Java Code Samples

Java Performance Notes

Posted in Java by Cristian on August 13, 2015

JVM Overview
Collecting performance statistics
JVM Tuning

1) JVM Overview

1.1) JDK vs JRE
JRE = JVM + Class libraries
JDK = JRE + developer tools (javac, jconsole etc)
Server JRE (above Jre 7u21, no autoupdate )

1.2) Install the JDK
-Linux64 : server JRE 64 bit
-Solaris : in to steps first 32 and on top of that 64 bit version

1.3) Major Components of JVM

Hotspot Vm Runtime :
-command line option parsing
-JVM livecycle
-exception handling
-fatal exception handling
-class loading
-java native interface
-thread management and synchronization

Garbage Collector – Memory manager
Influence the performance of a java application
Hotspot JVM has 4 GC’s:
Two are know as ‘stop the world moment’ (STW GC) garbage collectors,the other two are a
combination of STW and concurrent GC

STW GC==> stops all java application threads.
Mostly concurrent GC ==> concurrenlty executes while java application is running

Young gen. vs Old gen.
Perm Gen (Java 6&7) class metadata , class data structures
PermGen does not exist in Java 8 , just metaspace

GC in hotspot:
-Serial GC , single threaded STW young generation collector + single threaded STW old gen collector
(small footprint)
-Throughput GC , multithreaded STW young + old gen collector
-CMS concurrent garbage collector , STW young and , mostly concurrent old generation
-G1 garbage collector (>jdk7u4) multithreaded STW region based young GC + combination of STW and mostly
concurrent old generation GC
G1vs CMS ==> G1 compact old gen without requiring a Full GC

JIT compiler

-takes bytecode ==> native code for the undelying platform.

Understanding the runtime system

java -XX:+PrintFlagsFinal -version ==> to see the runtime params of JVM

Visual GC plugin on VisualVM

Memory Pools plugin

Code Cache – the amount of code that is JIT compiled
For large enterprise application, code cache space might be exhausted so the application slows down because
it disables the JIT compilation

Metrics to monitor
-OS level

OS Level

-CPU usage : user CPU, system CPU and idle time
User CPU : time spent outside OS kernel by a program
Kernel (System) SPU – % spent executing kernel code
Idle CPU – % of CPU not being utilized.
Goal is to execute more User CPU

-Virtual Memory Usage
Attention to swapping !!!

-Process behaviour : context switching,CPU scheduling and thread migrations

Two kidns of context switching :

-voluntary : applicatio threads voluntarily takes itself off the CPU as a result of locks or wating on IO
High values of this ==> indication of lock contention
-involuntary:==> there are a large number of application threads more then the CPU cores available

CPU scheduling queue —> large number of app. threads vs low number of CPU cores ==> system slugish

Disk I/O

Network I/O

Monitor Metrics on Windows
PerfMon – Visual tool
Privileged time – kernel time


ex typeperf -si 5 -cf typeperf-cpu.txt

Monitoring CPU scheduling

Monitorign Virtual Memory Usage

Monitoring Avalable memory and paging activity

If paging is too often ==> swapping



SSH (Secure Shell) ,VNC – Dummy network stuff (old article I wrote long time ago)

Posted in Uncategorized by Cristian on February 13, 2015

Despite I’m a developer for many years I never really had to deal with
SSH.Even when I used it ,someone told me to do this and that and since it worked I did not payed attention to it.Nowdays the same happened but this time I was curious to know more.

So with this occasions I wrote a tutorial based on a VTC video tutorial I had but never watched before.So if you plan to nicely watch a video instead of reading then go an buy that tutorial :).

BTW: I wrote this without saying i am a specialist in this area.My expertise is programming. I did this for my learning purpose.

So what is SSH (Secure Shell) ?

SSH is a way to connect remotely to another computer .After you connect you may do administration tasks,or you can share files.All of this in a secure manner.

