Serializing into JSON
If you want to query JSON strings that are stored in Hazelcast, you can serialize them, using HazelcastJsonValue.
HazelcastJsonValue is a lightweight wrapper that tells a Hazelcast cluster to treat a given string as JSON. Using this information, members can create metadata to optimize queries for data in the string. As a result, it’s best to use HazelcastJsonValue when you want to be able to query JSON values stored in Hazelcast clusters.
Serializing into HazelcastJsonValue
To serialize a JSON string into HazelcastJsonValue, pass the string directly to the new HazelcastJsonValue() constructor.
Hazelcast does not validate the given string. It is your responsibility to use a well formed JSON string as a HazelcastJsonValue.
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String person1 = "{ \"name\": \"John\", \"age\": 35 }";
String person2 = "{ \"name\": \"Jane\", \"age\": 24 }";
String person3 = "{ \"name\": \"Trey\", \"age\": 17 }";
String person4 = "{ \"name\": \"Phil\", \"age\": 30 }";
String person5 = "{ \"name\": \"May\"}";
IMap<Integer, HazelcastJsonValue> idPersonMap = instance.getMap("jsonValues");
idPersonMap.put(1, new HazelcastJsonValue(person1));
idPersonMap.put(2, new HazelcastJsonValue(person2));
idPersonMap.put(3, new HazelcastJsonValue(person3));
idPersonMap.put(4, new HazelcastJsonValue(person4));
idPersonMap.put(5, new HazelcastJsonValue(person4));JSON Metadata
By default, for each HazelcastJsonValue object stored in a map, Hazelcast also stores a metadata object, which helps you to query JSON faster.
This metadata object is created every time
a HazelcastJsonValue is put into a map and is stored in the on-heap or off-heap
memory, depending on the map’s in-memory format setting.
Depending on your application’s needs, you may want to turn off metadata creation to both decrease latency when adding objects to a map and to increase throughput. You can configure this setting using a metadata policy.
Hazelcast Clients
HazelcastJsonValue does not require any Java classes on the member. As a result, clients can serialize data into JSON without any need to upload code to the member.
| Clients do not validate JSON strings. If you store malformed JSON strings on the cluster, the member will log formatting errors only when you try to query the JSON data. |
SQL
When you map columns to a json data type, SQL treats any strings in that column as JSON. As a result, you can either use raw JSON strings or HazelcastJsonValue.
To learn more about JSON in SQL, see Working with JSON Data in SQL.
