Question

我在Java程序中使用ThreadLocal，以便通过线程获取和设置某些数据成员。

我有一个包含以下内容的课程

public class ThreadLocalManager {
    public static final ThreadLocal<String> accountUsername = new ThreadLocal<String>();
    public static final ThreadLocal<String> accountPassword = new ThreadLocal<String>();
    public static final ThreadLocal<Long> accountId = new ThreadLocal<Long>();
    .....................
    .....................
    .....................

}

我在多线程应用程序中使用它没有任何问题。现在每个线程都将创建另一个线程，我希望将ThreadLocalManager传递给创建的新线程。怎么做？

Answer 1

编辑：我修改了原始建议（下面）中的示例代码以使用InheritableThreadLocal，我发现它更加简单，因此添加了更新后的代码。

这是更新的ThreadLocalManager：

package inheritableThreadLocal;

public class ThreadLocalManager {
    public static final InheritableThreadLocal<String> accountUsername = new InheritableThreadLocal<String>();
    public static final InheritableThreadLocal<String> accountPassword = new InheritableThreadLocal<String>();
    public static final InheritableThreadLocal<Long> accountId = new InheritableThreadLocal<Long>();
}

我还更新了Runner（参见下面的原文），但现在它唯一的目的是打印变量的值：

package inheritableThreadLocal;

public class Runner implements Runnable{

    @Override
    public void run() {
        System.out.println("Inside Runner's run");
        System.out.println(ThreadLocalManager.accountId.get());
        System.out.println(ThreadLocalManager.accountUsername.get());
        System.out.println(ThreadLocalManager.accountPassword.get());
    }

}

最后更新的类包含main方法：

package inheritableThreadLocal;

public class ThreadLocalMain {

    public static void main(String[] args) {
        System.out.println("At start of main");
        System.out.println(ThreadLocalManager.accountId.get());
        System.out.println(ThreadLocalManager.accountUsername.get());
        System.out.println(ThreadLocalManager.accountPassword.get());

        Thread t1 = new Thread(new Runnable(){

            @Override
            public void run() {
                ThreadLocalManager.accountId.set(new Long(12345));
                ThreadLocalManager.accountUsername.set("user1");
                ThreadLocalManager.accountPassword.set("pass1");

                System.out.println("In t1 run");
                System.out.println(ThreadLocalManager.accountId.get());
                System.out.println(ThreadLocalManager.accountUsername.get());
                System.out.println(ThreadLocalManager.accountPassword.get());

                Thread t2 = new Thread(new Runner());
                t2.start();
            }

        });
        t1.start();
    }

}

原始建议：

因此，您可以使用Thread个对象创建新的Runnable个对象。如果这样做，您可以创建实现Runnable的自定义对象，并可以保留ThreadLocal变量的值，直到新的Thread开始。新的Thread启动后（即调用run方法），这些自定义Runnable对象会设置ThreadLocal个变量。

这是一个我为此创建的主要课程：

package threadLocal;

public class ThreadLocalMain {

    public static void main(String[] args) {
        System.out.println("At start of main");
        System.out.println(ThreadLocalManager.accountId.get());
        System.out.println(ThreadLocalManager.accountUsername.get());
        System.out.println(ThreadLocalManager.accountPassword.get());

        Thread t1 = new Thread(new Runnable(){

            @Override
            public void run() {
                ThreadLocalManager.accountId.set(new Long(12345));
                ThreadLocalManager.accountUsername.set("user1");
                ThreadLocalManager.accountPassword.set("pass1");

                System.out.println("In t1 run");
                System.out.println(ThreadLocalManager.accountId.get());
                System.out.println(ThreadLocalManager.accountUsername.get());
                System.out.println(ThreadLocalManager.accountPassword.get());

                Thread t2 = new Thread(new Runner(ThreadLocalManager.accountUsername.get(),
                        ThreadLocalManager.accountPassword.get(),
                        ThreadLocalManager.accountId.get()));
                t2.start();
            }

        });
        t1.start();
    }

}

为了完整性，这里是我使用的ThreadLocalManager：

package threadLocal;

public class ThreadLocalManager {
    public static final ThreadLocal<String> accountUsername = new ThreadLocal<String>();
    public static final ThreadLocal<String> accountPassword = new ThreadLocal<String>();
    public static final ThreadLocal<Long> accountId = new ThreadLocal<Long>();
}

最后，这是我创建的自定义Runnable：

package threadLocal;

public class Runner implements Runnable{

    private String userName, password;
    private long acctId;

    public Runner(String user, String pword, long accountId){
        System.out.println("In Runner constructor");
        System.out.println(ThreadLocalManager.accountId.get());
        System.out.println(ThreadLocalManager.accountUsername.get());
        System.out.println(ThreadLocalManager.accountPassword.get());

        userName = user;
        password = pword;
        acctId = accountId;
    }

    @Override
    public void run() {
        System.out.println("Inside Runner's run");
        System.out.println(ThreadLocalManager.accountId.get());
        System.out.println(ThreadLocalManager.accountUsername.get());
        System.out.println(ThreadLocalManager.accountPassword.get());

        ThreadLocalManager.accountId.set(acctId);
        ThreadLocalManager.accountUsername.set(userName);
        ThreadLocalManager.accountPassword.set(password);

        System.out.println("Inside Runner's run - after setting");
        System.out.println(ThreadLocalManager.accountId.get());
        System.out.println(ThreadLocalManager.accountUsername.get());
        System.out.println(ThreadLocalManager.accountPassword.get());
    }

}

此代码将ThreadLocal变量的值传递到Runner实例，然后使用Runner实例创建新的Thread（正如您将看到的那样）如果您运行代码，则首先没有ThreadLocal变量的值。然后Runner设置ThreadLocal个变量，正如您从控制台输出中看到的那样，它们与t1的匹配。

希望这有帮助！

将ThreadLocal类传递给另一个线程？

1 个答案: