Spring MVC Controller传递枚举值示例

╰半夏微凉° 2023-03-13 13:48 16阅读 0赞

## 功能描述 ##

本文将通过一个小示例，展示在请求参数中传递枚举值。

## 枚举定义 ##

角色类定义：

public enum RoleEnum {
    	EMPLOYEE((short)1, "Employee"), MANAGER((short)2, "Manager");
    	
    	private Short value;
    	private String desc;
    	
    	private RoleEnum(Short value, String desc) {
    		this.value = value;
    		this.desc = desc;
    	}
    	
    	public Short value() {
    		return value;
    	}
    	
    	public String desc() {
    		return desc;
    	}
    }

## 定义Controller类 ##

@RestController
    @Slf4j
    public class HomeController {
    	@GetMapping("/home")
    	public String getDemo(@RequestParam("role") RoleEnum role) {
    		log.info("Role Enum:{}" + role);
    		
    		return role.desc();
    	}
    }

说明： 在这里RoleEnum之内作为@RequestParam参数。

## 请求示例 ##

Case1: http://localhost:8080/home?role=EMPLOYEE  
结论： 正确返回， Employee  
Case2: http://localhost:8080/home?role=Employee  
报错，具体信息如下：

Whitelabel Error Page
    
    This application has no explicit mapping for /error, so you are seeing this as a fallback.
    Thu May 14 11:21:32 CST 2020
    There was an unexpected error (type=Bad Request, status=400).
    Failed to convert value of type 'java.lang.String' to required type 'org.course.data.domain.RoleEnum'; nested exception is org.springframework.core.convert.ConversionFailedException: Failed to convert from type [java.lang.String] to type [@org.springframework.web.bind.annotation.RequestParam org.course.data.domain.RoleEnum] for value 'employee'; nested exception is java.lang.IllegalArgumentException: No enum constant org.course.data.domain.RoleEnum.employee
    org.springframework.web.method.annotation.MethodArgumentTypeMismatchException: Failed to convert value of type 'java.lang.String' to required type 'org.course.data.domain.RoleEnum'; nested exception is org.springframework.core.convert.ConversionFailedException: Failed to convert from type [java.lang.String] to type [@org.springframework.web.bind.annotation.RequestParam org.course.data.domain.RoleEnum] for value 'employee'; nested exception is java.lang.IllegalArgumentException: No enum constant org.course.data.domain.RoleEnum.employee
       at org.springframework.web.method.annotation.AbstractNamedValueMethodArgumentResolver.resolveArgument(AbstractNamedValueMethodArgumentResolver.java:133)
       at org.springframework.web.method.support.HandlerMethodArgumentResolverComposite.resolveArgument(HandlerMethodArgumentResolverComposite.java:127)
       at org.springframework.web.method.support.InvocableHandlerMethod.getMethodArgumentValues(InvocableHandlerMethod.java:167)
       at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:134)
       at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:105)
       at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:893)
       at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:798)
       at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)
       at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1040)
       at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:943)
       at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006)
       at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898)
       at javax.servlet.http.HttpServlet.service(HttpServlet.java:634)
       at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883)
       at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
       at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
       at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
       at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
       at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
       at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
       at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100)
       at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
       at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
       at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
       at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93)
       at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
       at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
       at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
       at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:94)
       at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
       at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
       at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
       at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201)
       at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
       at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
       at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
       at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202)
       at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
       at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541)
       at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
       at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
       at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)
       at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
       at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:367)
       at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
       at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868)
       at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1639)
       at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
       at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
       at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
       at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
       at java.lang.Thread.run(Thread.java:748)
    Caused by: org.springframework.core.convert.ConversionFailedException: Failed to convert from type [java.lang.String] to type [@org.springframework.web.bind.annotation.RequestParam org.course.data.domain.RoleEnum] for value 'employee'; nested exception is java.lang.IllegalArgumentException: No enum constant org.course.data.domain.RoleEnum.employee
       at org.springframework.core.convert.support.ConversionUtils.invokeConverter(ConversionUtils.java:47)
       at org.springframework.core.convert.support.GenericConversionService.convert(GenericConversionService.java:191)
       at org.springframework.beans.TypeConverterDelegate.convertIfNecessary(TypeConverterDelegate.java:129)
       at org.springframework.beans.TypeConverterSupport.convertIfNecessary(TypeConverterSupport.java:73)
       at org.springframework.beans.TypeConverterSupport.convertIfNecessary(TypeConverterSupport.java:53)
       at org.springframework.validation.DataBinder.convertIfNecessary(DataBinder.java:693)
       at org.springframework.web.method.annotation.AbstractNamedValueMethodArgumentResolver.resolveArgument(AbstractNamedValueMethodArgumentResolver.java:125)
       ... 51 more
    Caused by: java.lang.IllegalArgumentException: No enum constant org.course.data.domain.RoleEnum.employee
       at java.lang.Enum.valueOf(Enum.java:238)
       at org.springframework.core.convert.support.StringToEnumConverterFactory$StringToEnum.convert(StringToEnumConverterFactory.java:52)
       at org.springframework.core.convert.support.StringToEnumConverterFactory$StringToEnum.convert(StringToEnumConverterFactory.java:38)
       at org.springframework.core.convert.support.GenericConversionService$ConverterFactoryAdapter.convert(GenericConversionService.java:436)
       at org.springframework.core.convert.support.ConversionUtils.invokeConverter(ConversionUtils.java:41)
       ... 57 more

实现分析：

final class StringToEnumConverterFactory implements ConverterFactory<String, Enum> {
        StringToEnumConverterFactory() {
        }
    
        public <T extends Enum> Converter<String, T> getConverter(Class<T> targetType) {
            return new StringToEnumConverterFactory.StringToEnum(ConversionUtils.getEnumType(targetType));
        }
    
        private class StringToEnum<T extends Enum> implements Converter<String, T> {
            private final Class<T> enumType;
    
            public StringToEnum(Class<T> enumType) {
                this.enumType = enumType;
            }
    
            public T convert(String source) {
                return source.isEmpty() ? null : Enum.valueOf(this.enumType, source.trim());
            }
        }
    }

底层实现为将String转换为Enum值的过程。

## 结论 ##

基于枚举可以限定具体值，简单易用。但是缺点是在扩展enum之时，无法做法平滑过度升级，会吹安短暂的异常情况。