io.druid.java.util.common

Class FileUtils

java.lang.Object

io.druid.java.util.common.FileUtils

public class FileUtils
extends Object

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	FileUtils.FileCopyResult Keeps results of a file copy, including children and total size of the resultant files.
static interface	FileUtils.OutputStreamConsumer

Field Summary

Fields

Modifier and Type	Field and Description
static com.google.common.base.Predicate<Throwable>	IS_EXCEPTION Useful for retry functionality that doesn't want to stop Throwables, but does want to retry on Exceptions

Constructor Summary

Constructors

Constructor and Description
FileUtils()

Method Summary

Modifier and Type	Method and Description
static MappedByteBufferHandler	map(File file) Fully maps a file read-only in to memory as per FileChannel.map(FileChannel.MapMode, long, long).
static FileUtils.FileCopyResult	retryCopy(com.google.common.io.ByteSource byteSource, File outFile, com.google.common.base.Predicate<Throwable> shouldRetry, int maxAttempts) Copy input byte source to outFile.
static void	writeAtomically(File file, FileUtils.OutputStreamConsumer f) Write to a file atomically, by first writing to a temporary file in the same directory and then moving it to the target location.

Methods inherited from class java.lang.Object

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

Field Detail

IS_EXCEPTION

public static final com.google.common.base.Predicate<Throwable> IS_EXCEPTION

Useful for retry functionality that doesn't want to stop Throwables, but does want to retry on Exceptions

Constructor Detail

FileUtils

public FileUtils()

Method Detail

retryCopy

public static FileUtils.FileCopyResult retryCopy(com.google.common.io.ByteSource byteSource,
                                                 File outFile,
                                                 com.google.common.base.Predicate<Throwable> shouldRetry,
                                                 int maxAttempts)

Copy input byte source to outFile. If outFile exists, it is attempted to be deleted.

Parameters:

byteSource - Supplier for an input stream that is to be copied. The resulting stream is closed each iteration

outFile - Where the file should be written to.

shouldRetry - Predicate indicating if an error is recoverable and should be retried.

maxAttempts - The maximum number of assumed recoverable attempts to try before completely failing.

Throws:

RuntimeException - wrapping the inner exception on failure.

map

public static MappedByteBufferHandler map(File file)
                                   throws IOException

Fully maps a file read-only in to memory as per FileChannel.map(FileChannel.MapMode, long, long).

Files are mapped from offset 0 to its length.

This only works for files <= Integer.MAX_VALUE bytes.

Similar to Files.map(File), but returns MappedByteBufferHandler, that makes it easier to unmap the buffer within try-with-resources pattern:

 try (MappedByteBufferHandler fileMappingHandler = FileUtils.map(file)) {
   ByteBuffer fileMapping = fileMappingHandler.get();
   // use mapped buffer
 }

Parameters:

file - the file to map

Returns:

a MappedByteBufferHandler, wrapping a read-only buffer reflecting file

Throws:

FileNotFoundException - if the file does not exist

IOException - if an I/O error occurs

See Also:

FileChannel.map(FileChannel.MapMode, long, long)

writeAtomically

public static void writeAtomically(File file,
                                   FileUtils.OutputStreamConsumer f)
                            throws IOException

Write to a file atomically, by first writing to a temporary file in the same directory and then moving it to the target location. This function attempts to clean up its temporary files when possible, but they may stick around (for example, if the JVM crashes partway through executing the function). In any case, the target file should be unharmed. The OutputStream passed to the consumer is uncloseable; calling close on it will do nothing. This is to ensure that the stream stays open so we can fsync it here before closing. Hopefully, this doesn't cause any problems for callers. This method is not just thread-safe, but is also safe to use from multiple processes on the same machine.

Throws:

IOException