title: Spring Batch how to filter duplicated items before send it to ItemWriter
body: <p>I read a flat file (for example a .csv file with 1 line per User, Ex: <em>UserId;Data1;Date2</em>).</p>
  
  <p>But how to handle duplicated User item in the reader (where is no list of previus readed users...)</p>
  
  <pre><code>stepBuilderFactory.get("createUserStep1")
  .&lt;User, User&gt;chunk(1000)
  .reader(flatFileItemReader) // FlatFileItemReader
  .writer(itemWriter) // For example JDBC Writer
  .build();
  </code></pre>