Dependency Injection: Diagnostic for dependency class with no @Inject and no-arg constructor

[KidoVin01]

Which Java classes are managed beans?

• It has an appropriate constructor - either:
  • the class has a constructor with no parameters, or
  • the class declares a constructor annotated @Inject.

Injection using the bean constructor

When the container instantiates a managed bean with a constructor annotated @Inject, the container calls this constructor, passing an injectable reference to each parameter.

Diagnostics

1. Identify @Inject field/method/constructor
2. Check if dependency class has a constructor declared
3. If constructor has no @Inject annotating, deliver two different diagnostics
   • at the class declaration: indicating no default no-arg constructor found
   • at the existing constructor: indicating constructor needs to be annotated with @Inject (implemented in [diagnostic] Declaring Managed Bean #108, however it is delivering an error rather than a warning.)

Note: The diagnostic should be a WARNING if there are alternative managed beans, else it should be an ERROR.

Quick Fix

• Suggest adding snippet code to declare no-arg constructor
• Suggest annotating @Inject for the existing constructor that takes in parameters (implemented in [diagnostic] Declaring Managed Bean #108, however it does not check if the parameters are injection points as per the specifications, which depend son WebServlet annotation type check is unsound #159)

Example

The following is a faulty code snippet example:

@ApplicationScoped
public class Greeting {
  
        // No explicit no-arg constructor        

	public Greeting (String name) {}	

	public String greet(String name) {
        return "GreetingA, " + name;
    }
}

@WebServlet(name = "diUnCon", urlPatterns = { "/diUnCon" })
public class GreetingServlet extends HttpServlet {

    private static final long serialVersionUID = 1L;
        
    @Inject
    private Greeting greeting;

    @Override
	protected void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {
        res.setContentType("text/html;charset=UTF-8");
		res.getWriter().println(greeting.greet("Bob"));
	}
}

Note: The existing constructor cannot be annotated with @Inject because the parameters must be injectable as well according to the spec

Related to #153

[kathrynkodama]

Example link doesn't seem to work for me. Is this item for both a snippet and diagnostics? For the snippet, this might overlap with capabilities the Java language server offers. ie. I can generate a non-arg constructor with ctl-space:

public ServletDiagnosticsCollector() {
        // TODO Auto-generated constructor stub
    }

[KidoVin01]

Example link doesn't seem to work for me

Updated the example link.

For the snippet, this might overlap with capabilities the Java language server offers. ie. I can generate a non-arg constructor with ctl-space

Would the Jakarta LP be able to suggest those implemented capabilities in the diagnostics?