SSH is a suite of applications : ssh,scp,sftp etc.I will get back on them later in this tutorial.

SSH is also a network protocol.

SSH works on a variety of operating system like unix,linux,windows,mac os,bsd. Some of the platforms come SSH built-in like linux,unix,mac os. Windows require SSH to be installed as separate package. There are some versions on the market , but we will use one of the most common OpenSSH .

SSH operates by default on port 22 .The default port can be changed.

SSH may be used from command line ,but also there some SSH clients that are GUI based.

Note. For those not very familiar ,using SSH implies a client and a server.As i already mentioned unix and linux systems already have bundled everything necessary to use ssh as server or as client.In order to install SSH server on Vista please take a look on this: For installing a client go to Putty,a very popular SSH client and not only.

How to configure SSH ?

Well in order to configure the service edit the /etc/ssh/sshd_config file and to configure the client edit the /etc/ssh/ssh_config file.Notice that in normal case you will not want to edit these files.I just show you where to look in case you need for example to change the default port of the service.
You can see config files with: cat /etc/ssh/sshd_config or cat /etc/ssh/ssh_config.

FYI:On cygwin i noticed that sshd_config and ssh_config files are located in /etc/ not in /etc/ssh directory.

How to connect to a remote host that already runs ssh server (daemon,service) ?

Connecting to a ssh service is simple and it maybe done using Putty or from a command console : ssh username@remotehost where user name is a user on the remote host.After entering this a password promoter will appear.Enter the password and you be connected to that remote computer.You can browse files perform administration tasks on that remote computer now.

How to copy files from remote computer to your computer ?

Well that can be done using scp.This is not very very handy and practical since you have to know exactly what files you want to copy from the remote server.You can type man scp for more details.I will show you just a simple example from my personal setup environment:

scp sergiu@cristi:/cygdrive/c/*.* /cygdrive/c/temp

To translate I copy all the files from c: directory located on remote computer called cristi to my localhost’s c:/temp directory.(you can practice this with any path that fits your local directory structure). drive c in cygwing is mapped to /cygdrive/c. I cover more windows like situations using cygwing since on linux this is already covered very very well and windows users are more likely to not know this stuff.

How to use sftp to transfer data ?

SFTP is like SCP but it has an advantage: you can actually browse files on remote host.SFTP is the secured version of FTP.Command is sftp username@remotehost ,a password prompt will appear.Enter password then another prompt will appear. Something like this sftp> where you can use regulat ftp commands.Commands may be found here.
A nice visual tool that can be used from windows is called WinScp

How to use multiple sessions ?

Because you will not want to open many ssh connection and for each to have a terminal ,since that is resource consuming you will better user one terminal but with multiple screens.Command used for that is screen (man screen will help you more).
Is possible to use as well GUI tools or to visualize applications that run on server side.This is knows as X11 Forwarding.Note that x11 forwarding must be enabled both on client and server side.What I did not understood from beginning is that I need a X11 server running on client side,so don’f forget that in case you want to use this possibility.

How to use connect to a remote desktop with SSH ?

There are some desktop application like VNC that can be forwarded over ssh since they are not secure by default.
I tried the following scenario: On my ubuntu I activated the remote desktop.
The I downloaded vnc client.
So in order to connect on ubuntu desktop I started from another machine on which I have windows and I connect to the default VNC port 5900 without any problem.BUT the connection was not secure ! So here is the SSH comes into schema.
In order to have a secure connection with the remote desktop I did the following from windows cygwin console:

ssh -L 4444:localhost:5900 ubuntubox

This is translated start ssh connection on ubuntubox and alos listen on my localhost 4444 port and redirect any trafic to that port to ubuntubox 5900 port.

So I started the vncclient again but this time I connect it to locahost:4444 and it worked as previous time ,but encrypted !

Multiple versions of Java on OS X Mavericks

Posted in Java by Cristian on April 18, 2014

Of course after OS X Mountain Lion it was the time to update my java on OS X Mavericks.

