Guava cache: Auto load the object when it is not exist in cache

Cache interface provides 'get' method, which takes a callable as argument. This method get the object from callable if it is not exist in the cache.

 

Signature

V get(K key, Callable<? extends V> loader)

 

'get' method returns the object if it is not in the cache, else it return the object by executing the callable block.

 

Example

Employee emp = empCache.get(id, new Callable<Employee>() {

	@Override
	public Employee call() throws Exception {
		Employee emp = EmployeeService.getObject(id);
		empCache.put(id, emp);
		return emp;
	}

});

As you see the definition of callable method, I am getting the object from service layer, then I am updating the cache before returning this employee object.

 

Find the below working application.

 

Employee.java

package com.sample.app.cache.model;

public class Employee {
	private Integer id;
	private String firstName;
	private String lastName;

	public Employee(Integer id, String firstName, String lastName) {
		super();
		this.id = id;
		this.firstName = firstName;
		this.lastName = lastName;
	}

	public Integer getId() {
		return id;
	}

	public void setId(Integer id) {
		this.id = id;
	}

	public String getFirstName() {
		return firstName;
	}

	public void setFirstName(String firstName) {
		this.firstName = firstName;
	}

	public String getLastName() {
		return lastName;
	}

	public void setLastName(String lastName) {
		this.lastName = lastName;
	}

	@Override
	public String toString() {
		return "Employee [id=" + id + ", firstName=" + firstName + ", lastName=" + lastName + "]";
	}

}

EmployeeService.java

package com.sample.app.cache.service;

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.TimeUnit;

import com.sample.app.cache.model.Employee;

public class EmployeeService {

	private static Map<Integer, Employee> data = new HashMap<>();

	static {
		data.put(1, new Employee(1, "Krishna", "Gurram"));
		data.put(2, new Employee(2, "Lahari", "G"));
		data.put(3, new Employee(3, "Gopi", "Battu"));
	}

	public static Employee getObject(Integer key) throws InterruptedException {
		System.out.println("Loading object with id " + key + " from database....");
		TimeUnit.SECONDS.sleep(2);
		return data.get(key);
	}
}

HelloWorld.java

package com.sample.app.cache;

import java.util.Arrays;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.TimeUnit;

import com.google.common.cache.Cache;
import com.google.common.cache.CacheBuilder;
import com.sample.app.cache.model.Employee;
import com.sample.app.cache.service.EmployeeService;

public class HelloWorld {
	private static void printEmployee(Employee emp, Integer id) {
		if (emp == null) {
			System.out.println("Employee not exist for the id " + id);
			return;
		}
		System.out.println(emp);
	}

	private static void getAndPrintObjects(Cache<Integer, Employee> empCache, List<Integer> empIds)
			throws ExecutionException {

		for (Integer id : empIds) {
			Employee emp = empCache.get(id, new Callable<Employee>() {

				@Override
				public Employee call() throws Exception {
					Employee emp = EmployeeService.getObject(id);
					empCache.put(id, emp);
					return emp;
				}

			});
			printEmployee(emp, id);
		}
	}

	public static void main(String args[]) throws InterruptedException, ExecutionException {

		Cache<Integer, Employee> empCache = CacheBuilder.newBuilder().maximumSize(500)
				.expireAfterWrite(10, TimeUnit.SECONDS).build();

		System.out.println("Getting employee with ids 1, 2 and 3 from empCache");
		getAndPrintObjects(empCache, Arrays.asList(1, 2, 3));

		System.out.println("\nGoing to sleep for 2 seconds\n");
		TimeUnit.SECONDS.sleep(2);
		System.out.println("Getting employee with ids 1, 2 and 3 from empCache");
		getAndPrintObjects(empCache, Arrays.asList(1, 2, 3));

		System.out.println("\nGoing to sleep for 2 seconds\n");
		TimeUnit.SECONDS.sleep(2);
		System.out.println("Getting employee with ids 1, 2 and 3 from empCache");
		getAndPrintObjects(empCache, Arrays.asList(1, 2, 3));

		System.out.println("\nGoing to sleep for 8 seconds, so cache will expire\n");
		TimeUnit.SECONDS.sleep(8);
		System.out.println("Getting employee with ids 1, 2 and 3 from empCache");
		getAndPrintObjects(empCache, Arrays.asList(1, 2, 3));

	}

}

Output

Getting employee with ids 1, 2 and 3 from empCache
Loading object with id 1 from database....
Employee [id=1, firstName=Krishna, lastName=Gurram]
Loading object with id 2 from database....
Employee [id=2, firstName=Lahari, lastName=G]
Loading object with id 3 from database....
Employee [id=3, firstName=Gopi, lastName=Battu]

Going to sleep for 2 seconds

Getting employee with ids 1, 2 and 3 from empCache
Employee [id=1, firstName=Krishna, lastName=Gurram]
Employee [id=2, firstName=Lahari, lastName=G]
Employee [id=3, firstName=Gopi, lastName=Battu]

Going to sleep for 2 seconds

Getting employee with ids 1, 2 and 3 from empCache
Employee [id=1, firstName=Krishna, lastName=Gurram]
Employee [id=2, firstName=Lahari, lastName=G]
Employee [id=3, firstName=Gopi, lastName=Battu]

Going to sleep for 8 seconds, so cache will expire

Getting employee with ids 1, 2 and 3 from empCache
Loading object with id 1 from database....
Employee [id=1, firstName=Krishna, lastName=Gurram]
Loading object with id 2 from database....
Employee [id=2, firstName=Lahari, lastName=G]
Loading object with id 3 from database....
Employee [id=3, firstName=Gopi, lastName=Battu]

 

  

Previous                                                    Next                                                    Home