How to deserialize an array of objects using Jackson or any other api?

Question

I have a model defined to which i need to map the jsonArray.The model is as follows:

@JsonPropertyOrder({
    "Command",
    "Created",
    "Id",
    "Image",
    "Labels",
    "Names",
    "Ports",
    "Status"
})
public class Container {

    @JsonProperty("Command")
    private String Command;

    @JsonProperty("Created")
    private long Created;

    @JsonProperty("Id")
    private String Id;

    @JsonProperty("Image")
    private String Image;

    @JsonProperty("Labels")
    private List<String> Labels;

    @JsonProperty("Names")
    private List<String> Names = new ArrayList<String>();

    @JsonProperty("Ports")
    private List<Port> Ports = new ArrayList<Port>();

    @JsonProperty("Status")
    private String Status;

    //Getters and Setters
}

The response is JSONArray and this is what i have to map to the Container Class which is as follows:

[  
  {  
    "Command":"/usr/sbin/sshd -D",
    "Created":1429686533,
    "Id":"c00afc1ae5787282fd92b3dde748d203a83308d18aaa566741bef7624798af10",
    "Image":"jay8798:latest",
    "Labels":{  

    },
    "Names":[  
      "/jay8798"
    ],
    "Ports":[  
      {  
        "IP":"0.0.0.0",
        "PrivatePort":22,
        "PublicPort":32845,
        "Type":"tcp"
      },
      {  
        "IP":"0.0.0.0",
        "PrivatePort":3306,
        "PublicPort":32846,
        "Type":"tcp"
      }
    ],
    "Status":"Up 12 hours"
  },
  {  
    "Command":"/usr/sbin/sshd -D",
    "Created":1429686039,
    "Id":"d70f439231d99889c1a8e96148f13a77cb9b83ecf8c9d4c691ddefa40286c04c",
    "Image":"jay898:latest",
    "Labels":{  

    },
    "Names":[  
      "/jay898"
    ],
    "Ports":[  
      {  
        "IP":"0.0.0.0",
        "PrivatePort":22,
        "PublicPort":32841,
        "Type":"tcp"
      },
      {  
        "IP":"0.0.0.0",
        "PrivatePort":3306,
        "PublicPort":32842,
        "Type":"tcp"
      }
    ],
    "Status":"Up 12 hours"
  }
]

This is what I have tried but nothing seems to be working:

Container[] containerList = mapper.readValue(containerResponse, Container[].class);
int totalContainers = containerList.length;

//This will return correct length of the container.
System.out.println("This is the retrived size : " + containerList.length); 

for(Container cont : containerList) {
    // this statement will print 'null'.There is no exception thrown at this point.
    System.out.println("Container Id : "+cont.getId());
}

Or

List<Container> containerList = 
          mapper.readValue(containerResponse, new TypeReference<List<MyClass>>(){});

I followed Jackson Deserialize and tried all the solutions mentioned in the post. It is not able to map to the model.All the fields are null one it reads the values. No value is mapped to the attribute of Container class.Any thing missing in the model or do i need to write a customer logic to deserialize the json ?

Answer 1

First off, I'm assuming that

"Labels": {
},

should actually be

"Labels": [
],

since you've defined it to be a list of Strings and not an object of it's own.

This code works for me:

Port.java:

public class Port {
    @JsonProperty("IP")
    private String ip;

    @JsonProperty("PrivatePort")
    private int privatePort;

    @JsonProperty("PublicPort")
    private int publicPort;

    @JsonProperty("Type")
    private String type;

    // Getters and setters
}

main():

String json = ... // Your JSON with the above correction
ObjectMapper objectMapper = new ObjectMapper();
List<Container> containers = objectMapper.readValue(json, new TypeReference<List<Container>>() {});
System.out.println(containers.size());
for(Container container : containers) {
    System.out.println("Container Id : " + container.getId());
}

2
Container Id : c00afc1ae5787282fd92b3dde748d203a83308d18aaa566741bef7624798af10
Container Id : d70f439231d99889c1a8e96148f13a77cb9b83ecf8c9d4c691ddefa40286c04c

Answer 2

I'm surprised you are not getting an exception when trying to deserialize the object. When I run your code locally I get a

Exception in thread "main" com.fasterxml.jackson.databind.JsonMappingException: Can not deserialize instance of java.util.ArrayList out of START_OBJECT token

The reason looking like you are trying to serialize into an Array when it is a JSON object.

"Labels":{  

},

That is a JSON object, so you should change your type to reflect what it is, or change the serialization of that JSON property to be an array. If you just want to change the type in your Container class, you should use a Map :

@JsonProperty("Labels")
private Map<String, Object> Labels;