RandomAccessFilepublic class RandomAccessFile extends Object implements DataInput, DataOutput, CloseableInstances 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. |
| Fields Summary |
|---|
| private FileDescriptor | fd | | private FileChannel | channel | | private boolean | rw | | private static final int | O_RDONLY | | private static final int | O_RDWR | | private static final int | O_SYNC | | private static final int | O_DSYNC |
| Constructors Summary |
|---|
public 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. A new
{@link 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.
this(name != null ? new File(name) : null, mode);
| public RandomAccessFile(File file, String mode)Creates a random access file stream to read from, and optionally to
write to, the file specified by the {@link File} argument. A new {@link
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 {@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 "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.
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.
String name = (file != null ? file.getPath() : null);
int imode = -1;
if (mode.equals("r"))
imode = O_RDONLY;
else if (mode.startsWith("rw")) {
imode = O_RDWR;
rw = true;
if (mode.length() > 2) {
if (mode.equals("rws"))
imode |= O_SYNC;
else if (mode.equals("rwd"))
imode |= O_DSYNC;
else
imode = -1;
}
}
if (imode < 0)
throw new IllegalArgumentException("Illegal mode \"" + mode
+ "\" must be one of "
+ "\"r\", \"rw\", \"rws\","
+ " or \"rwd\"");
SecurityManager security = System.getSecurityManager();
if (security != null) {
security.checkRead(name);
if (rw) {
security.checkWrite(name);
}
}
if (name == null) {
throw new NullPointerException();
}
fd = new FileDescriptor();
open(name, imode);
|
| Methods Summary |
|---|
| public void | close()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.
if (channel != null)
channel.close();
close0();
| | private native void | close0()
| | public final java.nio.channels.FileChannel | getChannel()Returns the unique {@link java.nio.channels.FileChannel FileChannel}
object associated with this file.
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.
synchronized (this) {
if (channel == null)
channel = FileChannelImpl.open(fd, true, rw, this);
return channel;
}
| | public final java.io.FileDescriptor | getFD()Returns the opaque file descriptor object associated with this
stream.
if (fd != null) return fd;
throw new IOException();
| | public native long | getFilePointer()Returns the current offset in this file.
| | private static native void | initIDs()
| | public native long | length()Returns the length of this file.
| | private native void | open(java.lang.String name, int mode)Opens a file and returns the file descriptor. The file is
opened in read-write mode if the O_RDWR bit in mode
is true, else the file is opened as read-only.
If the name refers to a directory, an IOException
is thrown.
| | public native int | read()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 {@link InputStream#read()} method of
InputStream.
| | public int | read(byte[] b, int off, int len)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 {@link InputStream#read(byte[], int, int)} method of
InputStream.
return readBytes(b, off, len);
| | public int | read(byte[] b)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 {@link InputStream#read(byte[])} method of
InputStream.
return readBytes(b, 0, b.length);
| | public final boolean | readBoolean()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.
int ch = this.read();
if (ch < 0)
throw new EOFException();
return (ch != 0);
| | public final byte | readByte()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.
int ch = this.read();
if (ch < 0)
throw new EOFException();
return (byte)(ch);
| | private native int | readBytes(byte[] b, int off, int len)Reads a sub array as a sequence of bytes.
| | public final char | readChar()Reads a Unicode 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.
int ch1 = this.read();
int ch2 = this.read();
if ((ch1 | ch2) < 0)
throw new EOFException();
return (char)((ch1 << 8) + (ch2 << 0));
| | public final double | readDouble()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.
return Double.longBitsToDouble(readLong());
| | public final float | readFloat()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.
return Float.intBitsToFloat(readInt());
| | public final void | readFully(byte[] b)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(b, 0, b.length);
| | public final 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. 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.
int n = 0;
do {
int count = this.read(b, off + n, len - n);
if (count < 0)
throw new EOFException();
n += count;
} while (n < len);
| | public final int | readInt()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.
int ch1 = this.read();
int ch2 = this.read();
int ch3 = this.read();
int ch4 = this.read();
if ((ch1 | ch2 | ch3 | ch4) < 0)
throw new EOFException();
return ((ch1 << 24) + (ch2 << 16) + (ch3 << 8) + (ch4 << 0));
| | public final java.lang.String | readLine()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.
