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Creating Web Services with Apache Axis

by Dion Almaer
05/22/2002

Web services have been a buzzword for a while. A friend used to say "Web services are like high school sex. Everyone is talking about doing it, but hardly anyone is, and those that are probably aren't doing it well." These days, though, Web services are moving to college, so to speak, and lots of people are starting to "do it" more often and better than before. Tools are maturing, and creating and working with Web services isn't all that hard anymore.

IBM has given a lot of code to the Apache group, including SOAP4J, their group of SOAP tools. The Apache SOAP and SOAP4J guys got together and are working on the latest and greatest tool set called Apache AXIS, which features not only better performance, but also some new features that make it trivial to play in this new world. I see the most common actions being "I want to expose this functionality as a Web service," and "I want to access that Web service." Surely it should be very straight-forward to strap on this interface, and you shouldn't have to learn everything there is to know about the underlying platform. This is the same idea as not having to know about the IP and TCP layer when accessing a URL over HTTP. Let's keep it simple, folks.


Notes on running sample application

You can download the code and scripts to run the Fibonacci Web service. Your first step is to get Apache Axis running; then you can unzip the code and follow our steps. Read the README.txt in the distribution, as it covers how to set up your CLASSPATH and other deployment issues.

In this article, I will show two parts of this new system:

All of the code that is listed (and downloadable) was written for Apache Axis beta1. There are more instructions on running the code at the end of the article.


NOTE: I assume that you have basic knowledge of Web services. If you need to look up what a WSDL file is, checkout the Web services section of ONJava.com.


Deploying Your Code as a Web Service in One Easy Step

The Apache guys realized that it would be really nice to be able to drop some code somewhere and have it become a Web service "just like that." This simplicity is a current trend; Microsoft has it in .NET, and BEA in the WebLogic 7 platform. But just how easy is it to:

Deploy a Java Class as a Web service

Let's take the simple Calculator.java class from the samples.userguide.example2 package and expose its two methods (add() and subtract()) through Web services. We simply copy the Java file into the Axis Web application, using the extension .jws instead of .java:

% cp samples\usersguide\example2\Calculator.java %TOMCAT_HOME%\webapps\axis\Calculator.jws

Just by having the code (with the .jws extension) in the Web application deploys it and allows us to access it. If we open a browser and access the file (e.g. http://localhost:8080/axis/Calculator.jws) we will be told that we are talking to a Web service. How easy was that?! A simple copy command and we are done.

Java Web Services

Related Reading

Java Web Services
By David A. Chappell, Tyler Jewell

Write a Client That Accesses the Web Service

Now we have a deployed Web service; we need to access it. Let's look at a client that allows us to pass in a math operation (add or subtract) and the two amounts to work with.

package samples.userguide.example2;

import org.apache.axis.client.Call;
import org.apache.axis.client.Service;
import org.apache.axis.encoding.XMLType;
import org.apache.axis.utils.Options;

import javax.xml.rpc.ParameterMode;

public class CalcClient {
   public static void main(String [] args) throws Exception {
       Options options = new Options(args);

       String endpoint = "http://localhost:" + options.getPort() +
                         "/axis/Calculator.jws";

// Do argument checking
       args = options.getRemainingArgs();

       if (args == null || args.length != 3) {
           System.err.println("Usage: CalcClient <add|subtract arg1 arg2");
           return;
       }

       String method = args[0];
       if (!(method.equals("add") || method.equals("subtract"))) {
           System.err.println("Usage: CalcClient <add|subtract arg1 arg2");
           return;
       }

// Make the call
       Integer i1 = new Integer(args[1]);
       Integer i2 = new Integer(args[2]);

       Service  service = new Service();
       Call     call    = (Call) service.createCall();

       call.setTargetEndpointAddress(new java.net.URL(endpoint));
       call.setOperationName( method );
       call.addParameter("op1", XMLType.XSD_INT, ParameterMode.PARAM_MODE_IN);
       call.addParameter("op2", XMLType.XSD_INT, ParameterMode.PARAM_MODE_IN);
       call.setReturnType(XMLType.XSD_INT);

       Integer ret = (Integer) call.invoke( new Object [] { i1, i2 });

       System.out.println("Got result : " + ret);
   }
}

The code first imports all of the required classes. Then we set the URL of the Web service that we want to invoke. Skip past the argument checking, and we get to the meat: we configure the method that we want to call, the parameters to pass, and then invoke the service itself. So, we have deployed and accessed the Web service by writing a minimal amount of code.

