Hazelcast is an open-source in-memory data grid that provides distributed computing and caching capabilities. It allows developers to store and retrieve data from a distributed cluster of servers. One of the powerful features of Hazelcast is its query capabilities, which enable developers to search and filter data efficiently. In this blog post, we will explore how to use Hazelcast query capabilities in Java applications.

Setting Up Hazelcast

First, let’s start by setting up Hazelcast in our Java application. Here are the steps to get started:

1. Add the Hazelcast dependency to your project’s build file:

<dependencies>
    <dependency>
        <groupId>com.hazelcast</groupId>
        <artifactId>hazelcast</artifactId>
        <version>4.2</version>
    </dependency>
</dependencies>

1. Initialize Hazelcast in your application:

import com.hazelcast.core.Hazelcast;
import com.hazelcast.core.HazelcastInstance;

public class HazelcastExample {
    public static void main(String[] args) {
        HazelcastInstance hazelcastInstance = Hazelcast.newHazelcastInstance();
    }
}

Storing Data in Hazelcast

To demonstrate the query capabilities of Hazelcast, let’s assume we have a collection of Person objects with properties such as name, age, and city. We will store these objects in Hazelcast’s distributed map data structure.

import com.hazelcast.core.HazelcastInstance;
import com.hazelcast.core.IMap;

public class HazelcastExample {
    public static void main(String[] args) {
        HazelcastInstance hazelcastInstance = Hazelcast.newHazelcastInstance();

        IMap<Long, Person> map = hazelcastInstance.getMap("personsMap");

        Person person1 = new Person(1L, "John Doe", 30, "New York");
        Person person2 = new Person(2L, "Jane Smith", 25, "London");
        
        map.put(person1.getId(), person1);
        map.put(person2.getId(), person2);
    }
}

Querying Data in Hazelcast

Now that we have stored our Person objects in Hazelcast, let’s see how we can query them using the query capabilities provided by Hazelcast.

import com.hazelcast.core.HazelcastInstance;
import com.hazelcast.core.IMap;
import com.hazelcast.query.SqlPredicate;

public class HazelcastExample {
    public static void main(String[] args) {
        HazelcastInstance hazelcastInstance = Hazelcast.newHazelcastInstance();

        IMap<Long, Person> map = hazelcastInstance.getMap("personsMap");
        
        // Query for persons younger than 30
        SqlPredicate predicate = new SqlPredicate("age < 30");
        Collection<Person> youngerPersons = map.values(predicate);
        
        for (Person person : youngerPersons) {
            // Process the younger persons
        }
    }
}

In the above example, we create an SqlPredicate to filter out persons younger than 30. We then pass this predicate to the values() method of the distributed map to retrieve only the desired objects.

Conclusion

Hazelcast provides powerful query capabilities that allow developers to filter and retrieve data efficiently from a distributed cluster. In this blog post, we demonstrated how to set up Hazelcast in a Java application and use its query capabilities to search for specific data. By utilizing these features, developers can leverage Hazelcast’s distributed computing capabilities while still benefiting from efficient data retrieval. Happy querying!

#Hazelcast #Java