Java CDI framework Frequently Asked Questions Answers

Java CDI framework Frequently Asked Questions Answers The Java CDI (Contexts and Dependency Injection) framework is a Java EE standard for achieving dependency injection and context management.It provides a highly scalable and flexible way to manage components and dependencies of Java applications.When using the CDI framework, developers may encounter some common problems.Here are some common questions and their answers. At the same time, related Java code examples are provided. Question: How to inject dependencies in CDI applications? Answer: In CDI, we can use @inject annotations to inject dependencies.The injected class needs to define its life cycle using@Dependent,@RequestScoped,@SESSIONSCOPED or @ApplicationScope.For example, @RequestScoped public class MyBean { // ... } public class MyAnotherBean { @Inject private MyBean myBean; // ... } In the above example, the MyanoTherBean class injected a Mybean instance. Question: What does the scope of life cycle of CDI mean? Answer: CDI supports a variety of life cycles, such as@Dependent,@RequestScoped,@SESSIONSCOPED and @ApplicationScoped.@Dependent's life cycle is the same as the life cycle of dependence, and other life cycles can exist multiple instances in different contexts.For example, @RequestScoped public class MyRequestBean { // ... } @SessionScoped public class MySessionBean { // ... } @ApplicationScoped public class MyApplicationBean { // ... } In the above examples, a new instance of the MyrequestBean instance will produce a new instance during each request. The instance of MySessionbean shared between each session, and the instance of MyApplicationBean has only one instance in the entire application life cycle. Question: How to use CDI to manage trigger events and monitoring events? Answer: With the CDI framework, we can use @ObServes annotations and Event APIs to manage trigger events and monitoring events.First, we need to define an event class, such as: public class MyEvent { // ... } Then, we can inject the event class and use the Fire () method to trigger the event in the class of trigger events: public class EventTrigger { @Inject private Event<MyEvent> event; public void triggerEvent() { MyEvent myEvent = new MyEvent(); event.fire(myEvent); } } Finally, use the @OobServes annotation in the class of the monitoring event to identify the monitoring method: public class EventListener { public void onEvent(@Observes MyEvent event) { // Treatment event } } In the above examples, when the TrigGerevent () method in the EventTrigger class is called, MyEvent will be triggered, and the Onevent () method in the EventListener class will be called to handle the event. Question: How to use a limited character in the CDI application? Answer: In CDI, we can use the limited character to identify different instances with the same type.Limited symbols can be customized annotations.First, we need to define a limited conclusion: @Qualifier @Retention(RUNTIME) @Target({METHOD, FIELD, PARAMETER, TYPE}) public @interface MyQualifier { // ... } Then, we can use the limited conclusion solution at the injection point and instance: @MyQualifier public class MyBean { // ... } public class MyAnotherBean { @Inject @MyQualifier private MyBean myBean; // ... } In the above examples, the MyBean class is marked as@myqualifier, and the Mybean field in the Myanotherbean class uses @myqualifier limited character to inject the MyBean instance. The above are some common Java CDI framework questions and their answers.The CDI framework provides a strong dependency injection and context management function for Java applications to help developers better organize and manage code.By fully understanding the working principle of the CDI framework and how to solve the common problems, we can use CDI to develop more efficiently.