Jersey HK2 依赖注入

Question

我正在编写一个简单的微服务，它公开REST API。因此，我开始使用Jersey工作，当然我需要将我的对象注入到jersey资源中。基本上，我有两个类定义了一组资源，其中一些需要使用另一个服务。

所以，基本上我有：

public interface MyService {

String getServiceName();

void doService();

}

这个接口有两个实现（MyServiceBean和MyAlternativeServiceBean）。

根据我阅读的Jersey文档，我定义了一个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());

}

我将这个绑定器注册到ApplicationConfig类。

public class ApplicationConfig extends ResourceConfig{

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

}

适当地注释资源。

@Path("first")
    public class First {

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

    @Path("second")
    public class Second {

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

所有的工作都在MyService实现中没有参数构造函数时进行。但是在某些情况下，我也需要向MyAlternativeServiceBean提供依赖项。

这是构造函数：

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

但是我收到一个异常：

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)

基本上，我不知道如何在hk2中注入属性/常量（例如，我可以从配置文件中读取）。

谢谢

敬礼

- Raffaele

---

构造函数长什么样？你期望这些构造函数参数来自哪里？ - Paul Samsotha

我想知道怎样完全将Jersey与HK2集成：我的意思是，HK2可以为我构建对象，然后将这些对象注入到Jersey资源（当然也包括其他需要的对象）中。目前我不知道如何告诉HK2创建两个单例"MyServiceBean"和"MyAlternativeServiceBean"。我正在考虑采用Spring的方式，即框架为我构建对象并将这些对象保存在AppContext中。 - Raffaele

不确定你的意思。错误提示你找不到合适的构造函数，因为你添加了不适合注入点的构造函数参数，即要么没有服务可以注入到构造函数中，要么你没有使用@Inject将构造函数标记为注入点。这与Spring的工作方式没有区别。如果你尝试使用构造函数参数并且没有使用@Autowired将其标记为注入点或者没有可注入的bean，你会得到类似的错误。这没有任何区别。 - Paul Samsotha

我编辑了我的问题。当然，对于MyServiceBean来说，所有的工作都按预期进行，因为它不需要任何属性/依赖项，所以它有一个无参数的构造函数。 - Raffaele

这里是更新后的版本。在InjectionResolver中，您需要从构造函数参数中获取注释。否则，injectee.getParent()就是实际的构造函数，而不是参数，这会导致空值。此外，构造函数参数指示器也应该返回true。 - Paul Samsotha

Answer 1

您可以创建自定义注释

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

然后创建一个 InjectionResolver（允许使用自定义注释进行注入）

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; }
}

这个例子只使用了一个 Map，但我相信你可以想出如何让它使用 Properties。一旦你注册了 InjectionResolver，现在你只需要这样做：

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

这是一个完整的测试用例。

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));
    }
}

- Paul Samsotha