Web Services Homework Exercise

Objective

Prerequisites

1. This exercise assumes that you have some preliminary experience with Java. If you have never programmed in Java then you should spend some time going through the tutorial on Learning the Java Language at http://java.sun.com/docs/books/tutorial/java.

2. This exercise also assumes that you have had exposure to some basic Internet concepts. Some helpful references for this are at:
   • http://www.webopedia.com/quick_ref/OSI_Layers.asp
   • http://www.cs.kent.edu/~farrell/lectures/grid02.pdf

Overview

The steps of this exercise are:

1. Read some preparation material on Web Services
2. Create Web service source code as a jws (Java Web Service) file
3. Generate several Java source files representing the service from that jws file using the Axis tool
4. Compile the files created in the previous step
5. Create the client source
6. Compile the client source
7. Execute the client to access the service.
8. Extend the service by adding functionality
9. Answer the post-exercise questions.

STEP 0: Preparation

STEP 1: Define the Service with Java

public class MyMath 
{
  public int squared(int x) 
  {
    return x * x;
  }			
}

Part of the Apache open source project is support for web services, http://ws.apache.org/. That support includes the Axis tool, http://ws.apache.org/axis/. Axis is an implementation of the Simple Object Access Protocol (SOAP) which is a key protocol in web services. As part of supporting SOAP, Axis includes a program called WSDL2Java that will accept a Java source file, containing a Java class that implements a service, and will generate the Java source files needed to make that Java class into a web service. The input Java source file must have the extension jws to indicate that the Java source is intended to be a Java Web Service.

Axis expects the jws file to be in one of several standard locations. To support that requirement we have created another directory for you that is at $CATALINA_HOME/webapps/axis/yourusername/. CATALINA_HOME is the environment variable specifying the path to the home directory of the Apache Tomcat java servlet container. You can see the value of this environment variable by using the following command.

[yourusername@cohn
/local/opt/tomcat
[yourusername@cohn WebServices]$

You can see the directory that has been created for you and that it is currently empty by the following command.

[yourusername@cohn WebServices]$ ls $CATALINA_HOME/webapps/axis/yourusername/
[yourusername@cohn WebServices]$

[yourusername@cohn WebServices]$cp MyMath.jws  $CATALINA_HOME/webapps/axis/yourusername/

You can see that the file has been copied by doing the following command.

[yourusername@cohn WebServices]$ ls $CATALINA_HOME/webapps/axis/yourusername/
MyMath.jws
[yourusername@cohn WebServices]$

STEP 2: Create the Java source files needed for a web service

/opt/IBMJava2-142/bin/java -classpath $AXISCLASSPATH org.apache.axis.wsdl.WSDL2Java http://cohn.cs.kent.edu:8080/axis/farrell/MyMath.jws?wsdl

[yourusername@cohn WebServices]$/opt/IBMJava2-142/bin/java  -classpath     \
$AXISCLASSPATH org.apache.axis.wsdl.WSDL2Java      \
http://cohn.cs.kent.edu:8080/axis/yourusername/MyMath.jws?wsdl

The Axis WSDL2Java program finds the MyMath.jws file and creates the needed Java source files. The second argument is a URL (Universal Resource Location) specifying the web server that is listening on TCP port 8080 on the local machine. On cohn the Apache tomcat web server is running and listening on that port.

The result of executing the WSDL2Java program is to create in the current directory, /home/yourusername/WebServices, a directory named edu, with a subdirectory kent, with a subdirectory cs, subdirectory cohn. You can use the ls command to see this. This directory has a subdirectory named axis which has a subdirectory named yourusername which has a subdirectory named MyMath_jws. This series of directories was created because it follows the parts of the URL http://cohn.cs.kent.edu:8080/axis/yourusername/MyMath.jws?wsdl. The directory MyMath_jws that has four files in it.

• MyMath.java: source for Java interface for MyMath class
• MyMathService.java: source for Java interface that includes the getMyMath method specification
• MyMathServiceLocator.java: source for Java class MyMathServiceLocator
• MyMathSoapBindingStub.java: source for Java class MyMathSoapBindingStub

[yourusername@cohn WebServices]$ java -classpath $AXISCLASSPATH    \
org.apache.axis.wsdl.WSDL2Java      \
http://localhost:8080/axis/yourusername/MyMath.jws?wsdl

STEP 3: Compile Java Source Files Just Generated

[yourusername@cohn WebServices]$ /opt/IBMJava2-142/bin/javac -classpath $AXISCLASSPATH edu/kent/cs/cohn/axis/yourusername/MyMath_jws/*.java

STEP 4: Write Client Source

import edu.kent.cs.cohn.axis.yourusername.MyMath_jws.MyMathServiceLocator;
import edu.kent.cs.cohn.axis.axis.yourusername.MyMath_jws.MyMathService;
import edu.kent.cs.cohn.axis.axis.yourusername.MyMath_jws.MyMath;

public class MyMathClient {
public static void main(String args[]) throws 
	Exception {
    MyMathService service = new MyMathServiceLocator();
    MyMath myMath = service.getMyMath();
    int x = (new Integer(args[0])).intValue();
    System.out.println("The square of " + args[0] + 
" is " + myMath.squared(x));
  }
}

This client exercises the service by calling it to compute and return the square of the number passed as an argument.

