title: Merging recusrive Hashmap in java 8
body: <p>I need to merge multiple <code>HashMap</code>s</p>
  
  <p>map1:</p>
  
  <pre><code>{"41666":
   {"oyo_id":"KSD900",
   "contracted_rooms":null,
   "status":"live"
   },
   "41667":
   {"oyo_id":"JGH900",
   "contracted_rooms":null,
   "status":"live"
   }
  }
  </code></pre>
  
  <p>map2:</p>
  
  <pre><code>{"41666":
   {"oyo_id":null,
   "contracted_rooms":31,
   "status":null
   },
   "41667":
   {"oyo_id":null,
   "contracted_rooms":3,
   "status":null
   }
  }
  </code></pre>
  
  <p>Expected result</p>
  
  <pre><code>{"41666":
   {"oyo_id":"KSD900",
   "contracted_rooms":31,
   "status":"live"
   },
   "41667":
   {"oyo_id":"JGH900",
   "contracted_rooms":3,
   "status":"live"
   }
  }
  </code></pre>
  
  <p>What I have tried:</p>
  
  <p><code>AssignedPropertiesResponse</code>:</p>
  
  <pre><code>@JsonProperty("oyo_id")
  private String oyoId;
  
  @JsonProperty("status")
  private String status;
  
  @JsonProperty("contractedRoomsCount")
  private Double contracted_rooms_count;
  </code></pre>
  
  <p>AssignedPropertiesResponseList:</p>
  
  <pre><code>HashMap&lt;String, AssignedPropertiesResponse&gt;
  
  map1.putAll(map2);
  </code></pre>
  
  <p>But this is overwriting values of map2 into map2.</p>