CacheBuilder using guava cache for query resultant - guava

Question

To reduce the DB hits to read the data from DB using the query, I am planning to keep resultant in the cache. To do this I am using guava caching.
studentController.java
public Map<String, Object> getSomeMethodName(Number departmentId, String departmentType){
ArrayList<Student> studentList = studentManager.getStudentListByDepartmentType(departmentId, departmentType);
----------
----------
}
StudentHibernateDao.java(criteria query )
#Override
public ArrayList<Student> getStudentListByDepartmentType(Number departmentId, String departmentType) {
Criteria criteria =sessionFactory.getCurrentSession().createCriteria(Student.class);
criteria.add(Restrictions.eq("departmentId", departmentId));
criteria.add(Restrictions.eq("departmentType", departmentType));
ArrayList<Student> studentList = (ArrayList)criteria.list();
return studentList;
}
To cache the criteria query resultant i started off with building CacheBuilder, like below.
private static LoadingCache<Number departmentId, String departmentType, ArrayList<Student>> studentListCache = CacheBuilder
.newBuilder().expireAfterAccess(1, TimeUnit.MINUTES)
.maximumSize(1000)
.build(new CacheLoader<Number departmentId, String departmentType, ArrayList<Student>>() {
public ArrayList<Student> load(String key) throws Exception {
return getStudentListByDepartmentType(departmentId, departmentType);
}
});
Here I dont know where to put CacheBuilder function and how to pass multiple key parameters(i.e departmentId and departmentType) to CacheLoader and call it.
Is this the correct way of caching using guava. Am I missing anything?

Answer 1

Guava's cache only accepts two type parameters, a key and a value type. If you want your key to be a compound key then you need to build a new compound type to encapsulate it. Effectively it would need to look like this (I apologize for my syntax, I don't use Java that often):
// Compound Key type
class CompoundDepartmentId {
public CompoundDepartmentId(Long departmentId, String departmentType) {
this.departmentId = departmentId;
this.departmentType = departmentType;
}
}
private static LoadingCache<CompoundDepartmentId, ArrayList<Student>> studentListCache =
CacheBuilder
.newBuilder().expireAfterAccess(1, TimeUnit.MINUTES)
.maximumSize(1000)
.build(new CacheLoader<CompoundDepartmentId, ArrayList<Student>>() {
public ArrayList<Student> load(CompoundDepartmentId key) throws Exception {
return getStudentListByDepartmentType(key.departmentId, key.departmentType);
}
});