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

阿新 • • 發佈：2017-09-19

erro 後綁定 false zip ons type() eba veh manager

引言：

接上一篇文章，對@RequestMapping進行地址映射講解之後，該篇主要講解request 數據到handler method 參數數據的綁定所用到的註解和什麽情形下使用；

簡介：

handler method 參數綁定常用的註解,我們根據他們處理的Request的不同內容部分分為四類：（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：

[java] view plaincopyprint?

@Controller
@RequestMapping("/owners/{ownerId}")
public class RelativePathUriTemplateController {
@RequestMapping("/pets/{petId}")
public void findPet(@PathVariable String ownerId,@PathVariable String petId, Model model) {
// implementation omitted
}
}

[java] view plain copy print?

@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：

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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

[plain] view plain copy print?

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

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

[java] view plain copy print?

@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：

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JSESSIONID=415A4AC178C59DACE0B2C9CA727CDD84

[java] view plain copy print?

JSESSIONID=415A4AC178C59DACE0B2C9CA727CDD84

參數綁定的代碼：

[java] view plaincopyprint?

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

[java] view plain copy print?

@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可直接轉換為簡單類型的情況（ String--> 簡單類型的轉換操作由ConversionService配置的轉換器來完成）；因為使用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: 為 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：

[java] view plaincopyprint?

@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";
}
// ...

[java] view plain copy print?

@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。

因為配置有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：

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@RequestMapping(value ="/something", method = RequestMethod.PUT)
public void handle(@RequestBody String body, Writer writer)throws IOException {
writer.write(body);
}

[java] view plain copy print?

@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：

[java] view plaincopyprint?

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

[java] view plain copy print?

@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，為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 啟用的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：

[java] view plaincopyprint?

// 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);
}

[java] view plain copy print?

// 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，為request對象的model裏put（“account”， Account）；

用在參數上的@ModelAttribute示例代碼：

[java] view plaincopyprint?

@RequestMapping(value="/owners/{ownerId}/pets/{petId}/edit", method = RequestMethod.POST)
public String processSubmit(@ModelAttribute Pet pet) {
}

[java] view plain copy print?

@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。

若要綁定的對象時復雜類型：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：

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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())) {
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;
}

[java] view plain copy print?

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：

[java] view plaincopyprint?

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

[java] view plain copy print?

@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。

[java] view plaincopyprint?

@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";
}

[java] view plain copy print?

@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。

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

erro 後綁定 false zip ons type() eba veh manager 引言：接上一篇文章，對@RequestMapping進行地址映射講解之後，該篇主要講解request 數據到handler method 參數數據的綁定所用到的註解和什麽情形下使用

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

引言：

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

引言：

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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問題：在不給定註解的情況下，參數是怎樣綁定的？