Download Distributed Web Software

Distributed Web Software
• Presentation-based, e.g., dynamic web pages
• Service-based – Web Services
Importance of Web Services
• Larry Page, on why Google introduced its
search API:
“Within a few years, there will be more
programs (agents) accessing Google than
people accessing Google.”
Problems with PresentationBased Services
• Server determines what to display and how
to display it.
• Combining services is difficult
– Web page wrappers/scrapers
Sample Web Apps
• Travel Site
– Access web services of all major airlines
– List in sorted order the best prices for desired
destination/time.
• WebTop
– Allows user to pull in context from various
sources.
Dynamic Web Pages
Database A
Database D
Database B
Database C
Web Services
Service D
Service A
Service B
Service C
Database A
Database D
Database B
Database C
Sample Web Service:
The Google API
• http://images.google.com/apis/
• Your Java/.Net program can call Google
functions.
• SOAP underneath the hood
• Let’s try it…
Google API Tutorial
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Download at http://images.google.com/apis/
Extract files from zip into directory “Google”
Register to get a key (same page).
Open the readme file that was downloaded.
Run the demo program from “Google” dir:
java -cp googleapi.jar
com.google.soap.search.GoogleAPIDemo <key>
search Foo
Where <key> is your registration key and Foo is
the item you wish to search for.
Google API Tutorial
• Check out the Google API
– Go to javadoc directory and click on index.html
– API Reference page is “APIs_Reference.html”
• Check out demo program
– GoogleAPIDemo.java in main dir.
– Run it.
Google API Assignment
• Write a class USFInward with a main
program that lists the URLs (only) of five
web pages that point to www.usfca.edu.
• Instead of beginning from scratch, modify
GoogleAPIDemo.java.
Google Assignment Solution
• SaveAs GoogleAPIDemo.java to USFInward.java.
• Rename class in source file.
• Replace the package statement at top with:
– import com.google.soap.search.*;
• Modify code to perform requested actions.
• javac -classpath googleapi.jar USFInward.java
• Add “.” to classpath in execution line:
java -cp .;googleapi.jar USFInward.java
Google Solution Issues
• Define a private static final int MAX=5
• Search string should be
“linkto:www.usfca.edu”
• Use GoogleSearchResult.getResults() to get
array, then loop on each
GoogleSearchResultElement calling
getURL()
Google Web Service:
Under the Hood
Java Client
C# Client
Java API
C# API
SOAP API
Google DB
Google Crawler
Other Client
Amazon Web Service
• http://associates.amazon.com/exec/panama/
associates/ntg/browse/-/1067662/0863054474-4553435
UDDI Registries
Writing Web Service Clients in Java
WSDL – Web Service Description Language
UDDI- Registry of Web Services
1. Fine Web Service WSDL document in UDDI.
2. Generate Java stubs to access service:
WSDL
wscompile
Java stubs
3. Write Java client that accesses service through stubs.
Creating a Web Service
• Similar to RMI, define a “Remote” interface
– public interface MathService extends Remote {
int add(int x, int y)
throws RemoteException;
//…
}
• Implement the interface
– public class MathServiceImpl implements
MathService { public int add( int x, int y) throws
RemoteException; { return x+y; }
Creating a Web Service (cont.)
• Use wsdeploy to create “ties” and WSDL file:
MathService.java
MathServiceImpl.java
wsdeploy
WSDL
Java ties
• Package and Deploy– Build Web App Resource (WAR) file
• web.xml descriptor file