feat(licensedb): Add exception handling classes for error management

[ADITYA-CODE-SOURCE]

Summary

Add custom exception classes for LicenseDB integration to handle various error scenarios when communicating with the external LicenseDB service.

Changes

Added 4 new exception classes in a new exception package:

Class	Purpose
LicenseDBException	Base exception for all LicenseDB errors
LicenseDBConnectionException	Thrown when LicenseDB server is unreachable
LicenseDBAuthenticationException	Thrown when OAuth2 authentication fails
LicenseDBDataException	Thrown when data validation fails

File Structure

rest/resource-server/src/main/java/org/eclipse/sw360/rest/resourceserver/licensedb/exception/
├── LicenseDBException.java
├── LicenseDBConnectionException.java
├── LicenseDBAuthenticationException.java
└── LicenseDBDataException.java

Example Usage

try {
    licenses = licenseDBClient.getAllLicenses();
} catch (LicenseDBConnectionException e) {
    log.error("Cannot connect to LicenseDB: {}", e.getMessage());
    return error("LicenseDB service unavailable");
} catch (LicenseDBAuthenticationException e) {
    log.error("OAuth2 auth failed: {}", e.getMessage());
    return error("LicenseDB authentication failed");
} catch (LicenseDBDataException e) {
    log.error("Invalid data from LicenseDB: {}", e.getMessage());
    return error("LicenseDB data validation failed");
}

Testing

• Files compile without errors
• Follow SW360 code style
• EPL-2.0 license headers included
• No dependencies on other components

Documentation

Each exception class includes Javadoc documentation explaining:

• When to use the exception
• Common causes
• Example usage

Dependencies

None - This is an independent component that does not require other components.

Related

• Fixes Add LicenseDB exception handling classes for error management #3893
• Parent issue: Add LicenseDB connection configuration properties #3685
• Related PR: feat(config): Add LicenseDB connection configuration properties #3686 (LicenseDB configuration)