Let’s see how to use multiple versions of java on OS X Mavericks.

I plan to use  Java7 and Java 8 from Oracle and to have an easy way of changing the default version.

As you probably know there is a difference between JRE and JDK.If not a very nice response you can find here.

Regarding JRE we should keep in mind that

1) “Only one JRE can be installed at a time. The system will not install a JRE that has a lower version than the current version. If you wish to install a lower version of the JRE, first uninstall the current version.”

2)”Installing a JRE from Oracle will not update java -version symlinks or add java to your path. To be able to do this, you need to install the JDK.”

I installed JdK 7 and Jdk 8

Right after I installed Jdk8 it seems that the simlinks were updated and java -version returned

MacCris:~ cristianchiovari$ java -version
java version "1.8.0_20-ea"
Java(TM) SE Runtime Environment (build 1.8.0_20-ea-b05)
Java HotSpot(TM) 64-Bit Server VM (build 25.20-b05, mixed mode)
MacCris:~ cristianchiovari$

as well java_home was set to Jdk 8

MacCris:~ cristianchiovari$ /usr/libexec/java_home

In my .profile i have as well defined

export JAVA_HOME=$(/usr/libexec/java_home)

As well i found very practical this command which is used to choose the default java_home. (it seems it iterates all java installations and the latest version is tool)

MacCris:~ cristianchiovari$ /usr/libexec/java_home -verbose
Matching Java Virtual Machines (7):
1.8.0_20, x86_64: "Java SE 8" /Library/Java/JavaVirtualMachines/jdk1.8.0_20.jdk/Contents/Home
1.7.0_45, x86_64: "Java SE 7" /Library/Java/JavaVirtualMachines/jdk1.7.0_45.jdk/Contents/Home
1.7.0_11, x86_64: "Java SE 7" /Library/Java/JavaVirtualMachines/jdk1.7.0_11.jdk/Contents/Home
1.7.0_10, x86_64: "Java SE 7" /Library/Java/JavaVirtualMachines/jdk1.7.0_10.jdk/Contents/Home
1.7.0_05, x86_64: "Java SE 7" /Library/Java/JavaVirtualMachines/1.7.0.jdk/Contents/Home
1.6.0_65-b14-462, x86_64: "Java SE 6" /System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home
1.6.0_65-b14-462, i386: "Java SE 6" /System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home

Now in order to have latest Jdk7 installed on my computer as default java I had to change in my .profile file

#export JAVA_HOME=$(/usr/libexec/java_home)
export JAVA_HOME="`/usr/libexec/java_home -v '1.7*'`"

After opening a new terminal

MacCris:~ cristianchiovari$ java -version
java version "1.7.0_45"
Java(TM) SE Runtime Environment (build 1.7.0_45-b18)
Java HotSpot(TM) 64-Bit Server VM (build 24.45-b08, mixed mode)


MacCris:~ cristianchiovari$ /usr/libexec/java_home

That however is not affecting the default java version as described above.
In order to change that you might need to uninstall the Jdk that points to or to use some kind of hacked
as in

Inspired from :


Java – Interpreted or Compiled ?

Posted in Java, Miscellaneous by Cristian on January 29, 2014

Well the answer is not so simple, but we will have one by the end of this short article 🙂

We all know that the source code of a Java file is ‘compiled’ into a .class file.

I put compiled in quotes because the .class file that results is not actually the machine code executed by the machine

The .class (JVM byte code) file might be seen as an intermediary language that might be even modified before is interpreted , compiled and executed.

This happens very often in an JEE environment and it is called weaving.Weaving is a technique of manipulating the byte-code of compiled Java classes.

After we have the final version (might be directly and not necessarily weaved),the byte-code is interpreted and the code is executed .

So where the code is then actually compiled !?

Well an interpreter can generate machine code to get a job done faster if this is important.

