org.apache.commons.lang3

## Class ThreadUtils

- java.lang.Object
- - org.apache.commons.lang3.ThreadUtils

-     public class ThreadUtils
      extends Object

  Helpers for `java.lang.Thread` and `java.lang.ThreadGroup`.

  #ThreadSafe#

  Since:
    3.5
  See Also:
    `Thread`, `ThreadGroup`

- - ### Nested Class Summary

    Nested Classes
    Modifier and Type | Class and Description
    --- | ---
    `static class` | `ThreadUtils.NamePredicate` A predicate implementation which matches a thread or threadgroup name.
    `static interface` | `ThreadUtils.ThreadGroupPredicate` A predicate for selecting threadgroups.
    `static class` | `ThreadUtils.ThreadIdPredicate` A predicate implementation which matches a thread id.
    `static interface` | `ThreadUtils.ThreadPredicate` A predicate for selecting threads.

  - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `static org.apache.commons.lang3.ThreadUtils.AlwaysTruePredicate` | `ALWAYS_TRUE_PREDICATE` Predicate which always returns true.

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `ThreadUtils()` ThreadUtils instances should NOT be constructed in standard programming.

  - ### Method Summary

    All Methods Static Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `static Thread` | `findThreadById(long threadId)` Finds the active thread with the specified id.
    `static Thread` | `findThreadById(long threadId, String threadGroupName)` Finds the active thread with the specified id if it belongs to a thread group with the specified group name.
    `static Thread` | `findThreadById(long threadId, ThreadGroup threadGroup)` Finds the active thread with the specified id if it belongs to the specified thread group.
    `static Collection<ThreadGroup>` | `findThreadGroups(ThreadGroup group, boolean recurse, ThreadUtils.ThreadGroupPredicate predicate)` Select all active threadgroups which match the given predicate and which is a subgroup of the given thread group (or one of its subgroups).
    `static Collection<ThreadGroup>` | `findThreadGroups(ThreadUtils.ThreadGroupPredicate predicate)` Select all active threadgroups which match the given predicate.
    `static Collection<ThreadGroup>` | `findThreadGroupsByName(String threadGroupName)` Finds active thread groups with the specified group name.
    `static Collection<Thread>` | `findThreads(ThreadGroup group, boolean recurse, ThreadUtils.ThreadPredicate predicate)` Select all active threads which match the given predicate and which belongs to the given thread group (or one of its subgroups).
    `static Collection<Thread>` | `findThreads(ThreadUtils.ThreadPredicate predicate)` Select all active threads which match the given predicate.
    `static Collection<Thread>` | `findThreadsByName(String threadName)` Finds active threads with the specified name.
    `static Collection<Thread>` | `findThreadsByName(String threadName, String threadGroupName)` Finds active threads with the specified name if they belong to a thread group with the specified group name.
    `static Collection<Thread>` | `findThreadsByName(String threadName, ThreadGroup threadGroup)` Finds active threads with the specified name if they belong to a specified thread group.
    `static Collection<ThreadGroup>` | `getAllThreadGroups()` Gets all active thread groups excluding the system thread group (A thread group is active if it has been not destroyed).
    `static Collection<Thread>` | `getAllThreads()` Gets all active threads (A thread is active if it has been started and has not yet died).
    `static ThreadGroup` | `getSystemThreadGroup()` Gets the system thread group (sometimes also referred as "root thread group").

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Field Detail

    - #### ALWAYS_TRUE_PREDICATE

          public static final org.apache.commons.lang3.ThreadUtils.AlwaysTruePredicate ALWAYS_TRUE_PREDICATE

      Predicate which always returns true.

  - ### Constructor Detail

    - #### ThreadUtils

          public ThreadUtils()

      ThreadUtils instances should NOT be constructed in standard programming. Instead, the class should be used as `ThreadUtils.getAllThreads()`

      This constructor is public to permit tools that require a JavaBean instance to operate.

