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REST Client

Hazelcast provides a REST interface: it provides an HTTP service in each cluster member so that you can access your map and queue using HTTP protocol. Assuming mapName and queueName are already configured in your Hazelcast, its structure is shown below:

http://member IP address:port/hazelcast/rest/maps/mapName/key

http://member IP address:port/hazelcast/rest/queues/queueName

For the operations to be performed, standard REST conventions for HTTP calls are used.

REST client request listener service is not enabled by default. You should enable it on your cluster members to use REST client. It can be enabled using the DATA endpoint group; see the Using the REST Endpoint Groups section.The previously used hazelcast.rest.enabled system property is deprecated.

All parameters that are used in REST API URLs, such as the distributed data structure and key names, must be URL encoded when composing a call. As an example, name.with/special@chars parameter value would be encoded as name.with%2Fspecial%40chars.

REST Client GET/POST/DELETE Examples

In the following GET, POST and DELETE examples, assume that your cluster members are as shown below.

Members [5] {
  Member [10.20.17.1:5701]
  Member [10.20.17.2:5701]
  Member [10.20.17.4:5701]
  Member [10.20.17.3:5701]
  Member [10.20.17.5:5701]
}plain

All of the requests below can return one of the following responses in case of a failure.

If the HTTP request syntax is not known, the following response is returned.
```
HTTP/1.1 400 Bad Request
Content-Length: 0 
```
In case of an unexpected exception, the following response is returned.
```
< HTTP/1.1 500 Internal Server Error
< Content-Length: 0 
```

Creating/Updating Entries in a Map for REST Client

You can put a new key1/value1 entry into a map by using POST call to http://<member IP address>:<port>/hazelcast/rest/maps/mapName/key1 URL. This call’s content body should contain the value of the key. Also, if the call contains the MIME type, Hazelcast stores this information, too.

An example POST call is shown below.

curl -v -X POST -H "Content-Type: text/plain" -d "bar"
    http://10.20.17.1:5701/hazelcast/rest/maps/mapName/fooplain

It returns the following response if successful:

< HTTP/1.1 200 OK
< Content-Type: text/plain
< Content-Length: 0plain

Retrieving Entries from a Map for REST Client

If you want to retrieve an entry, you can use a GET call to http://<member IP address>:<port>/hazelcast/rest/maps/mapName/key1. You can also retrieve this entry from another member of your cluster, such as http://<another member IP address>:<port>/hazelcast/rest/maps/mapName/key1.

An example of a GET call is shown below.

curl -X GET http://<member IP address>:<port>/hazelcast/rest/maps/mapName/foo

It returns the following response if there is a corresponding value:

< HTTP/1.1 200 OK
< Content-Type: text/plain
< Content-Length: 3
bar

This GET call returned a value, its length and also the MIME type (text/plain) since the POST call example shown above included the MIME type.

It returns the following if there is no mapping for the given key:

< HTTP/1.1 204 No Content
< Content-Length: 0plain

Removing Entries from a Map for REST Client

You can use a DELETE call to remove an entry. An example DELETE call is shown below with its response.

curl -v -X DELETE http://10.20.17.1:5701/hazelcast/rest/maps/mapName/fooplain

< HTTP/1.1 200 OK
< Content-Type: text/plain
< Content-Length: 0

If you leave the key empty as follows, the DELETE call deletes all entries from the map.

curl -v -X DELETE http://10.20.17.1:5701/hazelcast/rest/maps/mapNameplain

< HTTP/1.1 200 OK
< Content-Type: text/plain
< Content-Length: 0plain

Offering Items on a Queue for REST Client

You can use a POST call to create an item on the queue. An example is shown below.

curl -v -X POST -H "Content-Type: text/plain" -d "foo"
    http://10.20.17.1:5701/hazelcast/rest/queues/myEventsplain

The above call is equivalent to HazelcastInstance.getQueue("myEvents").offer("foo");.

It returns the following if successful:

< HTTP/1.1 200 OK
< Content-Type: text/plain
< Content-Length: 0plain

It returns the following if the queue is full and the item is not able to be offered to the queue:

< HTTP/1.1 503 Service Unavailable
< Content-Length: 0plain

Retrieving Items from a Queue for REST Client

You can use a DELETE call for retrieving items from a queue. Note that you should state the poll timeout while polling for queue events by an extra path parameter.

An example is shown below (10 being the timeout value).

curl -v -X DELETE \http://10.20.17.1:5701/hazelcast/rest/queues/myEvents/10plain

The above call is equivalent to HazelcastInstance.getQueue("myEvents").poll(10, SECONDS);. Below is the response.

< HTTP/1.1 200 OK
< Content-Type: text/plain
< Content-Length: 3
fooplain

When the timeout is reached, the response is No Content success, i.e., there is no item on the queue to be returned.

< HTTP/1.1 204 No Content
< Content-Length: 0plain

Getting the size of the queue for REST Client

curl -v -X GET \http://10.20.17.1:5701/hazelcast/rest/queues/myEvents/sizeplain

The above call is equivalent to HazelcastInstance.getQueue("myEvents").size();. Below is an example response.

< HTTP/1.1 200 OK
< Content-Type: text/plain
< Content-Length: 1
5plain

Checking the Status of the Cluster for REST Client

Besides the above operations, you can check the status of your cluster, an example of which is shown below.

curl -v http://127.0.0.1:5701/hazelcast/rest/clusterplain

The response is as follows:

< HTTP/1.1 200 OK
< Content-Length: 119

Members [5] {
  Member [10.20.17.1:5701] this
  Member [10.20.17.2:5701]
  Member [10.20.17.4:5701]
  Member [10.20.17.3:5701]
  Member [10.20.17.5:5701]
}

ConnectionCount: 5
AllConnectionCount: 20plain

RESTful access is provided through any member of your cluster. You can even put an HTTP load-balancer in front of your cluster members for load balancing and fault tolerance.

You need to handle the failures on REST polls as there is no transactional guarantee.

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