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

引言:

接上一篇文章,对@RequestMapping进行地址映射讲解之后,该篇主要讲解request 数据到handler method 参数数据的绑定所用到的注解和什么情形下使用;

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:

[java] view plaincopy

  1. @Controller
  2. @RequestMapping("/owners/{ownerId}") 
  3. public class RelativePathUriTemplateController { 
  4. @RequestMapping("/pets/{petId}") 
  5. public void findPet(@PathVariable String ownerId, @PathVariable String petId, Model model) {     
  6. // implementation omitted
  7.   } 

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:

[plain] view plaincopy

  1. Host                    localhost:8080 
  2. Accept                  text/html,application/xhtml+xml,application/xml;q=0.9 
  3. Accept-Language         fr,en-gb;q=0.7,en;q=0.3 
  4. Accept-Encoding         gzip,deflate 
  5. Accept-Charset          ISO-8859-1,utf-8;q=0.7,*;q=0.7 
  6. Keep-Alive              300 

[java] view plaincopy

  1. @RequestMapping("/displayHeaderInfo.do") 
  2. public void displayHeaderInfo(@RequestHeader("Accept-Encoding") String encoding, 
  3. @RequestHeader("Keep-Alive") long keepAlive)  { 
  4. //...

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:

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  1. JSESSIONID=415A4AC178C59DACE0B2C9CA727CDD84 

参数绑定的代码:

[java] view plaincopy

  1. @RequestMapping("/displayHeaderInfo.do") 
  2. public void displayHeaderInfo(@CookieValue("JSESSIONID") String cookie)  { 
  3. //...

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:

[java] view plaincopy

  1. @Controller
  2. @RequestMapping("/pets") 
  3. @SessionAttributes("pet") 
  4. public class EditPetForm { 
  5. // ...
  6. @RequestMapping(method = RequestMethod.GET) 
  7. public String setupForm(@RequestParam("petId") int petId, ModelMap model) { 
  8.         Pet pet = this.clinic.loadPet(petId); 
  9.         model.addAttribute("pet", pet); 
  10. return "petForm"; 
  11.     } 
  12. // ...

@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:

[java] view plaincopy

  1. @RequestMapping(value = http://www.mamicode.com/"/something", method = RequestMethod.PUT) 
  2. public void handle(@RequestBody String body, Writer writer) throws IOException { 
  3.   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:

[java] view plaincopy

  1. @Controller
  2. @RequestMapping("/editPet.do") 
  3. @SessionAttributes("pet") 
  4. public class EditPetForm { 
  5. // ...

@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:

[java] view plaincopy

  1. // Add one attribute
  2. // The return value of the method is added to the model under the name "account"
  3. // You can customize the name via @ModelAttribute("myAccount")
  4. @ModelAttribute
  5. public Account addAccount(@RequestParam String number) { 
  6. 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:

[java] view plaincopy

  1. @RequestMapping(value=http://www.mamicode.com/"/owners/{ownerId}/pets/{petId}/edit", method = RequestMethod.POST) 
  2. 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:

