Deserialize array of strings to csv

I have a json payload with:

"host_names": [
    "www.host1.com",
    "www.host2.com"
]

How can I deserialize this as a csv using Jackson - e.g.:

"www.host1.com,www.host2.com"

Previously I was deserializing this as a String[] but I can't persist that with hibernate, so now I'm trying to deserialize it as a csv.

EDIT:

I want to use annotations to turn the json array into a string, where each element of the array is separated by a comma. Perhaps something like @JsonRawValue. The goal is to then persist the value to a data via hibernate.

public static void main(String[] args) {
		String jsonStr = "{\"host_names\": [\r\n" + 
				"    \"www.host1.com\",\r\n" + 
				"    \"www.host2.com\"\r\n" + 
				"]}";
		JSONObject jsonObject = new JSONObject(jsonStr);
		JSONArray hostNames = jsonObject.getJSONArray("host_names");
		String result = "";
		for(int i=0;i<hostNames.length(); i++) {
			if(!result.isEmpty())
			result = result+",\""+hostNames.getString(i)+"\"";
			else
				result = "\""+hostNames.getString(i)+"\"";
		}
		System.out.println(result);	
	}

result

"www.host1.com","www.host2.com"

Other approach based on annotation

Create a class

class Server{
	
	@JsonProperty(value = "host_names")
	private List<String> hostNames;

	public List<String> getHostNames() {
		return hostNames;
	}

	public void setHostNames(List<String> hostNames) {
		this.hostNames = hostNames;
	}
}

Now use com.fasterxml.jackson.databind.ObjectMapper to parse the JSON into this class

public static void main(String[] args) throws JsonMappingException, JsonProcessingException {
		String jsonStr = "{\"host_names\": [\r\n" + 
				"    \"www.host1.com\",\r\n" + 
				"    \"www.host2.com\"\r\n" + 
				"]}";
		ObjectMapper mapper = new ObjectMapper();
		Server server = mapper.readValue(jsonStr, Server.class);
		System.out.println(server.getHostNames());
	}

output

[www.host1.com, www.host2.com]

You can slightly modify your setter / getter for host_names property as

Bean Class

public class Server {

    @JsonProperty("host_names")
    private List<String> hostNames;

    @JsonGetter("host_names")
    public String getHostNames() {
        return String.join(",", hostNames);
    }

    @JsonSetter("host_names")
    public void setHostNames(List<String> hostNames) {
        this.hostNames = hostNames;
    }
}

Main Method

public static void main(String[] args) throws JsonProcessingException {

    ObjectMapper mapper = new ObjectMapper();
    Server server = mapper.readValue("{\"host_names\":[\"www.host1.com\",\"www.host2.com\"]}", Server.class);
    String json = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(server);
    System.out.println(json);
}

Output

{
  "host_names" : "www.host1.com,www.host2.com"
}

This way you can serialize as comma separated string, and array of string while deserializing.

Another Solution using @JsonValue Annotation.
Define your bean class as:

public class Server {

    @JsonProperty("host_names")
    private List<String> hostNames;

    @JsonValue
    public String hostNames() {
        return String.join(",", hostNames);
    }

    public List<String> getHostNames() {
        return hostNames;
    }

    public void setHostNames(List<String> hostNames) {
        this.hostNames = hostNames;
    }
}

Main Method

public static void main(String[] args) throws JsonProcessingException {

    ObjectMapper mapper = new ObjectMapper();
    Server server = mapper.readValue("{\"host_names\":[\"www.host1.com\",\"www.host2.com\"]}", Server.class);
    String json = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(server);
    System.out.println(json);
}

Output

"www.host1.com,www.host2.com"

This method will only be useful if your bean class has no other fields to serialize.