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.
public RandomAccessFile(String name, String mode) throws FileNotFoundException
Creates a random access file stream to read from, and optionally to write to, a file with the specified name. A new FileDescriptor
object is created to represent the connection to the file.
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 mode
IllegalArgumentException
- if the mode argument is not equal to one of "r"
, "rw"
, "rws"
, or "rwd"
FileNotFoundException
- 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 fileSecurityException
- if a security manager exists and its checkRead
method denies read access to the file or the mode is "rw" and the security manager's checkWrite
method denies write access to the fileSecurityException
, SecurityManager.checkRead(java.lang.String)
, SecurityManager.checkWrite(java.lang.String)
public RandomAccessFile(File file, String mode) throws FileNotFoundException
Creates a random access file stream to read from, and optionally to write to, the file specified by the File
argument. A new FileDescriptor
object is created to represent this file connection.
The mode
argument specifies the access mode in which the file is to be opened. The permitted values and their meanings are:
Value | Meaning |
---|---|
"r" | Open for reading only. Invoking any of the write methods of the resulting object will cause an 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. |
"rws"
and "rwd"
modes work much like the force(boolean)
method of the 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. 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 above
IllegalArgumentException
- if the mode argument is not equal to one of "r"
, "rw"
, "rws"
, or "rwd"
FileNotFoundException
- 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 fileSecurityException
- if a security manager exists and its checkRead
method denies read access to the file or the mode is "rw" and the security manager's checkWrite
method denies write access to the fileSecurityManager.checkRead(java.lang.String)
, SecurityManager.checkWrite(java.lang.String)
, FileChannel.force(boolean)
public final FileDescriptor getFD() throws IOException
Returns the opaque file descriptor object associated with this stream.
IOException
- if an I/O error occurs.FileDescriptor
public final FileChannel getChannel()
Returns the unique FileChannel
object associated with this file.
The position
of the returned channel will always be equal to this object's file-pointer offset as returned by the 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 int read() throws IOException
Reads a byte of data from this file. The byte is returned as an integer in the range 0 to 255 (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 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, int off, int len) throws IOException
Reads up to 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 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.NullPointerException
- If b
is null
.IndexOutOfBoundsException
- If off
is negative, len
is negative, or len
is greater than b.length - off
public int read(byte[] b) throws IOException
Reads up to 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 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.NullPointerException
- If b
is null
.public final void readFully(byte[] b) throws IOException
Reads 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.
readFully
in interface DataInput
b
- the buffer into which the data is read.EOFException
- if this file reaches the end before reading all the bytes.IOException
- if an I/O error occurs.public final void readFully(byte[] b, int off, int len) throws IOException
Reads exactly 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.
readFully
in interface DataInput
b
- the buffer into which the data is read.off
- the start offset of the data.len
- the number of bytes to read.EOFException
- if this file reaches the end before reading all the bytes.IOException
- if an I/O error occurs.public int skipBytes(int n) throws IOException
Attempts to skip over 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.
skipBytes
in interface DataInput
n
- the number of bytes to be skipped.IOException
- if an I/O error occurs.public void write(int b) throws IOException
Writes the specified byte to this file. The write starts at the current file pointer.
write
in interface DataOutput
b
- the byte
to be written.IOException
- if an I/O error occurs.public void write(byte[] b) throws IOException
Writes b.length
bytes from the specified byte array to this file, starting at the current file pointer.
write
in interface DataOutput
b
- the data.IOException
- if an I/O error occurs.public void write(byte[] b, int off, int len) throws IOException
Writes len
bytes from the specified byte array starting at offset off
to this file.
write
in interface DataOutput
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 long getFilePointer() throws IOException
Returns the current offset in this file.
IOException
- if an I/O error occurs.public void seek(long pos) throws IOException
Sets the file-pointer offset, measured from the beginning of this file, at which the next read or write occurs. The offset may be set beyond the end of the file. Setting the offset beyond the end of the file does not change the file length. The file length will change only by writing after the offset has been set beyond the end of the file.
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 long length() throws IOException
Returns the length of this file.
IOException
- if an I/O error occurs.public void setLength(long newLength) throws IOException
Sets the length of this file.
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 void close() throws IOException
Closes this random access file stream and releases any system resources associated with the stream. A closed random access file cannot perform input or output operations and cannot be reopened.
If this file has an associated channel then the channel is closed as well.
close
in interface Closeable
close
in interface AutoCloseable
IOException
- if an I/O error occurs.public final boolean readBoolean() throws IOException
Reads a 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.
readBoolean
in interface DataInput
boolean
value read.EOFException
- if this file has reached the end.IOException
- if an I/O error occurs.public final byte readByte() throws IOException
Reads a signed eight-bit value from this file. This method reads a byte from the file, starting from the current file pointer. If the byte read is 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.
readByte
in interface DataInput
byte
.EOFException
- if this file has reached the end.IOException
- if an I/O error occurs.public final int readUnsignedByte() throws IOException
Reads an unsigned eight-bit number from this file. This method reads a byte from this file, starting at the current file pointer, and returns that byte.
