Jersey HK2 Dependency Injection

Question

I'm writing a simple microservices that exposes REST API. So I started working with Jersey and of course I need to Inject my object into jersey resources. Basically I have 2 classes that defines a set of resources and some of them need to use another service.

So basically I have:

public interface MyService {

String getServiceName();

void doService();

}

2 implementations of this interface (MyServiceBean and MyAlternativeServiceBean)

and, as far as I understood reading jersey docs, I defined an hk2 Binder:

public class MyBinder implements Binder{

@Override
public void bind(DynamicConfiguration config) {

    DescriptorImpl descriptor = BuilderHelper.link(MyServiceBean.class).named("MyServiceBean").to(MyService.class).build();
    config.bind(descriptor);


    config.bind(BuilderHelper.link(MyAlternativeServiceBean.class).named("MyAlternativeServiceBean").to(MyService.class).build());

}

I registered this binder to the ApplicationConfig class

public class ApplicationConfig extends ResourceConfig{

public ApplicationConfig(){
    property("property.value", "MyAlternativeServiceImplementation");
    registerInstances(new MyBinder());
}

}

And annotated properly into the resources

@Path("first")
    public class First {

        @Inject @Named(value = "MyServiceBean")
        private MyService myService;
    //...
    }

    @Path("second")
    public class Second {

        @Inject @Named(value = "MyAlternativeServiceBean")
        private MyService myService;
    //...
    }

All works until MyService implementation have no args constructor. But in 1 case I need to provide a dependency also to MyAlternativeServiceBean.

Here is the constructor

@Inject @Named("property.value")
    public MyAlternativeServiceBean(String property){
        this.property = property;
    }

But I get an exception:

javax.servlet.ServletException: A MultiException has 5 exceptions.  They are:|1. org.glassfish.hk2.api.UnsatisfiedDependencyException: There was no object available for injection at Injectee(requiredType=String,parent=MyAlternativeServiceBean,qualifiers={}),position=0,optional=false,self=false,unqualified=null,2080509613)|2. java.lang.IllegalArgumentException: While attempting to resolve the dependencies of com.hpe.services.MyAlternativeServiceBean errors were found|3. java.lang.IllegalStateException: Unable to perform operation: resolve on com.hpe.services.MyAlternativeServiceBean|4. java.lang.IllegalArgumentException: While attempting to resolve the dependencies of com.hpe.tests.SecondEntryPoint errors were found|5. java.lang.IllegalStateException: Unable to perform operation: resolve on com.hpe.tests.SecondEntryPoint|
    at org.glassfish.jersey.servlet.WebComponent.service(WebComponent.java:392)
    at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:381)
    at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:344)
    at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:219)
    at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:684)
    at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:501)
    at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:229)
    at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1086)
    at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:427)
    at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:193)
    at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1020)
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:135)
    at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:116)
    at org.eclipse.jetty.server.Server.handle(Server.java:370)
    at org.eclipse.jetty.server.AbstractHttpConnection.handleRequest(AbstractHttpConnection.java:494)
    at org.eclipse.jetty.server.AbstractHttpConnection.headerComplete(AbstractHttpConnection.java:973)
    at org.eclipse.jetty.server.AbstractHttpConnection$RequestHandler.headerComplete(AbstractHttpConnection.java:1035)
    at org.eclipse.jetty.http.HttpParser.parseNext(HttpParser.java:641)
    at org.eclipse.jetty.http.HttpParser.parseAvailable(HttpParser.java:231)
    at org.eclipse.jetty.server.AsyncHttpConnection.handle(AsyncHttpConnection.java:82)
    at org.eclipse.jetty.io.nio.SelectChannelEndPoint.handle(SelectChannelEndPoint.java:696)
    at org.eclipse.jetty.io.nio.SelectChannelEndPoint$1.run(SelectChannelEndPoint.java:53)
    at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:608)
    at org.eclipse.jetty.util.thread.QueuedThreadPool$3.run(QueuedThreadPool.java:543)
    at java.lang.Thread.run(Thread.java:745)

Basically I don't konw how to inject properties/constants (that I can read from a configuration file for instance) in hk2

Thanks

Regards

Answer 1

What you can do is create a custom annotation

@Target({ElementType.FIELD, ElementType.PARAMETER})
@Retention(RetentionPolicy.RUNTIME)
public @interface Config {
    String value();
}

Then create an InjectionResolver for it (which allows for injection using custom annotations)

public static class ConfigInjectionResolver implements InjectionResolver<Config> {

    private static final Map<String, String> properties = new HashMap<>();

    public ConfigInjectionResolver() {
        properties.put("greeting.message", "Hello World");
    }