Obtain the WSDL For the Deployed Web Service

What if we wanted to retrieve a WSDL file to give to a programmer who needs to talk to our particular service (and who may be using .NET or Python or something else to access it)? Once again, the Apache folk thought of this. We can grab the definition file simply by accessing the Web service and appending?WSDL to the end of the URL. If I simply point my browser to http://localhost:8080/axis/Calculator.jws?WSDL, I get the XML descriptor sent back to me.

Working With a Production Web Service

Although it is really easy and convenient to shove our Java code under the Axis directory as a .jws file, that will not be the way you deploy all of your Web services. A lot of the time we want more fine-grained control over the Web service, to tweak it, and to use other more advanced features. Luckily, with other tools, it is still easy for us to work with our code in a more formal manner.

Let's walk through the following process:

  1. We have a piece of code that calculates the Fibonacci sequence for a given iteration.
  2. We want to take the existing code, wrap it up as a Web service, and then deploy it to the Apache Axis system.
  3. Once we have a running service on the server side, we will create Java stubs that allow us to communicate with the service, only requiring the WSDL.

After going through this full process, you will be able to create clients to any Web services (when given the WSDL), and wrap up any code, exposing it as a Web service.

Here are the steps we will walk through:

  1. View: Take a peek at the existing Fibonacci code.
  2. Java2WSDL: Generate the WSDL file for the given Fibonacci interface.
  3. WSDL2Java: Generate the server side wrapper code, and stubs for easy client access.
  4. FibonacciSoapBindingImpl: Fill in wrapper to call the existing Fibonacci code.
  5. Deploy: Deploy the service to Apache Axis.
  6. Client: Write a client that uses the generated stubs, to easily access the Web service.

1. View: Take a Peek at the Existing Fibonacci Code

There are two files of our existing code: an interface and an implementation class. First, we have defined the Fibonacci interface that has methods for calculating one, or a range of Fibonacci sequences.

Example 1. Fibonacci.java

package fibonacci;

public interface Fibonacci {

        // Method to calculate the fibonacci sequence
        public int calculateFibonacci( int num );
        // Method to return an array of results
        public int[] calculateFibonacciRange(int start, int stop);
}

Then we have the real implementation of that code. Don't spend time studying how the Fibonacci sequence is calculated, though; that isn't the point.

Example 2. FibonacciImpl.java

package fibonacci;

public class FibonacciImpl {

        public int calculateFibonacci( int num ) {

                if (num <= 0) return 0;
                if (num == 1) return 1;

                int previous1 = 1, previous2 = 0, fib = 0;


                for (int i=2; i <= num; i++) {
                // the fib is the answer of the previous two answers
                        fib = previous1 + previous2;

                        // reset the previous values
                        previous2 = previous1;

                        previous1 = fib;

                }

                return fib;
        }

        public int[] calculateFibonacciRange(int start, int stop) {
                int[] results = new int[stop + 1];

                for (int x=start; x <= stop; x++) {
                        results[x] = this.calculateFibonacci( x );
                }
                return results;
        }
}

2. Java2WSDL: Generate the WSDL File For the Given Fibonacci Interface

Now we have the Fibonacci code, and we compile it (javac). Here comes the first tool that helps us out as we endeavor to make that code a Web service. The Java2WSDL command line will generate a standard WSDL file that conforms to a given interface. We tell the program the information it needs to know as it builds the file, such as:

The full command for our example becomes something like:

% java org.apache.axis.wsdl.Java2WSDL -o fib.wsdl -l"http://localhost:8080/axis/services/fibonacci" -n urn:fibonacci -p"fibonacci" urn:fibonacci fibonacci.Fibonacci

After the program runs, we see that a new file, fib.wsdl, was created for us. If we look inside the file, we see 114 lines of information that needed to be created for this Web service. Aren't you glad that you didn't need to write the whole thing? How do people write them by hand?