This method blocks until the byte is read, the end of the stream is detected, or an exception is thrown.
readUnsignedByte
in interface DataInput
EOFException
- if this file has reached the end.IOException
- if an I/O error occurs.public final short readShort() throws IOException
Reads a signed 16-bit number from this file. The method reads two bytes from this file, starting at the current file pointer. If the two bytes read, in order, are 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.
readShort
in interface DataInput
EOFException
- if this file reaches the end before reading two bytes.IOException
- if an I/O error occurs.public final int readUnsignedShort() throws IOException
Reads an unsigned 16-bit number from this file. This method reads two bytes from the file, starting at the current file pointer. If the bytes read, in order, are 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.
readUnsignedShort
in interface DataInput
EOFException
- if this file reaches the end before reading two bytes.IOException
- if an I/O error occurs.public final char readChar() throws IOException
Reads a character from this file. This method reads two bytes from the file, starting at the current file pointer. If the bytes read, in order, are 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.
readChar
in interface DataInput
char
.EOFException
- if this file reaches the end before reading two bytes.IOException
- if an I/O error occurs.public final int readInt() throws IOException
Reads a signed 32-bit integer from this file. This method reads 4 bytes from the file, starting at the current file pointer. If the bytes read, in order, are 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.
readInt
in interface DataInput
int
.EOFException
- if this file reaches the end before reading four bytes.IOException
- if an I/O error occurs.public final long readLong() throws IOException
Reads a signed 64-bit integer from this file. This method reads eight bytes from the file, starting at the current file pointer. If the bytes read, in order, are 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.
readLong
in interface DataInput
long
.EOFException
- if this file reaches the end before reading eight bytes.IOException
- if an I/O error occurs.public final float readFloat() throws IOException
Reads a 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.
readFloat
in interface DataInput
float
.EOFException
- if this file reaches the end before reading four bytes.IOException
- if an I/O error occurs.readInt()
, Float.intBitsToFloat(int)
public final double readDouble() throws IOException
Reads a 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.
readDouble
in interface DataInput
double
.EOFException
- if this file reaches the end before reading eight bytes.IOException
- if an I/O error occurs.readLong()
, Double.longBitsToDouble(long)
public final String readLine() throws IOException
Reads the next line of text from this file. This method successively reads bytes from the file, starting at the current file pointer, until it reaches a line terminator or the end of the file. Each byte is converted into a character by taking the byte's value for the lower eight bits of the character and setting the high eight bits of the character to zero. This method does not, therefore, support the full Unicode character set.
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.
readLine
in interface DataInput
IOException
- if an I/O error occurs.public final String readUTF() throws IOException
Reads in a string from this file. The string has been encoded using a modified UTF-8 format.
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.
readUTF
in interface DataInput
EOFException
- if this file reaches the end before reading all the bytes.IOException
- if an I/O error occurs.UTFDataFormatException
- if the bytes do not represent valid modified UTF-8 encoding of a Unicode string.readUnsignedShort()
public final void writeBoolean(boolean v) throws IOException
Writes a 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.
writeBoolean
in interface DataOutput
v
- a boolean
value to be written.IOException
- if an I/O error occurs.public final void writeByte(int v) throws IOException
Writes a byte
to the file as a one-byte value. The write starts at the current position of the file pointer.
writeByte
in interface DataOutput
v
- a byte
value to be written.IOException
- if an I/O error occurs.public final void writeShort(int v) throws IOException
Writes a short
to the file as two bytes, high byte first. The write starts at the current position of the file pointer.
writeShort
in interface DataOutput
v
- a short
to be written.IOException
- if an I/O error occurs.public final void writeChar(int v) throws IOException
Writes a char
to the file as a two-byte value, high byte first. The write starts at the current position of the file pointer.
writeChar
in interface DataOutput
v
- a char
value to be written.IOException
- if an I/O error occurs.public final void writeInt(int v) throws IOException
Writes an int
to the file as four bytes, high byte first. The write starts at the current position of the file pointer.
writeInt
in interface DataOutput
v
- an int
to be written.IOException
- if an I/O error occurs.public final void writeLong(long v) throws IOException
Writes a long
to the file as eight bytes, high byte first. The write starts at the current position of the file pointer.
writeLong
in interface DataOutput
v
- a long
to be written.IOException
- if an I/O error occurs.public final void writeFloat(float v) throws IOException
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. The write starts at the current position of the file pointer.
writeFloat
in interface DataOutput
v
- a float
value to be written.IOException
- if an I/O error occurs.Float.floatToIntBits(float)
public final void writeDouble(double v) throws IOException
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. The write starts at the current position of the file pointer.
writeDouble
in interface DataOutput
v
- a double
value to be written.IOException
- if an I/O error occurs.Double.doubleToLongBits(double)
public final void writeBytes(String s) throws IOException
Writes the string to the file as a sequence of bytes. Each character in the string is written out, in sequence, by discarding its high eight bits. The write starts at the current position of the file pointer.
writeBytes
in interface DataOutput
s
- a string of bytes to be written.IOException
- if an I/O error occurs.public final void writeChars(String s) throws IOException
Writes a string to the file as a sequence of characters. Each character is written to the data output stream as if by the writeChar
method. The write starts at the current position of the file pointer.
writeChars
in interface DataOutput
s
- a String
value to be written.IOException
- if an I/O error occurs.writeChar(int)
public final void writeUTF(String str) throws IOException
Writes a string to the file using modified UTF-8 encoding in a machine-independent manner.
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.
writeUTF
in interface DataOutput
str
- a string to be written.IOException
- if an I/O error occurs.
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Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
Various third party code in OpenJDK is licensed under different licenses (see Debian package).
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