Generic Caching Implementation.

What is the purpose of this article?

This article entails the generic implementation on how a caching should be implemented.

Pseudo-Code for Cache function.

The general idea to use cache should be made in a function and placed in a single place. Based on the input parameters, this function would either fetch the value from the cache or force refresh the cache and update the cache from the source.

If input parameter does not specify function to force refresh then we will fetch the value form cache. If the value against the cache key is found to be null, then it means the cache has expired, after which we will fetch the details from the source, set it against the case and return the value from the function.

Object cacheManager(String k1, String k2, Long k3, boolean forceRefresh) {
    1. Create the cache key, if the cache key is dynamic (created by combination of values k1, k2, k3),
    then pass the individual key as input parameter.
    
    2. Fetch the value from the cache using the cache key and store in a variable.
    Lets assume the variable as "cacheValue".
    
    3. If "cacheValue" is equals to null (meaning cache has expired) OR forceRefresh is set
    set to true, then
        
        3.1 Fetch the current value from the source (database, mongo, bigquery) 
            and save it against the variable "cacheValue".
        3.2 Set the current value against the same key in cache along with cache expiration time.
    
    4. return "cacheValue" variable.
}

Object cacheManager(forceRefresh) {
    // Prepare cache key.
    String cacheKey = Constants.CACHE_KEY_TEMP;
    
    // Fetch value from cache
    Object cacheValue = CacheClient.getValueByKey(cacheKey);
    
    // Condition for forceRefresh
    if (cacheValue == null || forceRefresh) {
        // Get value from source
        cacheValue = dao.getValueFromSource();
        // Update cache
        CacheClient.setValueByKey(cacheKey, cacheValue, Constants.CACHE_EXPIRY_TIME);
    }
    
    return cacheValue;
}

How Cache manager is supposed to be used.

To fetch the cached value.

When we wish to fetch the value from the cache, we will pass the call the function and pass the forceRefresh key as false. Doing so will fetch the value from the cache and return the value.

To update the cached value.

When we have updated any value in the source and wish to update the cache with the current value, call the function with forceRefresh as true. Doing so will fetch the current value from the source and cache will be updated.