A modern VM will use all kind of techniques to do it faster and efficient. For example, for each instruction in the intermediate language the VM could ask which is going to be quicker: to call a routine or to generate machine code to get the job done. This approach is often called Just-In-Time or JIT compilation. It is usually explained as the VM compiling the intermediate language just before it is run, but this isn’t really a good way to think of it.

So the JIT is a sort of mixture of interpreting the code and compiling the code according to what makes best use of the real machine.

To respond to the initial question : it is both !

A diagram that describe the above:


Tagged with: , , on MAC OS X

Posted in Miscellaneous by Cristian on November 12, 2013

While trying to start an Apache Derby server on Mac I got: MacCris: MacCris: nodename nor servname provided, or not known

To solve this:

Step 1 – Open the Terminal

Step 2 – Go to the host file

$ sudo nano /private/etc/hosts
Type your user password when prompted.

Step 3 – Edit the hosts file localhost MacCris
Of course you will replace MacCris with your hostname.

Step 4 – Save the hosts file

When done editing the hosts file, press Control+x to save the file.

Have fun !

Debug problem with weblogic

Posted in Uncategorized by Cristian on November 5, 2013
While debugging some application on Weblogic

]] Root cause of ServletException.
java.lang.AssertionError: the tube must call the add(…) method to register itself before start copying other pipes, but weblogic.wsee.jaxws.tubeline.FlowControlTube$FlowControlAwareTube@d10de7 hasn’t done so
at weblogic.wsee.jaxws.tubeline.FlowControlTube.<init>(
at weblogic.wsee.jaxws.tubeline.FlowControlTube.copy(
at weblogic.wsee.jaxws.tubeline.FlowControlTube.copy(

Problem was solved by

modifying the setDomainEnv.cmd by adding



if "%debugFlag%"=="true" (
	set JAVA_DEBUG=-Xdebug -Xnoagent -Xrunjdwp:transport=dt_socket,address=%DEBUG_PORT%,server=y,suspend=n -Djava.compiler=NONE
	set JAVA_OPTIONS=%JAVA_OPTIONS% %enableHotswapFlag% -ea -da:com.bea... -da:javelin... -da:weblogic... -ea:com.bea.wli... -ea:com.bea.sbconsole...
) else (
	set JAVA_OPTIONS=%JAVA_OPTIONS% %enableHotswapFlag% -da

Just to remember in case it happens again.

Tagged with: , , ,

Enterprise Service Bus Notes

Posted in Miscellaneous by Cristian on October 24, 2012

A thing to know about ESB is that there is not perfect definition for it. The scope and role may vary depending on the needs.
One of the most important things that you can do via ESB is to decouple the client from the service providers

ESB helps to have:

  • a service location transparency
  • sharing of services accross the enterprise
  • separate the business service from service implementation

 Esb Capabilities 

The ability to redirect a client request to a particular service provider based on deterministic or variable routing criteria.
Types of routing to consider:

  • static or deterministic routing
  • content based routing
  • policy based routing
  • complex rules based routing

Message transformation
The ability to transform the client request to the format the service provider expects it. Most used transformations are:

  • Xml -> Xml
  • Xml -> Cobol
  • Object -> Xml Xml -> Json etc.

Message enforcement

The ability to enrich,enhance the message that comes as request as the service provide requires.Types of message enforcement:

  • Date format conversion
  • Data conversion (ex: transform spaces to 0)
  • Rule based enhancements. (ex: if message is from x add some information to the request)etc.

Protocol transformation

The ability to accept from the consumer one type of protocol as input (ex SOAP/JMS) and communicate to the service provider other protocol (ex: IIOP)

Service Mapping

The ability to translate a business service into the corresponding service implementation and provide binding and location information

Message processing

The ability to manage state and perform request management by accepting an input request and ensuring delivery back to the client via message synchronization.

Process choreography

The ability to manage complex business processes that require the coordination of multiple business services to fulfill a single business request.

