更改参数的Guice配置

Question

Lets say I have a class that verifies passwords according to a set of rules. How exactly this password is verified, depends on the person that calls the server. Each different kind of person has a different implementation for some rules. Lets say the LengthRule would requiere a length of 12 in a strict validation 8 in a normal validation and 5 in a lax validation.
What is the best way to change the binding of all rules according to the passed parameter , for example group wirings and switch them dynamically?

public void verifyPassword(String password, Person person) {
    if (isBusinessClient(person)) {
            // Apply strict wiring  
            PasswordChecker checker = new PasswordChecker();
            passwordChecker.check(password)
    } else if (wasBusinessClient(person)) {
            // Apply normal wiring 
            PasswordChecker checker = new PasswordChecker();
            passwordChecker.check(password)
    } else {
            // Apply lax wiring
            PasswordChecker checker = new PasswordChecker();
            passwordChecker.check(password)
    }
}

Answer 1

this is an answer based on MultiBindings in guice. General: You can bind multiple implementations to a given interface and then inject a set of implementations.

What I am going to do is to bind all my Password checkers, inject them and then use that set to determine what to do.

This is the complete running example:

public class TestMultiBinding {

    public static void main(String[] args) {

        Injector injector = Guice.createInjector( new AbstractModule() {

            @Override
            protected void configure() {
                Multibinder<PasswordChecker> multiBinder = Multibinder.newSetBinder(binder(), PasswordChecker.class);
                multiBinder.addBinding().to(BusinessChecker.class);
                multiBinder.addBinding().to(ClientChecker.class);

                bind(Test.class).in(Singleton.class);
            }
        });


        Test test = injector.getInstance(Test.class);
        test.verifyPassword("hello", Person.P1);
        test.verifyPassword("hello", Person.P2);
    }

    public static class Test {

        private Set<PasswordChecker> checkers;

        @Inject
        public Test(final Set<PasswordChecker> checker) {
            this.checkers = checker;
        }

        public void verifyPassword(final String pass, final Person p) {
            getPasswordChecker(p).check(pass);
        }

        public PasswordChecker getPasswordChecker(final Person p) {
            Optional<PasswordChecker> checker = checkers.stream().filter(c -> c.isApplicable(p)).findFirst();
            if(checker.isPresent()) {
                return checker.get();
            }
            return null; // or default
        }
    }


    public static interface PasswordChecker {
        public void check(String s);
        boolean isApplicable(Person P);
    }

    public static class BusinessChecker implements PasswordChecker {

        @Override
        public void check(String s) {
            System.out.println("User Business Checker");
        }

        @Override
        public boolean isApplicable(Person P) {
            return P.equals(Person.P1);
        }
    }

    public static class ClientChecker implements PasswordChecker {

        @Override
        public void check(String s) {
            System.out.println("User Client Checker");
        }

        @Override
        public boolean isApplicable(Person P) {
            return P.equals(Person.P2);
        }
    }

    public enum Person {
        P1, P2;
    }
}

The Test class is your example. It takes a password and a Person enum.

Each PasswordChecker implements a method called "isApplicable" to determine if the given Person can use this checker. Alternatively, at injection time, you could map the PasswordChecker to the correct person (using the stream.collect(Collectors.toMap(...)) methods). That way you would only have to do a hashmap lookup to get the correct implementation.

In my module, I define a multibinding for password checkers. I add my bindings to it.

The rest you can see.

Calling my code will print:

User Business Checker
User Client Checker

I hope this is what you were looking for :) let me know!

Artur