How Can I Create a Time-Based Expiring Map or Cache in Java Using Guava?

Java Time-Based Map/Cache with Expiring Keys

In the Java programming language, managing time-based entries in a map or cache is a common requirement. This article provides a solution using Google Collections (Guava) for automatic purging of expired entries.

Solution

Guava's MapMaker class can create a time-based map with adjustable expiration settings. The MapMaker API allows customization of various parameters, such as:

• Concurrency level
• Key and value types (strong/soft/weak)
• Maximum size
• Expiration time

Usage Example

The following code snippet demonstrates how to create a concurrent time-based map:

ConcurrentMap<Key, Graph> graphs = new MapMaker()
   .concurrencyLevel(4)
   .softKeys()
   .weakValues()
   .maximumSize(10000)
   .expiration(10, TimeUnit.MINUTES)
   .makeComputingMap(
       new Function<Key, Graph>() {
         public Graph apply(Key key) {
           return createExpensiveGraph(key);
         }
       });

In this example, the map automatically purges expired entries every 10 minutes.

Update

In Guava 10.0 and later, the MapMaker methods have been deprecated in favor of the CacheBuilder:

LoadingCache<Key, Graph> graphs = CacheBuilder.newBuilder()
    .maximumSize(10000)
    .expireAfterWrite(10, TimeUnit.MINUTES)
    .build(
        new CacheLoader<Key, Graph>() {
          public Graph load(Key key) throws AnyException {
            return createExpensiveGraph(key);
          }
        });

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