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

青旅半醒 2022-03-01 06:50 225阅读 0赞

转:[https://www.cnblogs.com/guoyinli/p/7056146.html][https_www.cnblogs.com_guoyinli_p_7056146.html]

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}") 
    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

@RequestMapping("/displayHeaderInfo.do") 
    public void 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：

JSESSIONID=415A4AC178C59DACE0B2C9CA727CDD84 
    JSESSIONID=415A4AC178C59DACE0B2C9CA727CDD84

参数绑定的代码：

@RequestMapping("/displayHeaderInfo.do") 
    public void 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") 
    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"; 
        } 
     
        // ...

@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) 
    public void 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") 
    public class 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++; 
                    } 
                    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())) { 
                                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; 
                        } 
                        else if (HttpEntity.class.isAssignableFrom(paramType)) { 
                            args[i] = resolveHttpEntityRequest(methodParam, webRequest); 
                        } 
                        elseif (Errors.class.isAssignableFrom(paramType)) { 
                            throw new 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); 
                } 
                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; 
        }

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。

[https_www.cnblogs.com_guoyinli_p_7056146.html]: https://www.cnblogs.com/guoyinli/p/7056146.html