是否将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。

我有一节课，内容如下

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

在我的多线程应用程序中，我一直在使用它，没有遇到任何问题。现在每个线程都将创建另一个线程，我希望ThreadLocalManager被传递给创建的新线程。如何做到这一点？

Answer 1

EDIT:我修改了我的示例代码，从我最初的建议(如下)中使用InheritableThreadLocal，我发现它要简单得多，所以添加了更新的代码。

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(见下文原件)，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要方法：

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对象来创建新的Thread对象。如果这样做，您可以创建实现Runnable的自定义对象，并且可以保持ThreadLocal变量的值，直到新的Thread启动为止。一旦新的Thread启动(即调用run方法)，这些自定义Runnable对象就会设置ThreadLocal变量。

这是一个类，我为此创建了一个main：

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，这里是我创建的自定义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实例中，然后使用Runner实例创建一个新的Thread(如果您运行此代码，则会看到它最初没有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匹配。

希望这能有所帮助！