定的值來源於:
A) @SessionAttributes 啓用的attribute 對象上;
B) @ModelAttribute 用於方法上時指定的model對象;
C) 上述兩種狀況都沒有時,new一個須要綁定的bean對象,而後把request中按名稱對應的方式把值綁定到bean中。
用到方法上@ModelAttribute的示例代碼:
// Add one attribute // The return value of the method is added to the model under the name "account" // You can customize the name via @ModelAttribute("myAccount") @ModelAttribute public Account addAccount(@RequestParam String number) { return accountManager.findAccount(number); }
這種方式實際的效果就是在調用@RequestMapping的方法以前,爲request對象的model裏put(「account」, Account);
用在參數上的@ModelAttribute示例代碼:
@RequestMapping(value="/owners/{ownerId}/pets/{petId}/edit", method = RequestMethod.POST) public String processSubmit(@ModelAttribute Pet pet) { }
首先查詢 @SessionAttributes有無綁定的Pet對象,若沒有則查詢@ModelAttribute方法層面上是否綁定了Pet對象,若沒有則將URI template中的值按對應的名稱綁定到Pet對象的各屬性上。
經過分析AnnotationMethodHandlerAdapter和RequestMappingHandlerAdapter的源代碼發現,方法的參數在不給定參數的狀況下:
若要綁定的對象時簡單類型: 調用@RequestParam來處理的。
若要綁定的對象時複雜類型: 調用@ModelAttribute來處理的。
這裏的簡單類型指java的原始類型(boolean, int 等)、原始類型對象(Boolean, Int等)、String、Date等ConversionService裏能夠直接String轉換成目標對象的類型;
下面貼出AnnotationMethodHandlerAdapter中綁定參數的部分源代碼:
private Object[] resolveHandlerArguments(Method handlerMethod, Object handler, NativeWebRequest webRequest, ExtendedModelMap implicitModel) throws Exception { Class[] paramTypes = handlerMethod.getParameterTypes(); Object[] args = new Object[paramTypes.length]; for (int i = 0; i < args.length; i++) { MethodParameter methodParam = new MethodParameter(handlerMethod, i); methodParam.initParameterNameDiscovery(this.parameterNameDiscoverer); GenericTypeResolver.resolveParameterType(methodParam, handler.getClass()); String paramName = null; String headerName = null; boolean requestBodyFound = false; String cookieName = null; String pathVarName = null; String attrName = null; boolean required = false; String defaultValue = null; boolean validate = false; Object[] validationHints = null; int annotationsFound = 0; Annotation[] paramAnns = methodParam.getParameterAnnotations(); for (Annotation paramAnn : paramAnns) { if (RequestParam.class.isInstance(paramAnn)) { RequestParam requestParam = (RequestParam) paramAnn; paramName = requestParam.value(); required = requestParam.required(); defaultValue = parseDefaultValueAttribute(requestParam.defaultValue()); annotationsFound++; } else if (RequestHeader.class.isInstance(paramAnn)) { RequestHeader requestHeader = (RequestHeader) paramAnn; headerName = requestHeader.value(); required = requestHeader.required(); defaultValue = parseDefaultValueAttribute(requestHeader.defaultValue()); annotationsFound++; } else if (RequestBody.class.isInstance(paramAnn)) { requestBodyFound = true; annotationsFound++; } else if (CookieValue.class.isInstance(paramAnn)) { CookieValue cookieValue = (CookieValue) paramAnn; cookieName = cookieValue.value(); required = cookieValue.required(); defaultValue = parseDefaultValueAttribute(cookieValue.defaultValue()); annotationsFound++; } else if (PathVariable.class.isInstance(paramAnn)) { PathVariable pathVar = (PathVariable) paramAnn; pathVarName = pathVar.value(); annotationsFound++; } else if (ModelAttribute.class.isInstance(paramAnn)) { ModelAttribute attr = (ModelAttribute) paramAnn; attrName = attr.value(); annotationsFound++; } else if (Value.class.isInstance(paramAnn)) { defaultValue = ((Value) paramAnn).value(); } else if (paramAnn.annotationType().getSimpleName().startsWith("Valid")) { validate = true; Object value = AnnotationUtils.getValue(paramAnn); validationHints = (value instanceof Object[] ? (Object[]) value : new Object[] {value}); } } if (annotationsFound > 1) { throw new IllegalStateException("Handler parameter annotations are exclusive choices - " + "do not specify more than one such annotation on the same parameter: " + handlerMethod); } if (annotationsFound == 0) {// 若沒有發現註解 Object argValue = resolveCommonArgument(methodParam, webRequest); //判斷WebRquest是否可賦值給參數 if (argValue != WebArgumentResolver.UNRESOLVED) { args[i] = argValue; } else if (defaultValue != null) { args[i] = resolveDefaultValue(defaultValue); } else { Class<?> paramType = methodParam.getParameterType(); if (Model.class.isAssignableFrom(paramType) || Map.class.isAssignableFrom(paramType)) { if (!paramType.isAssignableFrom(implicitModel.getClass())) { throw new IllegalStateException("Argument [" + paramType.getSimpleName() + "] is of type " + "Model or Map but is not assignable from the actual model. You may need to switch " + "newer MVC infrastructure classes to use this argument."); } args[i] = implicitModel; } else if (SessionStatus.class.isAssignableFrom(paramType)) { args[i] = this.sessionStatus; } else if (HttpEntity.class.isAssignableFrom(paramType)) { args[i] = resolveHttpEntityRequest(methodParam, webRequest); } else if (Errors.class.isAssignableFrom(paramType)) { throw new IllegalStateException("Errors/BindingResult argument declared " + "without preceding model attribute. Check your handler method signature!"); } else if (BeanUtils.isSimpleProperty(paramType)) {// 判斷是否參數類型是不是簡單類型,如果在使用@RequestParam方式來處理,不然使用@ModelAttribute方式處理 paramName = ""; } else { attrName = ""; } } } if (paramName != null) { args[i] = resolveRequestParam(paramName, required, defaultValue, methodParam, webRequest, handler); } else if (headerName != null) { args[i] = resolveRequestHeader(headerName, required, defaultValue, methodParam, webRequest, handler); } else if (requestBodyFound) { args[i] = resolveRequestBody(methodParam, webRequest, handler); } else if (cookieName != null) { args[i] = resolveCookieValue(cookieName, required, defaultValue, methodParam, webRequest, handler); } else if (pathVarName != null) { args[i] = resolvePathVariable(pathVarName, methodParam, webRequest, handler); } else if (attrName != null) { WebDataBinder binder = resolveModelAttribute(attrName, methodParam, implicitModel, webRequest, handler); boolean assignBindingResult = (args.length > i + 1 && Errors.class.isAssignableFrom(paramTypes[i + 1])); if (binder.getTarget() != null) { doBind(binder, webRequest, validate, validationHints, !assignBindingResult); } args[i] = binder.getTarget(); if (assignBindingResult) { args[i + 1] = binder.getBindingResult(); i++; } implicitModel.putAll(binder.getBindingResult().getModel()); } } return args; }
RequestMappingHandlerAdapter中使用的參數綁定,代碼稍微有些不一樣,有興趣的同仁能夠分析下,最後處理的結果都是同樣的。
示例:
@RequestMapping ({"/", "/home"}) public String showHomePage(String key){ logger.debug("key="+key); return "home"; }
這種狀況下,就調用默認的@RequestParam來處理。
@RequestMapping (method = RequestMethod.POST) public String doRegister(User user){ if(logger.isDebugEnabled()){ logger.debug("process url[/user], method[post] in "+getClass()); logger.debug(user); } return "user"; }
這種狀況下,就調用@ModelAttribute來處理。
一、 Spring Web Doc:
spring-3.1.0/docs/spring-framework-reference/html/mvc.html