How to use ThreadLocal ?

1. Context.java  - Bean holding the data : transactionId

public class Context {

  private String transactionId = null;

  /* getters and setters here */

}

2. MyThreadLocal.java - Container to hold our context object

Creating a ThreadLocal object as a static field which can be used by rest of the code to set/get thread local variables.

public class MyThreadLocal {

  public static final ThreadLocal userThreadLocal = new ThreadLocal();

  public static void set(Context user) {

    userThreadLocal.set(user);

  }

  public static void unset() {

    userThreadLocal.remove();

  }

  public static Context get() {

    return userThreadLocal.get();

  }

}

3. BusinessService.java - read from thread local and use the value

public class BusinessService {

  public void businessMethod() {

    // get the context from thread local

   Context context = MyThreadLocal.get();

   System.out.println(context.getTransactionId());

  }

}

4. Main class - generate and set the transaction ID in thread local and then call the business method.

public class ThreadLocalDemo extends Thread {

  public static void main(String args[]) {

    Thread threadOne = new ThreadLocalDemo();

    threadOne.start();

    Thread threadTwo = new ThreadLocalDemo();

    threadTwo.start();

  }

  @Override

  public void run() {

    // sample code to simulate transaction ID

    Context context = new Context();

    context.setTransactionId(getName());

     // set the context object in thread local to access it somewhere else

     MyThreadLocal.set(context);

     // note that we are not explicitly passing the transaction id

     new BusinessService().businessMethod();

     MyThreadLocal.unset();

  }

}