Service Orchestration

The ability to manage the coordination of multiple implementation services.

Transaction management

The ability to provide a single unit of work for a business service request by providing a framework for the coordination of multiple resources across multiple disparate services
(see more WS – Coordination)

The ability to protect enterprise services from unauthorized access
ESB should provide 4A’s of security :

  • Authentication
  • Authorization
  • Auditing
  • Administration
Tagged with:

Multiple versions of Java on OS X Mountain Lion

Posted in Java, Miscellaneous by Cristian on September 16, 2012

@This article is deprecated and might be used only for MounatinLion 10.8.1

Before Mountain Lion, Java was bundled inside OS X. It seems that during the upgrade, the Java 6 version I had on my machine was removed.
Apparently the reason for uninstalling Java during the upgrade process was caused by a security issue that the Java runtime had.In this way you are forced to install the latest version which fixed this security problem.

So I went to /Applications/Utilities/ open a Terminal and executed the following command:
java -version ==> “No Java runtime present …”
A window prompted asking to install Java.Click “Install” and get the latest version.I installed it but right after I downloaded and installed the JDK SE 7 from Oracle.

After installation, open the Java Preferences (Launchapad/Others ) and you will see :

Now I knew I had two versions of Java but which one I am using it ?

$ java -version
java version &quot;1.6.0_35&quot;
Java(TM) SE Runtime Environment (build 1.6.0_35-b10-428-11M3811)
Java HotSpot(TM) 64-Bit Server VM (build 20.10-b01-428, mixed mode)

So what if i want to use JDK SE 7 from Oracle ?
Then I had just to drag Java SE 7 in the Java Preferences window to the first position in the list.

This time :

$ java -version
java version &quot;1.7.0_05&quot;
Java(TM) SE Runtime Environment (build 1.7.0_05-b06)
Java HotSpot(TM) 64-Bit Server VM (build 23.1-b03, mixed mode)

I said to myself let’s find out more out how Java is installed on OS X so I dug for more.

There are some very useful commands : whereis and which and ls -l.

whereis java ==&gt; /usr/bin/java
ls -l /usr/bin/java ==&gt; /System/Library/Frameworks/JavaVM.framework/Versions/Current/Commands/java

When I saw this I was a little bit curious so I went to list the Versions directory:

cd /System/Library/Frameworks/JavaVM.framework/Versions
ls ==&gt;
1.4 1.5 1.6 A CurrentJDK
1.4.2 1.5.0 1.6.0 Current

Now why do I have this old versions of Java on my machine ? So I asked on Ask Different

$ sw_vers
ProductName:	Mac OS X
ProductVersion:	10.8.1
BuildVersion:	12B19
$ ls -l /System/Library/Frameworks/JavaVM.framework/Versions
total 64
lrwxr-xr-x  1 root  wheel   10 Sep 16 15:55 1.4 -&gt; CurrentJDK
lrwxr-xr-x  1 root  wheel   10 Sep 16 15:55 1.4.2 -&gt; CurrentJDK
lrwxr-xr-x  1 root  wheel   10 Sep 16 15:55 1.5 -&gt; CurrentJDK
lrwxr-xr-x  1 root  wheel   10 Sep 16 15:55 1.5.0 -&gt; CurrentJDK
lrwxr-xr-x  1 root  wheel   10 Sep 16 15:55 1.6 -&gt; CurrentJDK
lrwxr-xr-x  1 root  wheel   10 Sep 16 15:55 1.6.0 -&gt; CurrentJDK
drwxr-xr-x  7 root  wheel  238 Sep 16 16:08 A
lrwxr-xr-x  1 root  wheel    1 Sep 16 15:55 Current -&gt; A
lrwxr-xr-x  1 root  wheel   59 Sep 16 15:55 CurrentJDK -&gt; /System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents

It seems all the old versions are links to the CurrentJDK version , which is the Apple version, except A and Current which is linked to A.I read something about this on this question.For me A acts like a temp variable. If in Java Preferences you set the in the first position Java 6 from Apple A will have Java 6 from Apple if you put on the first position Java SE 7 from Oracle A will point to this version.Current points to A.

