Summary

Create a configurable 2-level cache.

##Requirements

• Cache should implement the following interface:

public interface Cache<K, T> {
 void put(K key, T value);
 T get(K key);
}

• Cache should have 2 levels: L1 - memory, L2 - file system.
• Cache should support different eviction policies.
• Cache size and eviction policy should be configurable.
• Code should be covered by unit tests using JUnit/TestNG + any mock library Mockito, EasyMock, etc.
• Project should be build via Maven, Gradle, Ant or similar tool.
• Cache should be thread safe.

Build

mvn clean test

Note: There are some tests slow tests for thread safety. They are all tagged with:

@Category(SlowTest.class)

For your convenience, I modified the number of iterations to 100 (instead of 1000). Anyway, to run only the fast tests use

mvn clean test -DexcludedGroups="ro.j.test.SlowTest"

Github

git@github.com:ojusti/cache.git

Design

The cache is MultiLevelCache. If correctly set up, it overflows to another cache (who could be another instance of MultiLevelCache...).

EvictionPolicy

A policy is not a simple comparator, it implements its own data structures (a double linked list for LRU, FIFO and LFU). Arguably, they are a little more complex to implement, but the design is more open.

Concurrency

Map insertions and policy's data structure updates in the Cache's put method are protected by a synchronized block. I think it is acceptable, given that this is a fairly simple solution which respects the requirements (thread-safety).

I used ConcurrentHashMap as the cache backend as this allows letting the get method not synchronized.

File backend

Disk store is an implementation of Cache. It delegates almost everything to its collaborators: it use a Function to calculate a filename from a key, a Marshaller to serialize and a Folder. I provided basic implementations for all of them.

Builders & Usage

'Complicated' objects are set up using builders. See examples in CacheBuilderTest.