title: Stream<Map<String,String>> to Set<String> values in java 8
body: <p>I have a stream of Map how can i get Set having values of Map?</p>
  
  <p>here i what i've done partially</p>
  
  <pre><code>Set&lt;String&gt; jcfTargetTables = measure.getConditionMap().values()
          .stream()
          .map(Condition::getJoinConditionFilter)
          .filter(jcf -&gt; jcf!=null)
          .map(JoinConditionFilter::getTableMapping);
  </code></pre>
  
  <p>the last line gives me a <code>Stream&lt;Map&lt;String,String&gt;&gt;</code>, how do i proceed to get Set that is values of Map?</p>