Create a JSON Field from the existing string fields

[patrick007 (Patrick)]

I want to create a JSON object my existing string fields in Logstash for storing in Elasticsearch

Example :
"id" : "0001"
"name: "John",
"designation": "Writer",
"age": 25

I would like to create a JSON object called employee like this to store in Elastisearch

"employee" : {
"id" : "0001"
"name: "John",
"designation": "Writer",
"age": 25
}