title: Maven shade plugin warning: we have a duplicate - how to fix?
body: <p>This is my project <a href="http://hastebin.com/raw/hodujivive" rel="noreferrer">POM (link to the paste, so you can right click > save as pom.xml)</a></p>
  
  <pre class="lang-xml prettyprint-override"><code>&lt;project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"&gt;
      &lt;modelVersion&gt;4.0.0&lt;/modelVersion&gt;
  
      &lt;groupId&gt;com.zybnet&lt;/groupId&gt;
      &lt;artifactId&gt;excel-reporter&lt;/artifactId&gt;
      &lt;version&gt;0.0.1-SNAPSHOT&lt;/version&gt;
      &lt;packaging&gt;jar&lt;/packaging&gt;
  
      &lt;name&gt;mvn1&lt;/name&gt;
      &lt;url&gt;http://maven.apache.org&lt;/url&gt;
  
      &lt;properties&gt;
          &lt;project.build.sourceEncoding&gt;UTF-8&lt;/project.build.sourceEncoding&gt;
      &lt;/properties&gt;
  
      &lt;dependencies&gt;
          &lt;dependency&gt;
              &lt;groupId&gt;junit&lt;/groupId&gt;
              &lt;artifactId&gt;junit&lt;/artifactId&gt;
              &lt;version&gt;3.8.1&lt;/version&gt;
              &lt;scope&gt;test&lt;/scope&gt;
          &lt;/dependency&gt;
          &lt;dependency&gt;
              &lt;groupId&gt;log4j&lt;/groupId&gt;
              &lt;artifactId&gt;log4j&lt;/artifactId&gt;
              &lt;version&gt;1.2.17&lt;/version&gt;
          &lt;/dependency&gt;
          &lt;dependency&gt;
              &lt;groupId&gt;org.apache.poi&lt;/groupId&gt;
              &lt;artifactId&gt;poi&lt;/artifactId&gt;
              &lt;version&gt;3.8&lt;/version&gt;
          &lt;/dependency&gt;
          &lt;dependency&gt;
              &lt;groupId&gt;net.sf.jasperreports&lt;/groupId&gt;
              &lt;artifactId&gt;jasperreports&lt;/artifactId&gt;
              &lt;version&gt;4.6.0&lt;/version&gt;
          &lt;/dependency&gt;
          &lt;dependency&gt;
              &lt;groupId&gt;org.codehaus.groovy&lt;/groupId&gt;
              &lt;artifactId&gt;groovy-all&lt;/artifactId&gt;
              &lt;version&gt;2.0.0&lt;/version&gt;
          &lt;/dependency&gt;
      &lt;/dependencies&gt;
  
      &lt;build&gt;
          &lt;resources&gt;
              &lt;resource&gt;
                  &lt;directory&gt;${project.build.sourceDirectory}&lt;/directory&gt;
              &lt;/resource&gt;
          &lt;/resources&gt;
          &lt;plugins&gt;
              &lt;plugin&gt;
                  &lt;artifactId&gt;maven-jar-plugin&lt;/artifactId&gt;
                  &lt;configuration&gt;
                      &lt;finalName&gt;${artifactId}-${version}-tmp&lt;/finalName&gt;
                  &lt;/configuration&gt;
              &lt;/plugin&gt;
              &lt;plugin&gt;
                  &lt;groupId&gt;org.apache.maven.plugins&lt;/groupId&gt;
                  &lt;artifactId&gt;maven-shade-plugin&lt;/artifactId&gt;
                  &lt;version&gt;1.7.1&lt;/version&gt;
                  &lt;executions&gt;
                      &lt;execution&gt;
                          &lt;phase&gt;package&lt;/phase&gt;
                          &lt;goals&gt;
                              &lt;goal&gt;shade&lt;/goal&gt;
                          &lt;/goals&gt;
                          &lt;configuration&gt;
                              &lt;filters&gt;
                                  &lt;filter&gt;
                                      &lt;artifact&gt;*:*&lt;/artifact&gt;
                                      &lt;excludes&gt;
                                          &lt;exclude&gt;META-INF/*.SF&lt;/exclude&gt;
                                          &lt;exclude&gt;META-INF/*.DSA&lt;/exclude&gt;
                                          &lt;exclude&gt;META-INF/*.RSA&lt;/exclude&gt;
                                      &lt;/excludes&gt;
                                  &lt;/filter&gt;
                              &lt;/filters&gt;
                              &lt;transformers&gt;
                                  &lt;transformer
                                      implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer"&gt;
                                      &lt;mainClass&gt;com.zybnet.Main&lt;/mainClass&gt;
                                  &lt;/transformer&gt;
                              &lt;/transformers&gt;
                          &lt;/configuration&gt;
                      &lt;/execution&gt;
                  &lt;/executions&gt;
              &lt;/plugin&gt;
          &lt;/plugins&gt;
      &lt;/build&gt;
  
  &lt;/project&gt;
  </code></pre>
  
  <p>I followed the advice of configuring the default jar plugin as advertised in <a href="http://docs.codehaus.org/display/MAVENUSER/Shade+Plugin" rel="noreferrer">the FAQ</a>, but still when I run <code>mvn package</code> about 20K warnings are issued. Running <code>mvn clean</code> does not help either.</p>
  
  <p>According to <a href="https://stackoverflow.com/a/9807806/315306">this answer</a>, I could manually exclude some dependencies. However, I don't know if it's the right way, and the dependency tree is rather complex so it's difficult to argue where to start.</p>
  
  <p>I know that these issues are not harmful, but I'm used to treat warnings as something that must be fixed. Moreover, I'm a beginner with Maven, so I'd like to understand what's wrong with my understanding, and how to troubleshoot problems.</p>
  
  <p><em>(Using maven assembly plugin is not an option here)</em></p>