title: Group validation
body: <p>Is it possible to validate a bean ensuring that at least one of three fields is not null without implementing a custom validator?</p>
  
  <p>So:</p>
  
  <pre><code>public class Foo {
  
      @NotNull(groups = {AtLeastOne.class})
      private Bar b1;
  
      @NotNull(groups = {AtLeastOne.class})
      private Bar b2;
  
      @NotNull(groups = {AtLeastOne.class})
      private Bar b3;
  }
  </code></pre>
  
  <p>But without the groups meaning that I want to validate them all in one go. I want either b1 or b2 or b3 to be not null. </p>
  
  <p>Cheers,</p>