Develop Reference

How provide variants with Daggers in a multi-module project? [duplicate]

I have a BIG Android app that needs to run different code for depending on the OS version, the manufacturer, and many other things. This app however needs to be a single APK. It needs to be smart enough at runtime to determine which code to use. Until now we have been using Guice but performance issues are causing us to consider migrating to Dagger. However, I've been unable to determine if we can achieve the same use case.
The main goal is for us have some code that runs at startup to provide a list of compatible Modules. Then pass that this list to Dagger to wire everything up.
Here is some pseudocode of the current implementation in Guice we want to migrate
import com.google.inject.AbstractModule;
#Feature("Wifi")
public class WifiDefaultModule extends AbstractModule {
#Override
protected void configure() {
bind(WifiManager.class).to(WifiDefaultManager.class);
bind(WifiProcessor.class).to(WifiDefaultProcessor.class);
}
}
#Feature("Wifi")
#CompatibleWithMinOS(OS > 4.4)
class Wifi44Module extends WifiDefaultModule {
#Override
protected void configure() {
bind(WifiManager.class).to(Wifi44Manager.class);
bindProcessor();
}
#Override
protected void bindProcessor() {
(WifiProcessor.class).to(Wifi44Processor.class);
}
}
#Feature("Wifi")
#CompatibleWithMinOS(OS > 4.4)
#CompatibleWithManufacturer("samsung")
class WifiSamsung44Module extends Wifi44Module {
#Override
protected void bindProcessor() {
bind(WifiProcessor.class).to(SamsungWifiProcessor.class);
}
#Feature("NFC")
public class NfcDefaultModule extends AbstractModule {
#Override
protected void configure() {
bind(NfcManager.class).to(NfcDefaultManager.class);
}
}
#Feature("NFC")
#CompatibleWithMinOS(OS > 6.0)
class Nfc60Module extends NfcDefaultModule {
#Override
protected void configure() {
bind(NfcManager.class).to(Nfc60Manager.class);
}
}
public interface WifiManager {
//bunch of methods to implement
}
public interface WifiProcessor {
//bunch of methods to implement
}
public interface NfcManager {
//bunch of methods to implement
}
public class SuperModule extends AbstractModule {
private final List<Module> chosenModules = new ArrayList<Module>();
public void addModules(List<Module> features) {
chosenModules.addAll(features);
}
#Override
protected void configure() {
for (Module feature: chosenModules) {
feature.configure(binder())
}
}
}
so at startup the app does this:
SuperModule superModule = new SuperModule();
superModule.addModules(crazyBusinessLogic());
Injector injector = Guice.createInjector(Stage.PRODUCTION, superModule);
where crazyBusinessLogic() reads the annotations of all the modules and determines a single one to use for each feature based on device properties. For example:
a Samsung device with OS = 5.0 will have crazyBusinessLogic() return the list { new WifiSamsung44Module(), new NfcDefaultModule() }
a Samsung device with OS = 7.0 will have crazyBusinessLogic() return the list { new WifiSamsung44Module(), new Nfc60Module() }
a Nexus device with OS = 7.0 will have crazyBusinessLogic() return the list { new Wifi44Module(), new Nfc60Module() }
and so on....
Is there any way to do the same with Dagger? Dagger seems to require you to pass the list of modules in the Component annotation.
I read a blog that seems to work on a small demo, but it seems clunky and the extra if statement and extra interfaces for components might cause my code to balloon.
https://blog.davidmedenjak.com/android/2017/04/28/dagger-providing-different-implementations.html
Is there any way to just use a list of modules returned from a function like we are doing in Guice? If not, what would be the closest way that would minimize rewriting the annotations and the crazyBusinessLogic() method?

Dagger generates code at compile-time, so you are not going to have as much module flexibility as you did in Guice; instead of Guice being able to reflectively discover #Provides methods and run a reflective configure() method, Dagger is going to need to know how to create every implementation it may need at runtime, and it's going to need to know that at compile time. Consequently, there's no way to pass an arbitrary array of Modules and have Dagger correctly wire your graph; it defeats the compile-time checking and performance that Dagger was written to provide.
That said, you seem to be okay with a single APK containing all possible implementations, so the only matter is selecting between them at runtime. This is very possible in Dagger, and will probably fall into one of four solutions: David's component-dependencies-based solution, Module subclasses, stateful module instances, or #BindsInstance-based redirection.
Component dependencies
As in David's blog you linked, you can define an interface with a set of bindings that you need to pass in, and then supply those bindings through an implementation of that interface passed into the builder. Though the structure of the interface makes this well-designed to pass Dagger #Component implementations into other Dagger #Component implementations, the interface may be implemented by anything.
However, I'm not sure this solution suits you well: This structure is also best for inheriting freestanding implementations, rather than in your case where your various WifiManager implementations all have dependencies that your graph needs to satisfy. You might be drawn to this type of solution if you need to support a "plugin" architecture, or if your Dagger graph is so huge that a single graph shouldn't contain all of the classes in your app, but unless you have those constraints you may find this solution verbose and restrictive.
Module subclasses
Dagger allows for non-final modules, and allows for the passing of instances into modules, so you can simulate the approach you have by passing subclasses of your modules into the Builder of your Component. Because the ability to substitute/override implementations is frequently associated with testing, this is described on the Dagger 2 Testing page under the heading "Option 1: Override bindings by subclassing modules (don’t do this!)"—it clearly describes the caveats of this approach, notably that the virtual method call will be slower than a static #Provides method, and that any overridden #Provides methods will necessarily need to take all parameters that any implementation uses.
// Your base Module
#Module public class WifiModule {
#Provides WifiManager provideWifiManager(Dep1 dep1, Dep2 dep2) {
/* abstract would be better, but abstract methods usually power
* #Binds, #BindsOptionalOf, and other declarative methods, so
* Dagger doesn't allow abstract #Provides methods. */
throw new UnsupportedOperationException();
}
}
// Your Samsung Wifi module
#Module public class SamsungWifiModule {
#Override WifiManager provideWifiManager(Dep1 dep1, Dep2 dep2) {
return new SamsungWifiManager(dep1); // Dep2 unused
}
}
// Your Huawei Wifi module
#Module public class HuaweiWifiModule {
#Override WifiManager provideWifiManager(Dep1 dep1, Dep2 dep2) {
return new HuaweiWifiManager(dep1, dep2);
}
}
// To create your Component
YourAppComponent component = YourAppComponent.builder()
.baseWifiModule(new SamsungWifiModule()) // or name it anything
// via #Component.Builder
.build();
This works, as you can supply a single Module instance and treat it as an abstract factory pattern, but by calling new unnecessarily, you're not using Dagger to its full potential. Furthermore, the need to maintain a full list of all possible dependencies may make this more trouble than it's worth, especially given that you want all dependencies to ship in the same APK. (This might be a lighter-weight alternative if you need certain kinds of plugin architecture, or you want to avoid shipping an implementation entirely based on compile-time flags or conditions.)
Module instances
The ability to supply a possibly-virtual Module was really meant more for passing module instances with constructor arguments, which you could then use for choosing between implementations.
// Your NFC module
#Module public class NfcModule {
private final boolean useNfc60;
public NfcModule(boolean useNfc60) { this.useNfc60 = useNfc60; }
#Override NfcManager provideNfcManager() {
if (useNfc60) {
return new Nfc60Manager();
}
return new NfcDefaultManager();
}
}
// To create your Component
YourAppComponent component = YourAppComponent.builder()
.nfcModule(new NfcModule(true)) // again, customize with #Component.Builder
.build();
Again, this doesn't use Dagger to its fullest potential; you can do that by manually delegating to the right Provider you want.
// Your NFC module
#Module public class NfcModule {
private final boolean useNfc60;
public NfcModule(boolean useNfc60) { this.useNfc60 = useNfc60; }
#Override NfcManager provideNfcManager(
Provider<Nfc60Manager> nfc60Provider,
Provider<NfcDefaultManager> nfcDefaultProvider) {
if (useNfc60) {
return nfc60Provider.get();
}
return nfcDefaultProvider.get();
}
}
Better! Now you don't create any instances unless you need them, and Nfc60Manager and NfcDefaultManager can take arbitrary parameters that Dagger supplies. This leads to the fourth solution:
Inject the configuration
// Your NFC module
#Module public abstract class NfcModule {
#Provides static NfcManager provideNfcManager(
YourConfiguration yourConfiguration,
Provider<Nfc60Manager> nfc60Provider,
Provider<NfcDefaultManager> nfcDefaultProvider) {
if (yourConfiguration.useNfc60()) {
return nfc60Provider.get();
}
return nfcDefaultProvider.get();
}
}
// To create your Component
YourAppComponent component = YourAppComponent.builder()
// Use #Component.Builder and #BindsInstance to make this easy
.yourConfiguration(getConfigFromBusinessLogic())
.build();
This way you can encapsulate your business logic in your own configuration object, let Dagger provide your required methods, and go back to abstract modules with static #Provides for the best performance. Furthermore, you don't need to use Dagger #Module instances for your API, which hides implementation details and makes it easier to move away from Dagger later if your needs change. For your case, I recommend this solution; it'll take some restructuring, but I think you'll wind up with a clearer structure.
Side note about Guice Module#configure(Binder)
It's not idiomatic to call feature.configure(binder()); please use install(feature); instead. This allows Guice to better describe where errors occur in your code, discover #Provides methods in your Modules, and to de-duplicate your module instances in case a module is installed more than once.

Is there any way to just use a list of modules returned from a
function like we are doing in Guice? If not, what would be the closest
way that would minimize rewriting the annotations and the
crazyBusinessLogic() method?
Not sure this is the answer you're looking for, but just in case you do have other options and for other community members I will describe completely different approach.
I would say that the way you used Guice until now is an abuse of DI framework, and you will be much better off leveraging this opportunity to remove this abuse instead of implementing it in Dagger.
Let me explain.
The main goal of dependency injection architectural pattern is to have construction logic segregated from functional logic.
What you basically want to achieve is standard polymorphism - provide different implementations based on a set of parameters.
If you use Modules and Components for that purpose, you will end up structuring your DI code according to business rules governing the need for these polymorphic implementations.
Not only will this approach requires much more boilerplate, but it also prevents emergence of cohesive Modules that have meaningful structure and provide insights into application's design and architecture.
In addition, I doubt you will be able to unit test these business rules "encoded" inside dependency injection logic.
There are two approaches which are much better IMHO.
First approach is still not very clean, but, at least, it doesn't compromise the large scale structure of dependency injection code:
#Provides
WifiManager wifiManager(DeviceInfoProvider deviceInfoProvider) {
if (deviceInfoProvider.isPostKitKat() ) {
if (deviceInfoProvider.isSamsung()) {
return new WifiMinagerSamsungPostKitKat();
} else {
return new WifiMinagerPostKitKat();
}
} else {
return new WifiMinagerPreKitKat();
}
}
The logic that chooses between implementation still resides in DI code, but, at least, it did not make it into the large scale structure of that part.
But the best solution in this case is to make a proper object oriented design, instead of abusing DI framework.
I'm pretty sure that the source code of all these classes is very similar. They might even inherit from one another while overriding just one single method.
In this case, the right approach is not duplication/inheritance, but composition using Strategy design pattern.
You would extract the "strategy" part into a standalone hierarchy of classes, and define a factory class that constructs them based on system's parameters. Then, you could do it like this:
#Provides
WiFiStrategyFactory wiFiStrategyFactory(DeviceInfoProvider deviceInfoProvider) {
return new WiFiStrategyFactory(deviceInfoProvider);
}
#Provides
WifiManager wifiManager(WiFiStrategyFactory wiFiStrategyFactory) {
return new WifiMinager(WiFiStrategyFactory.newWiFiStrategy());
}
Now construction logic is simple and clear. The differentiation between strategies encapsulated inside WiFiStrategyFactory and can be unit tested.
The best part of this proper approach is that when a new strategy will need to be implemented (because we all know that Android fragmentation is unpredictable), you won't need to implement new Modules and Components, or make any changes to DI structure. This new requirement will be handled by just providing yet another implementation of the strategy and adding the instantiation logic to the factory.
All that while being kept safe with unit tests.

Conditionally instantiating classes that use #Inject

I'm trying to understand how to handle conditionally creating new instances of a class that uses #Inject. In the below example I have a factory that instantiates classes based on a parameter.
AnimalFactory does not have access to the injector the main class of my application has, so I can't use injector.getInstance(Cat.class)
class AnimalFactory {
public IAnimal create(AnimalType type) {
if (type.equals(AnimalType.CAT)) {
return new Cat(); // Cat uses #Inject, so this won't work of course. But ???
} else if (type.equals(AnimalType.DOG)) {
return new Dog();
}
}
}
In the rest of my app, classes are injected into my constructors because I always need them. Guice creates an instance/singleton for each. But in this scenario, I do not want to create and inject instances for each animal because all but one are needed.

You can use a MapBinder as described here:
public class AnimalModule extends AbstractModule {
public void configure() {
MapBinder<AnimalType, IAnimal> animalBinder= MapBinder.newMapBinder(binder(), AnimalType.class, IAnimal.class);
animalBinder.addBinding(AnimalType.DOG).to(Dog.class);
...
}
}
And than use it in your factory:
class AnimalFactory {
#Inject
Map<AnimalType, IAnimal> animals;
public IAnimal create(AnimalType type) {
return animals.get(type);
}
}

Actually I worked on exactly the same issue and I wrote a feature that allows you to create self-populating factory. Meaning that if you work in Spring/Spring-boot environment you can create a factory that can access and provide any interface implementing class that is managed by Spring-boot without injecting in the factory. You can also give the instances custom names. So, it seems like it fits your case exactly. Here is a link to an article that describes the feature in great detail: Non-intrusive access to "Orphaned" Beans in Spring framework. Also, in MgntUtils library Javadoc there is a good description of the feature here enter link description here. The library itself including source code could be found on Github here and in the package com.mgnt.lifecycle.management.example there is a working example. Maven artifacts are here

How to auto install all implementations of an interface with guice?

I have the following interface:
public interface IFilterFactory<T extends IFilter> {
T create(IFilterConfig config);
}
And multiple implementations of it:
public class AndFilter implements IFilter {
public interface IAndFilterFactory extends IFilterFactory<AndFilter> {}
// ...
}
public class OrFilter implements IFilter {
public interface IOrFilterFactory extends IFilterFactory<OrFilter> {}
// ...
}
in my Guice module, I'm currently installing each module I add this way:
install(new FactoryModuleBuilder().build(IAndFilterFactory.class));
install(new FactoryModuleBuilder().build(IOrFilterFactory.class));
The And and Or filters are just examples but I have many more, some of them requiring specific objects to be injected, thus the factories.
Is there a way with Guice to just say "install all implementations of IFilterFactory" without having to use reflection myself ?

There's nothing for classpath scanning built-in, and despite a lot of existing library options, there's reason to believe that a perfect solution simply can't exist for Java. In any case, enumerating all available classes is known to be slow even in heavily-used libraries, and such a solution would scale with the number of classes in your application, not the number of filters you use.
(To be clear, you're not quite even asking to "install all implementations of IFilterFactory", you're asking "create and install a module with FactoryModuleBuilder for all implementations of IFilterFactory". The factory interface implementation doesn't exist until you generate it with FactoryModuleBuilder.)
You can, however, extract everything aside from the class name itself, so you only have one easy-to-maintain list of classes to bind:
List<Class<?>> filterFactories = ImmutableList.<Class<?>>of(
IAndFilterFactory.class,
IOrFilterFactory.class,
IXorFilterFactory.class,
HelpIAmTrappedInAFilterFactory.class
);
for (Class<?> clazz : filterFactories) {
install(new FactoryModuleBuilder().build(clazz));
}

Storing all classes that use an interface with reflection? [duplicate]

Can I do it with reflection or something like that?

I have been searching for a while and there seems to be different approaches, here is a summary:
reflections library is pretty popular if u don't mind adding the dependency. It would look like this:
Reflections reflections = new Reflections("firstdeveloper.examples.reflections");
Set<Class<? extends Pet>> classes = reflections.getSubTypesOf(Pet.class);
ServiceLoader (as per erickson answer) and it would look like this:
ServiceLoader<Pet> loader = ServiceLoader.load(Pet.class);
for (Pet implClass : loader) {
System.out.println(implClass.getClass().getSimpleName()); // prints Dog, Cat
}
Note that for this to work you need to define Petas a ServiceProviderInterface (SPI) and declare its implementations. you do that by creating a file in resources/META-INF/services with the name examples.reflections.Pet and declare all implementations of Pet in it
examples.reflections.Dog
examples.reflections.Cat
package-level annotation. here is an example:
Package[] packages = Package.getPackages();
for (Package p : packages) {
MyPackageAnnotation annotation = p.getAnnotation(MyPackageAnnotation.class);
if (annotation != null) {
Class<?>[] implementations = annotation.implementationsOfPet();
for (Class<?> impl : implementations) {
System.out.println(impl.getSimpleName());
}
}
}
and the annotation definition:
#Retention(RetentionPolicy.RUNTIME)
#Target(ElementType.PACKAGE)
public #interface MyPackageAnnotation {
Class<?>[] implementationsOfPet() default {};
}
and you must declare the package-level annotation in a file named package-info.java inside that package. here are sample contents:
#MyPackageAnnotation(implementationsOfPet = {Dog.class, Cat.class})
package examples.reflections;
Note that only packages that are known to the ClassLoader at that time will be loaded by a call to Package.getPackages().
In addition, there are other approaches based on URLClassLoader that will always be limited to classes that have been already loaded, Unless you do a directory-based search.

What erickson said, but if you still want to do it then take a look at Reflections. From their page:
Using Reflections you can query your metadata for:
get all subtypes of some type
get all types annotated with some annotation
get all types annotated with some annotation, including annotation parameters matching
get all methods annotated with some

In general, it's expensive to do this. To use reflection, the class has to be loaded. If you want to load every class available on the classpath, that will take time and memory, and isn't recommended.
If you want to avoid this, you'd need to implement your own class file parser that operated more efficiently, instead of reflection. A byte code engineering library may help with this approach.
The Service Provider mechanism is the conventional means to enumerate implementations of a pluggable service, and has become more established with the introduction of Project Jigsaw (modules) in Java 9. Use the ServiceLoader in Java 6, or implement your own in earlier versions. I provided an example in another answer.

Spring has a pretty simple way to acheive this:
public interface ITask {
void doStuff();
}
#Component
public class MyTask implements ITask {
public void doStuff(){}
}
Then you can autowire a list of type ITask and Spring will populate it with all implementations:
#Service
public class TaskService {
#Autowired
private List<ITask> tasks;
}

The most robust mechanism for listing all classes that implement a given interface is currently ClassGraph, because it handles the widest possible array of classpath specification mechanisms, including the new JPMS module system. (I am the author.)
try (ScanResult scanResult = new ClassGraph().whitelistPackages("x.y.z")
.enableClassInfo().scan()) {
for (ClassInfo ci : scanResult.getClassesImplementing("x.y.z.SomeInterface")) {
foundImplementingClass(ci); // Do something with the ClassInfo object
}
}

With ClassGraph it's pretty simple:
Groovy code to find implementations of my.package.MyInterface:
#Grab('io.github.classgraph:classgraph:4.6.18')
import io.github.classgraph.*
new ClassGraph().enableClassInfo().scan().withCloseable { scanResult ->
scanResult.getClassesImplementing('my.package.MyInterface').findAll{!it.abstract}*.name
}