/java -version
java version &quot;1.6.0_35&quot;
Java(TM) SE Runtime Environment (build 1.6.0_35-b10-428-11M3811)
Java HotSpot(TM) 64-Bit Server VM (build 20.10-b01-428, mixed mode)
./java -version
java version &quot;1.7.0_05&quot;
Java(TM) SE Runtime Environment (build 1.7.0_05-b06)
Java HotSpot(TM) 64-Bit Server VM (build 23.1-b03, mixed mode)

So it means that in this Current directory will point to the first Java Version found in the Java Preferences.
A very interesting thing is the following information

lrwxr-xr-x  1 root  wheel   59 Sep 16 15:55 CurrentJDK -&gt; /System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents

This means Java from Apple is actually installed here :”/System/Library/Java/JavaVirtualMachines/1.6.0.jdk/”
What about Java SE 7 ? I could search the filesystem to see but I found an easier way:

If in Java Preferences on the first position is Java SE 7 ==>

$ /usr/libexec/java_home

If in Java Preferences on the first position is Java SE 6 (System) ==>

$ /usr/libexec/java_home

So Java on Mountain Lion (OSX) is more likely to be installed in one of this locations :

  • /System/Library/Java/JavaVirtualMachines
  • /Library/Java/JavaVirtualMachines
  • ~/Library/Java/JavaVirtualMachines

What about /System/Library/Frameworks/JavaVM.framework/Versions ?
It seems that is linked to the so called “Java bridge“.Here it seems is the native part of the Java on OSX installation.

Understanding the concept behind ThreadLocal

Posted in Code samples, Java by Cristian on July 11, 2012


I was aware of thread local but never had the occasion of really using it until recently.
So I start digging a little bit on the subject because I needed an easy way of  propagating some user information
via the different layers of my web application without changing the signature of each method called.

Small prerequisite info

A thread is an individual process that has its own call stack.In Java, there is one thread per call stack or one call stack per thread.Even if you don’t create any new threads in your program, threads are there running without your knowledge.Best example is whenyou just start  a simple Java program via main method,then you do not implicitly call new Thread().start(),  but the JVM creates a main thread for you in order to run the main method.

The main thread is quite special because it is the thread from which all the other thread will spawn and when this
thread is finished, the application ends it’s lifecycle.

In a web application server normally there is  a pool of of threads ,because a Thread is class quite heavyweight to create.All JEE servers (Weblogic,Glassfish,JBoss etc) have a self tuning thread pool, meaning that the thread pool increase and decrease when is needed so there is not thread created on each request, and existing ones are reused.

Understanding thread local

In order to understand better thread local I will show very simplistic implementation of one custom thread local.

package ccs.progest.javacodesamples.threadlocal.ex1;

import java.util.HashMap;
import java.util.Map;

public class CustomThreadLocal {

	private static Map threadMap = new HashMap();

	public static void add(Object object) {
		threadMap.put(Thread.currentThread(), object);

	public static void remove(Object object) {

	public static Object get() {
		return threadMap.get(Thread.currentThread());


So you can call anytime in your application the add method on CustomThreadLocal and what it will do is to put in a map the current thread as key and as value the object you want to associate with this thread. This object might be an object that you want to have access to from anywhere within the current executed thread, or it might be an expensive object you want to keep associated with the thread and reuse as many times you want.
You define a class ThreadContext where you  have all information you want to propagate within the thread.

package ccs.progest.javacodesamples.threadlocal.ex1;

public class ThreadContext {

	private String userId;

	private Long transactionId;

	public String getUserId() {
		return userId;

	public void setUserId(String userId) {
		this.userId = userId;

	public Long getTransactionId() {
		return transactionId;

	public void setTransactionId(Long transactionId) {
		this.transactionId = transactionId;

	public String toString() {
		return "userId:" + userId + ",transactionId:" + transactionId;


