Caching

Caching is disabled by default.

A basic cache is provided for simple usages. Any other cache can be plugged in by implementing the MessageFormatLoadingCacheProvider interface, see Guava Cache example.

Be aware of thread-safety when using caching.

Why use a cache?

MessageFormats can be costly to instantiate. When performance matters, if the same message is going to be formatted over and over it is better to only instantiate it once.

Avoid

class Example {

  {
    for (int i = 0; i < 5; i++) {
      System.out.println(
          new MessageFormat("Welcome {username}!").format(ImmutableMap.of("username", "Bob")));
    }
  }
}

Prefer

Instantiate the MessageFormat outside of the loop and keep re-using it.

class Example {

  {
    MessageFormat messageFormat = new MessageFormat("Welcome {username}!");
    for (int i = 0; i < 5; i++) {
      System.out.println(messageFormat.format(ImmutableMap.of("username", "Bob")));
    }
  }
}

Multiple messages / different scopes

Maintaining instances for multiple messages and scope can become tedious. L10nMessages will solve this with cache enabled.

class Example {

  {
    ConcurrentHashMap<String, MessageFormat> messagesConcurrentHashMap = new ConcurrentHashMap<>();
    messagesConcurrentHashMap.put("welcome_user", new MessageFormat("Welcome {username}!"));
    messagesConcurrentHashMap.put("bye_user", new MessageFormat("Bye {username}!"));

    scope1:
    {
      for (int i = 0; i < 5; i++) {
        System.out.println(
            messagesConcurrentHashMap.get("welcome_user")
                .format(ImmutableMap.of("username", "Bob")));
      }
    }

    scope2:
    {
      for (int i = 0; i < 5; i++) {
        System.out.println(
            messagesConcurrentHashMap.get("welcome_user")
                .format(ImmutableMap.of("username", "Bob")));
        System.out.println(
            messagesConcurrentHashMap.get("bye_user").format(ImmutableMap.of("username", "Bob")));
      }
    }
  }
}

Similarly with disabled cache

Following code will re-create the MessageFormat in each iteration

class Example {

  {
    L10nMessages<Messages> m = L10nMessages.builder(Messages.class).build();

    for (int i = 0; i < 5; i++) {
      System.out.println(m.format(welcome_user, "username", "Bob"));
    }
  }
}

With cache enabled

The MessageFormats will be instantiated only once, and accessing them is transparent.

class Example {

  {
    L10nMessages<Messages> m =
        L10nMessages.builder(Messages.class)
            .messageFormatLoadingCacheProvider(CONCURRENT_HASH_MAP)
            .build();

    scope1:
    {
      for (int i = 0; i < 5; i++) {
        System.out.println(m.format(welcome_user, "username", "Bob"));
      }
    }

    scope2:
    {
      for (int i = 0; i < 5; i++) {
        System.out.println(m.format(welcome_user, "username", "Bob"));
        System.out.println(m.format(bye_user, "username", "Bob"));
      }
    }
  }
}

Basic Cache

A basic cache based on a ConcurrentHashMap is available.

class Example {

  {
    L10nMessages<Messages> m =
        L10nMessages.builder(Messages.class)
            .messageFormatLoadingCacheProvider(CONCURRENT_HASH_MAP)
            .build();
  }
}

Guava Cache

This is an example how to implement the MessageFormatLoadingCacheProvider interface with a Guava Cache. For the cache configuration itself, check more information at Guava Caches Explained

class Example {

  {
    L10nMessages<Messages> m =
        L10nMessages.builder(Messages.class)
            .messageFormatLoadingCacheProvider(
                (locale, messageFormatProvider) ->
                    CacheBuilder.newBuilder()
                        .maximumSize(10000)
                        .build(
                            CacheLoader.from(
                                (String message) -> messageFormatProvider.get(message, locale)))
                        ::getUnchecked)
            .build();
  }
}

Thread Safety

When using a cache, it is important to understand the thread-safety of the underlying MessageFormat before sharing the L10nMessages instance between multiple threads.

Consider having 1 instance of L10nMessages per thread, or to have some sort of synchronization around the MessageFormat instance.

From the ICU4J documentation:

MessageFormats are not synchronized.

It is recommended to create separate format instances for each thread. If multiple threads access a format concurrently, it must be synchronized externally.