Jersey #Context scope - dependency-injection

Question

I have a hard time understanding the injection mechanism of Jersey. The JAX-RS Specification (http://jsr311.java.net/nonav/releases/1.1/spec/spec3.html#x3-520005) states that injection via #Context is possible in Application subclasses, root resource classes and providers.
I now have a class that is instantiated at startup and has a method which is called on every request. Inside the method I need access to the current UriInfo object. The problem is, that this method is not called from my code. So I can't pass UriInfo directly to the method.
I actually want to do something like this:
public class MyClass implements ThirdPartyInterface {
// not possible because class is no Application subclass, root resource class or provider
#Context
private UriInfo uriInfo;
public void methodCallebByThirdPartyCode() {
Uri requestUri = uriInfo.getRequestUri();
// do something
}
}
I tried this. Obviously with no success:
public class MyClass implements ThirdPartyInterface {
private UriInfo uriInfo;
public MyClass(UriInfo uriInfo) {
this.uriInfo = uriInfo;
}
public void methodCallebByThirdPartyCode() {
Uri requestUri = uriInfo.getRequestUri();
// do something
}
}
#Provider
#Produces(MediaType.WILDCARD)
public class MyBodyWriter implements MessageBodyWriter<MyView> {
#Context
private UriInfo uriInfo;
private MyClass myClass;
private ThirdPartyClass thirdPartyClass;
public MyBodyWriter() {
// uriInfo is null at this time :(
myClass = new MyClass(uriInfo);
thirdPartyClass = new ThirdPartyClass();
thirdPartyClass.register(myClass);
}
public void writeTo(final MyView view, final Class<?> type, /* and so on */) throws IOException, WebApplicationException {
// execute() calls MyClass#methodCallebByThirdPartyCode()
thirdPartyClass.execute();
}
}
The only workaround I can think of is this. I don't think it's very clean:
public class MyClass implements ThirdPartyInterface {
private UriInfo uriInfo;
public void setUriInfo(final UriInfo uriInfo) {
this.uriInfo = uriInfo;
}
public void methodCallebByThirdPartyCode() {
Uri requestUri = uriInfo.getRequestUri();
// do something
}
}
#Provider
#Produces(MediaType.WILDCARD)
public class MyBodyWriter implements MessageBodyWriter<MyView> {
#Context
private UriInfo uriInfo;
private MyClass myClass;
private ThirdPartyClass thirdPartyClass;
public MyBodyWriter() {
myClass = new MyClass();
thirdPartyClass = new ThirdPartyClass();
thirdPartyClass.register(myClass);
}
public void writeTo(final MyView view, final Class<?> type, /* and so on */) throws IOException, WebApplicationException {
myClass.setUriInfo(uriInfo);
// execute() calls MyClass#methodCallebByThirdPartyCode()
thirdPartyClass.execute();
myClass.setUriInfo(null);
}
}
I hope there is a better solution, but maybe I'm completely on the wrong track.
Thanks!

Answer 1

Late answer, but a good question ... so lets go:
You can use a org.glassfish.hk2.api.Factory and javax.inject.Provider for injections. I don't know since which version this is available, so maybe you have to upgrade your jersery version. For the following samples i used jersey 2.12.
First you have to implement and register/bind a Factory for your MyClass:
MyClassFactory:
import javax.inject.Inject;
import javax.ws.rs.core.UriInfo;
import org.glassfish.hk2.api.Factory;
// ...
public class MyClassFactory implements Factory<MyClass> {
private final UriInfo uriInfo;
// we will bind MyClassFactory per lookup later, so
// the constructor will be called everytime we need the factory
// meaning, uriInfo is also per lookup
#Inject
public MyClassFactory(final UriInfo uriInfo) {
this.uriInfo = uriInfo;
}
#Override
public MyClass provide() {
return new MyClass(uriInfo)
}
#Override
public void dispose(UriInfo uriInfo) {
// ignore
}
}
Registration via ResourceConfig:
import org.glassfish.hk2.api.PerLookup;
import org.glassfish.hk2.utilities.binding.AbstractBinder;
import org.glassfish.jersey.server.ResourceConfig;
// ...
public class MyResourceConfig extends ResourceConfig {
public MyResourceConfig() {
register(new AbstractBinder() {
#Override
protected void configure() {
bindFactory(MyClassFactory.class).to(MyClass.class).in(PerLookup.class);
// ... bind additional factories here
}
});
// ...
}
}
Now you are able to inject MyClass per lookup to providers, resources etc.
But Attention: Afaig there are two approaches and only one will work as eventually aspected for providers ...
import javax.inject.Inject;
import javax.ws.rs.Produces;
import javax.ws.rs.ext.MessageBodyWriter;
import javax.ws.rs.ext.Provider;
// ...
#Provider
#Produces("application/foo-bar")
public class MyBodyWriter implements MessageBodyWriter<MyView> {
// first approache - don't do it!
// will only injected once, cause MyBodyWriter is only instantiated once
#Inject
private MyClass myClass;
// second approache - works fine!
private final javax.inject.Provider<MyClass> provider;
// MyBodyWriter instantiate once
// get an inject provider here
#Inject
public MyBodyWriter(javax.inject.Provider<MyClass> myClassProvider) {
this.provider = myClassProvider;
}
#Override
public boolean isWriteable(Class<?> t, Type g, Annotation[] a, MediaType m) {
return t == MyView.class;
}
#Override
public long getSize(MyView t, Class<?> c, Type g, Annotation[] a, MediaType m) {
// deprecated by JAX-RS 2.0 and ignored by Jersey runtime
return 0;
}
#Override
public void writeTo(MyView v, Class<?> c, Type t, Annotation[] a, MediaType m, MultivaluedMap<String, Object> s, OutputStream o) throws IOException, WebApplicationException {
// attention: its not per lookup !!!
MyClass myClassDirectInjected = myClass;
System.out.println(myClassDirectInjected); // same instance everytime
// but this is ;)
MyClass myClassFromProvider = provider.get();
System.out.println(myClassFromProvider); // it's a new instance everytime
// ...
}
}
Hope this was somehow helpfull.