Add provider#getService to locate the service implementation.

apm-collector/apm-collector-core/src/main/java/org/skywalking/apm/collector/core/module/ModuleProvider.java

@@ -116,4 +116,13 @@ public abstract class ModuleProvider {
             throw new ServiceNotProvidedException("Provide more service implementations than Module requirements.");
         }
     }
+
+    public <T extends Service> T getService(Class<T> serviceType) throws ServiceNotProvidedException {
+        Service serviceImpl = services.get(serviceType);
+        if (serviceImpl != null) {
+            return (T)serviceImpl;
+        }
+
+        throw new ServiceNotProvidedException("Service " + serviceType.getName() + " should not be provided, based on module define.");
+    }
 }

apm-collector/apm-collector-core/src/test/java/org/skywalking/apm/collector/core/module/BaseModuleA.java

@@ -31,7 +31,7 @@ public class BaseModuleA extends Module {
     }
 
     public interface ServiceABusiness1 extends Service {
-
+        void print();
     }
 
     public interface ServiceABusiness2 extends Service {

apm-collector/apm-collector-core/src/test/java/org/skywalking/apm/collector/core/module/ModuleAProvider.java

@@ -50,6 +50,9 @@ public class ModuleAProvider extends ModuleProvider {
 
     public class Business1 implements BaseModuleA.ServiceABusiness1 {
 
+        @Override public void print() {
+            System.out.println("ModuleA.Business1.print()");
+        }
     }
 
     public class Business2 implements BaseModuleA.ServiceABusiness2 {

apm-collector/apm-collector-core/src/test/java/org/skywalking/apm/collector/core/module/ModuleManagerTest.java

@@ -25,7 +25,7 @@ import org.junit.Test;
  */
 public class ModuleManagerTest {
     @Test
-    public void testInit() throws ServiceNotProvidedException, ModuleNotFoundException, ProviderNotFoundException {
+    public void testInit() throws ServiceNotProvidedException, ModuleNotFoundException, ProviderNotFoundException, DuplicateProviderException {
         ApplicationConfiguration configuration = new ApplicationConfiguration();
         configuration.addModule("Test").addProviderConfiguration("TestModule-Provider", null);
         configuration.addModule("BaseA").addProviderConfiguration("P-A",null);
@@ -33,5 +33,8 @@ public class ModuleManagerTest {
 
         ModuleManager manager = new ModuleManager();
         manager.init(configuration);
+
+        BaseModuleA.ServiceABusiness1 serviceABusiness1 = manager.find("BaseA").provider().getService(BaseModuleA.ServiceABusiness1.class);
+        serviceABusiness1.print();
     }
 }