Now we have defined our Web service.

3. WSDL2Java: Generate the Server-side Wrapper Code and Stubs For Easy Client Access

Our next step is to take this WSDL and generate all of the glue code for deploying the service, as well as stubs for accessing it. The WSDL2Java tool comes to our aid here to take that chore out of our hands.

Let's generate this code into the fibonacci.ws package, to keep it separate from the original code. Once again, we need to tell this command line some information so it can go ahead and do its work:

The full command for our example becomes something like:

% java org.apache.axis.wsdl.WSDL2Java -o . -d Session -s -p fibonacci.ws fib.wsdl

After running this program, a slew of code has been generated for us in the fibonacci\ws directory:

4. FibonacciSoapBindingImpl: Fill-in Wrapper to Call the Existing Fibonacci Code

We need to tweak one of the output source files to tie the Web service to FibonacciImpl.java. FibonacciSoapBindingImpl.java is waiting for us to add the stuff into the methods that it created. The lines that we added are in bold:

package fibonacci.ws;

import fibonacci.FibonacciImpl;

public class FibonacciSoapBindingImpl implements fibonacci.ws.Fibonacci {
        FibonacciImpl fib = new FibonacciImpl();

    public int calculateFibonacci(int in0) throws java.rmi.RemoteException {
        return fib.calculateFibonacci(in0);
    }

    public int[] calculateFibonacciRange(int in0, int in1) throws java.rmi.RemoteException {
        return fib.calculateFibonacciRange(in0, in1);
    }

}

We are simply tying in to the existing class. We could have hard-coded the methods in this class, but in the real world, we probably want to wrap logic as Web services, and not just enable access via that interface.

5. Deploy: Deploy the Service to Apache Axis

Now we are ready to deploy this service. We have to do the following:

Compile the Service Code:

We first have to javac fibonacci\ws\*.java

Package the code for Axis to find:

Next, we package all of the code that we have and copy it into Axis' classpath:


% jar cvf fib.jar fibonacci/*.class fibonacci/ws/*.class

% mv fib.jar %TOMCAT_HOME%/webapps/axis/WEB-INF/lib
Deploy the Web Service using the WSDD Deployment Descriptor:

Apache Axis has an Admin client command line tool that we can use to do tasks such as (un)deployment, and listing the current deployments. We pass the deployment descriptor to this program so it can do its work:


% java org.apache.axis.client.AdminClient deploy.wsdd
<admin>Done processing</admin>

Now our Fibonacci Web service is alive and running in the server!

6. Client: Write a Client That Uses the Generated Stubs to Easily Access the Web Service

We should check to see if it is working, right? Let's write a simple client that uses the generated client code from the WSDL2Java step, to calculate the Fibonacci number at the 10th step.

All we need to do in the code is to get access to the service via the ServiceLocator, and then call methods on the remote handle that we have to the service. It looks just like normal Java; none of that silly SOAP or RPC code is in sight. Isn't that nicer? (Take another look at the CalcClient that we used at the beginning, and compare it to this code.)

package fibonacci;

public class FibonacciTester {
  public static void main(String [] args) throws Exception {
    // Make a service
    fibonacci.ws.FibonacciService service = 
         new fibonacci.ws.FibonacciServiceLocator();


    // Now use the service to get a stub to the service
    fibonacci.ws.Fibonacci fib = service.getFibonacci();

    // Make the actual call
    System.out.println("Fibonacci(10) = " +
                     fib.calculateFibonacci(10));
    }
}

Ahh, much nicer.

Conclusion

We have seen that it is much simpler to work with Web services when using nice tools such as the open source Apache Axis toolkit. Web services should be easy, and they are finally becoming that way. Take another look at the steps that we went through, and notice how little code we wrote to expose our original code as a Web service. These tools are only going to get better; at some point we will just think, "I want this as a Web service," and it will happen.

Dion Almaer is a Principal Technologist for The Middleware Company, and Chief Architect of TheServerSide.Com J2EE Community.


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