引言:
接上一篇文章,對(duì)@RequestMapping進(jìn)行地址映射講解之后,該篇主要講解request 數(shù)據(jù)到handler method 參數(shù)數(shù)據(jù)的綁定所用到的注解和什么情形下使用;
簡(jiǎn)介:
handler method 參數(shù)綁定常用的注解,我們根據(jù)他們處理的Request的不同內(nèi)容部分分為四類:(主要講解常用類型)
A、處理requet uri 部分(這里指uri template中variable,不含queryString部分)的注解: @PathVariable;
B、處理request header部分的注解: @RequestHeader, @CookieValue;
C、處理request body部分的注解:@RequestParam, @RequestBody;
D、處理attribute類型是注解: @SessionAttributes, @ModelAttribute;
1、 @PathVariable
當(dāng)使用@RequestMapping URI template 樣式映射時(shí), 即 someUrl/{paramId}, 這時(shí)的paramId可通過 @Pathvariable注解綁定它傳過來(lái)的值到方法的參數(shù)上。
示例代碼:
- @Controller
- @RequestMapping("/owners/{ownerId}")
- public class RelativePathUriTemplateController {
-
- @RequestMapping("/pets/{petId}")
- public void findPet(@PathVariable String ownerId, @PathVariable String petId, Model model) {
-
- }
- }
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(shù)上。若方法參數(shù)名稱和需要綁定的uri template中變量名稱不一致,需要在@PathVariable("name")指定uri template中的名稱。
2、 @RequestHeader、@CookieValue
@RequestHeader 注解,可以把Request請(qǐng)求header部分的值綁定到方法的參數(shù)上。
示例代碼:
這是一個(gè)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(shù)encoding上了, Keep-Alive header的值綁定到參數(shù)keepAlive上。
@CookieValue 可以把Request header中關(guān)于cookie的值綁定到方法的參數(shù)上。
例如有如下Cookie值:
- JSESSIONID=415A4AC178C59DACE0B2C9CA727CDD84
參數(shù)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(shù)cookie上。
3、@RequestParam, @RequestBody
@RequestParam
A) 常用來(lái)處理簡(jiǎn)單類型的綁定,通過Request.getParameter() 獲取的String可直接轉(zhuǎn)換為簡(jiǎn)單類型的情況( String--> 簡(jiǎn)單類型的轉(zhuǎn)換操作由ConversionService配置的轉(zhuǎn)換器來(lái)完成);因?yàn)槭褂胷equest.getParameter()方式獲取參數(shù),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(lái)處理Content-Type: 為 application/x-www-form-urlencoded
編碼的內(nèi)容,提交方式GET、POST;
C) 該注解有兩個(gè)屬性: value、required; value用來(lái)指定要傳入值的id名稱,required用來(lái)指示參數(shù)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
該注解常用來(lái)處理Content-Type: 不是application/x-www-form-urlencoded
編碼的內(nèi)容,例如application/json, application/xml等;
它是通過使用HandlerAdapter 配置的HttpMessageConverters
來(lái)解析post data body,然后綁定到相應(yīng)的bean上的。
因?yàn)榕渲糜蠪ormHttpMessageConverter,所以也可以用來(lái)處理 application/x-www-form-urlencoded
的內(nèi)容,處理完的結(jié)果放在一個(gè)MultiValueMap<String, String>里,這種情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);
- }
4、@SessionAttributes, @ModelAttribute
@SessionAttributes:
該注解用來(lái)綁定HttpSession中的attribute對(duì)象的值,便于在方法中的參數(shù)里使用。
該注解有value、types兩個(gè)屬性,可以通過名字和類型指定要使用的attribute 對(duì)象;
示例代碼:
- @Controller
- @RequestMapping("/editPet.do")
- @SessionAttributes("pet")
- public class EditPetForm {
-
- }
@ModelAttribute
該注解有兩個(gè)用法,一個(gè)是用于方法上,一個(gè)是用于參數(shù)上;
用于方法上時(shí): 通常用來(lái)在處理@RequestMapping之前,為請(qǐng)求綁定需要從后臺(tái)查詢的model;
用于參數(shù)上時(shí): 用來(lái)通過名稱對(duì)應(yīng),把相應(yīng)名稱的值綁定到注解的參數(shù)bean上;要綁定的值來(lái)源于:
A) @SessionAttributes 啟用的attribute 對(duì)象上;
B) @ModelAttribute 用于方法上時(shí)指定的model對(duì)象;
C) 上述兩種情況都沒有時(shí),new一個(gè)需要綁定的bean對(duì)象,然后把request中按名稱對(duì)應(yīng)的方式把值綁定到bean中。
用到方法上@ModelAttribute的示例代碼:
-
-
-
-
- @ModelAttribute
- public Account addAccount(@RequestParam String number) {
- return accountManager.findAccount(number);
- }
這種方式實(shí)際的效果就是在調(diào)用@RequestMapping的方法之前,為request對(duì)象的model里put(“account”, Account);
用在參數(shù)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(wú)綁定的Pet對(duì)象,若沒有則查詢@ModelAttribute方法層面上是否綁定了Pet對(duì)象,若沒有則將URI template中的值按對(duì)應(yīng)的名稱綁定到Pet對(duì)象的各屬性上。
補(bǔ)充講解:
問題: 在不給定注解的情況下,參數(shù)是怎樣綁定的?
通過分析AnnotationMethodHandlerAdapter和RequestMappingHandlerAdapter的源代碼發(fā)現(xiàn),方法的參數(shù)在不給定參數(shù)的情況下:
若要綁定的對(duì)象時(shí)簡(jiǎn)單類型: 調(diào)用@RequestParam來(lái)處理的。
若要綁定的對(duì)象時(shí)復(fù)雜類型: 調(diào)用@ModelAttribute來(lái)處理的。
這里的簡(jiǎn)單類型指java的原始類型(boolean, int 等)、原始類型對(duì)象(Boolean, Int等)、String、Date等ConversionService里可以直接String轉(zhuǎn)換成目標(biāo)對(duì)象的類型;
下面貼出AnnotationMethodHandlerAdapter中綁定參數(shù)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) {
- Object argValue = resolveCommonArgument(methodParam, webRequest);
- 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)) {
- 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(shù)綁定,代碼稍微有些不同,有興趣的同仁可以分析下,最后處理的結(jié)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,就調(diào)用默認(rèn)的@RequestParam來(lái)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,就調(diào)用@ModelAttribute來(lái)處理。
參考文檔:
1、 Spring Web Doc:
spring-3.1.0/docs/spring-framework-reference/html/mvc.html