Solution for wss4j module compilation failure while building WSO2 Carbon Kernel

Problem - Building WSO2 Carbon often ended up with the following error, if there is a mismatch in the JDK version.

[ERROR] COMPILATION ERROR :
[INFO] -------------------------------------------------------------
[ERROR] /home/rajkumar/workspace/Building-Carbon/kernal/4.2.0/dependencies/wss4j/1.5.11-wso2v6/src/org/apache/ws/security/kerberos/KrbTicketDecoder.java:[10,24] EncryptionKey is internal proprietary API and may be removed in a future release

[ERROR] /home/rajkumar/workspace/Building-Carbon/kernal/4.2.0/dependencies/wss4j/1.5.11-wso2v6/src/org/apache/ws/security/kerberos/KrbTicketDecoder.java:[11,33] EncTicketPart is internal proprietary API and may be removed in a future release

[ERROR] /home/rajkumar/workspace/Building-Carbon/kernal/4.2.0/dependencies/wss4j/1.5.11-wso2v6/src/org/apache/ws/security/kerberos/KrbTicketDecoder.java:[12,33] Ticket is internal proprietary API and may be removed in a future release

[ERROR] /home/rajkumar/workspace/Building-Carbon/kernal/4.2.0/dependencies/wss4j/1.5.11-wso2v6/src/org/apache/ws/security/kerberos/KrbTicketDecoder.java:[13,40] KeyUsage is internal proprietary API and may be removed in a future release

[ERROR] /home/rajkumar/workspace/Building-Carbon/kernal/4.2.0/dependencies/wss4j/1.5.11-wso2v6/src/org/apache/ws/security/kerberos/KrbTicketDecoder.java:[14,24] DerInputStream is internal proprietary API and may be removed in a future release

[ERROR] /home/rajkumar/workspace/Building-Carbon/kernal/4.2.0/dependencies/wss4j/1.5.11-wso2v6/src/org/apache/ws/security/kerberos/KrbTicketDecoder.java:[15,24] DerValue is internal proprietary API and may be removed in a future release

. . . . etc.

Solution - WSO2 Carbon supports Java 1.6, at this point of writing. Hence, if you build using Java 1.7, you will get the above error.

Install Java 1.6, set the environments variables accordingly and try to build.