后台服务报错captchaImage接口空指针异常，无法启动项目：
[http-nio-4431-exec-27] ERROR c.r.f.w.e.GlobalExceptionHandler - [handleRuntimeException,93] - 请求地址'/captchaImage',发生未知异常.
java.lang.NullPointerException: null
at sun.awt.FontConfiguration.getVersion(FontConfiguration.java:1264)
at sun.awt.FontConfiguration.readFontConfigFile(FontConfiguration.java:219)
at sun.awt.FontConfiguration.init(FontConfiguration.java:107)
at sun.awt.X11FontManager.createFontConfiguration(X11FontManager.java:774)
at sun.font.SunFontManager$2.run(SunFontManager.java:431)
at java.security.AccessController.doPrivileged(Native Method)
at sun.font.SunFontManager.<init>(SunFontManager.java:376)
at sun.awt.FcFontManager.<init>(FcFontManager.java:35)
at sun.awt.X11FontManager.<init>(X11FontManager.java:57)
at sun.reflect.GeneratedConstructorAccessor75.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at java.lang.Class.newInstance(Class.java:442)
at sun.font.FontManagerFactory$1.run(FontManagerFactory.java:83)
at java.security.AccessController.doPrivileged(Native Method)
at sun.font.FontManagerFactory.getInstance(FontManagerFactory.java:74)
at java.awt.Font.getFont2D(Font.java:491)
at java.awt.Font.access$000(Font.java:224)
at java.awt.Font$FontAccessImpl.getFont2D(Font.java:228)
at sun.font.FontUtilities.getFont2D(FontUtilities.java:180)
at sun.font.StandardGlyphVector.initFontData(StandardGlyphVector.java:1126)
at sun.font.StandardGlyphVector.init(StandardGlyphVector.java:1115)
at sun.font.StandardGlyphVector.<init>(StandardGlyphVector.java:167)
at java.awt.Font.createGlyphVector(Font.java:2545)
at com.google.code.kaptcha.text.impl.DefaultWordRenderer.renderWord(DefaultWordRenderer.java:67)
at com.google.code.kaptcha.impl.DefaultKaptcha.createImage(DefaultKaptcha.java:43)
at com.ruoyi.web.controller.common.CaptchaController.getCode(CaptchaController.java:70)
at sun.reflect.GeneratedMethodAccessor34.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:205)
at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:150)
at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:117)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:895)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:808)
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1072)
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:965)
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:529)
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:623)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:209)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:111)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:111)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153)
at com.alibaba.druid.support.http.WebStatFilter.doFilter(WebStatFilter.java:114)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153)
at com.ruoyi.common.filter.RepeatableFilter.doFilter(RepeatableFilter.java:39)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:327)
at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:115)
at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:81)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)
at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:121)
at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:115)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)
at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:126)
at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:81)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)
at org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:105)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)
at org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:149)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)
at org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:63)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)
at com.ruoyi.framework.security.filter.JwtAuthenticationTokenFilter.doFilterInternal(JwtAuthenticationTokenFilter.java:42)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:111)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)
at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:103)
at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:89)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)
at org.springframework.web.filter.CorsFilter.doFilterInternal(CorsFilter.java:91)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)
at org.springframework.security.web.header.HeaderWriterFilter.doHeadersAfter(HeaderWriterFilter.java:90)
at org.springframework.security.web.header.HeaderWriterFilter.doFilterInternal(HeaderWriterFilter.java:75)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)
at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:110)
at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:80)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)
at org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:55)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)
at org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:211)
at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:183)
at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:354)
at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:267)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153)
at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153)
at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153)
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:167)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:90)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:481)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:130)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:93)
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:390)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:63)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:926)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1791)
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:52)
at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191)
at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:748)
出现这个问题有两个原因
问题1：前端缺少字体，解决办法在前端添加依赖
npm install fontconfig
问题2：java环境缺少字体，切换服务器上的java-dockerfile
openjdk:8-jre
按照上述流程执行即可解决服务端空指针异常问题
参考资料：
若依开源框架部署到linux后访问首页报空指针问题_若依 导出异常,x11font-CSDN博客
若依框架+docker+openjdk 8-alpine导出报错空指针_若依 导出异常,x11font 空指针-CSDN博客