Now is the time to use the ThreadContext.
I will start two threads and in each thread I will add a new ThreadContext instance that will hold information I want to propagate for each thread.

package ccs.progest.javacodesamples.threadlocal.ex1;

public class ThreadLocalMainSampleEx1 {

	public static void main(String[] args) {
		new Thread(new Runnable() {
			public void run() {
				ThreadContext threadContext = new ThreadContext();
				threadContext.setUserId("User 1");
				//here we call a method where the thread context is not passed as parameter
		new Thread(new Runnable() {
			public void run() {
				ThreadContext threadContext = new ThreadContext();
				threadContext.setUserId("User 2");
				//here we call a method where the thread context is not passed as parameter

CustomThreadLocal.add(threadContext)  is the line of code where the current thread is associated with the ThreadContext instance
As you will see executing this code the result will be:

userId:User 1,transactionId:1
userId:User 2,transactionId:2

How this is possible because we did not passed as parameter ThreadContext ,userId or trasactionId to printThreadContextValues ?

package ccs.progest.javacodesamples.threadlocal.ex1;

public class PrintThreadContextValues {
	public static void printThreadContextValues(){

Simple enough 🙂
When CustomThreadLocal.get() is called from the internal map of CustomThreadLocal it is retrived the object associated with the current thread.
Now let’s see the samples when  is used a real ThreadLocal class. (the above CustomThreadLocal class is just to understand the principles behind ThreadLocal class which is very fast and uses memory in an optimal way)

package ccs.progest.javacodesamples.threadlocal.ex2;

public class ThreadContext {

	private String userId;
	private Long transactionId;

	private static ThreadLocal threadLocal = new ThreadLocal(){
        protected ThreadContext initialValue() {
            return new ThreadContext();

	public static ThreadContext get() {
		return threadLocal.get();
	public String getUserId() {
		return userId;
	public void setUserId(String userId) {
		this.userId = userId;
	public Long getTransactionId() {
		return transactionId;
	public void setTransactionId(Long transactionId) {
		this.transactionId = transactionId;

	public String toString() {
		return "userId:" + userId + ",transactionId:" + transactionId;

As javadoc describes : ThreadLocal instances are typically private static fields in classes that wish to associate state with a thread

package ccs.progest.javacodesamples.threadlocal.ex2;

public class ThreadLocalMainSampleEx2 {

	public static void main(String[] args) {
		new Thread(new Runnable() {
			public void run() {
				ThreadContext threadContext = ThreadContext.get();
				threadContext.setUserId("User 1");
				//here we call a method where the thread context is not passed as parameter
		new Thread(new Runnable() {
			public void run() {
				ThreadContext threadContext = ThreadContext.get();
				threadContext.setUserId("User 2");
				//here we call a method where the thread context is not passed as parameter

When get is called , a new ThreadContext instance is associated with the current thread,then the desired values are set the ThreadContext instance.
As you see the result is the same as for the first set of samples.

userId:User 1,transactionId:1
userId:User 2,transactionId:2

(it might be the reverse order ,so don’t worry if you see ‘User 2’ first)

package ccs.progest.javacodesamples.threadlocal.ex2;

public class PrintThreadContextValues {
	public static void printThreadContextValues(){

Another very usefull usage of ThreadLocal is the situation when you have a non threadsafe instance of an quite expensive object.Most poular sample I found was with SimpleDateFormat (but soon I’ll come with another example when webservices ports will be used)

package ccs.progest.javacodesamples.threadlocal.ex4;

import java.text.SimpleDateFormat;
import java.util.Date;

public class ThreadLocalDateFormat {
	// SimpleDateFormat is not thread-safe, so each thread will have one
	private static final ThreadLocal formatter = new ThreadLocal() {
		protected SimpleDateFormat initialValue() {
			return new SimpleDateFormat("MM/dd/yyyy");
	public String formatIt(Date date) {
		return formatter.get().format(date);


There are many uses for thread locals.Here I describe only two: (I think most used ones)

  • Genuine per-thread context, such as user id or transaction id.
  • Per-thread instances for performance.
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Installing Weblogic on MacOS short notes (reminder for later …)

Posted in Java by Cristian on July 4, 2012

I had some problems that when I tried to launch the installer from Weblogic the installer UI did not detected the JAVA_HOME.