  - ### Method Detail

    - #### findThreadById

          public static Thread findThreadById(long threadId,
                                              ThreadGroup threadGroup)

      Finds the active thread with the specified id if it belongs to the specified thread group.
      Parameters:
        `threadId` - The thread id
        `threadGroup` - The thread group
      Returns:
        The thread which belongs to a specified thread group and the thread's id match the specified id. `null` is returned if no such thread exists
      Throws:
        `IllegalArgumentException` - if the specified id is zero or negative or the group is null
        `SecurityException` - if the current thread cannot access the system thread group
        `SecurityException` - if the current thread cannot modify thread groups from this thread's thread group up to the system thread group

    - #### findThreadById

          public static Thread findThreadById(long threadId,
                                              String threadGroupName)

      Finds the active thread with the specified id if it belongs to a thread group with the specified group name.
      Parameters:
        `threadId` - The thread id
        `threadGroupName` - The thread group name
      Returns:
        The threads which belongs to a thread group with the specified group name and the thread's id match the specified id. `null` is returned if no such thread exists
      Throws:
        `IllegalArgumentException` - if the specified id is zero or negative or the group name is null
        `SecurityException` - if the current thread cannot access the system thread group
        `SecurityException` - if the current thread cannot modify thread groups from this thread's thread group up to the system thread group

    - #### findThreadsByName

          public static Collection<Thread> findThreadsByName(String threadName,
                                                             ThreadGroup threadGroup)

      Finds active threads with the specified name if they belong to a specified thread group.
      Parameters:
        `threadName` - The thread name
        `threadGroup` - The thread group
      Returns:
        The threads which belongs to a thread group and the thread's name match the specified name, An empty collection is returned if no such thread exists. The collection returned is always unmodifiable.
      Throws:
        `IllegalArgumentException` - if the specified thread name or group is null
        `SecurityException` - if the current thread cannot access the system thread group
        `SecurityException` - if the current thread cannot modify thread groups from this thread's thread group up to the system thread group

    - #### findThreadsByName

          public static Collection<Thread> findThreadsByName(String threadName,
                                                             String threadGroupName)

      Finds active threads with the specified name if they belong to a thread group with the specified group name.
      Parameters:
        `threadName` - The thread name
        `threadGroupName` - The thread group name
      Returns:
        The threads which belongs to a thread group with the specified group name and the thread's name match the specified name, An empty collection is returned if no such thread exists. The collection returned is always unmodifiable.
      Throws:
        `IllegalArgumentException` - if the specified thread name or group name is null
        `SecurityException` - if the current thread cannot access the system thread group
        `SecurityException` - if the current thread cannot modify thread groups from this thread's thread group up to the system thread group

    - #### findThreadGroupsByName

          public static Collection<ThreadGroup> findThreadGroupsByName(String threadGroupName)

      Finds active thread groups with the specified group name.
      Parameters:
        `threadGroupName` - The thread group name
      Returns:
        the thread groups with the specified group name or an empty collection if no such thread group exists. The collection returned is always unmodifiable.
      Throws:
        `IllegalArgumentException` - if group name is null
        `SecurityException` - if the current thread cannot access the system thread group
        `SecurityException` - if the current thread cannot modify thread groups from this thread's thread group up to the system thread group

    - #### getAllThreadGroups

          public static Collection<ThreadGroup> getAllThreadGroups()

      Gets all active thread groups excluding the system thread group (A thread group is active if it has been not destroyed).
      Returns:
        all thread groups excluding the system thread group. The collection returned is always unmodifiable.
      Throws:
        `SecurityException` - if the current thread cannot access the system thread group
        `SecurityException` - if the current thread cannot modify thread groups from this thread's thread group up to the system thread group

    - #### getSystemThreadGroup

          public static ThreadGroup getSystemThreadGroup()

      Gets the system thread group (sometimes also referred as "root thread group").
      Returns:
        the system thread group
      Throws:
        `SecurityException` - if the current thread cannot modify thread groups from this thread's thread group up to the system thread group

