guice: multiple implementations, different object graphs

Question

How do you do the following in guice?

There is class XmlSerializer that depends on an interface XmlFormatter. There are 2 implementations of XmlFormatter: CompactXmlFormatter and PrettyXmlFormatter.

Another class MyApplication depends on 2 instances of XmlSerializer. One instance should be configured with a CompactXmlFormatter and the other PrettyXmlFormatter

public class XmlSerializer {
    public XmlSerializer(XmlFormatter formatter) {
       ...
    }
}

public interface XmlFormatter {
    ...
}

public class CompactXmlFormatter implements XmlFormatter {
    ...
}

public class PrettyXmlFormatter implements XmlFormatter {
    ...
}

public class MyApplication {
    public MyApplication(XmlSerializer compactSerializer, XmlSerializer prettySerializer) {
        ...
    }
}

How do you construct such a graph?

I know that, once you have the 2 XmlSerializer instances, injecting them to MyApplication requires annotations in the parameters of the MyApplication constructor.

I am more interested in how do you bind XmlFormatter to both CompactXmlFormatter and PrettyXmlFormatter.

Answer 1

Use binding annotations to differentiate each XmlFormatter.

In your Module:

bind(XmlFormatter.class).aannotatedWith(Pretty.class)
    .to(PrettyXmlFormatter.class);
bind(XmlFormatter.class).aannotatedWith(Compact.class)
    .to(CompactXmlFormatter.class);

And:

@Inject public MyApplication(
    @Compact XmlSerializer compactSerializer, 
    @Pretty XmlSerializer prettySerializer) {
    ...

Of course you'll have to define @Pretty and @Compact annotations:

@BindingAnnotation 
@Target({ FIELD, PARAMETER, METHOD }) 
@Retention(RUNTIME) 
public @interface Pretty {}

@BindingAnnotation 
@Target({ FIELD, PARAMETER, METHOD }) 
@Retention(RUNTIME) 
public @interface Compact {}