title: how to concat all columns in a spark dataframe, using java?
body: <p>This is how I do do for 2 specific columns:</p>
  <pre><code>dataSet.withColumn(&quot;colName&quot;, concat(dataSet.col(&quot;col1&quot;), lit(&quot;,&quot;),dataSet.col(&quot;col2&quot;) ));
  </code></pre>
  <p>but <code>dataSet.columns()</code> retruns Sting array, and not Column array.
  How should I craete a  <code>List&lt;Column&gt;</code>?</p>
  <p>Thanks!</p>