Unfortunately, Web Services are a different story. Indeed there is the JAX-WS specification, but there are still too many unanswered questions as well as alternative approaches of applying Web Services. Which SOAP implementation is suitable depends on the requirements and the environment. The sections below are describing the tools and standards that are available for developers of Web Services.
Apache Axis2
Axis 2 is the follow-up of the popular Axis1 framework. Axis2 is based on a completely new architecture and has been re-developed from scratch.
The deployment of services for Axis 1 has often been criticized. Therefore Axis 2 has a completely new deployment model. An Axis 2 runtime is a Web application and can be installed on every JEE compliant Application Server. The Axis 2 web application itself is a container for Web Services now. Web Services are packed into an own file format with the file extension aar. Due to these archives, Web Services can be installed and configured by a simple user interface at run time. In Axis 2 the services can be configured by the traditional deployment descriptors, e.g. the file services.xml.
Modules providing additional functionality, for example WS-* standard support, can also be installed during runtime. A Web Service is regarded as an independent package which can be installed into the Axis 2 runtime environment.
Writing an Axis 2 project requires a lot of knowledge about the build tool Ant. Knowledge about the build tool is essential to write an Axis 2 project. For example the WSDL2JAVA task is generating a temporary project including a build-file. Then the projects build-file has to call the generated build-file. If a Web Service uses a library, e.g. a JDBC driver, then the library has to be copied into the generated project using Ant on each build. So development with Axis 2 will be very difficult if you are not familiar with Ant.
Apache CXF
CXF is also a project of the Apache software foundation. CXF came up from a fusion of the XFire and Ionas Celtix projects.
CXF was developed with the intention to integrate it into other systems. This is reflected in CXF API and the use of the Spring framework. Therefore it is very simple to integrate CXF into existing systems.
CXF respectively its predecessor XFire was integrated into numerous open and closed source projects like ServiceMix or Mule.
A proprietary API as well as the standardized JAX-WS interface are available for the development and use of Web Services.
JAX-WS
The Java API for XML based Web Services is the successor of the JAX-RPC specification. JAX-WS respectively its predecessor is message based and supports asynchronous communication. The Configuration is managed by annotations therefore Java 5 or higher is required. JAX-WS isn't downwardly compatible to its predecessor JAX-RPC. With JAX-WS it is pretty easy to write and consume Web Services. The default values of numerous parameters are comfortable for the programmer, so that simple Pojos declared with a @WebService annotation can be used as a Service. Listing 1 shows a simple implementation of a Web Service using the @WebService annotation.
import javax.jws.WebService;
import javax.jws.WebMethod;
@WebService
public class HelloWorldService {
public String helloWorld() {
return "Hello World!";
}
}
Listing 1: HelloWorld Web Service using JAX-WS
A suitable WSDL document can also be generated from the class. Other annotations can concertedly exert influence of the WSDL document. For example other namespaces or element names can be used. If JAXB is already known, its annotations can be used to define the serialization in every detail. With the contract first approach a Service Interface, JAXB annotated classes for serialization and a skeleton for the implementation can be generated. According to the WSDL document the generated classes can have numerous annotations. Annotations are also the main point of criticism of JAX-WS. Despite this criticism the JAX-WS specification came out well. It is well attuned and combinable with other Java and Java EE specifications. For example, Listing 2 shows a stateless EJB 3.0 Bean which acts as a Web Service at the same time.
@WebService
@Stateless
public class MyService{
public String hello(String name) {
return "Hallo"+name;
}
}
Listing 2: Stateless SessionBean acting as Web Service
JAX-WS Reference Implementation
The JAX-WS Reference Implementation represents the core piece of the Web Services protocol stack Metro. The Metro Stack provides support for the following Web Services standards:
WS-Addressing
WS-Policy
Web Services Security aka WS-Security
WS-Transaction
WS-Reliable Messaging
WS-Trust
WS-SecureConversation
Metro is documented in detail. Apart from the JAX-WS, JAXB and JWS specifications there are numerous tutorials und samples. The Netbeans IDE as well as the tutorials of the enterprise pack makes it particularly easy to get started. Of course, Eclipse can also be used for the development with Metro.
Web applications containing Web Services which have been realized with JAX-WS are executable in the Glassfish Application Server. To make services also executable in other application servers, two libraries (JAX-WS and JAXB) have to be installed. Application servers such as JBoss, WebSphere or Tomcat can be upgraded with JAX-WS within about 10 minutes.
Performance
Due to the modern streaming XML parser, the performance of all three SOAP engines is very well. The ping time for a locale roundtrip is about 2-4 milliseconds (message size about 3KB, Dual Core Notebook). Therefore the time delay by the SOAP communication is negligible in many projects.
WS-* Standards
The support of the WS-Standard family can also be decisive for the selection of a SOAP engine. For example, messages sent to services can be secured with signatures as described in the Web Service Security standard (in short WSS). Table 1 shows the support for WS*-Standards of the toolkits.
Conclusion
None of the Web Services frameworks is in general superior to the others. Axis 2 is structured modularly, has many features and can be used as an application server for Web Services. A special feature of Axis 2 is the support of removable binding frameworks, for example XMLBeans. Axis 2 together with the XMLBeans framework included is well suited for Web Services which are using very complex schema definitions. The disadvantages of Axis 2 are its complexity as well as the insufficient JAX-WS support. Therefore anyone who wants to work with JAX-WS should choose Apache CXF or the reference implementation.
Those who prefer a seamless integration with the Spring framework are well advised with the JAX-WS implementation. Furthermore CXF is slim and easy to use. CXF is the tool of choice if a SOAP engine has to be embedded into an existing software.
Who just wants to code against the standard is well advised with the JAX-WS implementation. The enterprise pack of the Netbeans development environment supports JAX-WS RI very well. Only a few clicks are needed to build a server or to call a Web Service.
I hope this article could help you with the decision for a WS toolkit.
| Standards | Axis2 | CXF | JAX-WS/Metro |
| WS-Addressing | X | X | X |
| WS-Coordination | X(2) | X | |
| WS-MetadataExchange | X | ||
| WS-Policy | X | X | X |
| WS-ReliableMessaging | X(3) | X | X |
| Web Services Security | X(1) | X(4) | X |
| WS-SecureConversation | X(1) | X | |
| WS-SecurityPolicy | X | ||
| WS-Transaction | X(2) | X | |
| WS-Trust | X | X | |
| WS-Federation |
Table 1: Support for WS-* Standards (stand: Juli 2008)
(1) Supported by the additional module Apache Rampart
(2) Supported by the additional module Apache Kandula2
(3) Supported by the additional module Apache Sandesha2
(4) By Apache WSS4J Interceptor
1 comment:
I think this a copy of Thomas Bayer's article
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