执行以下两行命令后，重启应用即可

 # yum install fontconfig 
 # fc-cache --force

 

java.lang.NullPointerException
    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:441)
    at java.security.AccessController.doPrivileged(AccessController.java:682)
    at sun.font.SunFontManager.<init>(SunFontManager.java:386)
    at sun.awt.FcFontManager.<init>(FcFontManager.java:35)
    at sun.awt.X11FontManager.<init>(X11FontManager.java:57)
    at java.lang.J9VMInternals.newInstanceImpl(Native Method)
    at java.lang.Class.newInstance(Class.java:2060)
    at sun.font.FontManagerFactory$1.run(FontManagerFactory.java:83)
    at java.security.AccessController.doPrivileged(AccessController.java:682)
    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:2549)
    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.system.SysCaptchaController.getKaptchaImage(SysCaptchaController.java:59)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    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.apache.shiro.web.servlet.ProxiedFilterChain.doFilter(ProxiedFilterChain.java:61)
    at org.apache.shiro.web.servlet.AdviceFilter.executeChain(AdviceFilter.java:108)
    at org.apache.shiro.web.servlet.AdviceFilter.doFilterInternal(AdviceFilter.java:137)
    at org.apache.shiro.web.servlet.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:154)
    at org.apache.shiro.web.servlet.ProxiedFilterChain.doFilter(ProxiedFilterChain.java:66)
    at org.apache.shiro.web.servlet.AdviceFilter.executeChain(AdviceFilter.java:108)
    at org.apache.shiro.web.servlet.AdviceFilter.doFilterInternal(AdviceFilter.java:137)
    at org.apache.shiro.web.servlet.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:154)
    at org.apache.shiro.web.servlet.ProxiedFilterChain.doFilter(ProxiedFilterChain.java:66)
    at org.apache.shiro.web.servlet.AbstractShiroFilter.executeChain(AbstractShiroFilter.java:458)
    at org.apache.shiro.web.servlet.AbstractShiroFilter$1.call(AbstractShiroFilter.java:373)
    at org.apache.shiro.subject.support.SubjectCallable.doCall(SubjectCallable.java:90)
    at org.apache.shiro.subject.support.SubjectCallable.call(SubjectCallable.java:83)
    at org.apache.shiro.subject.support.DelegatingSubject.execute(DelegatingSubject.java:387)
    at org.apache.shiro.web.servlet.AbstractShiroFilter.doFilterInternal(AbstractShiroFilter.java:370)
    at org.apache.shiro.web.servlet.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:154)
    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 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:826)