title: How to create a async step in spring-batch?
body: <p>I have an existing spring-batch <code>Step</code> and would like to refactor it with <code>Async</code> processor + writer.</p>
  
  <pre><code>StepBuilderFactory steps;
  steps.get("test").chunk(1000)
          .reader(new FlatFileItemReader&lt;String&gt;())
          .processor(new AsyncItemProcessor&lt;String, String&gt;())
          .writer(new AsyncItemWriter&lt;String&gt;())
          .build();
  </code></pre>
  
  <p>This does not work and complains for the processor:</p>
  
  <p><code>The method processor(ItemProcessor&lt;? super Object,? extends Object&gt;) in the type SimpleStepBuilder&lt;Object,Object&gt; is not applicable for the arguments (AsyncItemProcessor&lt;String,String&gt;)</code>.</p>
  
  <p>How is a step to be build using async?</p>