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REST Client

Hazelcast provides a REST interface, i.e. it provides an HTTP service in each node 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://node IP address:port/hazelcast/rest/maps/mapName/key

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

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

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]
}

image NOTE: 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 will be returned.
HTTP/1.1 400 Bad Request
Content-Length: 0
  • In case of an unexpected exception, the following response will be returned.
< HTTP/1.1 500 Internal Server Error
< Content-Length: 0

Creating/Updating Entries in a Map

You can put a new key1/value1 entry into a map by using POST call to http://10.20.17.1:5701/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.

A sample 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/foo

It will return the following response if successful:

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

Retrieving Entries from a Map

If you want to retrieve an entry, you can use a GET call to http://10.20.17.1:5701/hazelcast/rest/maps/mapName/key1. You can also retrieve this entry from another member of your cluster, such as http://10.20.17.3:5701/hazelcast/rest/ maps/mapName/key1.

An example of a GET call is shown below.

$ curl -X GET http://10.20.17.3:5701/hazelcast/rest/maps/mapName/foo

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

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

Removing Entries from a Map

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

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

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

If you leave the key empty as follows, DELETE will delete all entries from the map.

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

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

Offering Items on a Queue

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

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

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

It will return the following if successful:

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

It will return 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: 0

Retrieving Items from a Queue

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/10

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
foo

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

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

Getting the size of the queue

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

The above call is equivalent to HazelcastInstance#getQueue("myEvents").size();. Below is a sample response.

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

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

$ curl -v http://127.0.0.1:5701/hazelcast/rest/cluster

The return will be similar to the following:

< 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: 20

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.

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