title: eclipse imported maven project cannot resolve symbols in other imported maven project
body: <p>I imported "flink" projects from its git clone and configured related settings. I can compile/package it successfully in command line with "mvn".</p>
  
  <p>Several projects report errors that symbols cannot be resolved. For example: "MathUtils cannot be resolved  AbstractAlignedProcessingTimeWindowOperator.java    /flink-streaming-java_2.10/src/main/java/org/apache/flink/streaming/runtime/operators/windowing line 109    Java Problem".</p>
  
  <p>"MathUtils" lies in project "flink-runtime_2.10" which has been compiled and packaged into a jar and its output classes folders are empty.</p>
  
  <p>For project "flink-streaming-java_2.10", its "java build path"->Libraries->"Maven dependencies" includes a reference item for "flink-runtime_2.10". But it cannot resolve the symbols in "flink-runtime_2.10". </p>
  
  <p>In the project group, all java projects whose builders are "java builder" and "maven proejct builder" have such problems, but projects whose builders are "scala builder" and "maven project builder", or simple "maven project builder" have no problem.</p>