Some call it hot deploy, some refer to runtime class reload/redefine, but whatsoever….
It is just mechanism to reload compiled class file during jvm runtime, to avoid ordinary java development life cycle of “code change -> build -> deploy”, which will significantly save lot’s of wait time (especially when you have multiple modules dependency project).

Both open source project: HotSwapAgent and Spring-Loaded works pretty well for me, but if you are looking for commercial product, JRebel will be the choice.

Hit into this error when tying to get the “Content-Disposition” header using XMLHttpRequest.

Refused to get unsafe header "Content-Disposition"

Finally found the solution is to include CORS access control headers in HTTP response….

httpResponse.addHeader("Access-Control-Expose-Headers", "Content-Disposition");

Take note that it’s not Access-Control-Allow-Headers but Access-Control-Expose-Headers

Credit to this stackoverflow post.

Just finished Test-Driven Java Development (but will take longer time to digest), and  notice there are few tools/framework worth to share.

Test Driven Development Framework

Behavior Driven Development Framework

Overall this is quite a good book if you practice TDD, as it include bunch of  hands on tutorial. Personally I think practicing TDD is good if we have solid requirement (or at least not changing every few days), else we will waste a lot of time just to maintain unit test for immature requirement 🙂

Accidentally found this util class while reading an ebook, and think it worth sharing since myself always found this a tedious code especially prefix and suffix the string.

We used to construct CSV string as below:

StringBuilder nameCsv = new StringBuilder();
nameCsv.append("Maria").append(",");
nameCsv.append("Ken").append(",");
nameCsv.append("Collin");
System.out.println(nameCsv.toString());
//OUTPUT: Maria,Ken,Collin

With new StringJoiner util in Java 1.8, we can do it in a cleaner way.

StringJoiner nameCsv = new StringJoiner(",");
nameCsv.add("Maria");
nameCsv.add("Ken");
nameCsv.add("Collin");
System.out.println(nameCsv.toString());
//OUTPUT: Maria,Ken,Collin

The constructor also allow us to prefix and suffix the string.

StringJoiner nameCsv = new StringJoiner(",", "{", "}");
nameCsv.add("Maria");
nameCsv.add("Ken");
nameCsv.add("Collin");
System.out.println(nameCsv.toString());
//OUTPUT: {Maria,Ken,Collin}

Knowing SecurityContextHolder using ThreadLocal to store user related information. Meaning it does not use HttpSession due to some security concern (not discuss here). Wrote a main method to test that out.

public class NormalThreadExample {

    public class MyThread implements Runnable {

        private Integer normalInteger;

        @Override
        public void run() {
            try {
                Integer randomInt = (int) (Math.random() * 999);
                System.out.println(Thread.currentThread().getName() + " SET " + randomInt);
                normalInteger = randomInt;
                Thread.sleep(2000);
                System.out.println(Thread.currentThread().getName() + " GET " + normalInteger);

            } catch (InterruptedException ex) {
                // SOME HANDLER
            }
        }
    }

    public void haveFun() throws InterruptedException{
        MyThread myThread = new MyThread();
        Thread thread1 = new Thread(myThread);
        Thread thread2 = new Thread(myThread);
        thread1.start();
        thread2.start();

    }
    
    public static void main(String[] args) throws InterruptedException {
        NormalThreadExample example = new NormalThreadExample();
        example.haveFun();
    }
}

//Output : 
Thread-0 SET 737
Thread-1 SET 404
Thread-1 GET 404
Thread-0 GET 404

public class ThreadLocalExample {

    public class MyThread implements Runnable {
        
        private ThreadLocal<Integer> threadLocalInteger = new ThreadLocal<>();
        
        @Override
        public void run() {
            try {
                Integer randomInt = (int) (Math.random() * 999);
                System.out.println(Thread.currentThread().getName() + " SET " + randomInt);
                threadLocalInteger.set(randomInt);
                Thread.sleep(2000);
                System.out.println(Thread.currentThread().getName() + " GET " + threadLocalInteger.get());
            } catch (InterruptedException ex) {
                // SOME HANDLER
            }
        }
    }

    public void haveFun() throws InterruptedException{
        MyThread myThread = new MyThread();
        Thread thread1 = new Thread(myThread);
        Thread thread2 = new Thread(myThread);
        thread1.start();
        thread2.start();
    }
    
    public static void main(String[] args) throws InterruptedException {
        ThreadLocalExample example = new ThreadLocalExample();
        example.haveFun();
    }
}

//Output
Thread-0 SET 3
Thread-1 SET 860
Thread-1 GET 860
Thread-0 GET 3

Note: Output result may be vary since it’s using random generator.