java - 将 ThreadLocal 类传递给另一个线程？

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。

我有一堂包含以下内容的类(class)

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>();
    .....................
    .....................
    .....................

}

我一直在我的多线程应用程序中使用它，没有出现任何问题。现在每个线程将创建另一个线程，我希望将 ThreadLocalManager 传递给创建的新线程。这将如何完成？

Answer 1

编辑:我根据最初的建议(如下)修改了示例代码以使用InheritableThreadLocal，并且我发现它要简单得多，因此添加更新的代码。

这是更新后的 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)，但现在它的唯一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());
    }

}

最后更新的类包含主方法:

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 Runnable 对象创建新的 Thread 对象。如果这样做，您可以创建实现 Runnable 的自定义对象，并可以保存 Thr​​eadLocal 变量的值，直到新的 Thread 启动。一旦新的Thread启动(即调用run方法)，这些自定义的Runnable对象就会设置ThreadLocal变量。

这是一个带有我为此创建的 main 的类:

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();
    }

}

为了完整起见，这是我使用的 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 实例创建一个新的 >Thread(如果您运行代码，您将看到，首先没有 ThreadLocal 变量的值)。然后，Runner 设置 ThreadLocal 变量，正如您从控制台输出中看到的，它们与 t1 的内容匹配。

希望这有帮助!