I understand why we would want to have the database be queried if we have, say, a cache Miss/Mrs./Ms. or a cache-hard-down, but I would suggest a more Interface-oriented/Compositional approach, like the below which may end up being more testable and with a consistent interface for cients.
Created
July 2, 2015 23:45
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Java example for caching and composition
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| // Assume we had a series of adapters which had this simple interface | |
| public interface CacheReadingInterface{ | |
| public boolean writeValueToHash(String hashName, String hashKey, Object value); | |
| } | |
| // And assume you had a Redis cache that implemented it | |
| // Further assume RedisConnectionExcepion and RedisProtocolException… | |
| public class MyCacheClass implements CacheReadingInterface{ | |
| protected Jredis client; | |
| public MyCacheClass(Jredis _client){ | |
| client = _client; | |
| } | |
| protected boolean checkHashNameAndKey(String hashName, String hashKey) throws InvalidArgumentException{ | |
| String tmpName = hashName.trim(), | |
| tmpKey = hashKey.trim(); | |
| if(tmpName != hashName){ | |
| throw new InvalidArgumentException("Unexpected whitespace in hash name"); | |
| } | |
| else if(tmpName.length() == 0){ | |
| throw new InvalidArgumentException("Hash name is empty"); | |
| } | |
| if(tmpKey != hashKey){ | |
| throw new InvalidArgumentException("Unexpected whitespace in hash key"); | |
| } | |
| else if(tmpKey.length() == 0){ | |
| throw new InvalidArgumentException("Hash key is empty"); | |
| } | |
| return true; | |
| } | |
| public boolean writeValueToHash(String hashName, String hashKey, Object value) throws | |
| RedisConnectionExcepion, | |
| RedisProtocolException, | |
| InvalidArgumentException | |
| { | |
| checkHashNameAndKey(hashName,hashKey); | |
| String valueAsString = value.toString(); | |
| // Assume that calling the client here would throw one of the Redis exceptions | |
| return client.hset(hashName, hashKey, value.toString()); | |
| } | |
| public Object getValueFromHash(String hashName, String hashKey) throws | |
| RedisConnectionExcepion, | |
| RedisProtocolException, | |
| InvalidArgumentException { | |
| checkHashNameAndKey(hashName,hashKey); | |
| // Assume that calling the client here would throw one of the Redis exceptions | |
| return client.hget(hashName, hashKey); | |
| } | |
| } | |
| // And assume you had a DB touching adapter class that did roughly the same thing | |
| public class MyDBAccessClass implements CacheReadingInterface{ | |
| Connection db; | |
| PreparedStmt productToPlatformStmt; | |
| public MyDBAccessClass(Connection _db){ | |
| db = _db; | |
| productToPlatformStmt = db.prepare('SELECT * FROM … WHERE platform_id = ?'); | |
| } | |
| public Object getValueFromHash(String hashName, String hashKey) throws DBException, InvalidException, blah, blah, blah{ | |
| // And excuse my using a switch() - was the quickest way to show it off… | |
| switch(hashName){ | |
| case 'productToPlatform': | |
| return productToPlatformStmt.execute(hashKey).fetchOne(); | |
| default: | |
| throw new InvalidArgumentException("Unknown lookup type <" + hashName + ">"); | |
| } | |
| } | |
| } | |
| // Then we can create a Composite object that also implements the interface | |
| // that makes us not care where the data is coming from | |
| public class DataAcquirer implements CacheReadingInterface{ | |
| protected ArrayList<CacheReadingInterface> datasources; | |
| public function DataAcquirer(ArrayList<CacheReadingInterface> _datasources){ | |
| datasources = _datasources; | |
| } | |
| public Object getValueFromHash(String hashName, String hashKey) throws Exception { | |
| // Then we can loop through the datasources in order | |
| for(CacheReadingInterface source : datasources){ | |
| try{ | |
| // If they can return, they will… | |
| return source.getValueFromHash(hashName,hashKey); | |
| } | |
| catch(Exception e){ | |
| // Log me | |
| } | |
| } | |
| // And if we exhaust all sources, throw a specific exception to note this | |
| throw new DataNotFoundException("Exhausted datasources - no value found"); | |
| } | |
| } |
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| // This works, right? | |
| import *.*; | |
| Jredis redis = …; | |
| Connection connection = …; | |
| ArrayList<CacheReadingInterface> lookupClient = new ArrayList( | |
| new MyCacheClass(jredis), | |
| new MyDBAccessClass(connection) | |
| ); | |
| try{ | |
| Object value = lookupClient.getValueFromHash('productToPlatform','w'); | |
| } | |
| catch(Exception e){ | |
| // Ohs nos… | |
| } |
On line 13 of runtime.java, don't you need to get an item from the ArrayList first before calling getValueFromHash?
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Slick! I like this!