title: Compilation error in compiling Protobufs in Java using SBT build tool
body: <p>I am using the Play framework (which uses SBT build tool) with Java where I need to consume a Protobuf. So I have <code>xxx.proto</code> file. I got binary protoc compiler and added to class path. so I see -</p>
  <blockquote>
  <p>protoc --version<br />
  libprotoc 3.1.0</p>
  </blockquote>
  <p>I have compiled the xxx.proto file using -
  <code>protoc -I=$SRC_DIR --java_out=$DST_DIR $SRC_DIR/xxx.proto</code> so it has generated xxx.java file.</p>
  <p>Now when I am compiling this xxx.java file ( the project using sbt build tool)</p>
  <pre><code>[error] /my_project/app/helpers/xxx.java:7: package com.google.protobuf        does not exist
  [error] com.google.protobuf.ExtensionRegistryLite
  [error] /my_project/app/helpers/xxx.java:11: package com.google.protobuf does not exist
  [error] com.google.protobuf.ExtensionRegistry
  [error] /my_project/app/helpers/xxx.java:6182: package com.google.protobuf.Descriptors does not exist
  [error] com.google.protobuf.Descriptors.Descriptor
  [error] /my_project/app/helpers/xxx.java:6185: package com.google.protobuf.GeneratedMessageV3 does not exist
  [error] com.google.protobuf.GeneratedMessageV3.FieldAccessorTable`
  </code></pre>
  <p>I see in my installed library - <code>com.google.protobuf</code> jar is there.</p>
  <p>My <code>xxx.proto</code> looks following -</p>
  <pre><code> // Generated by the protocol buffer compiler.  DO NOT EDIT!
   // source: xxx.proto
  
   public final class xxx {
   private xxx() {}
   public static void registerAllExtensions(
    com.google.protobuf.ExtensionRegistryLite registry) {
   }
  
    public static void registerAllExtensions(
    com.google.protobuf.ExtensionRegistry registry) {
     registerAllExtensions(
      (com.google.protobuf.ExtensionRegistryLite) registry);
   }
   ......
  </code></pre>
  <p>Is there anything I have missed while generating the <code>xxx.java</code> file?
  How should I fix these compilation error?</p>