If you have Enterprise JavaBeans (EJB)
applications that are exposed using a local interface view, you can
expose a RESTful interface to the enterprise bean using Java™ API for RESTful Web Services (JAX-RS).
By implementing JAX-RS annotated enterprise beans, you keep the EJB
functionality including transaction support, injection of Java EE components and resources, and other
EJB session bean capabilities.
Before you begin
Before EJB 3.1, enterprise beans that required an EJB local
client view also needed a separate Java interface,
usually located in a separate file, that declared the local view methods.
The enterprise bean specified that it implemented the EJB local view
interface using deployment descriptors or EJB annotations.
Using
the EJB 3.1 specification, you have the option of exposing a local
view of an enterprise bean without an explicit EJB local interface.
Instead, the enterprise bean has a no-interface client view that
is based on the public methods of your bean class. No-interface view
enterprise beans can be more simple to develop than a local view enterprise
bean for the following reasons:
- No-interface view enterprise beans do not require a separate Java interface declaration.
- No-interface view enterprise beans do not require specifying additional
metadata in the deployment descriptor or when using annotations.
See the EJB 3.1 specification for more details on no-interface
views of an enterprise bean.
JAX-RS supports the use of enterprise
beans that declare a local business interface and no-interface view
enterprise beans.
This task describes implementing RESTful
views of an enterprise bean with a local interface to enable the enterprise
bean to expose JAX-RS resources.
About this task
You can create a simple enterprise bean with JAX-RS annotations.
Even though this task specifically describes how to implement RESTful
views of a local interface view enterprise bean, it is important that
you consider the full scope of your application architecture and how
you want to expose resources as you decide your resource model and
determine which RESTful views are appropriate for your enterprise
beans application. These considerations are beyond the scope of this
task.
JAX-RS supports stateless and singleton session beans.
You can add JAX-RS annotations to the local interface of a session
bean. Also, with EJB 3.1, you can add JAX-RS annotations directly
to an EJB class if the enterprise bean exposes a no-interface view.
With
the EJB 3.1 packaging rules, you can add JAX-RS enterprise beans in
the web application archive (WAR) file either directly in the WEB-INF/classes
directory or using a Java archive
(JAR) file in the WEB-INF/lib directory. You can declare an enterprise
bean using annotations, or using an EJB deployment descriptor, or
using both annotations and a deployment descriptor.
JAX-RS
annotated enterprise beans in a stand-alone or in a separate ejb-jar
file that is included in an EAR is not supported.
最佳作法: Although you can declare enterprise beans in different
ways, it is a best practice to directly implement the EJB business
local interface and to always declare the @javax.ejb.Local annotation.
By using this method, the EJB bean is required to implement the local
business interface, which eliminates errors in typing method names
and changes to argument types. By always using the @javax.ejb.Local
annotation, if there are ever multiple business interfaces, you can
simply add the business interface to the annotation value. You can
also use this approach to modify the enterprise bean using a deployment
descriptor.
bprac
Procedure
- Create enterprise bean local interfaces for your enterprise
bean application. The following example demonstrates a
simple local business interface, the Purchasable EJB local interface,
for items to purchase:
package com.example.jaxrs;
@javax.ws.rs.Path("itemsForPurchase/{itemID}")
public interface Purchasable {
public int getItemsLeft(String itemID);
@javax.ws.rs.POST
public Order purchase(
@javax.ws.rs.PathParam("itemID") String itemID,
@javax.ws.rs.QueryParam("orderId") String orderID);
}
The getItemsLeft method is a regular EJB method that
is not JAX-RS related. A javax.ws.rs.Path annotation denotes the HTTP
request path to use. When an HTTP POST request is made to the itemsForPurchase/{itemID} object,
the JAX-RS runtime environment finds an EJB bean that implements the Purchasable local
interface and invokes the purchase method on the enterprise bean.
You
can still use the purchase method outside of a JAX-RS runtime environment
request. You can use injection or a JNDI lookup for a purchasable
enterprise bean and invoke the purchase method with the two String
arguments, itemID and orderID.
最佳作法: If there are multiple enterprise beans that implement
a local business interface, the JAX-RS runtime environment chooses
a random EJB bean to use when a JAX-RS request is made. It is a best
practice to only enable one bean class to implement a JAX-RS annotated
EJB local interface. If necessary, create a separate EJB local interface,
use the JAX-RS annotations on the new interface, and then modify the
metadata for the bean class so that it implements the new EJB local
interface.
bprac
- Create the enterprise bean that implements the local business
interface. The following example illustrates the Purchasable
EJB bean:
public int getItemsLeft(String itemID) {
// Return the number of items left.
}
public Order purchase(String itemID, String orderId) {
// Add the given item to the order id and return it.
