Gary Han - A Nerd Who Tries To Be Cool And Failed Thus Far

OK! After selling my 4 bitcoins I had left back in the days for $10,000 few months ago to now what claimed to be $16k for 1??!!!

I had to write something about bitcoin...

First of all, the idea of crypto-currency is very promising. HOWEVER how bitcoin implemented the currency has huge issues.

1. The so called mining process uses a trial and error method to find the next nonce value that will create a hash value that is smaller than the previous hash value. And the time to find that next nonce is the "work" you need to do. (which i think is stupid and waste of power)

few ways to get the user information:

-User user= (User) SecurityContextHolder.getContext().getAuthentication().getPrincipal();
this pulls the whole user object.

- Principal userPrincipal = request.getUserPrincipal();
this pulls the user principal, which has access to the username by doing:
userPrincipal.getName();

- User currentUser = request.getSession(false).getAttribute("SPRING_SECURITY_CONTEXT").getAuthentication().getPrincipal();
you may do a few null checks, but this is the long and early way to get the user. Works in the filters too.

Just a fun note,

I was having a discussion with a group of programmers from different backgrounds.

And I was asked the question whats a better language and why do you prefer Java.

So my answer is, I like to build using Lego not PlayDoh.

When I program in Java, I feel my program is very safe and consistent.

when I program in PHP, Python or Ruby, I feel my program is very squishy.

A simply example is:

We can go on and on about feature differences on Oracle and Mysql. Table locking, stored proc, recovery, transaction control blah blah blah...
As a software user (yes, they are just regular software we use) I don't really care as long as it works and does what I need.

So today I want to get to the point and take note of the performance differences in Oracle and Mysql.

The key difference in Oracle over Mysql is its ability to perform fast CRUDs even under large number of threads and transactions.

Since so many people are talking about this issue, I will join too.

Openssl has a very simple yet dangerous flaw in the programming when they implemented the heartbeat feature.

Heartbeat is used to keep the session alive by having client server send a request over and the hosting server sends a response back.

But the issue with that is the request contains both the package and the package size.

and openssl simply echos back the original package and append anything after it with whatever package size it was specified?
REALLY? SERIOUSLY?

Websphere is a pain in the butt to deal with.

So whenever you have issues deploying a war file or any kind of issues,

first thing to try is to clear the websphere cache! I will do the trick 99% of the time!

to do so:

shut down websphere server.

/{websphereInstallPath}/IBM/WebSphere/AppServer/bin/clearClassCache.sh
rm -rf /{websphereInstallPath}/IBM/WebSphere/AppServer/profiles/AppSrv01/logs/*
rm -rf /{websphereInstallPath}/IBM/WebSphere/AppServer/profiles/AppSrv01/wstemp/*
rm -rf /{websphereInstallPath}/IBM/WebSphere/AppServer/profiles/AppSrv01/temp/*

If you are putting your database to maintenance, and you want to kill off all sessions from connecting your db so you can do whatever you want with it.

Do the follow for a quick clean up:

STARTUP FORCE;
ALTER SYSTEM ENABLE RESTRICTED SESSION;

now you are free to do whatever you want with your database.

when you are done:

ALTER SYSTEM UNQUIESCE;

now all other connections can start hitting your database again.

simple reminder to enable ftp on server:

yum -y install vsftpd

vi /etc/vsftpd/vsftpd.conf

ensure a line listen_port=21 is added to the config file,
and remove #connect_from_port_20=YES

vi /etc/vsftpd/ftpusers
remove root as not allowed user

vi /etc/vsftpd/user_list
remove root as not allowed user

When working with special characters we sometimes run into the issue where the string is not recognizing these characters.
Especially when trying to parse files from one platform from another.

I had the following line in a txt file on windows: (saved as ANSI)

éèêë

I had the following code that parses and replaces these characters:
(Java file is saved as UTF-8)
-------------------
File file = new File("/windowsPathMappedOnLinux");
FileInputStream fis = null;
BufferedInputStream bis = null;
DataInputStream dis = null;
String fileContent = "";

When you get a database dump from a server and try to import it to one another, often u will face errors like:

 DEFAULT '1753-01-01 00:00:00', "end_date" DATE DEFAULT '1753-01-01
ORA-39083: Object type TABLE failed to create with error:
ORA-01861: literal does not match format string

This indicates that the database dump might be using a string format which is different from your server.

To prove this, login to sqlplus, and do:

select sysdate from dual;

if the result is not of: