title: Jackson detection of duplicate JSON POJO properties and Map keys
body: <p>I'm trying to catch duplicate POJO properties or Map keys are past to my WebService.</p>
  
  <p>So for instance I want to throw an error if <code>field1</code> appears twice or map key <code>1</code> appears twice:</p>
  
  <pre><code>{
    "field1" : 1,
    "field1" : 2,
    "map" : {
      "1" : {
        "fieldA" : "null",
        "fieldB" : "2"
      },
      "1" : {
        "fieldX" : "null",
        "fieldY" : "2"
      }
    }
  }
  </code></pre>