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File file = …;
RandomAccessFile raf = new RandomAccessFile(file, "rw");
Based on 41 examples
RandomAccessFile r = new RandomAccessFile("myfile", "rw");
Based on 36 examples
public class RandomAccessFile extends Object implements DataOutput, DataInput, Closeable
Instances of this class support both reading and writing to 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;
input operations read bytes starting at the file pointer and advance
the file pointer past the bytes read. If the random access file is
created in read/write mode, then output operations are also available;
output operations write bytes starting at the file pointer and advance
the file pointer past the bytes written. Output operations that write
past the current end of the implied array cause the array to be
extended. The file pointer can be read by the
getFilePointer
method and set by the seek
method.
It is generally true of all the reading routines in this class that
if end-of-file is reached before the desired number of bytes has been
read, an EOFException
(which is a kind of
IOException
) is thrown. If any byte cannot be read for
any reason other than end-of-file, an IOException
other
than EOFException
is thrown. In particular, an
IOException
may be thrown if the stream has been closed.
Constructor Summary | |
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RandomAccessFile(File file, String mode) Creates a random access file stream to read from, and optionally to write to, the file specified by the java.io.File argument. |
|
RandomAccessFile(String name, String mode) Creates a random access file stream to read from, and optionally to write to, a file with the specified name. |
Method Summary | |
---|---|
void |
close() Closes this random access file stream and releases any system resources associated with the stream. |
FileChannel |
Returns the unique java.nio.channels.FileChannel object associated with this file. |
FileDescriptor |
getFD() Returns the opaque file descriptor object associated with this stream. |
native long |
Returns the current offset in this file. |
native long |
length() Returns the length of this file. |
native int |
read() Reads a byte of data from this file. |
int |
read(byte[] b) Reads up to b.length bytes of data from this file
into an array of bytes.
|
int |
read(byte[] b, int off, int len) Reads up to len bytes of data from this file into an
array of bytes.
|
boolean |
Reads a boolean from this file.
|
byte |
readByte() Reads a signed eight-bit value from this file. |
char |
readChar() Reads a character from this file. |
double |
Reads a double from this file.
|
float |
Reads a float from this file.
|
void |
readFully(byte[] b) Reads b.length bytes from this file into the byte
array, starting at the current file pointer.
|
void |
readFully(byte[] b, int off, int len) Reads exactly len bytes from this file into the byte
array, starting at the current file pointer.
|
int |
readInt() Reads a signed 32-bit integer from this file. |
String |
readLine() Reads the next line of text from this file. |
long |
readLong() Reads a signed 64-bit integer from this file. |
short |
Reads a signed 16-bit number from this file. |
int |
Reads an unsigned eight-bit number from this file. |
int |
Reads an unsigned 16-bit number from this file. |
String |
readUTF() Reads in a string from this file. |
native void |
seek(long pos) Sets the file-pointer offset, measured from the beginning of this file, at which the next read or write occurs. |
native void |
setLength(long newLength) Sets the length of this file. |
int |
skipBytes(int n) Attempts to skip over n bytes of input discarding the
skipped bytes.
|
void |
write(byte[] b) Writes b.length bytes from the specified byte array
to this file, starting at the current file pointer.
|
void |
write(byte[] b, int off, int len) Writes len bytes from the specified byte array
starting at offset off to this file.
|
native void |
write(int b) Writes the specified byte to this file. |
void |
writeBoolean(boolean v) Writes a boolean to the file as a one-byte value.
|
void |
writeByte(int v) Writes a byte to the file as a one-byte value.
|
void |
writeBytes(String s) Writes the string to the file as a sequence of bytes. |
void |
writeChar(int v) Writes a char to the file as a two-byte value, high
byte first.
|
void |
writeChars(String s) Writes a string to the file as a sequence of characters. |
void |
writeDouble(double v) Converts the double argument to a long using the
doubleToLongBits method in class Double ,
and then writes that long value to the file as an
eight-byte quantity, high byte first.
|
void |
writeFloat(float v) Converts the float argument to an int using the
floatToIntBits method in class Float ,
and then writes that int value to the file as a
four-byte quantity, high byte first.
|
void |
writeInt(int v) Writes an int to the file as four bytes, high byte first.
|
void |
writeLong(long v) Writes a long to the file as eight bytes, high byte first.
|
void |
writeShort(int v) Writes a short to the file as two bytes, high byte first.
|
void |
Writes a string to the file using modified UTF-8 encoding in a machine-independent manner. |
Methods inherited from class java.lang.Object |
---|
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Constructor Detail |
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public RandomAccessFile(File file, String mode) throws FileNotFoundException
The mode argument specifies the access mode in which the file is to be opened. The permitted values and their meanings are:
The "rws" and "rwd" modes work much like the {@link java.nio.channels.FileChannel#force(boolean) force(boolean)} method of the {@link java.nio.channels.FileChannel} class, passing arguments of true and false, respectively, except that they always apply to every I/O operation and are therefore often more efficient. If the file resides on a local storage device then when an invocation of a method of this class returns it is guaranteed that all changes made to the file by that invocation will have been written to that device. This is useful for ensuring that critical information is not lost in the event of a system crash. If the file does not reside on a local device then no such guarantee is made.
