Hazelcast - IList

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The java.util.List provides an interface for holding collections of objects that do not necessarily need to be unique. The ordering of elements does not matter.

Similarly, IList implements a distributed version of Java List. It provides similar functions: add, forEach, etc.

All the data which is present in IList is stored/present on a single JVM. Data is still accessible to all the JVMs, but the list cannot be scaled beyond a single machine/JVM.

The list supports synchronous backup as well as asynchronous backup. Synchronous backup ensures that even if the JVM holding the list goes down, all the elements would be preserved and available from the backup.

Let's look at an example of the useful functions.

Adding elements and reading elements

Let’s execute the following code on 2 JVMs. The producer code on one and consumer code on other.

Example

The first piece is the producer code which creates a list and adds item to it.

public static void main(String... args) throws IOException, InterruptedException {
   //initialize hazelcast instance
   HazelcastInstance hazelcast = Hazelcast.newHazelcastInstance();
   // create a list
   IList<String> hzFruits = hazelcast.getList("fruits");
   hzFruits.add("Mango");
   hzFruits.add("Apple");
   hzFruits.add("Banana");

   // adding an existing fruit
   System.out.println(hzFruits.add("Apple"));
   System.out.println("Size of list:" + hzFruits.size());
   System.exit(0);
}

The second piece is of consumer code which reads the list elements.

public static void main(String... args) throws IOException, InterruptedException {
   //initialize hazelcast instance
   HazelcastInstance hazelcast = Hazelcast.newHazelcastInstance();
   // create a list
   IList<String> hzFruits = hazelcast.getList("fruits");
   Thread.sleep(2000);
   hzFruits.forEach(System.out::println);
   System.exit(0);
}

Output

The output for the code for the producer shows that it is not able to add an existing element.

true
4

The output for the code for the consumer prints the list size and the fruits are in expected order.

4
Mango
Apple
Banana
Apple

Useful Methods