BufferedImage图形验证报错Could not initialize class sun.awt.X11GraphicsEnvironment解决办法

使用Servlet生成图形验证码功能，启动后正常，调用时报如下错误：

Jul 27, 2018 10:17:03 AM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [verifyCodeServlet] in context with path [/mobile] threw exception [Servlet execution threw an exception] with root cause
java.lang.NoClassDefFoundError: Could not initialize class sun.awt.X11GraphicsEnvironment
    at java.lang.Class.forName0(Native Method)
    at java.lang.Class.forName(Class.java:169)
    at java.awt.GraphicsEnvironment.getLocalGraphicsEnvironment(GraphicsEnvironment.java:68)
    at java.awt.image.BufferedImage.createGraphics(BufferedImage.java:1135)
    at cn.lovecto.common.servlet.VerifyCodeServlet.service(VerifyCodeServlet.java:87)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:304)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at cn.lovecto.mobile.filter.TimingLogFilter.doFilter(TimingLogFilter.java:69)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at cn.lovecto.mobile.filter.CorsDomainFilter.doFilter(CorsDomainFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at cn.lovecto.common.filter.ClientIPFilter.doFilter(ClientIPFilter.java:21)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at cn.lovecto.common.filter.AuthenticationFilter.doFilter(AuthenticationFilter.java:29)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at cn.lovecto.common.filter.CharacterEncodingFilter.doFilter(CharacterEncodingFilter.java:32)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:240)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:164)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:498)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:164)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:394)
    at org.apache.coyote.http11.Http11NioProcessor.process(Http11NioProcessor.java:391)
    at org.apache.coyote.http11.Http11NioProtocol$Http11ConnectionHandler.process(Http11NioProtocol.java:357)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1531)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
    at java.lang.Thread.run(Thread.java:662)

解决办法：

在catalina.sh启动脚本中的JAVA_OPTS中加入”-Djava.awt.headless=true”，亦可以正常访问图形验证码，修改下如下：

JAVA_OPTS="$JAVA_OPTS -Djava.protocol.handler.pkgs=org.apache.catalina.webresources -Djava.awt.headless=true"

经查，出现这种情况一般就是启动tomcat的用户无法访问Xserver，包括Xserver没有启动或者没有权限访问。加入上面所说的选项，即可正常。