网上很多解决
org.apache.shiro.UnavailableSecurityManagerException的文章，但很多都是使用的Spring MVC。
另外很多文章内容重复，文章排版也不是很友好，翻阅过程中耗费了很多时间。
为了避免其他人像我一样在无效的方案上浪费时间，我决定记录一下自己对这个异常的排查与解决经历，以供大家参考。
案发现场
- SpringBoot + Shiro + 普通接口 一切正常。
- SpringBoot + Shiro + 接口使用异延迟结果（DeferredResult）报错 UnavailableSecurityManagerException
talk is cheap, show me the exception.
异常的完整信息如下：
2020-06-03 10:26:48.543 [http-nio-8080-exec-5] ERROR o.a.c.c.C.[.[.[/itplh].[dispatcherServlet]:175 - Servlet.service() for servlet [dispatcherServlet] threw exception
org.apache.shiro.UnavailableSecurityManagerException: No SecurityManager accessible to the calling code, either bound to the org.apache.shiro.util.ThreadContext or as a vm static singleton. This is an invalid application configuration.
at org.apache.shiro.SecurityUtils.getSecurityManager(SecurityUtils.java:123)
at org.apache.shiro.subject.Subject$Builder.<init>(Subject.java:626)
at org.apache.shiro.SecurityUtils.getSubject(SecurityUtils.java:56)
at org.apache.shiro.web.servlet.ShiroHttpServletRequest.getSubject(ShiroHttpServletRequest.java:89)
at org.apache.shiro.web.servlet.ShiroHttpServletRequest.getSubjectPrincipal(ShiroHttpServletRequest.java:94)
at org.apache.shiro.web.servlet.ShiroHttpServletRequest.getUserPrincipal(ShiroHttpServletRequest.java:112)
at org.springframework.web.servlet.FrameworkServlet.getUsernameForRequest(FrameworkServlet.java:1159)
at org.springframework.web.servlet.FrameworkServlet.publishRequestHandledEvent(FrameworkServlet.java:1144)
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1022)
at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:908)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:660)
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:882)
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.springframework.boot.actuate.metrics.web.servlet.WebMvcMetricsFilter.filterAndRecordMetrics(WebMvcMetricsFilter.java:117)
at org.springframework.boot.actuate.metrics.web.servlet.WebMvcMetricsFilter.doFilterInternal(WebMvcMetricsFilter.java:106)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
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.ApplicationDispatcher.invoke(ApplicationDispatcher.java:712)
at org.apache.catalina.core.ApplicationDispatcher.doDispatch(ApplicationDispatcher.java:633)
at org.apache.catalina.core.ApplicationDispatcher.dispatch(ApplicationDispatcher.java:601)
at org.apache.catalina.core.AsyncContextImpl$AsyncRunnable.run(AsyncContextImpl.java:561)
at org.apache.catalina.core.AsyncContextImpl.doInternalDispatch(AsyncContextImpl.java:350)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:197)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:490)
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.asyncDispatch(CoyoteAdapter.java:235)
at org.apache.coyote.AbstractProcessor.dispatch(AbstractProcessor.java:241)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:53)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:834)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1415)
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)
原因分析
看了上面的报错信息，错误栈的包信息全部都是第三方路径。
所以我们基本能确定是整合第三方的配置出了问题。
异常信息已经提示了解决方法：
No SecurityManager accessible to the calling code, either bound to the org.apache.shiro.util.ThreadContext or as a vm static singleton. This is an invalid application configuration.
要么绑定到ThreadContext，要么作为虚拟机的静态单例。
推测应该是SecurityManager没有被绑定到ThreadContext中，所以我们可以手动绑定一下。
解决方案
@Bean
public SecurityManager securityManager(ShiroRealm myRealm){
DefaultWebSecurityManager securityManager = new DefaultWebSecurityManager();
securityManager.setRealm(myRealm);
// [重点]解决报错 org.apache.shiro.UnavailableSecurityManagerException
ThreadContext.bind(securityManager);
return securityManager;
}