    - #### getAllThreads

          public static Collection<Thread> getAllThreads()

      Gets all active threads (A thread is active if it has been started and has not yet died).
      Returns:
        all active threads. The collection returned is always unmodifiable.
      Throws:
        `SecurityException` - if the current thread cannot access the system thread group
        `SecurityException` - if the current thread cannot modify thread groups from this thread's thread group up to the system thread group

    - #### findThreadsByName

          public static Collection<Thread> findThreadsByName(String threadName)

      Finds active threads with the specified name.
      Parameters:
        `threadName` - The thread name
      Returns:
        The threads with the specified name or an empty collection if no such thread exists. The collection returned is always unmodifiable.
      Throws:
        `IllegalArgumentException` - if the specified name is null
        `SecurityException` - if the current thread cannot access the system thread group
        `SecurityException` - if the current thread cannot modify thread groups from this thread's thread group up to the system thread group

    - #### findThreadById

          public static Thread findThreadById(long threadId)

      Finds the active thread with the specified id.
      Parameters:
        `threadId` - The thread id
      Returns:
        The thread with the specified id or `null` if no such thread exists
      Throws:
        `IllegalArgumentException` - if the specified id is zero or negative
        `SecurityException` - if the current thread cannot access the system thread group
        `SecurityException` - if the current thread cannot modify thread groups from this thread's thread group up to the system thread group

    - #### findThreads

          public static Collection<Thread> findThreads(ThreadUtils.ThreadPredicate predicate)

      Select all active threads which match the given predicate.
      Parameters:
        `predicate` - the predicate
      Returns:
        An unmodifiable `Collection` of active threads matching the given predicate
      Throws:
        `IllegalArgumentException` - if the predicate is null
        `SecurityException` - if the current thread cannot access the system thread group
        `SecurityException` - if the current thread cannot modify thread groups from this thread's thread group up to the system thread group

    - #### findThreadGroups

          public static Collection<ThreadGroup> findThreadGroups(ThreadUtils.ThreadGroupPredicate predicate)

      Select all active threadgroups which match the given predicate.
      Parameters:
        `predicate` - the predicate
      Returns:
        An unmodifiable `Collection` of active threadgroups matching the given predicate
      Throws:
        `IllegalArgumentException` - if the predicate is null
        `SecurityException` - if the current thread cannot access the system thread group
        `SecurityException` - if the current thread cannot modify thread groups from this thread's thread group up to the system thread group

    - #### findThreads

          public static Collection<Thread> findThreads(ThreadGroup group,
                                                       boolean recurse,
                                                       ThreadUtils.ThreadPredicate predicate)

      Select all active threads which match the given predicate and which belongs to the given thread group (or one of its subgroups).
      Parameters:
        `group` - the thread group
        `recurse` - if `true` then evaluate the predicate recursively on all threads in all subgroups of the given group
        `predicate` - the predicate
      Returns:
        An unmodifiable `Collection` of active threads which match the given predicate and which belongs to the given thread group
      Throws:
        `IllegalArgumentException` - if the given group or predicate is null
        `SecurityException` - if the current thread cannot modify thread groups from this thread's thread group up to the system thread group

    - #### findThreadGroups

          public static Collection<ThreadGroup> findThreadGroups(ThreadGroup group,
                                                                 boolean recurse,
                                                                 ThreadUtils.ThreadGroupPredicate predicate)

      Select all active threadgroups which match the given predicate and which is a subgroup of the given thread group (or one of its subgroups).
      Parameters:
        `group` - the thread group
        `recurse` - if `true` then evaluate the predicate recursively on all threadgroups in all subgroups of the given group
        `predicate` - the predicate
      Returns:
        An unmodifiable `Collection` of active threadgroups which match the given predicate and which is a subgroup of the given thread group
      Throws:
        `IllegalArgumentException` - if the given group or predicate is null
        `SecurityException` - if the current thread cannot modify thread groups from this thread's thread group up to the system thread group

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