【多线程】如何通过线程返回值？如何使用多线程并发查询数据

使用Callable声明可返回值的线程

使用Callable声明可返回值的线程：

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.concurrent.*;

public class MyThreadA implements Callable<String> {

    private Logger logger = LoggerFactory.getLogger(this.getClass());

    @Override
    public String call() throws Exception {
        this.logger.info("开始执行MyThreadA");
        this.logger.info("假设耗时3秒");
        TimeUnit.SECONDS.sleep(3);

        return "data a";
    }

}

如何并发执行线程

紧接上一例子的Callable，我们多谢一个线程：

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.concurrent.Callable;
import java.util.concurrent.TimeUnit;

public class MyThreadB implements Callable<String> {

    private Logger logger = LoggerFactory.getLogger(this.getClass());

    @Override
    public String call() throws Exception {
        this.logger.info("开始执行MyThreadB");
        this.logger.info("假设耗时5秒");
        TimeUnit.SECONDS.sleep(5);

        return "data b";
    }

}

写一个测试类，并发调用两个线程：

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.concurrent.*;

public class Test {

    private static Logger logger = LoggerFactory.getLogger(Test.class);

    public static void main(String[] args) throws Exception {
        ExecutorService es = Executors.newCachedThreadPool();

        Future<String> futureA = es.submit(new MyThreadA());
        Future<String> futureB = es.submit(new MyThreadB());

        String resultA = futureA.get();
        String resultB = futureB.get();
        logger.info("已获得全部结果，resultA：{}，resultB：{}", resultA, resultB);
    }

}

查看下列日志，可以发现，第一个线程所需3秒，第二个线程所需5秒，两个线程并发执行，即5秒完成：

00:38:13.226 [pool-1-thread-1] INFO MyThreadA - 开始执行MyThreadA
00:38:13.244 [pool-1-thread-1] INFO MyThreadA - 假设耗时3秒
00:38:13.246 [pool-1-thread-2] INFO MyThreadB - 开始执行MyThreadB
00:38:13.246 [pool-1-thread-2] INFO MyThreadB - 假设耗时5秒
00:38:18.246 [main] INFO Test - 已获得全部结果，resultA：data a，resultB：data b

参考API

Callable<V>

Future<V>

ExecutorService.submit(java.util.concurrent.Callable)

InterruptedException

ExecutionException