SimpleDateFormat 线程不安全案例

SimpleDateFormat 线程不安全案例：

import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.*;

public class Test1 {

    private static SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");

    public static void main(String[] args) throws ExecutionException, InterruptedException {

        ExecutorService executorService = Executors.newFixedThreadPool(10);
        Integer count = 10;

        Callable<Object> callable = new Callable<Object>() {
            @Override
            public Object call() throws Exception {
                // 线程不安全
                return sdf.parse("2019-03-27");
            }
        };

        List<Future<Object>> list = new ArrayList<>();
        for (int i = 0; i < count; i++) {
            Future<Object> future = executorService.submit(callable);
            list.add(future);
        }
        for (Future<Object> future : list) {
            System.out.println(future.get());
        }

        executorService.shutdown();
    }

}

使用ThreadLocal解决SimpleDateFormat的线程不安全问题

import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;


public class DateFormatThreadLocal {

    private static final ThreadLocal<DateFormat> simpleDateFormat = new ThreadLocal<DateFormat>() {
        @Override
        protected DateFormat initialValue() {
            return new SimpleDateFormat("yyyy-MM-dd");
        }
    };

    public static Date convert(String str) throws ParseException {
        return simpleDateFormat.get().parse(str);
    }

}

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.*;

public class Test2 {

    public static void main(String[] args) throws ExecutionException, InterruptedException {
        ExecutorService executorService = Executors.newFixedThreadPool(10);
        Integer count = 10;

        Callable<Object> callable = new Callable<Object>() {
            @Override
            public Object call() throws Exception {
                return DateFormatThreadLocal.convert("2019-03-27");
            }
        };

        List<Future<Object>> list = new ArrayList<>();
        for (int i = 0; i < count; i++) {
            Future<Object> future = executorService.submit(callable);
            list.add(future);
        }
        for (Future<Object> future : list) {
            System.out.println(future.get());
        }

        executorService.shutdown();
    }


}