@QueryParam @RequestBody @PathVariable的區別
handler method 引數繫結常用的註解,我們根據他們處理的Request的不同內容部分分為四類:(主要講解常用型別)
A、處理requet uri 部分(這裡指uri template中variable,不含queryString部分)的註解: @PathVariable;
B、處理request header部分的註解: @RequestHeader, @CookieValue;
C、處理request body部分的註解:@RequestParam, @RequestBody;
D、處理attribute型別是註解: @SessionAttributes, @ModelAttribute;
1、 @PathVariable
當使用@RequestMapping URI template 樣式對映時, 即 someUrl/{paramId}, 這時的paramId可通過 @Pathvariable註解繫結它傳過來的值到方法的引數上。
示例程式碼:
@Controller @RequestMapping("/owners/{ownerId}") public class RelativePathUriTemplateController { @RequestMapping("/pets/{petId}") public void findPet(@PathVariable String ownerId, @PathVariable String petId, Model model) {// implementation omitted } }
上面程式碼把URI template 中變數 ownerId的值和petId的值,繫結到方法的引數上。若方法引數名稱和需要繫結的uri template中變數名稱不一致,需要在@PathVariable("name")指定uri template中的名稱。
2、 @RequestHeader、@CookieValue
@RequestHeader 註解,可以把Request請求header部分的值繫結到方法的引數上。
示例程式碼:
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) { //... }
上面的程式碼,把request header部分的 Accept-Encoding的值,繫結到引數encoding上了, Keep-Alive header的值繫結到引數keepAlive上。
@CookieValue 可以把Request header中關於cookie的值繫結到方法的引數上。
例如有如下Cookie值:
JSESSIONID=415A4AC178C59DACE0B2C9CA727CDD84
引數繫結的程式碼:
@RequestMapping("/displayHeaderInfo.do") public void displayHeaderInfo(@CookieValue("JSESSIONID") String cookie) { //... }
即把JSESSIONID的值繫結到引數cookie上。
3、@RequestParam, @RequestBody
@RequestParam
A) 常用來處理簡單型別的繫結,通過Request.getParameter() 獲取的String可直接轉換為簡單型別的情況( String--> 簡單型別的轉換操作由ConversionService配置的轉換器來完成);因為使用request.getParameter()方式獲取引數,所以可以處理get 方式中queryString的值,也可以處理post方式中 body data的值;
B)用來處理Content-Type: 為 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用來指示引數是否必須繫結;
示例程式碼:
@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
該註解常用來處理Content-Type: 不是application/x-www-form-urlencoded
編碼的內容,例如application/json, application/xml等;
它是通過使用HandlerAdapter 配置的HttpMessageConverters
來解析post data body,然後繫結到相應的bean上的。
因為配置有FormHttpMessageConverter,所以也可以用來處理 application/x-www-form-urlencoded
的內容,處理完的結果放在一個MultiValueMap<String, String>裡,這種情況在某些特殊需求下使用,詳情檢視FormHttpMessageConverter api;
示例程式碼:
@RequestMapping(value = "/something", method = RequestMethod.PUT) public void handle(@RequestBody String body, Writer writer) throws IOException { writer.write(body); }
4、@SessionAttributes, @ModelAttribute
@SessionAttributes:
該註解用來繫結HttpSession中的attribute物件的值,便於在方法中的引數裡使用。
該註解有value、types兩個屬性,可以通過名字和型別指定要使用的attribute 物件;
示例程式碼:
@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,一個是用於引數上;
用於方法上時: 通常用來在處理@RequestMapping之前,為請求繫結需要從後臺查詢的model;
用於引數上時: 用來通過名稱對應,把相應名稱的值繫結到註解的引數bean上;要繫結的值來源於:
A) @SessionAttributes 啟用的attribute 物件上;
B) @ModelAttribute 用於方法上時指定的model物件;
C) 上述兩種情況都沒有時,new一個需要繫結的bean物件,然後把request中按名稱對應的方式把值繫結到bean中。
用到方法上@ModelAttribute的示例程式碼:
// 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呼叫@RequestMapping的方法之前,為request物件的model裡put(“account”, Account);
用在引數上的@ModelAttribute示例程式碼:
@RequestMapping(value="/owners/{ownerId}/pets/{petId}/edit", method = RequestMethod.POST) public String processSubmit(@ModelAttribute Pet pet) { }
首先查詢 @SessionAttributes有無繫結的Pet物件,若沒有則查詢@ModelAttribute方法層面上是否綁定了Pet物件,若沒有則將URI template中的值按對應的名稱繫結到Pet物件的各屬性上。
補充講解:
問題: 在不給定註解的情況下,引數是怎樣繫結的?
通過分析AnnotationMethodHandlerAdapter和RequestMappingHandlerAdapter的原始碼發現,方法的引數在不給定引數的情況下:
若要繫結的物件時簡單型別: 呼叫@RequestParam來處理的。
若要繫結的物件時複雜型別: 呼叫@ModelAttribute來處理的。
這裡的簡單型別指java的原始型別(boolean, int 等)、原始型別物件(Boolean, Int等)、String、Date等ConversionService裡可以直接String轉換成目標物件的型別;
下面貼出AnnotationMethodHandlerAdapter中繫結引數的部分原始碼:
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是否可賦值給引數 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)) {// 判斷是否引數型別是否是簡單型別,若是在使用@RequestParam方式來處理,否則使用@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中使用的引數繫結,程式碼稍微有些不同,有興趣的同仁可以分析下,最後處理的結果都是一樣的。
示例:
@RequestMapping ({"/", "/home"}) public String showHomePage(String key){ logger.debug("key="+key); return "home"; }
這種情況下,就呼叫預設的@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"; }
這種情況下,就呼叫@ModelAttribute來處理。