Programmatic lookup of contextual instances

We may encounter some situations where it's not convenient to obtain a contextual instance through injection, which are as follows:

For these situations we obtain an instance of Instance parameterized to the bean type we require:

@Inject
Instance<BookSearch> bookSearch;

To retrieve a contextual instance:

BookSearch search = bookSearch.get();

We can also alter the bean types that will be retrieved from Instance by adding qualifiers either to the injection point or passing them to select().

Specifying qualifiers at the injection is simple:

@Inject
@Book(Category.NONFICTION)
Instance<BookSearch> bookSearch;

But sometimes it's necessary for the qualifiers to be specified dynamically. For us to use dynamic qualifiers we need to suppress the @Default qualifier by specifying @Any on the injection point:

@Inject
@Any
Instance<BookSearch> bookSearch;

Now, we need to create an instance of our annotation @Book so it can be passed to select(). However, as it's just an interface we aren't able to create one with new, we need an implementation of that interface. CDI helps us out by providing AnnotationLiteral, a helper class for creating annotation implementations. Our annotation implementation is:

public class BookLiteral extends
AnnotationLiteral<Book> implements Book {
  private final Category category;
  private final String description;

  public BookLiteral(Category category, String description) {
    this.category = category;
    this.description = description;
  }

  public Category value() {
    return category;
  }

  public String description() {
    return description;
  }
}

So retrieving a bean from Instance with a dynamic qualifier is:

Annotation qualifier = fiction ? new BookLiteral(Category.FICTION,
"") : new BookLiteral(Category.NONFICTION, "Non Fiction");
BookSearch search = bookSearch.select(qualifier).get();

If we had separate qualifiers for fiction and nonfiction books, such as @NonFiction and @Fiction, instead of @Book with a Category, we could use dynamic qualifiers without extending AnnotationLiteral by creating anonymous classes:

bookSearch.select(new AnnotationLiteral<NonFiction>() {}).get();