[java] view plaincopy

  1. private Object[] resolveHandlerArguments(Method handlerMethod, Object handler, 
  2.             NativeWebRequest webRequest, ExtendedModelMap implicitModel) throws Exception { 
  3.         Class[] paramTypes = handlerMethod.getParameterTypes(); 
  4.         Object[] args = new Object[paramTypes.length]; 
  5. for (int i = 0; i < args.length; i++) { 
  6.             MethodParameter methodParam = new MethodParameter(handlerMethod, i); 
  7.             methodParam.initParameterNameDiscovery(this.parameterNameDiscoverer); 
  8.             GenericTypeResolver.resolveParameterType(methodParam, handler.getClass()); 
  9.             String paramName = null; 
  10.             String headerName = null; 
  11. boolean requestBodyFound = false; 
  12.             String cookieName = null; 
  13.             String pathVarName = null; 
  14.             String attrName = null; 
  15. boolean required = false; 
  16.             String defaultValue = http://www.mamicode.com/null; 
  17. boolean validate = false; 
  18.             Object[] validationHints = null; 
  19. int annotationsFound = 0; 
  20.             Annotation[] paramAnns = methodParam.getParameterAnnotations(); 
  21. for (Annotation paramAnn : paramAnns) { 
  22. if (RequestParam.class.isInstance(paramAnn)) { 
  23.                     RequestParam requestParam = (RequestParam) paramAnn; 
  24.                     paramName = requestParam.value(); 
  25.                     required = requestParam.required(); 
  26.                     defaultValue = http://www.mamicode.com/parseDefaultValueAttribute(requestParam.defaultValue()); 
  27.                     annotationsFound++; 
  28.                 } 
  29. else if (RequestHeader.class.isInstance(paramAnn)) { 
  30.                     RequestHeader requestHeader = (RequestHeader) paramAnn; 
  31.                     headerName = requestHeader.value(); 
  32.                     required = requestHeader.required(); 
  33.                     defaultValue = http://www.mamicode.com/parseDefaultValueAttribute(requestHeader.defaultValue()); 
  34.                     annotationsFound++; 
  35.                 } 
  36. else if (RequestBody.class.isInstance(paramAnn)) { 
  37.                     requestBodyFound = true; 
  38.                     annotationsFound++; 
  39.                 } 
  40. else if (CookieValue.class.isInstance(paramAnn)) { 
  41.                     CookieValue cookieValue = http://www.mamicode.com/(CookieValue) paramAnn; 
  42.                     cookieName = cookieValue.value(); 
  43.                     required = cookieValue.required(); 
  44.                     defaultValue = http://www.mamicode.com/parseDefaultValueAttribute(cookieValue.defaultValue()); 
  45.                     annotationsFound++; 
  46.                 } 
  47. else if (PathVariable.class.isInstance(paramAnn)) { 
  48.                     PathVariable pathVar = (PathVariable) paramAnn; 
  49.                     pathVarName = pathVar.value(); 
  50.                     annotationsFound++; 
  51.                 } 
  52. else if (ModelAttribute.class.isInstance(paramAnn)) { 
  53.                     ModelAttribute attr = (ModelAttribute) paramAnn; 
  54.                     attrName = attr.value(); 
  55.                     annotationsFound++; 
  56.                 } 
  57. else if (Value.class.isInstance(paramAnn)) { 
  58.                     defaultValue = http://www.mamicode.com/((Value) paramAnn).value(); 
  59.                 } 
  60. else if (paramAnn.annotationType().getSimpleName().startsWith("Valid")) { 
  61.                     validate = true; 
  62.                     Object value = http://www.mamicode.com/AnnotationUtils.getValue(paramAnn); 
  63.                     validationHints = (value instanceof Object[] ? (Object[]) value : new Object[] {value}); 
  64.                 } 
  65.             } 
  66. if (annotationsFound > 1) { 
  67. throw new IllegalStateException("Handler parameter annotations are exclusive choices - " + 
  68. "do not specify more than one such annotation on the same parameter: " + handlerMethod); 
  69.             } 
  70. if (annotationsFound == 0) {// 若没有发现注解
  71.                 Object argValue = http://www.mamicode.com/resolveCommonArgument(methodParam, webRequest);    //判断WebRquest是否可赋值给参数
  72. if (argValue != WebArgumentResolver.UNRESOLVED) { 
  73.                     args[i] = argValue; 
  74.                 } 
  75. else if (defaultValue != null) { 
  76.                     args[i] = resolveDefaultValue(defaultValue); 
  77.                 } 
  78. else { 
  79.                     Class<?> paramType = methodParam.getParameterType(); 
  80. if (Model.class.isAssignableFrom(paramType) || Map.class.isAssignableFrom(paramType)) { 
  81. if (!paramType.isAssignableFrom(implicitModel.getClass())) { 
  82. throw new IllegalStateException("Argument [" + paramType.getSimpleName() + "] is of type " + 
  83. "Model or Map but is not assignable from the actual model. You may need to switch " + 
  84. "newer MVC infrastructure classes to use this argument."); 
  85.                         } 
  86.                         args[i] = implicitModel; 
  87.                     } 
  88. else if (SessionStatus.class.isAssignableFrom(paramType)) { 
  89.                         args[i] = this.sessionStatus; 
  90.                     } 
  91. else if (HttpEntity.class.isAssignableFrom(paramType)) { 
  92.                         args[i] = resolveHttpEntityRequest(methodParam, webRequest); 
  93.                     } 
  94. else if (Errors.class.isAssignableFrom(paramType)) { 
  95. throw new IllegalStateException("Errors/BindingResult argument declared " + 
  96. "without preceding model attribute. Check your handler method signature!"); 
  97.                     } 
  98. 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
  99.                         paramName = ""; 
  100.                     } 
  101. else { 
  102.                         attrName = ""; 
  103.                     } 
  104.                 } 
  105.             } 
  106. if (paramName != null) { 
  107.                 args[i] = resolveRequestParam(paramName, required, defaultValue, methodParam, webRequest, handler); 
  108.             } 
  109. else if (headerName != null) { 
  110.                 args[i] = resolveRequestHeader(headerName, required, defaultValue, methodParam, webRequest, handler); 
  111.             } 
  112. else if (requestBodyFound) { 
  113.                 args[i] = resolveRequestBody(methodParam, webRequest, handler); 
  114.             } 
  115. else if (cookieName != null) { 
  116.                 args[i] = resolveCookieValue(cookieName, required, defaultValue, methodParam, webRequest, handler); 
  117.             } 
  118. else if (pathVarName != null) { 
  119.                 args[i] = resolvePathVariable(pathVarName, methodParam, webRequest, handler); 
  120.             } 
  121. else if (attrName != null) { 
  122.                 WebDataBinder binder = 
  123.                         resolveModelAttribute(attrName, methodParam, implicitModel, webRequest, handler); 
  124. boolean assignBindingResult = (args.length > i + 1 && Errors.class.isAssignableFrom(paramTypes[i + 1])); 
  125. if (binder.getTarget() != null) { 
  126.                     doBind(binder, webRequest, validate, validationHints, !assignBindingResult); 
  127.                 } 
  128.                 args[i] = binder.getTarget(); 
  129. if (assignBindingResult) { 
  130.                     args[i + 1] = binder.getBindingResult(); 
  131.                     i++; 
  132.                 } 
  133.                 implicitModel.putAll(binder.getBindingResult().getModel()); 
  134.             } 
  135.         } 
  136. return args; 
  137.     } 

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:

[java] view plaincopy

  1. @RequestMapping ({"/", "/home"}) 
  2. public String showHomePage(String key){ 
  3.         logger.debug("key="+key); 
  4. return "home"; 
  5.     } 

这种情况下,就调用默认的@RequestParam来处理。

[java] view plaincopy

  1. @RequestMapping (method = RequestMethod.POST) 
  2. public String doRegister(User user){ 
  3. if(logger.isDebugEnabled()){ 
  4.         logger.debug("process url[/user], method[post] in "+getClass()); 
  5.         logger.debug(user); 
  6.     } 
  7. return "user"; 

这种情况下,就调用@ModelAttribute来处理。

参考文档:

1、 Spring Web Doc:

spring-3.1.0/docs/spring-framework-reference/html/mvc.html

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