EL1008E: Property or field 'timestamp' cannot be found on object of type 'java.util.HashMap' - maybe

完整的异常信息：

org.springframework.web.util.NestedServletException: Request processing failed; nested exception is org.springframework.expression.spel.SpelEvaluationException: EL1008E: Property or field 'timestamp' cannot be found on object of type 'java.util.HashMap' - maybe not public?

at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:982) ~[spring-webmvc-4.3.13.RELEASE.jar:4.3.13.RELEASE]

at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861) ~[spring-webmvc-4.3.13.RELEASE.jar:4.3.13.RELEASE]

at javax.servlet.http.HttpServlet.service(HttpServlet.java:687) ~[javax.servlet-api-3.1.0.jar:3.1.0]

at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846) ~[spring-webmvc-4.3.13.RELEASE.jar:4.3.13.RELEASE]

at javax.servlet.http.HttpServlet.service(HttpServlet.java:790) ~[javax.servlet-api-3.1.0.jar:3.1.0]

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-8.5.23.jar:8.5.23]

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.23.jar:8.5.23]

at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:728) ~[tomcat-embed-core-8.5.23.jar:8.5.23]

at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:469) ~[tomcat-embed-core-8.5.23.jar:8.5.23]

at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:392) ~[tomcat-embed-core-8.5.23.jar:8.5.23]

at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:311) ~[tomcat-embed-core-8.5.23.jar:8.5.23]

at org.apache.catalina.core.StandardHostValve.custom(StandardHostValve.java:395) [tomcat-embed-core-8.5.23.jar:8.5.23]

at org.apache.catalina.core.StandardHostValve.status(StandardHostValve.java:254) [tomcat-embed-core-8.5.23.jar:8.5.23]

at org.apache.catalina.core.StandardHostValve.throwable(StandardHostValve.java:349) [tomcat-embed-core-8.5.23.jar:8.5.23]

at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:175) [tomcat-embed-core-8.5.23.jar:8.5.23]

at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81) [tomcat-embed-core-8.5.23.jar:8.5.23]

at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87) [tomcat-embed-core-8.5.23.jar:8.5.23]

at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342) [tomcat-embed-core-8.5.23.jar:8.5.23]

at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:803) [tomcat-embed-core-8.5.23.jar:8.5.23]

at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) [tomcat-embed-core-8.5.23.jar:8.5.23]

at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868) [tomcat-embed-core-8.5.23.jar:8.5.23]

at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1459) [tomcat-embed-core-8.5.23.jar:8.5.23]

at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-8.5.23.jar:8.5.23]

at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [na:1.8.0_121]

at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [na:1.8.0_121]

at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-8.5.23.jar:8.5.23]

at java.lang.Thread.run(Thread.java:745) [na:1.8.0_121]

Caused by: org.springframework.expression.spel.SpelEvaluationException: EL1008E: Property or field 'timestamp' cannot be found on object of type 'java.util.HashMap' - maybe not public?

at org.springframework.expression.spel.ast.PropertyOrFieldReference.readProperty(PropertyOrFieldReference.java:226) ~[spring-expression-4.3.13.RELEASE.jar:4.3.13.RELEASE]

at org.springframework.expression.spel.ast.PropertyOrFieldReference.getValueInternal(PropertyOrFieldReference.java:94) ~[spring-expression-4.3.13.RELEASE.jar:4.3.13.RELEASE]

at org.springframework.expression.spel.ast.PropertyOrFieldReference.getValueInternal(PropertyOrFieldReference.java:81) ~[spring-expression-4.3.13.RELEASE.jar:4.3.13.RELEASE]

at org.springframework.expression.spel.ast.SpelNodeImpl.getValue(SpelNodeImpl.java:121) ~[spring-expression-4.3.13.RELEASE.jar:4.3.13.RELEASE]

at org.springframework.expression.spel.standard.SpelExpression.getValue(SpelExpression.java:262) ~[spring-expression-4.3.13.RELEASE.jar:4.3.13.RELEASE]

at org.springframework.boot.autoconfigure.web.ErrorMvcAutoConfiguration$ExpressionResolver.resolvePlaceholder(ErrorMvcAutoConfiguration.java:288) ~[spring-boot-autoconfigure-1.5.9.RELEASE.jar:1.5.9.RELEASE]

at org.springframework.boot.autoconfigure.web.NonRecursivePropertyPlaceholderHelper$NonRecursivePlaceholderResolver.resolvePlaceholder(NonRecursivePropertyPlaceholderHelper.java:56) ~[spring-boot-autoconfigure-1.5.9.RELEASE.jar:1.5.9.RELEASE]

at org.springframework.util.PropertyPlaceholderHelper.parseStringValue(PropertyPlaceholderHelper.java:147) ~[spring-core-4.3.13.RELEASE.jar:4.3.13.RELEASE]

at org.springframework.boot.autoconfigure.web.NonRecursivePropertyPlaceholderHelper.parseStringValue(NonRecursivePropertyPlaceholderHelper.java:38) ~[spring-boot-autoconfigure-1.5.9.RELEASE.jar:1.5.9.RELEASE]

at org.springframework.util.PropertyPlaceholderHelper.replacePlaceholders(PropertyPlaceholderHelper.java:126) ~[spring-core-4.3.13.RELEASE.jar:4.3.13.RELEASE]

at org.springframework.boot.autoconfigure.web.ErrorMvcAutoConfiguration$SpelView.render(ErrorMvcAutoConfiguration.java:226) ~[spring-boot-autoconfigure-1.5.9.RELEASE.jar:1.5.9.RELEASE]

at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1286) ~[spring-webmvc-4.3.13.RELEASE.jar:4.3.13.RELEASE]

at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1041) ~[spring-webmvc-4.3.13.RELEASE.jar:4.3.13.RELEASE]

at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:984) ~[spring-webmvc-4.3.13.RELEASE.jar:4.3.13.RELEASE]

at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:901) ~[spring-webmvc-4.3.13.RELEASE.jar:4.3.13.RELEASE]

at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970) ~[spring-webmvc-4.3.13.RELEASE.jar:4.3.13.RELEASE]