Despite I installed RcEnvironment ,
which is after installation accessible from bottom system preferences on Other ==> Env. Variables., it still did not worked !? 😦

I asked on fault :

However the above link solved some Path and Environment variable on my Mac but did not solved the real problem.

Update : The above is not valid for Mountain Lion 😦

For setting JAVA_HOME and other environment variables :

The problem was solved following a link that concern instalation of JDeveloper.
Here is the link :

So i run the command :
chmod +x
then ./

mkdir /system/library/java/javavirtualmachines/1.6.0.jdk/contents/home/jdk6
mkdir /system/library/java/javavirtualmachines/1.6.0.jdk/contents/home/jdk6/bin
ln -s /system/library/java/javavirtualmachines/1.6.0.jdk/contents/home/bin/java /system/library/java/javavirtualmachines/1.6.0.jdk/contents/home/jdk6/bin/java
ln -s /system/library/java/javavirtualmachines/1.6.0.jdk/contents/home/bin/javac /system/library/java/javavirtualmachines/1.6.0.jdk/contents/home/jdk6/bin/javac
ln -s /system/library/java/javavirtualmachines/1.6.0.jdk/contents/home/bin/javap /system/library/java/javavirtualmachines/1.6.0.jdk/contents/home/jdk6/bin/javap
ln -s /System/Library/Java/Support/Deploy.bundle/Contents/Home/bin/javaws /system/library/java/javavirtualmachines/1.6.0.jdk/contents/home/jdk6/bin/javaws
ln -s /system/library/java/javavirtualmachines/1.6.0.jdk/contents/home/bin/jar /system/library/java/javavirtualmachines/1.6.0.jdk/contents/home/jdk6/bin/jar
ln -s /system/library/java/javavirtualmachines/1.6.0.jdk/contents/home/bin/xjc /system/library/java/javavirtualmachines/1.6.0.jdk/contents/home/jdk6/bin/xjc
mkdir /system/library/java/javavirtualmachines/1.6.0.jdk/contents/home/jdk6/lib
ln -s /system/library/java/javavirtualmachines/1.6.0.jdk/contents/classes/classes.jar /system/library/java/javavirtualmachines/1.6.0.jdk/contents/home/jdk6/lib/tools.jar
mkdir /system/library/java/javavirtualmachines/1.6.0.jdk/contents/home/jdk6/jre
mkdir /system/library/java/javavirtualmachines/1.6.0.jdk/contents/home/jdk6/jre/bin
ln -s /system/library/java/javavirtualmachines/1.6.0.jdk/contents/home/bin/java /system/library/java/javavirtualmachines/1.6.0.jdk/contents/home/jdk6/jre/bin/java
mkdir /system/library/java/javavirtualmachines/1.6.0.jdk/contents/home/jdk6/jre/lib
ln -s /system/library/java/javavirtualmachines/1.6.0.jdk/contents/classes/classes.jar /system/library/java/javavirtualmachines/1.6.0.jdk/contents/home/jdk6/jre/lib/rt.jar

Update …

It seems now that I have Insufficient disk space no matter that in reality I have way more then 300GB free 🙂

Well luckily I am not the first one that had this problem so the solution came quite fast  :

As it is written in this blog the problem is that i need to run the installation jar with the following argument :

java -XX:MaxPermSize=512m -Xmx1024m -jar wls1034_generic.jar

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