What erikson said is best. Here's a related question and answer thread - http://www.velocityreviews.com/forums/t137693-find-all-implementing-classes-in-classpath.html
The Apache BCEL library allows you to read classes without loading them. I believe it will be faster because you should be able to skip the verification step. The other problem with loading all classes using the classloader is that you will suffer a huge memory impact as well as inadvertently run any static code blocks which you probably do not want to do.
The Apache BCEL library link - http://jakarta.apache.org/bcel/

Yes, the first step is to identify "all" the classes that you cared about. If you already have this information, you can enumerate through each of them and use instanceof to validate the relationship. A related article is here: https://web.archive.org/web/20100226233915/www.javaworld.com/javaworld/javatips/jw-javatip113.html

Also, if you are writing an IDE plugin (where what you are trying to do is relatively common), then the IDE typically offers you more efficient ways to access the class hierarchy of the current state of the user code.

I ran into the same issue. My solution was to use reflection to examine all of the methods in an ObjectFactory class, eliminating those that were not createXXX() methods returning an instance of one of my bound POJOs. Each class so discovered is added to a Class[] array, which was then passed to the JAXBContext instantiation call. This performs well, needing only to load the ObjectFactory class, which was about to be needed anyway. I only need to maintain the ObjectFactory class, a task either performed by hand (in my case, because I started with POJOs and used schemagen), or can be generated as needed by xjc. Either way, it is performant, simple, and effective.

A new version of #kaybee99's answer, but now returning what the user asks: the implementations...
Spring has a pretty simple way to acheive this:
public interface ITask {
void doStuff();
default ITask getImplementation() {
return this;
}
}
#Component
public class MyTask implements ITask {
public void doStuff(){}
}
Then you can autowire a list of type ITask and Spring will populate it with all implementations:
#Service
public class TaskService {
#Autowired(required = false)
private List<ITask> tasks;
if ( tasks != null)
for (ITask<?> taskImpl: tasks) {
taskImpl.doStuff();
}
}

How to inject package private classes using Guice

Firstly i like what Guice does however i have also like to make as few classes in my system public. All services in my system are package private w/ only the interface public. This presents a few problems for Guice if one does not use a provider. I would prefer some alternative that allows me to provide a strategy to do the following:
for component C
requires dependencies X, Y, Z
call this method w/ X, Y, Z to create instance.
.. repeat again for all components.
In step 2 of the above psuedo code Guice now scans for #inject annotations. If this strategy was available I could decide how id like to find my component's dependencies in a generic way.
Unfortunately Module.bind just doesnt work because it works w/ classes literals.
The strategy interface for the above might look like this
interface ComponentDiscoverer {
Set<ComponentDefinition> components();
}
interface ComponentDefinition<T> {
List<RequiredDependency> requiredDependencies(); // similar to Guice's Key
<T> create( List<SatisfiedDependency> dependencies ); // factory method.
}
Guice gets all components by calling a registered ComponentDiscoverer.
It then calls the registered ComponentDiscoverer.components();
For each ComponentDefinition.requiredDependencies()
on demand call ComponentDefinition.create
Is this any built into Guice way or third party library to achieve the above ?
SAMPLE
package companyX;
public interface Service {
void execute();
}
package companyX;
package private class ServiceImpl implements Service {
static ServiceImpl create( Dependency dependency){
return new ServiceImpl( dependency );
}
private ServiceImpl( Dependency dependency ){
}
void execute();
}
package companyX;
package private class ServiceImpl2 implements Service2{
}
package companyX;
public class Factory {
Service alpha( Dependency ){
return ServiceImpl.create( dependency );
}
Service beta( DifferentDependency ){
// boring left out
}
Service2 gamma( AnotherDifferentDependency);
}
My module lives in a different package and all creation goes thru Fatory because everything else is package private.

You shouldn't have just one Module unless your application is very simple. You should have a module for each package that you have package-private classes you want to use in. This allows you to bind those package-private classes to the public interfaces. This is a standard practice for using Guice, and it's mentioned in the Keep Constructors Hidden section of the documentation.
With a module in the package, you just need normal #Injectable constructors or provider methods:
#Provides #Alpha Service alpha(Dependency dependency) {
return ServiceImpl.create(dependency);
}