@RequestParam @RequestBody @PathVariable 等參數綁定註解詳解（轉載）

轉載自：http://blog.csdn.net/walkerjong/article/details/7946109

學習了下，對@RequestBody，@SessionAttributes,@ModelAttribute還不是很瞭解，繼續學習，也望知道的能告訴我一下，謝謝。

簡介：

handler method 參數綁定常用的註解,我們根據他們處理的Request的不同內容部分分爲四類：（主要講解常用類型）

A、處理requet uri 部分（這裏指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類型是註解： @SessionAttributes, @ModelAttribute;

1、 @PathVariable

當使用@RequestMapping URI template 樣式映射時，即 someUrl/{paramId}, 這時的paramId可通過 @Pathvariable註解綁定它傳過來的值到方法的參數上。

示例代碼：

@Controller 

@RequestMapping("/owners/{ownerId}") 

publicclass RelativePathUriTemplateController
{ 

  @RequestMapping("/pets/{petId}") 

  publicvoid findPet(@PathVariable String
ownerId, @PathVariable String petId,
Model model) {     

    // implementation
omitted 

  } 

}

@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 註解，可以把Request請求header部分的值綁定到方法的參數上。

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

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") 

publicvoid displayHeaderInfo(@RequestHeader("Accept-Encoding")
String encoding, 

                              @RequestHeader("Keep-Alive") long keepAlive) 
{ 

  //... 

}

@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 可以把Request header中關於cookie的值綁定到方法的參數上。

例如有如下Cookie值：

JSESSIONID=415A4AC178C59DACE0B2C9CA727CDD84 

JSESSIONID=415A4AC178C59DACE0B2C9CA727CDD84

參數綁定的代碼：

@RequestMapping("/displayHeaderInfo.do") 

publicvoid displayHeaderInfo(@CookieValue("JSESSIONID")
String cookie)  { 

  //... 

}

@RequestMapping("/displayHeaderInfo.do")
public void displayHeaderInfo(@CookieValue("JSESSIONID") String cookie)  {

  //...

}

即把JSESSIONID的值綁定到參數cookie上。

3、@RequestParam, @RequestBody

@RequestParam

A）常用來處理簡單類型的綁定，通過Request.getParameter() 獲取的String可直接轉換爲簡單類型的情況（ String--> 簡單類型的轉換操作由ConversionService配置的轉換器來完成）；因爲使用request.getParameter()方式獲取參數，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: 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") 

publicclass 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"; 

    } 

    // ...

@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，然後綁定到相應的bean上的。

因爲配置有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>裏，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) 

publicvoid handle(@RequestBody String
body, Writer writer) throws IOException
{ 

  writer.write(body); 

} 

@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，可以通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") 

publicclass EditPetForm
{ 

    // ... 

}

@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：通常用來在處理@RequestMapping之前，爲請求綁定需要從後臺查詢的model；

用於參數上時：用來通過名稱對應，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）上述兩種情況都沒有時，new一個需要綁定的bean對象，然後把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); 

}

// 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的方法之前，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)
{ 

    

} 

@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。

補充講解：

問題：在不給定註解的情況下，參數是怎樣綁定的？

通過分析AnnotationMethodHandlerAdapter和RequestMappingHandlerAdapter的源代碼發現，方法的參數在不給定參數的情況下：

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裏可以直接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++; 

                } 

                elseif (RequestHeader.class.isInstance(paramAnn))
{ 

                    RequestHeader requestHeader = (RequestHeader) paramAnn; 

                    headerName = requestHeader.value(); 

                    required = requestHeader.required(); 

                    defaultValue = parseDefaultValueAttribute(requestHeader.defaultValue()); 

                    annotationsFound++; 

                } 

                elseif (RequestBody.class.isInstance(paramAnn))
{ 

                    requestBodyFound = true; 

                    annotationsFound++; 

