[java] ThreadLocal 샘플

Java Thread Local – How to use and code sample

http://veerasundar.com/blog/2010/11/java-thread-local-how-to-use-and-code-sample/

ThreadLocal 을 위 예제와 같이 사용하면 된다.

package com.veerasundar;

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();

    }

}

package com.veerasundar;

/**

 * this class acts as a container to our thread local variables.

 * @author vsundar

 *

 */

public class MyThreadLocal {

private static final ThreadLocal<Context> userThreadLocal = new ThreadLocal<Context>();

public static void set(Context user) {

userThreadLocal.set(user);

}

public static void unset() {

userThreadLocal.remove();

}

public static Context get() {

return userThreadLocal.get();

}

}

원래 예제와 달라진 점은 ThreadLocal 변수를 선언할 때 <Context> 를 추가했다. 이렇게 하지 않으면 형변환 에러가 발생한다. 또 한 가지는 userThreadLocal 변수를 private 으로 변경해서 외부에서 함부로 접근하지 못하도록 했다.

package com.veerasundar;

public class Context {

private String transactionId = null;

// getter

public String getTransactionId() {

return transactionId;

}

// setter

public void setTransactionId(String transactionId) {

this.transactionId = transactionId;

}

}

package com.veerasundar;

public class BusinessService {

    public void businessMethod() {

        // get the context from thread local

        Context context = MyThreadLocal.get();

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

    }

}

[실행결과]

Thread-0

Thread-1

[첨부] Eclipse Project 를 zip 파일로 Export 한 파일.

ThreadLocalTest.zip