}
}
- Declare that the Book class is an enterprise bean and implements
a local interface. Use one of the following methods to
declare your class as an enterprise bean that implements the local
interface. In the following example, the Book class is declared an
enterprise bean that implements a local interface:
- Use the EJB annotations @javax.ejb.Stateless or @javax.ejb.Singleton
on the Book class to specify that you want the EJB to be stateless
or singleton. Also, add the @javax.ejb.Local annotation with the local
interfaces as the annotation value; for example:
@javax.ejb.Stateless
@javax.ejb.Local(Purchasable.class)
public class Book {
If you have implemented multiple
local business interfaces, add the interface classes to the @javax.ejb.Local
annotation value; for example:
@javax.ejb.Local({Purchasable.class, Rentable.class})
- You can use a deployment descriptor to declare that an EJB
bean and the business interfaces it implements; for example:
<ejb-jar xmlns="http://java.sun.com/xml/ns/javaee" version="3.1"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/ejb-jar_3_1.xsd">
<!--
This file must exist in the WEB-INF/
directory of your WAR file. See EJB 3.1 spec 20.4 for more details.
-->
<enterprise-beans>
<session>
<ejb-name>Book</ejb-name>
<business-local>com.example.jaxrs.Purchasable</business-local>
<ejb-class>com.example.jaxrs.Book</ejb-class>
<session-type>Stateless</session-type>
</session>
</enterprise-beans>
</ejb-jar>
If you have implemented multiple local
business interfaces, you must add business-local elements to each
local interface in your bean definition.
- If you have only one local business interface, you can implement
the interface directly; for example:
@javax.ejb.Stateless
public class Book implements Purchasable {
- (optional) Add @javax.annotation.Resource annotated Java EE resource fields and properties
to your JAX-RS EJB classes to easily access resources in your application. The Java EE injections
do not work in plain Java classes
with JAX-RS annotations. Injecting @javax.annotation.Resource annotated Java EE resource fields and properties
to your JAX-RS EJB classes only works if your JAX-RS annotated classes
are either an enterprise bean or a Java Context
and Dependency Injection (JCDI) (JSR-299) managed bean; for example:
package com.example.jaxrs;
@javax.ejb.Stateless
@javax.ejb.Local(Purchasable.class)
public class Book implements Purchasable {
@javax.annotation.Resource(name="jdcb/TestDataSource")
private javax.sql.DataSource datasource;
public int getItemsLeft(String itemID) {
// Reads from the datasource.
// Returns the number of items left.
}
public Order purchase(String itemID, String orderId) {
// Reads from the datasource.
// Adds the given item to the order id and returns it.
}
}
In this example, if a data source is properly configured
with the correct JNDI name, a DataSource object is injected into the
resource class.
- (optional) Use JAX-RS @javax.ws.rs.core.Context injection
to obtain access to information about the request. You
can add an @javax.ws.rs.core.Context UriInfo field to your JAX-RS
EJB class to access information about the request URI; for example:
package com.example.jaxrs;
@javax.ejb.Stateless
@javax.ejb.Local(Purchasable.class)
public class Book implements Purchasable {
@javax.ws.rs.core.Context
private UriInfo uriInfo;
public int getItemsLeft(String itemID) {
// Return the number of items left.
}
public Order purchase(String itemID, String orderId) {
// Add the given item to the order id and return it.
}
}
To read parameters from the request such as @javax.ws.rs.HeaderParam,
@javax.ws.rs.QueryParam, and @javax.ws.rs.PathParam, add a parameter
to your resource method; for example:
package com.example.jaxrs;
@javax.ws.rs.Path("itemsForPurchase/{itemID}")
public interface Purchasable {
public int getItemsLeft(String itemID);
@javax.ws.rs.POST
public Order purchase(
@javax.ws.rs.PathParam("itemID") String itemID,
@javax.ws.rs.QueryParam("orderId") String orderID);
}
package com.example.jaxrs;
@javax.ejb.Stateless
@javax.ejb.Local(Purchasable.class)
public class Book implements Purchasable {
@javax.ws.rs.core.Context
private UriInfo uriInfo;
public int getItemsLeft(String itemID) {
// Returns the number of items left.
}
public Order purchase(String itemID, String orderId) {
// The method parameters contain the request values.
// Add the given item to the order id and return it.
}
/* The following field will not be set. */
@javax.ws.rs.QueryParam("q")
private String willNotWork;
@javax.ws.rs.QueryParam("q")
public void setMyQueryParam(String q) {
/* This property will not be set. */
}
}
支援的配置: The JAX-RS parameter annotations
must be added to the resource methods in the EJB business interface
when using business interfaces. They cannot be added to the implementation
bean.
sptcfg
- Package the enterprise beans into the WEB-INF/classes directory
of the WAR file, or inside a JAR file that is included in the WEB-INF/lib
directory of your WAR file.
When a client makes a request
to a JAX-RS annotated enterprise bean, the JAX-RS runtime environment
looks up and uses an EJB instance of the class to then invoke the
JAX-RS resource method.
Results
You have enabled an existing enterprise bean with local
interfaces so that JAX-RS resources are exposed for consumption.