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
- }
- }
- @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。