It recently happened to me that I was stuck at work on a Windows installation without access to admin privileges. While I could use a bunch of portable apps I could not find a portable JDK. To get a portable JDK without admin privileges in Windows you have to follow three simple steps.

1. Download

Download the JDK from Oracle (e.g. JDK 8 8u111).

2. Extract

If you want to use the x86 version simply open the .exe file with 7-Zip. It contains a single file tools.zip, which contains all the files we need.

For x64 the tools.zip can be found in .rsrc\1033\JAVA_CAB10\111\

Extract the tools.zip to the desired JDK directory (e.g. “D:\JavaJDK\”).
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Often while programming you find yourself glueing pre-existing code fragments together. This works out sometimes but even more often it is rather annoying. These days i had to encrypt a pdf and do some other stuff with it in java and therefore put together some libraries i found. One of these libraries offered a method to encrypt the pdf and write the result into a ByteArrayOutputStream. Later then i had to push the encrypted pdf into another method that needed it as a ByteArrayInputStream. First i simply copied the content of the ByteArrayOutputStream as byte array into the ByteArrayInputStream, but this didn’t satisfy me since i knew that the ByteArrayInputStream just needed to be initialized with the internal buffer of the ByteArrayOutputStream. Since this internal buffer is hidden from outside i made up the ByteArrayInOutStream which is a ByteArrayOutputStream that has an additional method that returns a ByteArrayInputStream which is initialized with the internal buffer of the ByteArrayOutputStream. This allows for a instant ‘conversion’ that does not use up more memory than required.

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I recently needed to start a method asynchronously on the server start up.

I came up with this code (pseudocode):

@Singleton
@Startup
public StartupEJB {
   @PostConstruct
   private void postConstruct() {
      worker();
   }
 
   @Asynchronous
   public void worker() {
      // Do something heavy
   }
}

This approach failed, the worker() method was not executed asynchronously.

I then found out that the Application Server (in my case JBoss) calls the method directly when it is located inside the same EJB: source.

The solution was to use a seperate EJB that launched the worker Thread:

@Stateless
public class ExecutorBean {
 
   @Asynchronous
   public void execute(Runnable command) {
      command.run();
   }
}

and

@Singleton
@Startup
public StartupEJB {
   @EJB
   ExecutorBean executorBean;
 
   @PostConstruct
   private void postConstruct() {
      worker();
   }
 
   public void worker() {
      executorBean.execute(new Runnable() {
         @Override
         public void run() {
            // Do something heavy
         }        
      });      
   }
}