    @Override
    public Object resolve(Injectee injectee, ServiceHandle<?> handle) {
        if (String.class == injectee.getRequiredType()) {
            AnnotatedElement elem = injectee.getParent();
            if (elem instanceof Constructor) {
                Constructor ctor = (Constructor) elem;
                Config config = (Config) ctor.getParameterAnnotations()[injectee.getPosition()][0];
                return properties.get(config.value());
            } else {
                Config config = elem.getAnnotation(Config.class);
                return properties.get(config.value());
            }
        }
        return null;
    }

    @Override
    public boolean isConstructorParameterIndicator() { return true; }

    @Override
    public boolean isMethodParameterIndicator() { return false; }
}

This example just uses a Map, but I'm sure you can figure out how to make it use Properties. Once you register the InjectionResolver, you can now just do

public SomeService(@Config("some.property") String property) {}

Here is a complete test case

import org.glassfish.hk2.api.Injectee;
import org.glassfish.hk2.api.InjectionResolver;
import org.glassfish.hk2.api.ServiceHandle;
import org.glassfish.hk2.api.TypeLiteral;
import org.glassfish.hk2.utilities.binding.AbstractBinder;
import org.glassfish.jersey.filter.LoggingFilter;
import org.glassfish.jersey.server.ResourceConfig;
import org.glassfish.jersey.test.JerseyTest;
import org.junit.Test;

import javax.inject.Inject;
import javax.inject.Singleton;
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.core.Response;
import java.lang.annotation.*;
import java.lang.reflect.AnnotatedElement;
import java.lang.reflect.Constructor;
import java.util.HashMap;
import java.util.Map;
import java.util.logging.Logger;

import static org.junit.Assert.*;

/**
 * Run like any other JUnit Test. Only one required dependency
 *
 * <dependency>
 *   <groupId>org.glassfish.jersey.test-framework.providers</groupId>
 *   <artifactId>jersey-test-framework-provider-grizzly2</artifactId>
 *   <version>${jersey2.version}</version>
 * </dependency>
 *
 * @author Paul Samsotha
 */
public class ConfigExample extends JerseyTest {

    @Target({ElementType.FIELD, ElementType.PARAMETER})
    @Retention(RetentionPolicy.RUNTIME)
    public static @interface Config {
        String value();
    }

    public static class ConfigInjectionResolver implements InjectionResolver<Config> {

        private static final Map<String, String> properties = new HashMap<>();

        public ConfigInjectionResolver() {
            properties.put("greeting.message", "Hello World");
        }

        @Override
        public Object resolve(Injectee injectee, ServiceHandle<?> handle) {
            if (String.class == injectee.getRequiredType()) {
                AnnotatedElement elem = injectee.getParent();
                if (elem instanceof Constructor) {
                    Constructor ctor = (Constructor) elem;
                    Config config = (Config) ctor.getParameterAnnotations()[injectee.getPosition()][0];
                    return properties.get(config.value());
                } else {
                    Config config = elem.getAnnotation(Config.class);
                    return properties.get(config.value());
                }
            }
            return null;
        }

        @Override
        public boolean isConstructorParameterIndicator() { return true; }

        @Override
        public boolean isMethodParameterIndicator() { return false; }
    }


    private static interface GreetingService {
        String getGreeting();
    }

    private static class ConfiguredGreetingService implements GreetingService {
        private String message;

        public ConfiguredGreetingService(@Config("greeting.message") String message) {
            this.message = message;
        }

        @Override
        public String getGreeting() {
            return this.message;
        }
    }

    @Path("greeting")
    public static class GreetingResource {

        @Inject
        private GreetingService greetingService;

        @GET
        public String getConfigProp() {
            return greetingService.getGreeting();
        }
    }

    @Override
    public ResourceConfig configure() {
        ResourceConfig config = new ResourceConfig(GreetingResource.class);
        config.register(new LoggingFilter(Logger.getAnonymousLogger(), true));
        config.register(new AbstractBinder(){
            @Override
            protected void configure() {
                bind(ConfiguredGreetingService.class).to(GreetingService.class).in(Singleton.class);
                bind(ConfigInjectionResolver.class)
                        .to(new TypeLiteral<InjectionResolver<Config>>(){})
                        .in(Singleton.class);
            }
        });
        return config;
    }

    @Test
    public void should_get_configured_greeting() {
        final Response response = target("greeting")
                .request().get();
        assertEquals("Hello World", response.readEntity(String.class));
    }
}