Value
Meaning
"r" Open for reading only. Invoking any of the write methods of the resulting object will cause an {@link java.io.IOException} to be thrown. "rw" Open for reading and writing. If the file does not already exist then an attempt will be made to create it. "rws" Open for reading and writing, as with "rw", and also require that every update to the file's content or metadata be written synchronously to the underlying storage device. "rwd" Open for reading and writing, as with "rw", and also require that every update to the file's content be written synchronously to the underlying storage device.
The "rwd" mode can be used to reduce the number of I/O operations performed. Using "rwd" only requires updates to the file's content to be written to storage; using "rws" requires updates to both the file's content and its metadata to be written, which generally requires at least one more low-level I/O operation.
If there is a security manager, its checkRead
method is
called with the pathname of the file
argument as its
argument to see if read access to the file is allowed. If the mode
allows writing, the security manager's checkWrite
method is
also called with the path argument to see if write access to the file is
allowed.
file
- the file objectmode
- the access mode, as described
aboveFileNotFoundException
- if the mode is "r" but the given file object does
not denote an existing regular file, or if the mode begins
with "rw" but the given file object does not denote
an existing, writable regular file and a new regular file of
that name cannot be created, or if some other error occurs
while opening or creating the filepublic RandomAccessFile(String name, String mode) throws FileNotFoundException
The mode argument specifies the access mode with which the file is to be opened. The permitted values and their meanings are as specified for the RandomAccessFile(File,String) constructor.
If there is a security manager, its checkRead
method
is called with the name
argument
as its argument to see if read access to the file is allowed.
If the mode allows writing, the security manager's
checkWrite
method
is also called with the name
argument
as its argument to see if write access to the file is allowed.
name
- the system-dependent filenamemode
- the access modeFileNotFoundException
- if the mode is "r" but the given string does not
denote an existing regular file, or if the mode begins with
"rw" but the given string does not denote an
existing, writable regular file and a new regular file of
that name cannot be created, or if some other error occurs
while opening or creating the fileMethod Detail |
---|
public void close() throws IOException
If this file has an associated channel then the channel is closed as well.
IOException
- if an I/O error occurs.public final FileChannel getChannel()
The {@link java.nio.channels.FileChannel#position()
position
} of the returned channel will always be equal to
this object's file-pointer offset as returned by the {@link
#getFilePointer getFilePointer} method. Changing this object's
file-pointer offset, whether explicitly or by reading or writing bytes,
will change the position of the channel, and vice versa. Changing the
file's length via this object will change the length seen via the file
channel, and vice versa.
public final FileDescriptor getFD() throws IOException
IOException
- if an I/O error occurs.public native long getFilePointer() throws IOException
IOException
- if an I/O error occurs.public native long length() throws IOException
IOException
- if an I/O error occurs.public native int read() throws IOException
0x00-0x0ff
). This
method blocks if no input is yet available.
Although RandomAccessFile
is not a subclass of
InputStream
, this method behaves in exactly the same
way as the {@link InputStream#read()} method of
InputStream
.
-1
if the end of the
file has been reached.IOException
- if an I/O error occurs. Not thrown if
end-of-file has been reached.public int read(byte[] b) throws IOException
b.length
bytes of data from this file
into an array of bytes. This method blocks until at least one byte
of input is available.
Although RandomAccessFile
is not a subclass of
InputStream
, this method behaves in exactly the
same way as the {@link InputStream#read(byte[])} method of
InputStream
.
b
- the buffer into which the data is read.-1
if there is no more data because the end of
this file has been reached.IOException
- If the first byte cannot be read for any reason
other than end of file, or if the random access file has been closed, or if
some other I/O error occurs.public int read(byte[] b, int off, int len) throws IOException
len
bytes of data from this file into an
array of bytes. This method blocks until at least one byte of input
is available.
