JAVA多线程处理

针对io密集型任务，可以采用多线程方式处理，其消耗时间比单线程大幅度减少。

 

import lombok.extern.slf4j.Slf4j;

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

@Slf4j
public class ThreadPoolTest {

    public void multiThread(int num) {
        long start = System.currentTimeMillis();
        log.info("start ....");
        //声明线程池
//        ExecutorService executor = Executors.newFixedThreadPool(8);

        //针对IO密集型的任务
        int nThreads = Runtime.getRuntime().availableProcessors() * 2;
        log.info("nThreads:{}",nThreads);
        ThreadPoolExecutor executor = new ThreadPoolExecutor(nThreads, nThreads,
                0L, TimeUnit.MILLISECONDS,
                new LinkedBlockingQueue<Runnable>());
        //该拒绝策略，首先判断线程池是否关闭，如果未关闭，则直接执行该线程
        executor.setRejectedExecutionHandler(new ThreadPoolExecutor.CallerRunsPolicy());

        List<Future<Integer>> futures = new ArrayList<>();
        //批量提交任务
        for (int i = 0; i < num; i++) {
            int finalI = i;
            futures.add(
                    executor.submit(
                            //线程任务
                            new Callable<Integer>() {
                                @Override
                                public Integer call() throws Exception {
                                    task(finalI);
                                    return finalI;
                                }
                            }
                    ));
        }
        //获取执行完的结果
        for (Future<Integer> future : futures) {
            try {
                log.info(String.valueOf(future.get()));
            } catch (InterruptedException e) {
                e.printStackTrace();
            } catch (ExecutionException e) {
                e.printStackTrace();
            }
        }
        log.info("end cost {} ....", System.currentTimeMillis() - start);
        //关闭线程池
        executor.shutdown();
    }

    //要执行的任务，耗时200ms
    private void task(int num) {
        try {
            log.info(" task:{} ,currentThread: {} ", num, Thread.currentThread().getName());
            Thread.sleep(200L);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    //单线程执行
    public void singleThread(int num) {
        long start = System.currentTimeMillis();
        log.info("start ....");
        for (int i = 0; i < num; i++) {
            task(i);
        }
        log.info("end cost {} ....", System.currentTimeMillis() - start);
    }

    public static void main(String[] args) {
        ThreadPoolTest concurrentTest = new ThreadPoolTest();
        //单线程耗时2秒
//        concurrentTest.singleThread(10);
        //多线程耗时200毫秒
        concurrentTest.multiThread(10);
    }
}