轉(zhuǎn)自：http://blog.csdn.net/walkerjong/article/details/7946109

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(lèi)：（主要講解常用類(lèi)型）

• @PathVariable：處理requet uri（這里指uri template中variable，不含queryString部分）
• @RequestHeader涡驮、@CookieValue：處理request header部分
• @RequestParam骄噪、@RequestBody：處理request body部分
• @SessionAttributes共苛、@ModelAttribute：處理attribute類(lèi)型

@PathVariable

當(dāng)使用@RequestMapping URI template 樣式映射時(shí)嗤栓， 即 someUrl/{paramId}，這時(shí)的paramId可通過(guò) @Pathvariable注解綁定它傳過(guò)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){      
    // implementation omitted  
    }  
}  

上面代碼把URI template 中變量 ownerId的值和petId的值印颤，綁定到方法的參數(shù)上。若方法參數(shù)名稱(chēng)和需要綁定的uri template中變量名稱(chēng)不一致郊艘，需要在@PathVariable("name")指定uri template中的名稱(chēng)

@RequestHeader僚祷、@CookieValue

@RequestHeader

• 可以把Request請(qǐng)求header部分的值綁定到方法的參數(shù)上
• 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)  {  
    //...
}  

上面的代碼尺锚，把request header部分的Accept-Encoding的值綁定到參數(shù)encoding上酷师，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

@RequestParam讶凉、@RequestBody

@RequestParam

• 常用來(lái)處理簡(jiǎn)單類(lèi)型的綁定，通過(guò)Request.getParameter()獲取的String可直接轉(zhuǎn)換為簡(jiǎn)單類(lèi)型的情況（String-->簡(jiǎn)單類(lèi)型的轉(zhuǎn)換操作由ConversionService配置的轉(zhuǎn)換器來(lái)完成）山孔；因?yàn)槭褂胷equest.getParameter()方式獲取參數(shù)懂讯，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
• 用來(lái)處理Content-Type為：application/x-www-form-urlencoded編碼的內(nèi)容台颠，提交方式GET褐望、POST
• 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(chēng)串前，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

• 常用來(lái)處理Content-Type不是application/x-www-form-urlencoded編碼的內(nèi)容瘫里，例如application/json、application/xml等
• 它是通過(guò)使用HandlerAdapter配置的HttpMessageConverters來(lái)解析post data body荡碾，然后綁定到相應(yīng)的bean上的谨读；
  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)容玩荠，處理完的結(jié)果放在一個(gè)MultiValueMap<String, String>里漆腌，這種情況在某些特殊需求下使用贼邓，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阶冈、@ModelAttribute

@SessionAttributes

• 用來(lái)綁定HttpSession中的attribute對(duì)象的值，便于在方法中的參數(shù)里使用塑径，有value女坑、types兩個(gè)屬性，可以通過(guò)名字和類(lèi)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)用法统舀，一個(gè)是用于方法上匆骗，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(xún)的model
  用于參數(shù)上時(shí)： 用來(lái)通過(guò)名稱(chēng)對(duì)應(yīng)誉简，把相應(yīng)名稱(chēng)的值綁定到注解的參數(shù)bean上
• 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(méi)有時(shí)碉就，new一個(gè)需要綁定的bean對(duì)象，然后把request中按名稱(chēng)對(duì)應(yīng)的方式把值綁定到bean中闷串。

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(shí)際的效果就是在調(diào)用@RequestMapping的方法之前瓮钥，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(xún) @SessionAttributes有無(wú)綁定的Pet對(duì)象，若沒(méi)有則查詢(xún)@ModelAttribute方法層面上是否綁定了Pet對(duì)象，若沒(méi)有則將URI template中的值按對(duì)應(yīng)的名稱(chēng)綁定到Pet對(duì)象的各屬性上

補(bǔ)充講解：

問(wèn)題： 在不給定注解的情況下碉熄，參數(shù)是怎樣綁定的桨武？

通過(guò)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(lèi)型： 調(diào)用@RequestParam來(lái)處理的

若要綁定的對(duì)象時(shí)復(fù)雜類(lèi)型： 調(diào)用@ModelAttribute來(lái)處理的

這里的簡(jiǎn)單類(lèi)型指Java的原始類(lèi)型（boolean, int 等）锈津、原始類(lèi)型對(duì)象（Boolean, Int等）呀酸、String、Date等ConversionService里可以直接String轉(zhuǎn)換成目標(biāo)對(duì)象的類(lèi)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) {// 若沒(méi)有發(fā)現(xiàn)注解
            Object argValue = resolveCommonArgument(methodParam, webRequest);    //判斷WebRquest是否可賦值給參數(shù)
            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(shù)類(lèi)型是否是簡(jiǎn)單類(lèi)型琼梆，若是在使用@RequestParam方式來(lái)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中使用的參數(shù)綁定性誉，代碼稍微有些不同，有興趣的同仁可以分析下叮叹，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";  
}  

這種情況下艾栋，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