Using Java contexts and dependency injection with JAX-RS

Java™ API for RESTful Web Services (JAX-RS) root resources and providers can be used in a Java Contexts and Dependency Injection (JCDI) enabled web archive (WAR). Simply add a valid WEB-INF/beans.xml file to your WAR file and any JAX-RS root resources and providers that are valid JCDI beans can use JCDI functionality.

About this task

JAX-RS classes in a JCDI-enabled archive can have @javax.inject.Inject annotated injection points, participate in JCDI lifecycle scopes, raise JCDI events, and have method interceptors and decorators.

JAX-RS root resource and provider classes must have a valid JCDI managed bean constructor. In general, if your classes have a constructor that has a parameter annotated with the @javax.ws.rs.core.Context annotation or with any JAX-RS parameter annotation such as @javax.ws.rs.QueryParam, you must refactor your code to use JAX-RS-annotated bean properties or fields instead. You can add an @javax.annotation.PostConstruct annotated method to help construct your object.

Additionally, JAX-RS root resource and provider classes must have a JCDI specified scope. Scopes control the lifecycle of a JCDI managed bean. Root resource classes can have any valid scope such as @javax.enterprise.context.RequestScoped, which makes the JAX-RS root resource class behave the same as in a non-JCDI enabled application. The javax.ws.rs.core.Application subclasses and JAX-RS providers must have the @javax.enterprise.context.ApplicationScoped annotation.

You might want to use JCDI to more quickly and easily develop your application, as well as increase the testability of your code. JCDI enables modern programming techniques such as dependency injection, an event-based programming model, and a more aspect-oriented approach towards cross-cutting concerns. Developers can use aspect-oriented programming to cleanly add functionality that is not part of the core business logic to a method. For example, one cross-cutting concern is logging. Some developers need to log the entry and exit of every single time a certain business method is called in an application. Developers now can use JCDI functionality such as method interceptors and decorators to more cleanly add this functionality. Developers can use dependency injection to more easily insert their own mock implementations during unit testing. The decoupling of previously hard coded dependencies allows developers to more easily test individual components.

JCDI beans can inject Enterprise JavaBeans (EJBs) and use @javax.annotation.Resource injections to inject Java Platform, Enterprise Edition (Java EE) resources. EJBs can also be JCDI beans. EJBs with annotations such as @javax.ejb.Stateless can also use JCDI dependency injection and other JCDI features. The EJBs keep their transactional and other EJB features.

Java Contexts and Dependency Injection (JCDI) is a new Java Platform, Enterprise Edition (Java EE) 6 feature. It can change the programming model to make applications easier to develop while increasing maintainability. JAX-RS developers can use JCDI features, such as @javax.inject.Inject support, in root resource and provider classes.

Procedure

  1. Configure the development environment.
    1. Before you start developing JAX-RS applications, you must set up your development environment by adding the JAX-RS libraries on the class path.
  2. Define the resources in JAX-RS web applications.
    1. Resources are the basic building block of a RESTful service. Resources can contain static or dynamically updated data. Examples of resources from an online book store application include a book, an order from a store, and a collection of users. By identifying the resources in your application, you can make the service more useful and easier to develop.
  3. Configure the JAX-RS application.

    You can configure JAX-RS applications in multiple ways depending on your needs. To take advantage of the Java Platform, Enterprise Edition (Java EE) 6 functionality, you can use the annotation scanning capabilities. By using annotation scanning, you can omit a JAX-RS javax.ws.rs.core.Application subclass or have a minimally defined javax.ws.rs.core.Application subclass. Alternatively, you can specify the IBM® JAX-RS servlet or filter if you want to use the functionality available in the IBM JAX-RS servlet and filter.

    Using one of the JAX-RS Version 1.1 configuration methods, you can omit a javax.ws.rs.core.Application subclass in your application or have a javax.ws.rs.core.Application subclass that returns an empty set of classes to inform the JAX-RS runtime environment to find and use all the JAX-RS classes in the application. You might want to use this method when you do not want to manually add every relevant JAX-RS class to a javax.ws.rs.core.Application subclass as you develop the application.

    By specifying the specific IBM JAX-RS servlet and filter, you can take advantage of and ensure specific IBM JAX-RS behavior. For example, using the IBM JAX-RS filter can be helpful in developing a web application with a mix of JAX-RS resources and JavaServer Pages (JSP) files with the same URL patterns.

    Even though there is a JAX-RS V1.1 configuration method that supports the use of an optional web.xml file, if you want to specify security constraints or roles, or you want to take advantage of other features enabled using a web.xml file, you must specify the information in a web.xml file.

    Choose one of the following three methods to configure your JAX-RS application:

    • Configure JAX-RS applications using JAX-RS 1.1 methods

      Use this method if you want to use the annotation scanning capabilities or to use the JAX-RS 1.1 configuration methods. You can use the annotation scanning capabilities to promote application portability, to minimize the amount of configuration code, or to dynamically modify the application without changes to the application code.

    • Configure the web.xml file for JAX-RS servlets

      Use this method if you want to specify features that are enabled using servlet initialization parameters to change the behavior and ensure that you get the IBM JAX-RS servlet. When using servlets, you can define a servlet path in the web.xml file that is appended to the base URL.

    • Configure the web.xml file for JAX-RS filters

      Use this method if you want to use the filter when you have JSPs, other servlets and filters, and JAX-RS resources with a mix of URL patterns. You can configure the web.xml file to define filters that indicate the possible URLs on which the filter can be invoked.

  4. Implementing JAX-RS resources with JCDI functionality. You can use any of the JCDI features separately or with one another to make your applications easier to create, maintain, and test.
  5. Assemble JAX-RS web applications.
    1. After you develop the Java class files for your JAX-RS web application and edit the web.xml file to enable the JAX-RS servlet, you are ready to assemble the application. Assemble the web application into a WAR package. You can assemble the WAR package into an enterprise archive (EAR) package if required.
  6. Deploy JAX-RS web applications.
    1. After you have assembled your JAX-RS web application, you need to deploy your web archive (WAR) package or the enterprise archive (EAR) package onto the application server.

Results

You have enabled an enterprise bean so that JAX-RS resources with JCDI functionality are exposed for consumption.


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시간소인 아이콘 마지막 업데이트 날짜: July 9, 2016 6:13
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