title: Ability to read multiple files then write content per source file
body: <p>Reading file is working good but writing file is not. </p>
  
  <p>I would like to read multiple files then use <code>MultiResourceItemWriter</code> to write it separately, like:</p>
  
  <p>Read Files:</p>
  
  <pre><code>source/abc.csv
  source/cbd.csv
  source/efg.csv
  </code></pre>
  
  <p>Should write files separate like:</p>
  
  <pre><code>target/abc.csv
  target/cbd.csv
  target/efg.csv
  </code></pre>
  
  <p>But currently it's putting all data in one file.</p>
  
  <pre><code>    @Bean
      public MultiResourceItemWriter&lt;FooCsv&gt; multipleCsvWriter(@Value("${directory.destination}") Resource folder) throws Exception {
          MultiResourceItemWriter&lt;FooCsv&gt; writer = new MultiResourceItemWriter&lt;&gt;();
  
          writer.setResource(folder);
          writer.setDelegate(csvWriter(file));
  
          return writer;
      }
  </code></pre>
  
  <p>Note this is like copy and paste from source folder to target folder.</p>