... 26 common frames omitted

异常的产生：

直接访问：http://192.168.1.168:8085/error

/error 是Spring Boot 中对错误统一处理的一个地方，但这个 Controller 似乎中只能返回模板页面内容，并不能返回JSON格式的数据。

实现类代码：

package com.wanyu.configuration;

import java.util.Map;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.boot.autoconfigure.web.ErrorController;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;

@Controller
public class MyErrorController  implements ErrorController{

	public MyErrorController() {
		// TODO Auto-generated constructor stub
	}

	@RequestMapping("/error")
	@ResponseBody
    public Map index(Map map, HttpServletRequest request, HttpServletResponse response){
		Integer statusCode = (Integer) request.getAttribute("javax.servlet.error.status_code");
		String servlet_name = (String) request.getAttribute("javax.servlet.error.servlet_name");
		String message = (String) request.getAttribute("javax.servlet.error.message");
        map.put("code", statusCode);
//        Enumeration attrs = request.getAttributeNames();
//        String attrStr = "";
//        while (attrs.hasMoreElements()){
//        	attrStr += attrs.nextElement() + "\r\n";
//        }
//        System.out.println(attrStr);
        map.put("message", servlet_name + "\r\n" + message);
        return map;
    }
	
	@Override
	public String getErrorPath() {
		return "/error";
	}
	
	/**
	 * 
	 * javax.servlet.forward.request_uri
javax.servlet.forward.context_path
javax.servlet.forward.servlet_path
javax.servlet.forward.mapping
org.springframework.web.context.request.async.WebAsyncManager.WEB_ASYNC_MANAGER
javax.servlet.error.status_code
org.springframework.web.servlet.DispatcherServlet.CONTEXT
org.springframework.web.servlet.resource.ResourceUrlProvider
org.springframework.web.servlet.HandlerMapping.introspectTypeLevelMapping
javax.servlet.error.message
javax.servlet.error.servlet_name
org.springframework.web.servlet.DispatcherServlet.THEME_SOURCE
userToken
org.springframework.web.servlet.DispatcherServlet.LOCALE_RESOLVER
org.springframework.web.servlet.HandlerMapping.bestMatchingPattern
org.springframework.web.servlet.DispatcherServlet.OUTPUT_FLASH_MAP
org.springframework.web.servlet.HandlerMapping.pathWithinHandlerMapping
org.springframework.web.servlet.DispatcherServlet.FLASH_MAP_MANAGER
javax.servlet.error.request_uri
org.springframework.web.servlet.HandlerMapping.uriTemplateVariables
org.springframework.core.convert.ConversionService
org.springframework.web.servlet.DispatcherServlet.THEME_RESOLVER

	 */

}

虽然实现了这个类，但是在访问不存在的地址时，并不会得到 JSON 格式的错误信息，而是被 Servlet 容器（如Tomcat）等处理，如下图，访问一个不存在的地址：

关于这个问题的网页很少，只看到一篇有点用的：

其实仔细看就会发现原因： SpelView 需要  timestamp 这么一个变量，以进行渲染， 它其实是来自于 DefaultErrorAttributes 以配合SpelView 使用的。但是呢， 由于我自定义了boot 的Error viewController， 但是没有自定义errorview， 故还是使用的是 SpelView，也就是白标。
@Controller
public class ErrControlller implements ErrorController {

    @RequestMapping("/error")
    public String error() {
        System.out.println("ErrControlller.error");
        return "error";
    }

//    @Override
    public String getErrorPath() {
        return "error";
    }
}
但是呢， 当我自定义ErrorController 之后，下面的BasicErrorController 便不再会生效，也就是DefaultErrorAttributes 虽然注册成了bean，但是不会实际起作用。 
    @Bean
    @ConditionalOnMissingBean(
        value = {ErrorAttributes.class},
        search = SearchStrategy.CURRENT
    )
    public DefaultErrorAttributes errorAttributes() {
        return new DefaultErrorAttributes();
    }

    @Bean
    @ConditionalOnMissingBean(
        value = {ErrorController.class},
        search = SearchStrategy.CURRENT
    )
    public BasicErrorController basicErrorController(ErrorAttributes errorAttributes) {
        return new BasicErrorController(errorAttributes, this.serverProperties.getError(), this.errorViewResolvers);
    }
 
解决方案呢，我目前想到一个，那就是@RequestMapping("/error") 方法 不要再返回 "error"了， 不然， boot 又会去使用 SpelView来渲染：
    @RequestMapping("/error")
    public String error() {
        System.out.println("ErrControlller.error");
        return "err"; // 不使用/error， 可以返回其他的， 但是要保证这个视图存在， 比如存在 public/err.html 
    }
 
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