title: how to config Jenkins container run maven container to use a proxy
body: <p>all,
     As i try to use Jenkins to build-a-java-app-with-maven (<a href="https://jenkins.io/doc/tutorials/build-a-java-app-with-maven/" rel="nofollow noreferrer">https://jenkins.io/doc/tutorials/build-a-java-app-with-maven/</a>).
     I have a problem, my environment accessing network have to use private proxy.<br/>
  My Jenkins run in a container and when I use the below pipeline, the Jenkins container will pull maven image and maven run in the container but because the environment has a proxy, maven container was not config to use a proxy, so maven can not download dependencies.<br/></p>
  
  <p>Can anyone give me help on how to let the maven container to use a proxy? thanks</p>
  
  <pre><code>pipeline {
      agent {
          docker {
              image 'maven:3-alpine' 
              args '-v /root/.m2:/root/.m2' 
          }
      }
      stages {
          stage('Build') { 
              steps {
                  sh 'mvn -B -DskipTests clean package' 
              }
          }
      }
  }
  </code></pre>