java default sizes

to see the default stack, heap sizes in IBM JRE/JDK, run this command:
java -verbose:sizes -version

JNI issues on linux

Problem #1: when compiling JNI component on a linux machine, it was missing tons of type definitions from jni.h. It appears libgcj-devel-version needs to be installed as the jni.h in it has the native datatype definitions.

Problem #2: if you see an error message such as the following when executing JNI components:
wrong ELF class: ELFCLASS64 (Possible cause: architecture word width mismatch)
Chances are that your jni shared library .so was compiled to be 64bit but your JDK/JVM is 32-bit! just use 64-bit java to run it instead

response headers that prevents browser to cache JSP

// Set to expire far in the past.response.setHeader(”Expires”, “Tue, 23 May 1995 12:00:00 GMT”);
// Set standard HTTP/1.1 no-cache headers.response.setHeader(”Cache-Control”, “no-store, no-cache, must-revalidate”);
// Set IE extended HTTP/1.1 no-cache headersresponse.addHeader(”Cache-Control”, “post-check=0, pre-check=0″);
// Set standard HTTP/1.0 no-cache header.response.setHeader(”Pragma”, “no-cache”);

JNDI names of TransactionManager in J2EE application servers

java:comp/env/UserTransaction - Generic
java:comp/UserTransaction - Resin 2.x, Oracle OC4J (Orion), JOnAS (JOTM), BEA WebLogic
java:comp/TransactionManager - Resin 3.x, Geronimo
java:/TransactionManager - JBoss
jta/usertransaction - WebSphere (J2EE 1.2)
java:comp/UserTransaction - WebSphere (J2EE 1.3)