Get Thread by Name in Java

1. Overview

Threads are fundamental building blocks for concurrent programming in Java. In many applications, we might need to locate a specific thread by its name to perform operations like debugging, monitoring, or even interacting with the thread’s state.

In this tutorial, we’ll explore how to retrieve a thread by its name in Java.

2. Understanding Thread Names in Java

Each thread has a unique name that helps identify it during execution. While the JVM automatically names threads (e.g., Thread-0, Thread-1, etc.), we can assign custom names to threads for better traceability:

Thread customThread = new Thread(() -> {
    log.info("Running custom thread");
}, "MyCustomThread");

customThread.start();

This thread’s name is set to MyCustomThread.

Next, let’s explore ways to get a thread by its name.

3. Using Thread.getAllStackTraces()

The Thread.getAllStackTraces() method provides a map of all live threads and their corresponding stack traces. This map allows us to loop through all active threads and search for a specific thread by its name.

Here’s how we can use this method:

public static Thread getThreadByName(String name) {
    return Thread.getAllStackTraces()
      .keySet()
      .stream()
      .filter(thread -> thread.getName().equals(name))
      .findFirst()
      .orElse(null); // Return null if thread not found
}

Let’s dive into the details of what we’re doing in this method:

• The Thread.getAllStackTraces() method returns a Map<Thread, StackTraceElement[]> of all live threads.
• We use the stream() method for easier processing using Java’s Stream API, then filter the stream to include only threads whose name matches the input.
• If a match is found, we return that thread. Otherwise, we return null.

Let’s verify our method with a unit test:

@Test
public void givenThreadName_whenUsingGetAllStackTraces_thenThreadFound() throws InterruptedException {
    Thread testThread = new Thread(() -> {
        try {
            Thread.sleep(1000); // Simulate some work
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
        }
    }, "TestThread");
    testThread.start();

    Thread foundThread = ThreadFinder.getThreadByName("TestThread");
    assertNotNull(foundThread);
    assertEquals("TestThread", foundThread.getName());
    testThread.join(); // Ensure the thread finishes
}

Let’s see the key points of the test:

• Thread creation: We create a thread named TestThread that simulates some work by sleeping for a moment.
• Assertions: We check that the thread with the given name is found using each method and verify its name.
• Thread joining: Finally, we ensure the created thread finishes with join() to avoid lingering threads.

4. Using ThreadGroup

The ThreadGroup class is another option to locate a thread by its name. A ThreadGroup represents a group of threads and allows us to manage or inspect them as a collective entity. By querying a specific thread group, we can locate a thread by name.

There are multiple ways to access ThreadGroup:

• Get the current ThreadGroup via Thread.currentThread().getThreadGroup()
• Create a new ThreadGroup explicitly with new ThreadGroup(name)
• Navigate to the root group by following parent references

Here’s a solution using ThreadGroup:

public static Thread getThreadByThreadGroupAndName(ThreadGroup threadGroup, String name) {
    Thread[] threads = new Thread[threadGroup.activeCount()];
    threadGroup.enumerate(threads);

    for (Thread thread : threads) {
        if (thread != null && thread.getName().equals(name)) {
            return thread;
        }
    }
    return null; // Thread not found
}

Here’s what we do in this solution:

• The activeCount() method estimates the number of active threads in the thread group.
• The enumerate() method populates an array with all active threads.
• We iterate through the array to find and return the thread matching the desired name.
• If no match is found, we return null.

Let’s also have a unit test for this method:

@Test
public void givenThreadName_whenUsingThreadGroup_thenThreadFound() throws InterruptedException {
    ThreadGroup threadGroup = Thread.currentThread().getThreadGroup();
    Thread testThread = new Thread(threadGroup, () -> {
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
        }
    }, "TestThread");
    testThread.start();

    Thread foundThread = ThreadFinder.getThreadByThreadGroupAndName(threadGroup, "TestThread");
    assertNotNull(foundThread);
    assertEquals("TestThread", foundThread.getName());
    testThread.join();
}

5. Conclusion

In this article, we examined two ways to get a thread by its name in Java. The Thread.getAllStackTraces() method is simpler but retrieves all threads without scoping, while the ThreadGroup approach gives us more control over specific groups of threads.