title: Convert JavaPairRdd to JavaRdd by concatenating key and value
body: <p>I am new to Apache Spark. As the title says, I have a <code>JavaPairRdd&lt;String,String&gt;</code> and I want to produce a <code>JavaRdd&lt;String&gt;</code> with the concatenation of the key and the value of the <code>JavaPairRdd</code>. Is this possible?</p>
  
  <p>Example:</p>
  
  <pre><code>("1,Nick", "mail@sth.com,53")
  ("2,John", "mail@sth.com,53")
  </code></pre>
  
  <p>Result (<code>JavaRdd&lt;String&gt;</code> with):</p>
  
  <pre><code>"1,Nick,mail@sth.com,53"
  "2,John,mail@sth.com,53"
  </code></pre>