title: Spring cache keys for Collections
body: <p>In spring cache(ehcache), we can give a key for single parameter or result.
  As an example:</p>
  
  <pre><code>@CachePut(value="employeeCache", key="#employeeId")
  public void addEmployee( int employeeId ){ //body }
  
  @Cacheable(value="employeeCache", key="#result.id")
  public Employee getEmployee( int employeeId ){ return employeeObj; }
  </code></pre>
  
  <p>But How can we define keys for collections like Set, List using annotations? </p>