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The kernel has a framework for exposing a management view of the various sub systems of the platform. The management view is a lose term for defining how we can access relevant information about the system and how we can apply management operations. JMX is the de facto standard for exposing a management view in the Java Platform but we take in consideration other kind of views such as REST web services. Therefore, the framework is not tied to JMX, yet it provides a JMX part to define more precisely details related to the JMX management view. The legacy framework is still in use but is deprecated in favor of the new framework as it is less tested and less efficient. It will be removed by sanitization in the future.
The managed frameworks defines an API for exposing a management view of objects. The API is targeted for internal use and is not a public API. The framework leverages Java 5 annotations to describe the management view from an object.
The @Managed annotates elements that wants to expose a management view to a management layer.
@Managed for objects
The framework will export a management view for the objects annotated.
@Managed for getter/setter
Defines a managed property. An annotated getter defines a read property, an annotated setter defines a write property and if matching getter/setter are annotated it defines a read/write property.
@Managed on method
Defines a managed operation.
The @ManagedDescription annotation provides a description of a managed element. It is valid to annotated object or methods. It takes as sole argument a string that is the description value.
The @ManagedName annotation provides an alternative name for managed properties. It is used to accomodate legacy methods of an object that can be renamed for compatibility reasons. It takes as sole argument a string that is the name value.
The @Property annotation is used to within other annotations such as @NameTemplate or @NamingContext. It should be seen as a structural way for a list of properties. A property is made of a key and a value. The value can either be a string litteral or it can be surrounded by curly brace to be a dynamic property. A dynamic property is resolved against the instance of the object at runtime.
The @NameTemplate defines a template that is used at registration time of a managed object to create the JMX object name. The template is formed of properties.
@NameTemplate({
@Property(key="container", value="workspace"),
@Property(key="name", value="{Name}")})The @NamingContext annotations defines a set of properties which are used within a management context. It allows to propagate properties down to managed objects which are defined by an object implementing the ManagementAware interface. The goal is to scope different instances of the same class that would have the same object name otherwise.
@NamingContext(@Property(key="workspace", value="{Name}"))The cache service delegates most of the work to the CacheServiceManaged class by using the @ManagedBy annotation. At runtime when a new cache is created, it calls the CacheServiceManaged class in order to let the CacheServiceManaged object register the cache.
@ManagedBy(CacheServiceManaged.class)
public class CacheServiceImpl implements CacheService {
CacheServiceManaged managed;
...
synchronized private ExoCache createCacheInstance(String region) throws Exception {
...
if (managed != null) {
managed.registerCache(simple);
}
...
}
}The ExoCache interface is annotated to define its management view. The @NameTemplate is used to produce object name values when ExoCache instance are registered.
@Managed
@NameTemplate({@Property(key="service", value="cache"), @Property(key="name", value="{Name}")})
@ManagedDescription("Exo Cache")
public interface ExoCache {
@Managed
@ManagedName("Name")
@ManagedDescription("The cache name")
public String getName();
@Managed
@ManagedName("Capacity")
@ManagedDescription("The maximum capacity")
public int getMaxSize();
@Managed
@ManagedDescription("Evict all entries of the cache")
public void clearCache() throws Exception;
...
}The CacheServiceManaged is the glue code between the CacheService and the management view. The main reason is that only exo services are registered automatically against the management view. Any other managed bean must be registered manually for now. Therefore, it needs to know about the management layer via the management context. The management context allows an object implementing the ManagementAware interface to receive a context to perform further registration of managed objects.
@Managed
public class CacheServiceManaged implements ManagementAware {
/** . */
private ManagementContext context;
/** . */
private CacheServiceImpl cacheService;
public CacheServiceManaged(CacheServiceImpl cacheService) {
this.cacheService = cacheService;
//
cacheService.managed = this;
}
public void setContext(ManagementContext context) {
this.context = context;
}
void registerCache(ExoCache cache) {
if (context != null) {
context.register(cache);
}
}
}