Although RandomAccessFile
is not a subclass of
InputStream
, this method behaves in exactly the
same way as the {@link InputStream#read(byte[], int, int)} method of
InputStream
.
b
- the buffer into which the data is read.off
- the start offset in array b
at which the data is written.len
- the maximum number of bytes read.-1
if there is no more data because the end of
the file has been reached.IOException
- If the first byte cannot be read for any reason
other than end of file, or if the random access file has been closed, or if
some other I/O error occurs.public final boolean readBoolean() throws IOException
boolean
from this file. This method reads a
single byte from the file, starting at the current file pointer.
A value of 0
represents
false
. Any other value represents true
.
This method blocks until the byte is read, the end of the stream
is detected, or an exception is thrown.
boolean
value read.IOException
- if an I/O error occurs.public final byte readByte() throws IOException
b
, where
0 <= b <= 255
,
then the result is:
(byte)(b)
This method blocks until the byte is read, the end of the stream is detected, or an exception is thrown.
byte
.IOException
- if an I/O error occurs.public final char readChar() throws IOException
b1
and b2
, where
0 <= b1, b2 <= 255
,
then the result is equal to:
(char)((b1 << 8) | b2)
This method blocks until the two bytes are read, the end of the stream is detected, or an exception is thrown.
char
.IOException
- if an I/O error occurs.public final double readDouble() throws IOException
double
from this file. This method reads a
long
value, starting at the current file pointer,
as if by the readLong
method
and then converts that long
to a double
using the longBitsToDouble
method in
class Double
.
This method blocks until the eight bytes are read, the end of the stream is detected, or an exception is thrown.
double
.IOException
- if an I/O error occurs.public final float readFloat() throws IOException
float
from this file. This method reads an
int
value, starting at the current file pointer,
as if by the readInt
method
and then converts that int
to a float
using the intBitsToFloat
method in class
Float
.
This method blocks until the four bytes are read, the end of the stream is detected, or an exception is thrown.
float
.IOException
- if an I/O error occurs.public final void readFully(byte[] b) throws IOException
b.length
bytes from this file into the byte
array, starting at the current file pointer. This method reads
repeatedly from the file until the requested number of bytes are
read. This method blocks until the requested number of bytes are
read, the end of the stream is detected, or an exception is thrown.
b
- the buffer into which the data is read.IOException
- if an I/O error occurs.public final void readFully(byte[] b, int off, int len) throws IOException
len
bytes from this file into the byte
array, starting at the current file pointer. This method reads
repeatedly from the file until the requested number of bytes are
read. This method blocks until the requested number of bytes are
read, the end of the stream is detected, or an exception is thrown.
b
- the buffer into which the data is read.off
- the start offset of the data.len
- the number of bytes to read.IOException
- if an I/O error occurs.public final int readInt() throws IOException
b1
,
b2
, b3
, and b4
, where
0 <= b1, b2, b3, b4 <= 255
,
then the result is equal to:
(b1 << 24) | (b2 << 16) + (b3 << 8) + b4
This method blocks until the four bytes are read, the end of the stream is detected, or an exception is thrown.
int
.IOException
- if an I/O error occurs.public final String readLine() throws IOException
A line of text is terminated by a carriage-return character
('\r'
), a newline character ('\n'
), a
carriage-return character immediately followed by a newline character,
or the end of the file. Line-terminating characters are discarded and
are not included as part of the string returned.
This method blocks until a newline character is read, a carriage return and the byte following it are read (to see if it is a newline), the end of the file is reached, or an exception is thrown.
IOException
- if an I/O error occurs.public final long readLong() throws IOException
b1
, b2
, b3
,
b4
, b5
, b6
,
b7
, and b8,
where:
0 <= b1, b2, b3, b4, b5, b6, b7, b8 <=255,
then the result is equal to:
((long)b1 << 56) + ((long)b2 << 48) + ((long)b3 << 40) + ((long)b4 << 32) + ((long)b5 << 24) + ((long)b6 << 16) + ((long)b7 << 8) + b8
This method blocks until the eight bytes are read, the end of the stream is detected, or an exception is thrown.
long
.IOException
- if an I/O error occurs.public final short readShort() throws IOException
b1
and b2
, where each of the two values is
between 0
and 255
, inclusive, then the
result is equal to:
(short)((b1 << 8) | b2)
This method blocks until the two bytes are read, the end of the stream is detected, or an exception is thrown.
IOException
- if an I/O error occurs.public final int readUnsignedByte() throws IOException
This method blocks until the byte is read, the end of the stream is detected, or an exception is thrown.
IOException
- if an I/O error occurs.public final int readUnsignedShort() throws IOException
b1
and b2
, where
0 <= b1, b2 <= 255
,
then the result is equal to:
(b1 << 8) | b2
This method blocks until the two bytes are read, the end of the stream is detected, or an exception is thrown.
