Installing and deploying web applications using xml-axis

• Introduction
• Creating Webapps
• Installing Dependencies
• Installing Web Services
• Starting the web server
• Installation testing
• Deploying web services
• Testing

Introduction

This document describes how to install Apache Axis. It assumes you already know how to write and run Java code and not be scared of XML. You should also have an application server or servlet engine and be familiar with operating and deploying to it. If you need an application server, we recommend Jakarta Tomcat. [If you are installing tomcat, get the latest 4.1.x version, and the full distribution, not the LE version for Java1.4, as that omits the Xerces XML parser]. Other servlet engines are supported, provided they implement version 2.2 or greater of the servlet API. Note also that Axis client and server requires Java1.3 or later.

For more details on using Axis, please see the user guide.

Things you have to Know

Things you need to know to begin to write a Web Service:

1. Core Java datatypes, classes and programming concepts.
2. What threads are, race conditions, thread safety and sychronization.
3. What a classloader is, and what hierarchical classloaders are, or 'common causes of a ClassNotFoundException'.
4. How to diagnose trouble from exception traces, what a NullPointerException (NPE) and other common exceptions are, and how to fix them.
5. What a web application is; what a servlet is, where classes, libraries and data go in a web application.
6. How to start your application server and deploy a web application on it.
7. What a network is, the core concepts of the IP protocol suite and the sockets API. Specifically, what is TCP/IP.
8. What HTTP is. The core protocol and error codes, HTTP headers and perhaps the details of basic authentication.
9. What XML is. Not how to parse it or anything, just what constitutes well-formed and valid XML.

If you are completely new to Java, we recommend you start off with things like the Java Tutorials on Sun's web sites, and perhaps a classic book like Thinking in Java, until you have enough of a foundation to be able to work with Axis. It is also useful to have written a simple web application, as this will give you some knowledge of how HTTP works, and how Java applications servers integrate with HTTP.

Be aware that there is a lot more to know to use Axis and SOAP effectively than the listing above. The other big area is "how to write internet scale distributed applications". Nobody knows how to do that properly yet, so that you have to learn by doing.

Step 0: Concepts

SOAP messages are XML messages. These messages exchange structured information between SOAP systems. Messages consist of one or more SOAP elements inside an envelope, Headers and the SOAP Body. SOAP has two syntaxes for describing the data in these elements, Section 5, which is a clear descendent of the XML RPC system, and XML Schema, which is the newer (and usually better) system. Axis handles the magic of converting Java objects to SOAP data when it sends it over the wire or receives results. SOAP Faults are sent by the server when something goes wrong; Again Axis converts these to Java exceptions.

SOAP is intended to link disparate systems. It is not a mechanism to tightly bind Java programs written by the same team together. It can bind Java programs together, but not as tightly as RMI or Corba. If you try sending many Java objects that RMI would happily serialize, you will be disappointed at how badly Axis fails. This is by design: if Axis copied RMI and serialized Java objects to byte streams, you would be stuck to a particular version of Java everywhere.

Axis implements the JAX-RPC API, one of the standard ways to program Java services. If you look at the specification and tutorials on Sun's web site, you will understand the API. If you code to the API, your programs will work with other implementations of the API, such as those by Sun and BEA. Axis also provides extension features, and many ways that extend the JAX-RPC API. You can use these to write better programs, ones that only work with Axis. But since Axis is free and you get the source, that should not matter.

Axis is implemented in the JAR file axis.jar; implementing the JAX-RPC API declared in the JAR files jaxrpc.jar and saaj.jar. It needs various helper libraries, for logging, WSDL processing and introspection. All these files can be packaged into a web application, axis.war, that can be dropped into a servlet container. Axis ships with some sample SOAP services. You can add your own by adding new compiled classes to the Axis webapp registering them.

Before you can do that, you have to install it and get it working.

Step 1: creating the webapps

In your servlet installation, you should find a directory into which web applications ("webapps") are to be placed. Into this directory copy the webapps/axis directory from the xml-axis distribution. You can actually name this directory anything you want, just be aware that the name you choose will form the basis for the URL by which clients will access your service. The rest of this document assumes that the default webapp name, "axis" has been used; rename these references if appropriate.

Step 2: setting up the libraries

In the axis directory, you will find a WEB-INF sub-directory. This directory contains some basic configuration information, but can also be used to contain the dependencies and web services you wish to deploy.

In the WEB-INF directory, you'll find a "lib" directory. 

• In this directory, copy the jars associated with the JAXP 1.1 XML compliant parser of your choice. We recommend xerces jars from the xml-xerces distribution, though others work. If you omit this stage you may be able to use the default XML parser provided by the web application.

Tomcat 4.x and Java1.4

Step 3: starting the web server

This varies on a product-by-product basis. In many cases it is as simple as double clicking on a startup icon or running a command from the command line.

Step 4: Validate the Installation

After installing the web application and dependencies, you should make sure that the server is running the web application.

Look for the start page

Validate Axis with happyaxis

If any of the needed libraries are missing, Axis will not work.
You must not proceed until all needed libraries can be found, and this validation page is happy.
Optional components are optional; install them as your need arises. If you see nothing but an internal server error and an exception trace, then you probably have multiple XML parsers on the classpath, and this is causing version confusion.

Look for some services

Test a SOAP Endpoint

  <?xml version="1.0" encoding="UTF-8" ?> 
  <soapenv:Envelope 
      xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" 
      xmlns:xsd="http://www.w3.org/2001/XMLSchema" 
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
      <soapenv:Body>
      <getVersionResponse 
          soapenv:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/">
          <getVersionReturn 
              xsi:type="xsd:string">
              Apache Axis version: 1.0 Built on Nov 04, 2002 (01:30:37 PST)
          </getVersionReturn> 
      </getVersionResponse>
      </soapenv:Body>
  </soapenv:Envelope>

Test a JWS Endpoint

To test the JWS service, we make a request against a built in example, EchoHeaders.jws (look for this in the axis/ directory).

Point your browser at http://localhost:8080/axis/EchoHeaders.jws?method=list .

This should return an XML listing of your application headers, such as

<?xml version="1.0" encoding="UTF-8" ?> 
<soapenv:Envelope 
    xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" 
    xmlns:xsd="http://www.w3.org/2001/XMLSchema" 
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <soapenv:Body>
        <listResponse 
            soapenv:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/">
            <listReturn xsi:type="soapenc:Array" 
                soapenc:arrayType="xsd:string[6]" 
                xmlns:soapenc="http://schemas.xmlsoap.org/soap/encoding/">
                <item>accept:image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, */*</item> 
                <item>accept-language:en-us</item> 
                <item>accept-encoding:gzip, deflate</item> 
                <item>user-agent:Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1)</item> 
                <item>host:localhost:8080</item> 
                <item>connection:Keep-Alive</item> 
            </listReturn>
        </listResponse>
    </soapenv:Body>
</soapenv:Envelope>

Step 5: installing new Web Services

So far you have got Axis installed and working, now it is time to add your own Web Service.

The process here boils down to (1) get the classes and libraries of this new service into the axis WAR directory tree, (2) tell the AxisEngine about the new file. The latter is done by submitting an XML deployment descriptor to the service via the Admin web service, which is usually done with the AdminClient program or the <axis-admin> Ant task

In the WEB-INF directory, look for (or create) a "classes" directory (i.e. axis/WEB-INF/classes ). In this directory, copy the compiled Java classes you wish to install, being careful to preserve the directory structure of the Java packages.

If your classes services are already packaged into JAR files, feel free to drop them into the WEB-INF/lib directory instead. Also add any third party libraries you depend on into the same directory.

After adding new classes or libraries to the Axis webapp, you must restart the webapp. This can be done by restarting your application server, or by using a server-specific mechanism to restart a specific webapp.

Note: If your web service uses the simple authorization handlers provided with xml-axis (this is actually not recommended as these are merely illustrations of how to write a handler than intended for production use), then you will need to copy the corresponding perms.lst and users.lst files into the WEB-INF directory.

Step 6: deploying your own web services

The various classes and JARs you have just set up implement your new Web Service. What remains to be done is to tell Axis how to expose this web service. Axis takes a Web Service Deployment Descriptor, (a WSDD file), that describes in XML what the service is, what methods it exports and other aspects of the SOAP endpoint.

The users guide covers these WSDD files; here we are going to use one from the Axis samples; the stock quote service.

• Add axis.jar, commons-discovery.jar, commons-logging.jar, jaxrpc.jar, saaj.jar, log4j-1.2.8.jar (or whatever is appropriate for your chosen logging implementation), and the XML parser jar file or files (e.g., xerces.jar) to your classpath.
• Look in axis/samples/stock for the file deploy.wsdd. This is the deployment descriptor we want to tell Axis about.
• execute the following command from the samples/stock directory:

  java org.apache.axis.client.AdminClient
-lhttp://localhost:8080/axis/services/AdminService deploy.wsdd

Note: You may need to replace localhost with your host name, and 8080 with the port number used by your web server.If you have renamed the web application, something other than "axis" change the URL appropriately.

Step 7: testing

This step is optional, but highly recommended. For illustrative purposes, it is presumed that you have installed and deployed the stockquote demo.

• Add axis.jar, commons-discovery.jar, commons-logging.jar, jaxrpc.jar, saaj.jar, log4j-1.2.8.jar (or whatever is appropriate for your chosen logging implementation), and the XML parser jar file or files (e.g., xerces.jar), as well as the Axis installation directory to your classpath. Change directory to the distribution directory for xml-axis and execute the following command:

  java samples.stock.GetQuote
-lhttp://localhost:8080/axis/servlet/AxisServlet -uuser1 -wpass1 XXX

• You should get back "55.25" as a result.

Note: Again, you may need to replace localhost with your host name, and 8080 with the port number used by your web server. If you have renamed the web application, something other than "axis" change the URL appropriately.

Advanced Installation: adding Axis to your own Webapp

The core concepts are

1. Add axis.jar, wsdl.jar, saaj.jar, jaxrpc.jar and the other dependent libraries to your WAR file.
2. Copy all the Axis Servlet declarations and mappings from axis/WEB-INF/web.xml and add them to your own web.xml
3. Build and deploy your webapp.
4. Run the Axis AdminClient against your own webapp, instead of Axis, by changing the URL you invoke it with.

Summary