Instantiating class with dependency injection

Asked

Viewed 205 times

0

I have a method that calls other methods that are not predefined, I am using this library org.reflections and the method java.lang.reflect.Method#invoke to perform another method generically, that method(invoke) receives the first parameter with the instance of the class of the method I am going to execute and the other parameters are the args of the methods that will be executed, like this:

metodo.invoke(new InstanciaDaClasse(), args...);

The problem is, I’m running this invoke and passing as first parameter a new instance of a class that has an injected property, it has this:

@Inject
UsuarioController usuarioController;

The problem is that the q method I am running needs this usuarioController, but creating a new class instance with this @Inject this property is null, has some way to create a new instance of a class without losing the injections of dependencies in Runtime or make an injection of dependency "artificial"?

java dependency-injection

  • Why not pass the injected instance of the class you need to invoke?

  • @nullptr because I don’t know which class I’m going to instantiate, and I don’t know how to inject a class that I don’t know what it is, I’m making a generic method that executes other class methods that may have dependency injection

  • I’m not sure I understand the question, but according to what I understand why you need to pass the class of the method you are going to execute and its parameters? What is the reason for this?

  • @Gustavo the reason is that I need to run a generic method, so I found a way that’s the way I said it there in the question, what I explained in the question is how to run a method generically, and that’s right, it works, the problem is when this method is of a class that injects another class, because I need an instance of the class to be able to execute the method, understood?

  • What you can have is a map with all its classes injected, and in this your method pass the type of class desired instead of the instance, and search for the instance of this map.

  • In your class new InstanciaDaClasse() can have a constructor that receives the injected class. AI vc passes as parameter new InstanciaDaClasse(new ClasseInjetada()). I don’t know what the logic of your program is and there’s little code to be specific about. Maybe an option is to use the annotation @Qualifier tbm. Hard to say

  • @nullptr and Gustavo look at my class: https://github.com/brunoeas/poc-websocket-java/blob/master/src/main/java/br/com/poc_websocket_java/configuration/WebSocketConfiguration.java on line 119, the method invokeEventMethod calls another method "generically", I managed to solve the problem by making a method that makes an "injection of artificial dependencies", but I am not proud of this method no, it seems wrong, if you want to opinion, the will

Show 2 more comments

1 answer

0

I managed to solve the problem but not in the best possible way, I believe, so I will not consider the problem as solved.

A intenção was to perform a method generically, for that I use the method java.lang.reflect.Method#invoke library org.reflections, this method takes 2 or more parameters, the first is an instance of the class of the method I am going to execute, the second and the next parameters are considered parameters of the method I am going to execute, example:

metodoQueVaiSerExecutado.invoke(new ClasseDoMetodoQueVaiSerExecutado(), ...args);

O problema is that some classes have injection of dependencies, and just instantiating the class in this way would make their dependencies null.

A "solução" I created a method that instances the class, dependencies and dependencies of dependencies, in short that’s it:

/**
 * Injeta as dependências da classe e de todas suas dependências e retorna
 * uma nova instância da classe
 * 
 * @param classe - Classe que vai ser manipulada
 * @return Uma nova instância da classe passada por parâmetro
 * @throws Exception - Exception genérica
 */
private Object injectDependenciesAndReturnNewInstance(final Class<?> classe) throws Exception {

    final Object classToReturn = classe.newInstance();

    for (final Field field : classe.getDeclaredFields()) {
        if (!field.isAnnotationPresent(Inject.class)) {
            continue;
        }
        field.setAccessible(true);

        field.set(classToReturn, this.injectDependenciesAndReturnNewInstance(field.getType()));
    }

    return classToReturn;
}

So the method invoke was like this:

metodo.invoke(this.injectDependenciesAndReturnNewInstance(classe), ...args);

For more details you can ask me, and if help has the link of this class I’m doing in my repository: https://github.com/brunoeas/poc-websocket-java/blob/master/src/main/java/br/com/poc_websocket_java/configuration/WebSocketConfiguration.java

If anyone has any different ideas that can solve the problem they can send

Browser other questions tagged java dependency-injection

You are not signed in. Login or sign up in order to post.