4. Web Services Lab

 

 Overview:  you will create a WinForms client application that communicates with Google's web service to perform searches and display the results.  Note that this assignment requires an active connection to the Internet. 

To earn a passing grade for this lab, you must demonstrate a working program to the instructor no later than June 8.

Programming against Google's Web Service

1.       This is a great example of the power of web services.  Google.com has a free web service (up to 1000 searches per day) that allows you to perform Google-based searches and manipulate / display the results any way you want.  In essence, you submit a query to Google, and you get back an array of result objects, each object containing a URL (among other things).  

2.       Remember the security warning message you’ve been getting when creating projects on the H: drive?  Well, this application will NOT run from the H: drive.  Be sure to create and run this application on the C: drive.  When you are done, you will need to copy your project back to your permanent storage space.

3.       Startup Visual Studio and create a new C# Windows application.  Set the location bar to your directory on the C: drive.  Choose an appropriate name for your project.

4.       On the form place

·         a  text box for the search string,

·         a label and textbox for displaying the estimated number of matches (should be read only),

·         a list box for displaying the resulting URLs - make sure the list box is pretty wide since it will be used for displaying URLs,

·         a button for performing the search. 

5.       Add a web reference to your application to the Google web service. 

·         In the Solution Explorer window, right-click on References

·         Select Add Web Reference

·         In the dialog box that appears, type the following URL to gain access to the necessary web service description file (WSDL): 

http://api.google.com/GoogleSearch.wsdl 

·         Click on Go. 

·         When the com.google.api shows up in the Web reference name box, click the Add Reference box.

Once added, the web service classes will exist within the namespace "com.google.api".  This should be the name you see in the list of Web References for your project.

6.       Program the search button (double click on the control to get from the control to its underlying code).

·         Declare two local reference variables, one of type GoogleSearchResult and another of type GoogleSearchService.  Note that by default, you'll need to reference these classes using their namespace "com.google.api".   

com.google.api.GoogleSearchResult   result;

com.google.api.GoogleSearchService  google;

·         Next, create a new instance of GoogleSearchService. 

·         Finally, call the doGoogleSearch() method using this instance and assign the result to your local GoogleSearchResult variable. 

result = google.doGoogleSearch("license key string",                                     

     "search string", 0, 3,                                                                

      false, "", false, "", "", "");                                                                                                                                

·         The first parameter of the doGoogleSearch() method must be a non-empty string containing a valid license key.  For the purposes of this lab, feel free to use either of my own personal license keys: 

YN0swmlQFHJWWESzD6kKRxSBfBGxHNP0  

ICYk3yFQFHK1S8NLFb20d1CI4KqswxmI

However, in the future, if you plan to work with Google's web service, please register for a free Google account and obtain your own personal license key.  You can register for an account at:  https://www.google.com/accounts/CreateAccount.  After activating your account, go to http://www.google.com/apis/ and follow the link to Create Accounts.  Sign in and a copy of your google license key will be sent to your email address.  

·         The second parameter is the search string.  Initially hard code in a word or phrase you wish to search on.

·         The third parameter is 0 and the fourth is 3.  These ask Google to return the first 3 hits, numbered 0 .. 2.  (Ten is the maximum number of matches you can request at once). 

·         The rest of the parameters should match the pattern given above.

·         After the call to doGoogleSearch(), an object is returned of type GoogleSearchResult.  This object contains a field called estimatedTotalResultsCount, which denotes the estimated number of hits based on your search string.  Convert this value to a string and display it in your label. 

·         Now rebuild and run!  Remember to click the Search button.

7.       Once that works, the next step is to display the first 3 hits in your list box.  The GoogleSearchResult object contains a field called resultElements, which is an array of objects of type ResultElement.  Each ResultElement object contains a URL.  Using a foreach statement, loop through the resultElements array, displaying each URL in the list box. 

foreach  (com.google.api.ResultElement r in result.resultElements)                                                                       

     lstHits.Items.Add ( r.URL );                                                                                                                                       

8.       Now run!  Wow!

9.       Change the second parameter in the call to doGoogleSearch so the search string is taken from the contents of the text box.  Type in a search term and run.

10.   If you want to display more URLs, you need to make additional calls to Google via the doGoogleSearch() method.  All you need to do is change the 3rd parameter each time:  pass 3 to get matches 3 .. 5, then pass 6 to get matches 6 .. 8, and so on.  Write a simple loop to get the first 20 or so matches, and display these in the list box.  Run, and be amazed :-)

11.   DEMONSTRATE THIS SOLUTION NOW OR SAVE A COPY OF THIS VERSION AND DEMONSTRATE IT LATER

12.   How can you learn about all this?  Surf to http://www.google.com/apis/ for more information, API documentation, sample .NET code, etc.  Enjoy!