Package de.umass.lastfm.cache

Class Cache

java.lang.Object
de.umass.lastfm.cache.Cache
Direct Known Subclasses:
DatabaseCache, FileSystemCache, MemoryCache
public abstract class Cache extends Object
The Cache handles storing and loading to a permanent storage for last.fm api requests. This could be a file system or a sql database.
Author:
Janni Kovacs
See Also:

  • Constructor Details

    • Cache

      protected Cache()

  • Method Details

    • getExpirationPolicy

      public ExpirationPolicy getExpirationPolicy()
      Returns the active ExpirationPolicy
      Returns:
      the ExpirationPolicy

    • setExpirationPolicy

      public void setExpirationPolicy(ExpirationPolicy expirationPolicy)
      Sets the active ExpirationPolicy.
      Parameters:
      expirationPolicy - An ExpirationPolicy, not null

    • contains

      public abstract boolean contains(String cacheEntryName)
      Checks if the cache contains an entry with the given name.
      Parameters:
      cacheEntryName - An entry name
      Returns:
      true if the cache contains this entry

    • load

      public abstract InputStream load(String cacheEntryName)
      Loads the specified entry from the cache and returns an InputStream to be read from. Returns null if the cache does not contain the specified cacheEntryName.
      Parameters:
      cacheEntryName - An entry name
      Returns:
      an InputStream or null

    • remove

      public abstract void remove(String cacheEntryName)
      Removes the specified entry from the cache if available. Does nothing if no such entry is available.
      Parameters:
      cacheEntryName - An entry name

    • store

      public abstract void store(String cacheEntryName, InputStream inputStream, long expirationDate)
      Stores a request in the cache.
      Parameters:
      cacheEntryName - The entry name to be stored to
      inputStream - An InputStream containing the data to be cached
      expirationDate - The date of expiration represented in milliseconds since 1.1.1970

    • isExpired

      public abstract boolean isExpired(String cacheEntryName)
      Checks if the specified entry is expired.
      Parameters:
      cacheEntryName - An entry name
      Returns:
      true if the entry is expired

    • clear

      public abstract void clear()
      Clears the cache by effectively removing all cached data.

    • createCacheEntryName

      public static String createCacheEntryName(String method, Map<String,String> params)
      Creates a unique entry name string for a request. It consists of the method name and all the parameter names and values concatenated in alphabetical order. It is used to identify cache entries in the backend storage. If hashCacheEntryNames is set to true this method will return a MD5 hash of the generated name.
      Parameters:
      method - The request method
      params - The request parameters
      Returns:
      a cache entry name

    • setHashCacheEntryNames

      public static void setHashCacheEntryNames(boolean hashCacheEntryNames)
      If hashCacheEntryNames is set to true the createCacheEntryName(java.lang.String, java.util.Map<java.lang.String, java.lang.String>) method will return a hash of the original entry name instead of the name itself.
      Parameters:
      hashCacheEntryNames - true to generate hashes