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JAX-RS is an annotation-driven Java API that can be used for exposing Java beans as HTTP based services. For example, RESTful web services are developed using JAX-RS annotations to define the resources exposed by the service.  Web services developed using JAX-RS annotations consist of the following qualities:

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JAX-RS annotations are defined in JSR 311. They are also a way of mapping Java with HTTP requests. For example, @GET, @PUT, @POST, @DELETE and @HEAD are JAX-RS annotations that directly map to HTTP requests by the same name. See more details about JAX-RS annotations.

Shown below is an example of a simple web service that uses the following JAX-RS annotations: @Path, @GET, @Consumes and @Produces.

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<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:jaxrs="http://cxf.apache.org/jaxrs"
       xsi:schemaLocation="
         http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.0.xsd
         http://cxf.apache.org/jaxrs http://cxf.apache.org/schemas/jaxrs.xsd">
    <bean id="serviceBean" class="demo.jaxrs.server.CustomerService"/>
    <!-- The SecureAnnotationsInterceptor honors the @RolesAllowed, @PermitAll and @DenyAll annotations -->
    <bean id="authorizationInterceptor"
          class="org.apache.cxf.interceptor.security.SecureAnnotationsInterceptor">
        <property name="securedObject" ref="serviceBean"/>
    </bean>
    <jaxrs:server id="customerService" address="/customers">
        <!-- set the interceptor for the jaxrs:server for in-bound messages to authorize the user -->
        <jaxrs:inInterceptors>
            <ref bean="authorizationInterceptor"/>
        </jaxrs:inInterceptors>
        <jaxrs:serviceBeans>
            <ref bean="serviceBean"/>
        </jaxrs:serviceBeans>
    </jaxrs:server>
</beans>

Enabling CORS for JAX-RS

If required, you can enable CORS (cross origin resource sharing) for JAX-RS applications by adding the CORS filter to the web.xml file as shown in the following example. 

<filter>
    <filter-name>CorsFilter</filter-name>
    <filter-class>org.apache.catalina.filters.CorsFilter</filter-class>
    <init-param>
        <param-name>cors.allowed.origins</param-name>
        <param-value>*</param-value>
    </init-param>
    <init-param>
        <param-name>cors.allowed.methods</param-name>
        <param-value>GET,POST,HEAD,OPTIONS,PUT,DELETE,PATCH</param-value>
    </init-param>
</filter>
<filter-mapping>
    <filter-name>CorsFilter</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>

The parameters used in this example are as follows:  

• The cors.allowed.origins parameter is used to specify the web domains that should be allowed to share resources with the JAX-RS application. The domain names should be specified as parameter values. If the parameter value is set to '*' as shown above, or if this parameter is not used at all, resource sharing will be allowed for all origins (all web domains). 
• The cors.allowed.methods parameter is used to specify the type of requests for which CORS should be enabled. You can list the allowed methods as parameter values.

Developing RESTful service using JAX-RS

See how you can easily develop a RESTful web application using JAX-RS annotations in WSO2 Developer Studio. Once the web service is created, you can deploy it in WSO2 Application Server using the management console. Also, see the official Java documentation, for details about JAX-RS annotations and RESTful web services.