Sometimes you want to avoid the caching of entries, when the values are null. You can achieve this by throwing an exception in the cache loading logic.
CacheLoader<Integer, Employee> cacheLoader = new CacheLoader<Integer, Employee>() {
@Override
public Employee load(Integer key) throws Exception {
Employee emp = EmployeeService.getObject(key);
if (emp == null) {
throw new RuntimeException("Object not found with key " + key);
}
return emp;
}
};
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(3, new Employee(3, "Bomma", "Srikanth"));
}
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.ExecutionException;
import java.util.concurrent.TimeUnit;
import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;
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) {
System.out.println(emp +"\n");
}
private static void getAndPrintObjects(LoadingCache<Integer, Employee> empCache, List<Integer> empIds)
throws ExecutionException {
for (Integer id : empIds) {
try {
Employee emp = empCache.get(id);
printEmployee(emp, id);
}catch(Exception e) {
System.out.println(e.getMessage() + "\n");
}
}
}
public static void main(String args[]) throws InterruptedException, ExecutionException {
CacheLoader<Integer, Employee> cacheLoader = new CacheLoader<Integer, Employee>() {
@Override
public Employee load(Integer key) throws Exception {
Employee emp = EmployeeService.getObject(key);
if (emp == null) {
throw new RuntimeException("Object not found with key " + key);
}
return emp;
}
};
LoadingCache<Integer, Employee> empCache = CacheBuilder.newBuilder().maximumSize(500)
.expireAfterWrite(10, TimeUnit.SECONDS).recordStats().build(cacheLoader);
System.out.println("Getting employee with ids 1, 2 and 3 from empCache\n");
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.... java.lang.RuntimeException: Object not found with key 2 Loading object with id 3 from database.... Employee [id=3, firstName=Bomma, lastName=Srikanth]
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