解决alpine镜像运行springboot 无法获取验证码（缺少字体）的问题

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: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)

重新制作jdk镜像，添加fontconfig和一款字体dejavu,文件名称Dockerfile-8u201_jdk_alpine3.9

FROM openjdk:8u201-jdk-alpine3.9
ENV LANG en_US.UTF-8
RUN apk add --update ttf-dejavu fontconfig && rm -rf /var/cache/apk/*

编译命令:

docker build -f Dockerfile-8u201_jdk_alpine3.9 -t openjdk-font:8u201-jdk-alpine3.9 .

推送到自己的docker仓库或者中央仓库：

//登录
docker login 
Username:输入账号
Password:输入密码
//登录成功推送：这里如果是自己的服务器，要根据自己服务器重新打tag再推送
//比如服务器是hub.yexuejc.top 
docker tag openjdk-font:8u201-jdk-alpine3.9 hub.yexuejc.top/public/openjdk-font:8u201-jdk-alpine3.9
docker push openjdk-font:8u201-jdk-alpine3.9(或者hub.yexuejc.top/public/openjdk-font:8u201-jdk-alpine3.9)