Installing and deploying web applications using xml-axis |
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 Java 1.4, 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 Java 1.3 or later.
For more details on using Axis, please see the user guide.
Things you need to know to begin to write a Web Service:
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 application 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.
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.
Here we assume that you have a web server up and running on the localhost, at port 8080. If your server is on a different port, replace references to 8080 to your own port number.
In your Application Server 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.
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.
Axis needs to have an XML parser in its classpath. If your application server or Java runtime does not make one visible to web applications, you need to download and add it. Java 1.4 includes the Crimson parser, so you can omit this stage, though the Axis team prefer Xerces.
To add an XML parser, acquire the JAXP 1.1 XML compliant parser of your choice. We recommend Xerces jars from the xml-xerces distribution, though others mostly work. Unless your JRE or app server has its own specific requirements, you can add the parser's libraries to axis/WEB-INF/lib.
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.
After installing the web application and dependencies, you should make sure that the server is running the web application.
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. Eliminate the extra parsers,
restart the app server and try again.
From the start page, select View the list of deployed Web services. This will list all registered Web Services, unless the servlet is configured not to do so. On this page, You should be able to click on (wsdl) for each deployed Web service to make sure that your web service is up and running.
Note that the 'instant' JWS Web Services that Axis supports are not listed in this listing -so when you get to these services, as the user guide will, do not panic when the services are not listed.
getVersion method:
http://localhost:8080/axis/services/Version?method=getVersion
This should return something like
<?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: 1.1 Built on Apr 04, 2003 (01:30:37 PST)
</getVersionReturn>
</getVersionResponse>
</soapenv:Body>
</soapenv:Envelope>
The Axis version and build date may of course be different.
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>
Again, the exact return values will be different, and you may need to
change URLs to correct host, port and webapp specifics.
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. Both of these do the same thing: run the Axis SOAP client to talk to the Axis adminstration service, which is of course a SOAP service in its own right. It's a special SOAP service in one regard -to stop random people from administrating your service it is restricted to local callers only (not remote access) and is password protected. There is a default password that the client knows; if you change it then you need to pass the new password to the client.
The first step is to add your code to the server.
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 users.lst file into the WEB-INF directory.
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 and reference guide cover these WSDD files; here we are going to use one from the Axis samples; the stock quote service.
set AXIS_HOME=c:\tomcat\webapps\axis
set AXIS_LIB=%AXIS_HOME%\lib
set AXISCLASSPATH=%AXIS_LIB%\axis.jar;%AXIS_LIB%\commons-discovery.jar;
%AXIS_LIB%\commons-logging.jar;%AXIS_LIB%\jaxrpc.jar;%AXIS_LIB%\saaj.jar;
%AXIS_LIB%\log4j-1.2.8.jar;%AXIS_LIB%\xml-apis.jar;%AXIS_LIB%\xercesImpl.jar
Unix users have to do something similar:
set AXIS_HOME=/usr/tomcat/webapps/axis
set AXIS_LIB=$AXIS_HOME/lib
set AXISCLASSPATH=$AXIS_LIB/axis.jar:$AXIS_LIB/commons-discovery.jar:
$AXIS_LIB/commons-logging.jar:$AXIS_LIB/jaxrpc.jar:$AXIS_LIB/saaj.jar:
$AXIS_LIB/log4j-1.2.8.jar:$AXIS_LIB/xml-apis.jar:$AXIS_LIB/xercesImpl.jar
export AXIS_HOME; export AXIS_LIB; export AXISCLASSPATH
To use Axis client code, you can select the Axis classpath when invoking
Java by going
java -cp "%AXISCLASSPATH%" ...or
java -cp "$AXISCLASSPATH" ...depending on the platform. Omit the quotes if your classpath doesn't have spaces in it.
Look in axis/samples/stock for the file deploy.wsdd. This is the deployment descriptor we want to tell Axis about. Deployment descriptors are an Axis-specific XML file, that tells Axis how to deploy (or undeploy) a Web Service, and how to configure Axis itself. The Axis Administration Web Service lets the AdminClient program and its Ant sibling submit a new WSDD file for interpretation. The Axis 'engine' will update its configuration, then save its state.
By default Axis saves it state into the global configuration file, axis/WEB-INF/server-config.wsdd. Sometimes you see a warning message about such a file not being found -don't worry about this, because Axis auto-creates the file after you deploy something to it. You can check in the webapp to see what this file looks like -and even copy it to other systems if you want to give them identical configurations. Note that Axis needs an expanded webapplication and write access to the WEB-INF dir to save its state to this location.
java -cp %AXISCLASSPATH% org.apache.axis.client.AdminClient
-lhttp://localhost:8080/axis/services/AdminService deploy.wsdd
If you get some java client error (like ClassNotFoundException),
then you haven't set up your classpath right, mistyped the
classname, or done some other standard error. Tracking down such
problems is foundation Java development skills -if you don't know
how to do it, learn them now.
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.
If you get some AxisFault listing, then the client is working, but the deployment was unsuccessful. This is where the knowledge of the sockets API to TCP and the basics of the HTTP that Web Service development requires begins to be needed. If you got some socket error like connection refused, well, clearly the thing at the far end isnt talking to you, so find the cause of that fix it. If you get any Http error code back, well, you know what the error codes mean, right? If you are going to develop Web Services -you need to.
The user's guide covers the AdminClient in more detail, and there is also an Ant task to automate its use in your build process.
This step is optional, but highly recommended. For illustrative purposes, it is presumed that you have installed and deployed the stockquote demo.
java -cp "%AXISCLASSPATH%" samples.stock.GetQuote
-lhttp://localhost:8080/axis/servlet/AxisServlet -uuser1 -wpass1 XXX
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.
The core concepts are
We see a lot of people posting their problems on the axis-user mailing lists, and other axis users, and the developers do their best to help when they can. But before you rush to post your own problems to the mail list, a word of caution.
Axis is free. This means nobody gets paid to man the support lines. All the help you get from the community is voluntary and comes from the kindness of their hearts. They may be other users, willing to help you get past the same hurdles they had to be helped over, they may be the developers themselves. But it is all voluntary, so keep your expectations low.