dw.io
Class RandomAccessFileReader
dw.io.RandomAccessFileReaderInstances of this class support reading from a random access file. A random
access file behaves like a large array of bytes stored in the file system.
There is a kind of cursor, or index into the implied array, called the file
pointer. Read operations read bytes starting at the file pointer and advance
the file pointer past the bytes read. The file pointer can be read by the
getPosition method and set by the setPosition method.
Constants
MAX_READ_BYTES
:
Number = 10240L
The maximum number of bytes that a single call to readBytes(Number) can return == 10KB
Properties
position
:
Number
The current offset in this file.
Constructor Summary
RandomAccessFileReader(file
:
File)
Construct a reader for random read access to the provided file.
Method Summary
close()
:
void
Closes this random access file reader and releases any system resources associated with the stream.
getPosition()
:
Number
Returns the current offset in this file.
readByte()
:
Number
Reads a signed eight-bit value from the file starting from the current file pointer.
readBytes(numBytes
:
Number)
:
Bytes
Reads up to n bytes from the file starting at the current file pointer.
setPosition(position
:
Number)
:
void
Sets the file-pointer offset, measured from the beginning of this file, at which the next read occurs.
Methods inherited from class
Object
assign, create, create, defineProperties, defineProperty, entries, freeze, fromEntries, getOwnPropertyDescriptor, getOwnPropertyNames, getOwnPropertySymbols, getPrototypeOf, hasOwnProperty, is, isExtensible, isFrozen, isPrototypeOf, isSealed, keys, preventExtensions, propertyIsEnumerable, seal, setPrototypeOf, toLocaleString, toString, valueOf, values
Constructor Detail
RandomAccessFileReader
public RandomAccessFileReader(file
:
File)
Construct a reader for random read access to the provided file.
To release system resources, close the reader by calling close().
Parameters:
file
-
The file to be read. Must not be null.
Throws:
IOException
-
If the given file object does not denote an existing regular file
Method Detail
close
close()
:
void
Closes this random access file reader and releases any system resources
associated with the stream.
Throws:
IOException
-
if an I/O error occurs.
getPosition
getPosition()
:
Number
Returns the current offset in this file.
Returns:
the offset from the beginning of the file, in bytes, at which the next read occurs.
Throws:
IOException
-
if an I/O error occurs.
length
length()
:
Number
Returns the length of this file.
Returns:
the length of this file, measured in bytes.
Throws:
IOException
-
if an I/O error occurs.
readByte
readByte()
:
Number
Reads a signed eight-bit value from the file starting from the current
file pointer. Since the byte is interpreted as signed, the value returned
will always be between -128 and +127.
Returns:
the next byte of this file as a signed eight-bit byte.
Throws:
IOException
-
if an I/O error occurs or if this file has reached the end.
readBytes
Reads up to n bytes from the file starting at the current file pointer.
If there are fewer than n bytes remaining in the file, then as many bytes
as possible are read. If no bytes remain in the file, then null is
returned.
Parameters:
numBytes
-
The number of bytes to read. Must be non-negative and smaller than MAX_READ_BYTES or an exception will be thrown.
Returns:
A Bytes object representing the read bytes or null if no bytes were read.
Throws:
IOException
-
if an I/O error occurs.
IllegalArgumentException
-
if numBytes< 0 or numBytes > MAX_READ_BYTES.
setPosition
setPosition(position
:
Number)
:
void
Sets the file-pointer offset, measured from the beginning of this file,
at which the next read occurs. The offset may be set beyond the end of
the file.
Parameters:
position
-
the offset position, measured in bytes from the beginning of the file, at which to set the file pointer
Throws:
IOException
-
if position is less than 0 or if an I/O error occurs.