STEP 5: Compile Client Code

[yourusername@cohn WebServices]$ /opt/IBMJava2-142/bin/javac -classpath $AXISCLASSPATH:. MyMathClient.java 

STEP 6: Execute Web Service Program

[yourusername@cohn WebServices]$ /opt/IBMJava2-142/bin/java -classpath $AXISCLASSPATH:. MyMathClient 4 

The square of 4 is 16

STEP 7: Add Functionality to the Web Service Program

• (step one) Edit MyMath.jws to add an additional method named isEven that returns a Boolean value and has one int argument. This method should include the code to determine whether the argument is an even number.
• (step two) Copy the revised MyMath.jws file to the directory $CATALINA_HOME/webapps/axis/yourusername/
• (step three)Run the WSDL2Java Java program on your MyMath.jws file to create the Java source files needed to make MyMath a web service.
• (step four) Compile the newly created Java source files
• (step five) Revise your MyMathClient.java file which holds your client source code to include at least one call to the new isEven method of your service.
• (step six) Compile your client source file, MyMathClient.java.
• (step seven) Execute your web service by executing your client, MyMathClient.class, which will then call the service.

STEP 8: Answer the post-exercise questions

1. According to "Introduction to Web services and the WSDK V5.1" from IBM at https://www6.software.ibm.com/developerworks/education/ws-intwsdk51/index.html, what are the four components in the definition of a Web Service?
2. In what ways is Web Services an improvement over earlier technologies, including DCOM, Java RMI, and CORBA?
3. Describe the two participants of the Web Service.
4. What is WS-I and what is its purpose?
5. In this exercise you used a script, WSDL2Java, to generate the Java files that you needed for your Web Service. Alternatively, we could have written the WSDL files and used these to generate the Java files. An instance of the WSDL protocol describes several things. Using the course notes http://www.cs.kent.edu/~farrell/grid06/lectures/grid06.pdf, the W3C documents such as http://www.w3.org/TR/wsdl as sources, give a brief description of these four WSDL items: messages, portTypes, bindings, and services.
6. Describe the three main roles in a SOAP message transmission.
7. Describe the four parts of a SOAP message.
8. Given the example of a SOAP RPC-Style Call at https://www6.software.ibm.com/developerworks/education/ws-intwsdk51/section4.html#N106F8
   1. What tag indicates the start of the envelope element?
   2. Is there a header element? If so, what tag indicates the start of this element?
   3. What tag indicates the start of the body element?
   4. How many procedure calls are in the body? How many parameters does the getDVDs procedure have?
9. What does UDDI stand for and what is it used for?
10. What three kinds of registry data are supported by UDDI?

Also answer the following questions, which will help me to improve this assignment. Turn these answers in on a separate piece of paper without your name on it.

1. How many hours did you spend on this assignment?

   Rate each of the following on a scale of 1-10 where 1 is "none/not at all" and 10 is "completely/definitely"

2. Rate your prior experience with Web Services.
3. The assignment was reasonable, given your starting skills.
4. The preliminary reading material was sufficient. If it was not, can you describe what was missing?
5. The assignment was comprehensible.
6. The assignment was hard.
7. It was helpful to have completed the RMI assignment prior to the Web Services assignment.
8. The Web Services assignment depended on knowledge gained from the RMI assignment. If so, can you give some detail about what know from the RMI assignment helped in this assignment?
9. I feel prepared to write a more advanced Web Service on my own.
10. I understand what XML is and how it is used.
11. I understand what SOAP is and how it is used.
12. I understand what WSDL is and how it is used.
13. I understand what UDDI is and how is is used.
14. I wish that the assignment had covered more details on XML.
15. I wish that the assignment had covered more details on SOAP.
16. I wish that the assignment had covered more details on WSDL.
17. I wish that the assignment had covered more details on UDDI.
18. I wish that the assignment had covered more details on Apache and Axis.
19. The tools on cohn were sufficient for this assignment. If not, what tools would you suggest that we use instead?
20. What would you change about this assignment?

References

Acknowledgements