fix docker

.dockerignore

@@ -1,3 +1,5 @@
 *
 !Dockerfile
 !target/*.jar
+!src
+!pom.xml

Dockerfile

@@ -1,17 +1,16 @@
 # fiat-exchange-rates
-FROM library/openjdk:8-alpine
+FROM maven:alpine as builder
+ADD ./pom.xml pom.xml
+ADD ./src src/
+VOLUME /var/maven/.m2
+RUN mvn -DskipTests clean package
 
+FROM library/openjdk:8-alpine
 MAINTAINER "<qyvlik@qq.com>"
-
 WORKDIR /home/www
-
 RUN adduser -D -u 1000 www www \
     && chown www:www -R /home/www
-
-ADD target/*.jar /home/www/app.jar
-
+COPY --from=builder target/*.jar app.jar
 EXPOSE 8080
-
 USER www
-
 ENTRYPOINT ["java", "-jar", "/home/www/app.jar"]