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.

The example code from this tutorial can be found over on GitHub.