StringBuffer input = new StringBuffer();
int c = -1;
boolean eol = false;
while (!eol) {
switch (c = read()) {
case -1:
case '\n":
eol = true;
break;
case '\r":
eol = true;
long cur = getFilePointer();
if ((read()) != '\n") {
seek(cur);
}
break;
default:
input.append((char)c);
break;
}
}
if ((c == -1) && (input.length() == 0)) {
return null;
}
return input.toString();
| | public final long | readLong()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.
return ((long)(readInt()) << 32) + (readInt() & 0xFFFFFFFFL);
| | public final short | readShort()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.
int ch1 = this.read();
int ch2 = this.read();
if ((ch1 | ch2) < 0)
throw new EOFException();
return (short)((ch1 << 8) + (ch2 << 0));
| | public final java.lang.String | readUTF()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.
return DataInputStream.readUTF(this);
| | public final int | readUnsignedByte()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.
int ch = this.read();
if (ch < 0)
throw new EOFException();
return ch;
| | public final int | readUnsignedShort()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.
int ch1 = this.read();
int ch2 = this.read();
if ((ch1 | ch2) < 0)
throw new EOFException();
return (ch1 << 8) + (ch2 << 0);
| | public 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. 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.
| | public native void | setLength(long newLength)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.
| | public int | skipBytes(int n)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.
long pos;
long len;
long newpos;
if (n <= 0) {
return 0;
}
pos = getFilePointer();
len = length();
newpos = pos + n;
if (newpos > len) {
newpos = len;
}
seek(newpos);
/* return the actual number of bytes skipped */
return (int) (newpos - pos);
| | public native void | write(int b)Writes the specified byte to this file. The write starts at
the current file pointer.
| | public void | write(byte[] b)Writes b.length bytes from the specified byte array
to this file, starting at the current file pointer.
writeBytes(b, 0, b.length);
| | public void | write(byte[] b, int off, int len)Writes len bytes from the specified byte array
starting at offset off to this file.
writeBytes(b, off, len);
| | public final void | writeBoolean(boolean v)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.
write(v ? 1 : 0);
//written++;
| | public final void | writeByte(int v)Writes a byte to the file as a one-byte value. The
write starts at the current position of the file pointer.
write(v);
//written++;
| | private native void | writeBytes(byte[] b, int off, int len)Writes a sub array as a sequence of bytes.
| | public final void | writeBytes(java.lang.String s)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.
int len = s.length();
byte[] b = new byte[len];
s.getBytes(0, len, b, 0);
writeBytes(b, 0, len);
| | public final void | writeChar(int v)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.
write((v >>> 8) & 0xFF);
write((v >>> 0) & 0xFF);
//written += 2;
| | public final void | writeChars(java.lang.String s)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.
int clen = s.length();
int blen = 2*clen;
byte[] b = new byte[blen];
char[] c = new char[clen];
s.getChars(0, clen, c, 0);
for (int i = 0, j = 0; i < clen; i++) {
b[j++] = (byte)(c[i] >>> 8);
b[j++] = (byte)(c[i] >>> 0);
}
writeBytes(b, 0, blen);
| | public final 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. The write starts at the current
position of the file pointer.
writeLong(Double.doubleToLongBits(v));
| | public final 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. The write starts at the
current position of the file pointer.
writeInt(Float.floatToIntBits(v));
| | public final void | writeInt(int v)Writes an int to the file as four bytes, high byte first.
The write starts at the current position of the file pointer.
write((v >>> 24) & 0xFF);
write((v >>> 16) & 0xFF);
write((v >>> 8) & 0xFF);
write((v >>> 0) & 0xFF);
//written += 4;
| | public final void | writeLong(long v)Writes a long to the file as eight bytes, high byte first.
The write starts at the current position of the file pointer.
write((int)(v >>> 56) & 0xFF);
write((int)(v >>> 48) & 0xFF);
write((int)(v >>> 40) & 0xFF);
write((int)(v >>> 32) & 0xFF);
write((int)(v >>> 24) & 0xFF);
write((int)(v >>> 16) & 0xFF);
write((int)(v >>> 8) & 0xFF);
write((int)(v >>> 0) & 0xFF);
//written += 8;
| | public final void | writeShort(int v)Writes a short to the file as two bytes, high byte first.
The write starts at the current position of the file pointer.
write((v >>> 8) & 0xFF);
write((v >>> 0) & 0xFF);
//written += 2;
| | public final void | writeUTF(java.lang.String str)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.
DataOutputStream.writeUTF(str, this);
|
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