java8 ThreadLocal 초기화

java7에서 ThreadLocal을 초기화하는 코드이다.

참조 코드: https://docs.oracle.com/javase/8/docs/api/java/lang/ThreadLocal.html

import java.util.concurrent.atomic.AtomicInteger;


public class ThreadId {
 // Atomic integer containing the next thread ID to be assigned
 private static final AtomicInteger nextId = new AtomicInteger(0);

 // Thread local variable containing each thread's ID
 private static final ThreadLocal<Integer> threadId =
     new ThreadLocal<Integer>() {
      @Override protected Integer initialValue() {
       return nextId.getAndIncrement();
      }
     };

 // Returns the current thread's unique ID, assigning it if necessary
 public static int get() {
  return threadId.get();
 }
}
 

java8에서는 위의 코드를 

import java.util.concurrent.atomic.AtomicInteger;


public class ThreadId {
 // Atomic integer containing the next thread ID to be assigned
 private static final AtomicInteger nextId = new AtomicInteger(0);

 // Thread local variable containing each thread's ID
 private static final ThreadLocal<Integer> threadId = ThreadLocal.withInitial(()->new Integer(5));
 // Returns the current thread's unique ID, assigning it if necessary
 public static int get() {
  return threadId.get();
 }
}

또는

import java.util.concurrent.atomic.AtomicInteger;


public class ThreadId {
 // Atomic integer containing the next thread ID to be assigned
 private static final AtomicInteger nextId = new AtomicInteger(0);

 // Thread local variable containing each thread's ID
 private static final ThreadLocal<Integer> threadId =
   ThreadLocal.withInitial(() -> nextId.getAndIncrement());
 // Returns the current thread's unique ID, assigning it if necessary
 public static int get() {
  return threadId.get();
 }
}
 

간단 테스트 코드이다. 

public class ThreadLocalTest {
 public static void main(String[] args) {
  ThreadLocal<Integer> myThreadLocal = ThreadLocal.withInitial( ()-> new Integer(5));
  System.out.println(myThreadLocal.get());
  myThreadLocal.set(10);
  System.out.println(myThreadLocal.get());
 }
}