Java Client error handling

Communication Errors

The following list shows typical exceptions that might be thrown when communication problems with the system occur.

java.net.MalformedURLException

The URL is not valid.

java.net.UnknownHostException

The host name is not valid. This is the actual exception string, not the type of the Exception object.

java.net.ConnectException: Connection refused: connect

The web server not running or the port number is incorrect.

(405)Method not allowed

The URL is incomplete or inaccurate URL (typically the name of the virtual directory).

(500)Server Error

The URL is incomplete or inaccurate.

(500)Error loading module

The URL is incomplete or inaccurate.

System-specific errors

static int getErrorDescription (java.rmi.RemoteException e,
java.util.StringBuffer description)

Example

The following example demonstrates error handling in the system. It calls the method getAllCategories, which returns the list of knowledge base categories and handles the various possible errors.

1. try {
2. String[] kbCategories = bnsServer.getAllCategories (kbName);
3. // Application code that uses kbCategories
4. } catch (java.rmi.RemoteException e) {
5. StringBuffer errDescription = new StringBuffer();
6. int errNumber = BnsErrorLookup.getErrorDescription (e, errDescription);
7. if (errNumber == BnsErrorLookup.E_BNS_SERVICE_UNAVAILABLE) {
8. // Error handling for the case that the knowledge base is not running
9. }
10. else if (errNumber<0) {
11. if (errDescription.indexOf("(403)")>=0) {
12. // Error handling for "login failed"
13. }
14. else {
15. // Error handling for other server connection errors
16. }
17. }
18. else {
19. // Error handling for other server errors
20. }
21. } catch (Exception e) {
22. // Error handling
23. }

The purpose of each section of the preceding code is shown in the following list, by line numbers:

2

Call the Server method getAllCategories

5-6

Retrieve error code and description

7-8

Error handling for the specific case of the knowledge base not running

10-15

Error handling for server connection errors

11-12

Error handling for cases where logging on fails

18-19

Error handling for other server-specific errors

21-22

Error handling for general exceptions