Injecting generics with Guice
- by paradigmatic
I am trying to migrate a small project, replacing some factories with Guice (it is my first Guice trial). However, I am stuck when trying to inject generics. I managed to extract a small toy example with two classes and a module:
import com.google.inject.Inject;
public class Console<T> {
private final StringOutput<T> out;
@Inject
public Console(StringOutput<T> out) {
this.out = out;
}
public void print(T t) {
System.out.println(out.converter(t));
}
}
public class StringOutput<T> {
public String converter(T t) {
return t.toString();
}
}
import com.google.inject.AbstractModule;
import com.google.inject.Guice;
import com.google.inject.Injector;
import com.google.inject.TypeLiteral;
public class MyModule extends AbstractModule {
@Override
protected void configure() {
bind(StringOutput.class);
bind(Console.class);
}
public static void main(String[] args) {
Injector injector = Guice.createInjector( new MyModule() );
StringOutput<Integer> out = injector.getInstance(StringOutput.class);
System.out.println( out.converter(12) );
Console<Double> cons = injector.getInstance(Console.class);
cons.print(123.0);
}
}
When I run this example, all I got is:
Exception in thread "main" com.google.inject.CreationException: Guice creation errors:
1) playground.StringOutput<T> cannot be used as a key; It is not fully specified.
at playground.MyModule.configure(MyModule.java:15)
1 error
at com.google.inject.internal.Errors.throwCreationExceptionIfErrorsExist(Errors.java:354)
at com.google.inject.InjectorBuilder.initializeStatically(InjectorBuilder.java:152)
at com.google.inject.InjectorBuilder.build(InjectorBuilder.java:105)
at com.google.inject.Guice.createInjector(Guice.java:92)
I tried looking for the error message, but without finding any useful hints. Further on the Guice FAQ I stumble upon a question about how to inject generics. I tried to add the following binding in the configure method:
bind(new TypeLiteral<StringOutput<Double>>() {}).toInstance(new StringOutput<Double>());
But without success (same error message).
Can someone explain me the error message and provide me some tips ? Thanks.
