实现Callable接口

- 实现Callable接口，需要返回值类型 - 重写call方法，需要抛出异常 - 创建目标对象

步骤：

• 创建执行服务: ExecutorService ser = Executors.newFixedThreadPool(1);
• 提交执行: Future result1 = ser.submit(t1);
• 获取结果: boolean r1 = result1.get()
• 关闭服务: ser.shutdownNow();

public class TestCallable implements Callable {

    private String url;  //网络图片地址
    private String name; //保存文件名

    private TestCallable(String url, String name) {
        this.url = url;
        this.name = name;
    }


    @Override
    public Boolean call() {
        WebDownload webDownload = new WebDownload();
        webDownload.download(url, name);
        System.out.println("下载了文件名为:" + name);
        return true;
    }


    public static void main(String[] args) throws ExecutionException, InterruptedException {
        TestCallable t1 = new TestCallable("https://mmbiz.qpic.cn/mmbiz_jpg/uChmeeX1FpyB6WkMTL2IUapfTtGH6FFOialcoD9IRXH5jUskMiaHfPd8AKmWZYGAerLH3bpulF72IYhrK2kuia9Pg/640?wx_fmt=jpeg&tp=webp&wxfrom=5&wx_lazy=1&wx_co=1","1.png");
        TestCallable t2 = new TestCallable("https://mmbiz.qpic.cn/mmbiz_jpg/uChmeeX1FpyB6WkMTL2IUapfTtGH6FFOialcoD9IRXH5jUskMiaHfPd8AKmWZYGAerLH3bpulF72IYhrK2kuia9Pg/640?wx_fmt=jpeg&tp=webp&wxfrom=5&wx_lazy=1&wx_co=1","2.png");
        TestCallable t3 = new TestCallable("https://mmbiz.qpic.cn/mmbiz_jpg/uChmeeX1FpyB6WkMTL2IUapfTtGH6FFOialcoD9IRXH5jUskMiaHfPd8AKmWZYGAerLH3bpulF72IYhrK2kuia9Pg/640?wx_fmt=jpeg&tp=webp&wxfrom=5&wx_lazy=1&wx_co=1","3.png");

        //创建执行服务:
        ExecutorService ser = Executors.newFixedThreadPool(3);
        //提交执行:
        Future<Boolean> r1 = ser.submit(t1);
        Future<Boolean> r2 = ser.submit(t2);
        Future<Boolean> r3 = ser.submit(t3);

         // 获取结果:
        boolean rs1 = r1.get();
        boolean rs2 = r2.get();
        boolean rs3 = r3.get();
        //关闭服务:
         ser.shutdownNow();

    }

}

//下载器
class WebDownload {
    //下载方法
    public void download(String url, String name){
        try {
            FileUtils.copyURLToFile(new URL(url), new File(name));
        } catch (IOException e) {
            e.printStackTrace();
            System.out.println("IO异常，download方法出现问题");
        }
    }
}

优点

与Runnable相比，Callable更强大些

• 相比run方法，可以有返回值
• 方法可以抛出异常
• 支持泛型返回值
• 需要借助FutureTask类，比如获取返回值