Using @Context, @Provider and ContextResolver in JAX-RS
- by Tamás
I'm just getting acquainted with implementing REST web services in Java using JAX-RS and I ran into the following problem. One of my resource classes requires access to a storage backend, which is abstracted away behind a StorageEngine interface. I would like to inject the current StorageEngine instance into the resource class serving the REST requests and I thought a nice way of doing this would be by using the @Context annotation and an appropriate ContextResolver class. This is what I have so far:
In MyResource.java:
class MyResource {
@Context StorageEngine storage;
[...]
}
In StorageEngineProvider.java:
@Provider
class StorageEngineProvider implements ContextResolver<StorageEngine> {
private StorageEngine storage = new InMemoryStorageEngine();
public StorageEngine getContext(Class<?> type) {
if (type.equals(StorageEngine.class))
return storage;
return null;
}
}
I'm using com.sun.jersey.api.core.PackagesResourceConfig to discover the providers and the resource classes automatically, and according to the logs, it picks up the StorageEngineProvider class nicely (timestamps and unnecessary stuff left out intentionally):
INFO: Root resource classes found:
class MyResource
INFO: Provider classes found:
class StorageEngineProvider
However, the value of storage in my resource class is always null - neither the constructor of StorageEngineProvider nor its getContext method is called by Jersey, ever. What am I doing wrong here?
