Hazelcast IMDG Release Notes
Hazelcast Management Center IMDG 07/05/ IMDG Java Client 08/01/ Download ZIP ( MB) · Release Notes Reference Manual API Docs. See the Hazelcast IMDG Migration Guide for the detailed guidelines and ConnectionType enums and introduced free strings for them instead.
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The Java client is the most full featured Hazelcast native client. The main idea behind the Java client is to provide the same Hazelcast functionality by proxying each operation through a Hazelcast member.
It can access and change distributed data and it can listen to distributed events of an already established Hazelcast cluster from another Java application. Hundreds or even thousands of clients can be connected to the cluster. Imagine a trading application where all the trading data are stored and managed in a Hazelcast cluster with tens of members.
Simply include the hazelcast. Once included, you can start using this client as if you are using the Hazelcast API. The differences are discussed in the below sections. If you prefer to use Maven, simply add the hazelcast dependency to your pom. The first step is the configuration. You can configure the Java client declaratively or programmatically. We use the programmatic approach for this section, as shown below.
See the Configuring Java Client section for more information. The second step is initializing the HazelcastInstance to be connected to the cluster. This client interface is your gateway to access all Hazelcast distributed objects. As the final step, if and when you are done with your client, you can shut it down as shown below:. Smart Client : In the smart mode, the clients connect to each cluster member. Since each data partition uses the well known and consistent hashing algorithm, each client can send an operation to the relevant cluster member, which increases the overall throughput and efficiency.
Smart mode is the default mode. Unisocket Client : For some cases, the clients can be required to connect to a single member instead of to each member in the cluster. Firewalls, security, or some custom networking issues can be the reason for these cases.
In the unisocket client mode, the clients only connect to one of the configured addresses. This single member behaves as a gateway to the other members. For any operation requested from the client, it redirects the request to the relevant member and returns the response back to the client returned from that member.
While the client is trying to connect initially to one of the members in the ClientNetworkConfig. Instead of giving up, throwing an exception and stopping the client, the client retries to connect as configured which is described in the Configuring Client Connection Retry section. The client executes each operation through the already established connection to the cluster.
If this connection s disconnects or drops, the client tries to reconnect as configured. While sending the requests to related members, operations can fail due to various reasons.
Read-only operations are retried by default. If you want to enable retry for the other operations, you can set the redoOperation to true. See the Enabling Redo Operation section. You can set a timeout for retrying the operations sent to a member. This can be provided by using the property hazelcast. The client retries an operation within this given period, of course, if it is a read-only operation or you enabled the redoOperation as stated in the above paragraph.
This timeout value is important when there is a failure resulted by either of the following causes:. See the Client System Properties section for the description of the hazelcast. When any failure happens between a client and member such as an exception on the member side or connection issues , an operation is retried if:. If it is not certain whether the operation has run on the member, then the non-idempotent operations are not retried. However, as explained in the first paragraph of this section, you can force all client operations to be retried redoOperation when there is a failure between the client and member.
But in this case, you should know that some operations may run multiple times causing conflicts. For example, assume that your client sent a queue.
Since there will be no respond for this operation, you will not know whether it has run on the member or not. If you enabled redoOperation , that queue. Most of the Distributed Data Structures are supported by the Java client. When you use clients in other languages, you should check for the exceptions.
As a general rule, you configure these data structures on the server side and access them through a proxy on the client side. See the Distributed Map section for more information. See the Distributed MultiMap section for more information. See the Distributed Queue section for more information.
The distributed data structures listed below are also supported by the client. Since their logic is the same in both the member side and client side, you can see their sections as listed below. Hazelcast provides the services discussed below for some common functionalities on the client side. The distributed executor service is for distributed computing. It can be used to execute tasks on the cluster on a designated partition or on all the partitions.
It can also be used to process entries. See the Distributed Executor Service section for more information. After getting an instance of IExecutorService , you can use the instance as the interface with the one provided on the server side. See the Distributed Computing chapter for detailed usage. If you need to track clients and you want to listen to their connection events, you can use the clientConnected and clientDisconnected methods of the ClientService class.
This class must be run on the member side. The following is an example code. You use partition service to find the partition of a key. It returns all partitions. See the example code below. You can define labels in your Java client, similar to the way it can be done for the members. Through the client labels, you can assign special roles for your clients and use these roles to perform some actions specific to those client connections.
You can also group your clients using the client labels. These client groups can be blacklisted in the Hazelcast Management Center so that they can be prevented from connecting to a cluster. See the related section in the Hazelcast Management Center Reference Manual for more information on this topic. Declaratively, you can define the client labels using the client-labels configuration element. See the below example. See the code sample for the client labels to see them in action.
You can configure listeners to listen to various event types on the client side. You can configure global events not relating to any distributed object through Client ListenerConfig. You should configure distributed object listeners like map entry listeners or list item listeners through their proxies.
See the related sections under each distributed data structure in this Reference Manual. Transactional distributed objects are supported on the client side. See the Transactions chapter on how to use them. Java client can be configured to connect to a cluster in an async manner during the client start and reconnecting after a cluster disconnect.
Both of these options are configured via ClientConnectionStrategyConfig. Async client start is configured by setting the configuration element async-start to true. This configuration changes the behavior of HazelcastClient. It returns a client instance without waiting to establish a cluster connection.
If you want to check or wait the client to complete its cluster connection, you can use the built-in lifecycle listener:. The Java client can also be configured to specify how it reconnects after a cluster disconnection. The following are the options:. Client can open a connection to the cluster without blocking the waiting invocations. All invocations receive HazelcastClientOfflineException during the establishment of cluster connection.
If cluster connection is failed to connect, then client shutdown is triggered. See the Java Client Connection Strategy section to learn how to configure these. For declarative configuration, the Hazelcast client looks at the following places for the client configuration file:.
System property : The client first checks if hazelcast. Classpath : If config file is not set as a system property, the client checks the classpath for hazelcast-client. If the client does not find any configuration file, it starts with the default configuration hazelcast-client-default.
Before configuring the client, please try to work with the default configuration to see if it works for you. The default should be just fine for most users. If not, then consider custom configuration for your environment.
If you want to specify your own configuration file to create a Config object, the Hazelcast client supports the following:.