update build process

Using multi stage build in dockerfile

Dockerfile.jetty

@@ -1,3 +1,16 @@
+FROM maven:3-jdk-8 AS builder
+
+RUN apt-get update && apt-get install -y --no-install-recommends graphviz fonts-wqy-zenhei && rm -rf /var/lib/apt/lists/*
+
+COPY pom.xml /app/
+COPY src /app/src/
+
+ENV MAVEN_CONFIG=/app/.m2
+WORKDIR /app
+RUN mvn package
+
+########################################################################################
+
 FROM jetty
 MAINTAINER D.Ducatel
 
@@ -5,4 +18,6 @@ RUN apt-get update && \
     apt-get install -y --no-install-recommends graphviz fonts-wqy-zenhei && \
     rm -rf /var/lib/apt/lists/*
 
-ADD target/plantuml.war /var/lib/jetty/webapps/ROOT.war
+COPY --from=builder /app/target/plantuml.war /var/lib/jetty/webapps/ROOT.war
+
+