# Package org.apache.hadoop.util

Common utilities.

See: Description

- Interface Summary
  Interface | Description
  --- | ---
  CleanerUtil.BufferCleaner | Pass in an implementation of this interface to cleanup ByteBuffers.
  ExitCodeProvider | Get the exit code of an exception.
  GcTimeMonitor.GcTimeAlertHandler | The user can provide an instance of a class implementing this interface when initializing a GcTimeMonitor to receive alerts when GC time percentage exceeds the specified threshold.
  IdentityHashStore.Visitor<K,V> |
  IPList |
  LightWeightCache.Entry | Entries of `LightWeightCache`.
  LightWeightGSet.LinkedElement | Elements of `LightWeightGSet`.
  Progressable | A facility for reporting progress.
  Shell.CommandExecutor |
  Tool | A tool interface that supports handling of generic command-line options.

- Class Summary
  Class | Description
  --- | ---
  ApplicationClassLoader | A `URLClassLoader` for application isolation.
  AutoCloseableLock | This is a wrap class of a ReentrantLock.
  BasicDiskValidator | BasicDiskValidator is a wrapper around `DiskChecker`.
  CacheableIPList | CacheableIPList loads a list of subnets from a file.
  CloseableReferenceCount | A closeable object that maintains a reference count.
  CombinedIPList | Util class to stores ips/hosts/subnets.
  CombinedIPWhiteList |
  ComparableVersion | Generic implementation of version comparison.
  FastNumberFormat | Fast thread-safe version of NumberFormat
  FileBasedIPList | FileBasedIPList loads a list of subnets in CIDR format and ip addresses from a file.
  FindClass | This entry point exists for diagnosing classloader problems: is a class or resource present -and if so, where? Actions
  GcTimeMonitor | This class monitors the percentage of time the JVM is paused in GC within the specified observation window, say 1 minute.
  GcTimeMonitor.GcData | Encapsulates data about GC pauses measured at the specific timestamp.
  HostsFileReader.HostDetails | An atomic view of the included and excluded hosts
  LimitInputStream | Copied from guava source code v15 (LimitedInputStream) Guava deprecated LimitInputStream in v14 and removed it in v15.
  MachineList | Container class which holds a list of ip/host addresses and answers membership queries.
  MachineList.InetAddressFactory | InetAddressFactory is used to obtain InetAddress from host.
  NodeHealthScriptRunner | The class which provides functionality of checking the health of the node using the configured node health script and reporting back to the service for which the health checker has been asked to report.
  Options | This class allows generic access to variable length type-safe parameter lists.
  Options.BooleanOption |
  Options.ClassOption |
  Options.FSDataInputStreamOption |
  Options.FSDataOutputStreamOption |
  Options.IntegerOption |
  Options.LongOption |
  Options.PathOption |
  Options.ProgressableOption |
  Options.StringOption |
  PerformanceAdvisory |
  ProtoUtil |
  PureJavaCrc32 | A pure-java implementation of the CRC32 checksum that uses the same polynomial as the built-in native CRC32.
  PureJavaCrc32C | A pure-java implementation of the CRC32 checksum that uses the CRC32-C polynomial, the same polynomial used by iSCSI and implemented on many Intel chipsets supporting SSE4.2.
  ReadWriteDiskValidator | ReadWriteDiskValidator is the class to check a directory by to create a file, write some bytes into it, read back, and verify if they are identical.
  ReflectionUtils | General reflection utils
  Shell | A base class for running a Shell command.
  Shell.ShellCommandExecutor | A simple shell command executor.
  ShutdownHookManager | The `ShutdownHookManager` enables running shutdownHook in a deterministic order, higher priority first.
  ShutdownThreadsHelper | Helper class to shutdown `Thread`s and `ExecutorService`s.
  StopWatch | A simplified StopWatch implementation which can measure times in nanoseconds.
  StringInterner | Provides string interning utility methods.
  SysInfo | Plugin to calculate resource information on the system.
  ThreadUtil |
  ToolRunner | A utility to help run `Tool`s.
  VersionInfo | This class returns build information about Hadoop components.
  Waitable<T> | Represents an object that you can wait for.

- Enum Summary
  Enum | Description
  --- | ---
  DataChecksum.Type | The checksum types
  Shell.OSType |
  StringUtils.TraditionalBinaryPrefix | The traditional binary prefixes, kilo, mega, ..., exa, which can be represented by a 64-bit integer.

- Exception Summary
  Exception | Description
  --- | ---
  DiskChecker.DiskErrorException |
  DiskChecker.DiskOutOfSpaceException |
  ExitUtil.ExitException | An exception raised when a call to `ExitUtil.terminate(int)` was called and system exits were blocked.
  ExitUtil.HaltException | An exception raised when a call to `ExitUtil.terminate(int)` was called and system halts were blocked.
  InvalidChecksumSizeException | Thrown when bytesPerChecksun field in the meta file is less than or equal to 0 or type is invalid.
  Shell.ExitCodeException | This is an IOException with exit code added.

## Package org.apache.hadoop.util Description

Common utilities.

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