原因：
项目中需要使用图形验证码，本地使用没问题，部署到线上出现以下问题：
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.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
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)
主要原因是字体问题，修改方案如下：
只需要在项目的docker部署文件里面添加下面这一条即可：
RUN apk add --update ttf-dejavu fontconfig
添加后配置文件如下：
FROM openjdk:8-jdk-alpine
VOLUME /tmp
ADD xx.jar app.jar
RUN apk add --update ttf-dejavu fontconfig
ENTRYPOINT ["java","-Djava.security.egd=file:/dev/./urandom","-jar","/app.jar"]