                } 

                elseif (CookieValue.class.isInstance(paramAnn))
{ 

                    CookieValue cookieValue = (CookieValue) paramAnn; 

                    cookieName = cookieValue.value(); 

                    required = cookieValue.required(); 

                    defaultValue = parseDefaultValueAttribute(cookieValue.defaultValue()); 

                    annotationsFound++; 

                } 

                elseif (PathVariable.class.isInstance(paramAnn))
{ 

                    PathVariable pathVar = (PathVariable) paramAnn; 

                    pathVarName = pathVar.value(); 

                    annotationsFound++; 

                } 

                elseif (ModelAttribute.class.isInstance(paramAnn))
{ 

                    ModelAttribute attr = (ModelAttribute) paramAnn; 

                    attrName = attr.value(); 

                    annotationsFound++; 

                } 

                elseif (Value.class.isInstance(paramAnn))
{ 

                    defaultValue = ((Value) paramAnn).value(); 

                } 

                elseif (paramAnn.annotationType().getSimpleName().startsWith("Valid"))
{ 

                    validate = true; 

                    Object value = AnnotationUtils.getValue(paramAnn); 

                    validationHints = (value instanceof Object[]
? (Object[]) value : new Object[]
{value}); 

                } 

            } 

            if (annotationsFound
> 1) { 

                thrownew 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; 

                } 

                elseif (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()))
{ 

                            thrownew 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; 

                    } 

                    elseif (SessionStatus.class.isAssignableFrom(paramType))
{ 

                        args[i] = this.sessionStatus; 

                    } 

                    elseif (HttpEntity.class.isAssignableFrom(paramType))
{ 

                        args[i] = resolveHttpEntityRequest(methodParam, webRequest); 

                    } 

                    elseif (Errors.class.isAssignableFrom(paramType))
{ 

                        thrownew IllegalStateException("Errors/BindingResult
argument declared " + 

                                "without
preceding model attribute. Check your handler method signature!"); 

                    } 

                    elseif (BeanUtils.isSimpleProperty(paramType))
{// 判斷是否參數類型是否是簡單類型，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); 

            } 

            elseif (headerName
!= null)
{ 

                args[i] = resolveRequestHeader(headerName, required, defaultValue, methodParam, webRequest, handler); 

            } 

            elseif (requestBodyFound)
{ 

                args[i] = resolveRequestBody(methodParam, webRequest, handler); 

            } 

            elseif (cookieName
!= null)
{ 

                args[i] = resolveCookieValue(cookieName, required, defaultValue, methodParam, webRequest, handler); 

            } 

            elseif (pathVarName
!= null)
{ 

                args[i] = resolvePathVariable(pathVarName, methodParam, webRequest, handler); 

            } 

            elseif (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; 

    }

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否是簡單類型，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中使用的參數綁定，代碼稍微有些不同，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"; 

    }

@RequestMapping ({"/", "/home"})
	public String showHomePage(String key){
		
		logger.debug("key="+key);
		
		return "home";
	}

這種情況下，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"; 

}

	@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，就調用@ModelAttribute來處理。

夜-feng

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@RequestParam @RequestBody @PathVariable 等參數綁定註解詳解（轉載）

轉載自：http://blog.csdn.net/walkerjong/article/details/7946109

簡介：

1、 @PathVariable

2、 @RequestHeader、@CookieValue

3、@RequestParam, @RequestBody

4、@SessionAttributes, @ModelAttribute

補充講解：

問題：在不給定註解的情況下，參數是怎樣綁定的？

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https://yachay.unat.edu.pe/blog/index.php?comment_area=format_blog&comment_component=blog&comment_co

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@RequestParam @RequestBody @PathVariable 等參數綁定註解詳解（轉載）

轉載自：http://blog.csdn.net/walkerjong/article/details/7946109

簡介：

1、 @PathVariable

2、 @RequestHeader、@CookieValue

3、@RequestParam, @RequestBody

4、@SessionAttributes, @ModelAttribute

補充講解：

問題： 在不給定註解的情況下，參數是怎樣綁定的？

問題：在不給定註解的情況下，參數是怎樣綁定的？