欢迎您访问程序员文章站本站旨在为大家提供分享程序员计算机编程知识！
您现在的位置是： 首页  >  Java

@RequestParam @RequestBody @PathVariable 等参数绑定注解详解

程序员文章站 2022-04-01 11:09:19
...

简介：

handler method 参数绑定常用的注解,我们根据他们处理的Request的不同内容部分分为四类：（主要讲解常用类型）

A、处理requet uri 部分（这里指uri template中variable，不含queryString部分）的注解： @PathVariable;

B、处理request header部分的注解： @RequestHeader, @CookieValue;

C、处理request body部分的注解：@RequestParam, @RequestBody;

D、处理attribute类型是注解： @SessionAttributes, @ModelAttribute;

1、 @PathVariable

当使用@RequestMapping URI template 样式映射时， 即 someUrl/{paramId}, 这时的paramId可通过 @Pathvariable注解绑定它传过来的值到方法的参数上。

示例代码：

 
@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
  }
}

上面代码把URI template 中变量 ownerId的值和petId的值，绑定到方法的参数上。若方法参数名称和需要绑定的uri template中变量名称不一致，需要在@PathVariable("name")指定uri template中的名称。

2、 @RequestHeader、@CookieValue

@RequestHeader 注解，可以把Request请求header部分的值绑定到方法的参数上。

示例代码：

这是一个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


  1. @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)  {

  //...

}

上面的代码，把request header部分的 Accept-Encoding的值，绑定到参数encoding上了， Keep-Alive header的值绑定到参数keepAlive上。

@CookieValue 可以把Request header中关于cookie的值绑定到方法的参数上。

例如有如下Cookie值：

  1. JSESSIONID=415A4AC178C59DACE0B2C9CA727CDD84


JSESSIONID=415A4AC178C59DACE0B2C9CA727CDD84

参数绑定的代码：

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

即把JSESSIONID的值绑定到参数cookie上。

3、@RequestParam, @RequestBody

@RequestParam

A） 常用来处理简单类型的绑定，通过Request.getParameter() 获取的String可直接转换为简单类型的情况（ String--> 简单类型的转换操作由ConversionService配置的转换器来完成）；因为使用request.getParameter()方式获取参数，所以可以处理get 方式中queryString的值，也可以处理post方式中 body data的值；

B）用来处理Content-Type: 为 application/x-www-form-urlencoded编码的内容，提交方式GET、POST；

C) 该注解有两个属性： value、required； value用来指定要传入值的id名称，required用来指示参数是否必须绑定；

示例代码：

@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

该注解常用来处理Content-Type: 不是application/x-www-form-urlencoded编码的内容，例如application/json, application/xml等；

它是通过使用HandlerAdapter 配置的HttpMessageConverters来解析post data body，然后绑定到相应的bean上的。

因为配置有FormHttpMessageConverter，所以也可以用来处理 application/x-www-form-urlencoded的内容，处理完的结果放在一个MultiValueMap<String, String>里，这种情况在某些特殊需求下使用，详情查看FormHttpMessageConverter api;

示例代码：

 
@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:

该注解用来绑定HttpSession中的attribute对象的值，便于在方法中的参数里使用。

该注解有value、types两个属性，可以通过名字和类型指定要使用的attribute 对象；

示例代码：

 
@Controller 
@RequestMapping("/editPet.do") 
@SessionAttributes("pet") 
publicclass EditPetForm
 { 
    // ... 
}
@Controller
@RequestMapping("/editPet.do")
@SessionAttributes("pet")
public class EditPetForm {
    // ...
}

@ModelAttribute

该注解有两个用法，一个是用于方法上，一个是用于参数上；

用于方法上时： 通常用来在处理@RequestMapping之前，为请求绑定需要从后台查询的model；

用于参数上时： 用来通过名称对应，把相应名称的值绑定到注解的参数bean上；要绑定的值来源于：

A） @SessionAttributes 启用的attribute 对象上；

B） @ModelAttribute 用于方法上时指定的model对象；

C） 上述两种情况都没有时，new一个需要绑定的bean对象，然后把request中按名称对应的方式把值绑定到bean中。

用到方法上@ModelAttribute的示例代码：

// 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);
}

这种方式实际的效果就是在调用@RequestMapping的方法之前，为request对象的model里put（“account”， Account）；

用在参数上的@ModelAttribute示例代码：

@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) {
   
}

首先查询 @SessionAttributes有无绑定的Pet对象，若没有则查询@ModelAttribute方法层面上是否绑定了Pet对象，若没有则将URI template中的值按对应的名称绑定到Pet对象的各属性上。

补充讲解：

问题： 在不给定注解的情况下，参数是怎样绑定的？

通过分析AnnotationMethodHandlerAdapter和RequestMappingHandlerAdapter的源代码发现，方法的参数在不给定参数的情况下：

若要绑定的对象时简单类型： 调用@RequestParam来处理的。

若要绑定的对象时复杂类型： 调用@ModelAttribute来处理的。

这里的简单类型指java的原始类型(boolean, int 等)、原始类型对象（Boolean, Int等）、String、Date等ConversionService里可以直接String转换成目标对象的类型；

下面贴出AnnotationMethodHandlerAdapter中绑定参数的部分源代码：

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) {//
 若没有发现注解 
                Object argValue = resolveCommonArgument(methodParam, webRequest);    //判断WebRquest是否可赋值给参数 
                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))
 {// 判断是否参数类型是否是简单类型，若是在使用@RequestParam方式来处理,否则使用@ModelAttribute方式处理 
                        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) {// 若没有发现注解
				Object argValue = resolveCommonArgument(methodParam, webRequest);    //判断WebRquest是否可赋值给参数
				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)) {// 判断是否参数类型是否是简单类型，若是在使用@RequestParam方式来处理,否则使用@ModelAttribute方式处理
						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中使用的参数绑定，代码稍微有些不同，有兴趣的同仁可以分析下，最后处理的结果都是一样的。

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";
}

这种情况下，就调用默认的@RequestParam来处理。

 
@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";
}

这种情况下，就调用@ModelAttribute来处理。

以上就是@RequestParam @RequestBody @PathVariable 等参数绑定注解详解的内容，更多相关内容请关注PHP中文网（www.php.cn）！

相关标签： @RequestParam，@RequestBody，@PathVariable

上一篇： drupal7安装有关问题

下一篇： JavaScript bold方法入门实例（把指定文字显示为粗体）_基础知识

推荐阅读