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Extremely Serious

Category: Java 10

Java UTF-16LE Base64 CODEC

May 18, 2022 / / 0 Comments

The UTF-16LE base64 encoding is compatible to be used with powershell's encoded command.

Encoding

//The text to encode.
var command = "Write-Output \"Hello World\"";
var encodedString = Base64.getEncoder().encodeToString(command.getBytes(StandardCharsets.UTF_16LE));
System.out.printf("Base64: %s%n", encodedString);

Output

Base64: VwByAGkAdABlAC0ATwB1AHQAcAB1AHQAIAAiAEgAZQBsAGwAbwAgAFcAbwByAGwAZAAiAA==

The preceding output can be used with powershell like the following:

powershell -encodedcommand VwByAGkAdABlAC0ATwB1AHQAcAB1AHQAIAAiAEgAZQBsAGwAbwAgAFcAbwByAGwAZAAiAA==

Decoding

//The base64 text to decode.
var base64="VwByAGkAdABlAC0ATwB1AHQAcAB1AHQAIAAiAEgAZQBsAGwAbwAgAFcAbwByAGwAZAAiAA==";
byte[] decodedBytes = Base64.getDecoder().decode(base64);
String decodedString = new String(decodedBytes, StandardCharsets.UTF_16LE);
System.out.printf("Decoded: %s%n", decodedString);

Output

Decoded: Write-Output "Hello World"

Regex Capture Groups with Java

December 7, 2021 / / 0 Comments

The following java code extracts the group, artifact and version using regex capture groups:

import java.util.regex.Pattern;

public class Main {

    public static void main(String ... args) {
        //Text to extract the group, artifact and version
        var text = "org.junit.jupiter:junit-jupiter-api:5.7.0";

        //Regex capture groups for Group:Artifact:Version
        var pattern = "(.*):(.*):(.*)"; 

        var compiledPattern = Pattern.compile(pattern);
        var matcher = compiledPattern.matcher(text);
        if (matcher.find( )) {
            System.out.println("Whole text: " + matcher.group(0) );
            System.out.println("Group: " + matcher.group(1) );
            System.out.println("Artifact: " + matcher.group(2) );
            System.out.println("Version: " + matcher.group(3) );
        } else {
            System.out.println("NO MATCH");
        }
    }
}

Output

Whole text: org.junit.jupiter:junit-jupiter-api:5.7.0
Group: org.junit.jupiter
Artifact: junit-jupiter-api
Version: 5.7.0

ThreadPoolExecutor with ArrayBlockingQueue and Custom Thread Name

August 28, 2019 / / 0 Comments

Create an implementation of ThreadFactory to create a thread with custom name for ThreadPoolExecutor as follows:

class MyThreadFactory implements ThreadFactory {
    private AtomicLong threadCounter;

    private MyThreadFactory() {
        threadCounter = new AtomicLong();
    }

    @Override
    public Thread newThread(Runnable runnable) {
        var thread=new Thread(runnable);
        thread.setName(String.join("-","my-thread",
                String.valueOf(threadCounter.incrementAndGet())));
        return thread;
    }
}

The preceding class will generate a thread with the name starting with my-thread. Use the instance of this class in constructing the ThreadPoolExecutor as follows:

var executor = new ThreadPoolExecutor(2, 4, 60L, TimeUnit.SECONDS,
        new ArrayBlockingQueue<>(100), new MyThreadFactory(), 
        new ThreadPoolExecutor.CallerRunsPolicy());

The preceding declaration creates an instance of ThreadPoolExecutor with 2 core threads, 4 maximum threads, 60 seconds keep alive and supports 100 items in the queue. The queue size is defined by the instance of ArrayBlockingQueue class.

Start all the core threads as follows:

executor.prestartAllCoreThreads();

Using a profiling tool we can search for all the threads whose names starts with my-thread like the following screenshot:

Don't forget to call any shutdown/terminate methods when done using the executor.

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