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Chapter 2. Cache Managers
The main entry point to Data Grid is the CacheManager interface that lets you:
- Configure and obtain caches.
- Manage and monitor clustered Data Grid nodes.
- Execute code across your cluster.
If you embed Data Grid in your application, then you use an EmbeddedCacheManager. If you run Data Grid as a remote server, then you use a RemoteCacheManager.
Cache Managers are heavyweight objects so you should instantiate only one CacheManager instance per JVM in most cases.
EmbeddedCacheManager manager = new DefaultCacheManager(); 1- 1
- Starts a local, non-clustered, Cache Manager with no caches.
Cache Managers have lifecycles and the default constructors also call the start() method. Overloaded versions of the constructors are available, but they do not start the CacheManager. However, you must always start the CacheManager before you can create caches.
Likewise, you must call stop() when you no longer require a running CacheManager so that it releases resources. This also ensures that the Cache Manager safely stops any caches that it controls.
2.1. Obtaining caches
After you configure the CacheManager, you can obtain and control caches.
Invoke the getCache(String) method to obtain caches, as follows:
Cache<String, String> myCache = manager.getCache("myCache");
The preceding operation creates a cache named myCache, if it does not already exist, and returns it.
Using the getCache() method creates the cache only on the node where you invoke the method. In other words, it performs a local operation that must be invoked on each node across the cluster. Typically, applications deployed across multiple nodes obtain caches during initialization to ensure that caches are symmetric and exist on each node.
Invoke the createCache() method to create caches dynamically across the entire cluster, as follows:
Cache<String, String> myCache = manager.administration().createCache("myCache", "myTemplate");The preceding operation also automatically creates caches on any nodes that subsequently join the cluster.
Caches that you create with the createCache() method are ephemeral by default. If the entire cluster shuts down, the cache is not automatically created again when it restarts.
Use the PERMANENT flag to ensure that caches can survive restarts, as follows:
Cache<String, String> myCache = manager.administration().withFlags(AdminFlag.PERMANENT).createCache("myCache", "myTemplate");For the PERMANENT flag to take effect, you must enable global state and set a configuration storage provider.
For more information about configuration storage providers, see GlobalStateConfigurationBuilder#configurationStorage().
2.2. Clustering Information
The EmbeddedCacheManager has quite a few methods to provide information as to how the cluster is operating. The following methods only really make sense when being used in a clustered environment (that is when a Transport is configured).
2.3. Member Information
When you are using a cluster it is very important to be able to find information about membership in the cluster including who is the owner of the cluster.
The getMembers() method returns all of the nodes in the current cluster.
The getCoordinator() method will tell you which one of the members is the coordinator of the cluster. For most intents you shouldn’t need to care who the coordinator is. You can use isCoordinator() method directly to see if the local node is the coordinator as well.
