This set of tricky Java Spring questions and answers focuses on “Spring Dynamic Modules”.
1. To create services and have those automatically installed in the registry.
a) Spring Dynamic Modules
b) Spring DM Server
c) Spring Tooling
d) None of the mentioned
View Answer
Explanation: You can use Spring Dynamic Modules configuration schema to export a service. The service will be made available to other beans as well as other OSGi components.
2. Element to export the bean as an OSGi service, classified by the interface we specify.
a) osgix
b) osgi:service
c) all of the mentioned
d) none of the mentioned
View Answer
Explanation: We’ll use the osgi:service element to export the bean as an OSGi service, classified by the interface we specify.
3. These beans are proxies, some may load asynchronously or take a longer time to register.
<osgi:service interface="com.apress.springrecipes. osgi.helloworld.service.GreeterService"> <bean class="com.apress.springrecipes.osgi.helloworld. service.GreeterServiceImpl"/> </osgi:service>
a) True
b) False
View Answer
Explanation: This implies that you may have timing issues to resolve in configuring your service. For this, Spring Dynamic Modules provides the depends-on attribute, which lets your bean wait for another bean.
4. An anonymous bean specified inside of the osgi:service element allows you to avoid cluttering the namespace.
a) True
b) False
View Answer
Explanation: You can abbreviate the syntax by using an anonymous bean.
<osgi:service auto-export="all-classes" ref="greeterService"> <osgi:interfaces> <value>com.apress.springrecipes.osgi.helloworld.service.GreeterService</value> <value>com.apress.springrecipes.osgi.helloworld.service.GreetingRecorderService</value> </osgi:interfaces> </osgi:service>
5. The first, most direct connection to OSGi is the bean that’s created on your behalf when you export a service. This bean, an instance of:-
a) org.osgi.framework.ServiceRegistration
b) org.osgi.framework.Service
c) org.osgi.framework.ServiceRegister
d) none of the mentioned
View Answer
Explanation: This bean, an instance of org.osgi.framework.ServiceRegistration, is in turn a delegate to the Spring bean you have defined.
6. By default, beans created in a Spring application context are global to the entire OSGi runtime.
a) True
b) False
View Answer
Explanation: By default, beans created in a Spring application context are global to the entire OSGi runtime, including all clients that use it.
7. Sometimes, you may want to limit the visibility of a service so that multiple clients each get their own instance of the bean.
a) time
b) scope
c) attr
d) none of the mentioned
View Answer
Explanation: Spring Dynamic Modules provides a clever use of the scope attribute here, allowing you to limit beans exported as services to the client, or service importer.
8. Spring Dynamic Modules also supports injection and manipulation of bundles themselves. An injected bundle is of type:-
a) org.osgi.framework.savedBundle
b) org.osgi.framework.Bundle
c) org.osgi.framework.BundleInstance
d) none of the mentioned
View Answer
Explanation: The simplest use case is that you want to obtain an instance of the org.osgi.framework.Bundle class from an already loaded bundle in the system.
9. Once acquired, the Bundle can be interrogated to introspect information about the bundle itself, including any entries, its current state.
a) True
b) False
View Answer
Explanation: Once acquired, the Bundle can be interrogated to introspect information about the bundle itself, including any entries, its current state (which can be any of: UNINSTALLED, INSTALLED, RESOLVED, STARTING, STOPPING, or ACTIVE), and any headers specified on the bundle.
10. OSGi will let you maintain multiple versions of a service in your registry at the same time.
a) True
b) False
View Answer
Explanation: OSGi, and Spring Dynamic Modules on top of it, provides many tools for discriminating services both in publishing and consuming services.
11. Multiple services of the same interface may be registered inside of an OSGi environment, which necessitates a conflict-resolution process.
a) True
b) False
View Answer
Explanation: To aid in that, Spring Dynamic Modules provides a few features to help.
12. When specified on a service element, allows the ascription of a rank relative to other beans with the same interface.
a) Ranking
b) Service
c) All of the mentioned
d) None of the mentioned
View Answer
Explanation: Ranking is specified on the service element itself. When encountered, the OSGi runtime will return the service with the highest-ranking integer value.
13. A more robust solution to service discrimination is service attributes.
a) True
b) False
View Answer
Explanation: A service attribute is an arbitrary key and value pair that the service exports, and on which lookups for a service with multiple matches can be predicated.
14. There are frequently situations where OSGi will return more than one instance of a service that satisfies the interface.
a) True
b) False
View Answer
Explanation: Take, for example, a deployment where you have multiple GreeterServices deployed for various regions. Spring Dynamic Modules provides the set and list interfaces to retrieve multiple references and populate a java.util.Set and java.util.List, respectively.
15. Attribute, which, is the symbolic name of another bundle.
a) Fragment
b) Fragment-Host
c) All of the mentioned
d) None of the mentioned
View Answer
Explanation: The Fragment-Host attribute, in turn, is the symbolic name of another bundle.
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