IOException
- if an I/O error occurs.public final String readUTF() throws IOException
The first two bytes are read, starting from the current file
pointer, as if by
readUnsignedShort
. This value gives the number of
following bytes that are in the encoded string, not
the length of the resulting string. The following bytes are then
interpreted as bytes encoding characters in the modified UTF-8 format
and are converted into characters.
This method blocks until all the bytes are read, the end of the stream is detected, or an exception is thrown.
IOException
- if an I/O error occurs.public native void seek(long pos) throws IOException
pos
- the offset position, measured in bytes from the
beginning of the file, at which to set the file
pointer.IOException
- if pos
is less than
0
or if an I/O error occurs.public native void setLength(long newLength) throws IOException
If the present length of the file as returned by the
length
method is greater than the newLength
argument then the file will be truncated. In this case, if the file
offset as returned by the getFilePointer
method is greater
than newLength
then after this method returns the offset
will be equal to newLength
.
If the present length of the file as returned by the
length
method is smaller than the newLength
argument then the file will be extended. In this case, the contents of
the extended portion of the file are not defined.
newLength
- The desired length of the fileIOException
- If an I/O error occurspublic int skipBytes(int n) throws IOException
n
bytes of input discarding the
skipped bytes.
This method may skip over some smaller number of bytes, possibly zero.
This may result from any of a number of conditions; reaching end of
file before n
bytes have been skipped is only one
possibility. This method never throws an EOFException
.
The actual number of bytes skipped is returned. If n
is negative, no bytes are skipped.
n
- the number of bytes to be skipped.IOException
- if an I/O error occurs.public void write(byte[] b) throws IOException
b.length
bytes from the specified byte array
to this file, starting at the current file pointer.
b
- the data.IOException
- if an I/O error occurs.public void write(byte[] b, int off, int len) throws IOException
len
bytes from the specified byte array
starting at offset off
to this file.
b
- the data.off
- the start offset in the data.len
- the number of bytes to write.IOException
- if an I/O error occurs.public native void write(int b) throws IOException
b
- the byte
to be written.IOException
- if an I/O error occurs.public final void writeBoolean(boolean v) throws IOException
boolean
to the file as a one-byte value. The
value true
is written out as the value
(byte)1
; the value false
is written out
as the value (byte)0
. The write starts at
the current position of the file pointer.
v
- a boolean
value to be written.IOException
- if an I/O error occurs.public final void writeByte(int v) throws IOException
byte
to the file as a one-byte value. The
write starts at the current position of the file pointer.
v
- a byte
value to be written.IOException
- if an I/O error occurs.public final void writeBytes(String s) throws IOException
s
- a string of bytes to be written.IOException
- if an I/O error occurs.public final void writeChar(int v) throws IOException
char
to the file as a two-byte value, high
byte first. The write starts at the current position of the
file pointer.
v
- a char
value to be written.IOException
- if an I/O error occurs.public final void writeChars(String s) throws IOException
writeChar
method. The write starts at the current
position of the file pointer.
s
- a String
value to be written.IOException
- if an I/O error occurs.public final void writeDouble(double v) throws IOException
long
using the
doubleToLongBits
method in class Double
,
and then writes that long
value to the file as an
eight-byte quantity, high byte first. The write starts at the current
position of the file pointer.
v
- a double
value to be written.IOException
- if an I/O error occurs.public final void writeFloat(float v) throws IOException
int
using the
floatToIntBits
method in class Float
,
and then writes that int
value to the file as a
four-byte quantity, high byte first. The write starts at the
current position of the file pointer.
v
- a float
value to be written.IOException
- if an I/O error occurs.public final void writeInt(int v) throws IOException
int
to the file as four bytes, high byte first.
The write starts at the current position of the file pointer.
v
- an int
to be written.IOException
- if an I/O error occurs.public final void writeLong(long v) throws IOException
long
to the file as eight bytes, high byte first.
The write starts at the current position of the file pointer.
v
- a long
to be written.IOException
- if an I/O error occurs.public final void writeShort(int v) throws IOException
short
to the file as two bytes, high byte first.
The write starts at the current position of the file pointer.
v
- a short
to be written.IOException
- if an I/O error occurs.public final void writeUTF(String str) throws IOException
First, two bytes are written to the file, starting at the
current file pointer, as if by the
writeShort
method giving the number of bytes to
follow. This value is the number of bytes actually written out,
not the length of the string. Following the length, each character
of the string is output, in sequence, using the modified UTF-8 encoding
for each character.
str
- a string to be written.IOException
- if an I/O error occurs.
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