public class RandomAccessFile extends Object implements DataOutput, DataInput, Closeable
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 and Description |
|---|
RandomAccessFile(File file,
String mode)
Creates a random access file stream to read from, and optionally to
write to, the file specified by the
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.
|
| Modifier and Type | Method and Description |
|---|---|
void |
close()
Closes this random access file stream and releases any system
resources associated with the stream.
|
FileChannel |
getChannel()
Returns the unique
FileChannel
object associated with this file. |
FileDescriptor |
getFD()
Returns the opaque file descriptor object associated with this
stream.
|
long |
getFilePointer()
Returns the current offset in this file.
|
long |
length()
Returns the length of this file.
|
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 |
readBoolean()
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 |
readDouble()
Reads a
double from this file. |
float |
readFloat()
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 |
readShort()
Reads a signed 16-bit number from this file.
|
int |
readUnsignedByte()
Reads an unsigned eight-bit number from this file.
|
int |
readUnsignedShort()
Reads an unsigned 16-bit number from this file.
|
String |
readUTF()
Reads in a string from this file.
|
void |
seek(long pos)
Sets the file-pointer offset, measured from the beginning of this
file, at which the next read or write occurs.
|
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. |
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 |
writeUTF(String str)
Writes a string to the file using
modified UTF-8
encoding in a machine-independent manner.
|
public RandomAccessFile(String name, String mode) throws FileNotFoundException
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 modeIllegalArgumentException - 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
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. |
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
aboveIllegalArgumentException - 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
IOException - if an I/O error occurs.FileDescriptorpublic final FileChannel getChannel()
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
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
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 - offpublic 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 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
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 DataInputb - 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
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 DataInputb - 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
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 DataInputn - the number of bytes to be skipped.IOException - if an I/O error occurs.public void write(int b)
throws IOException
write in interface DataOutputb - the byte to be written.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.write in interface DataOutputb - 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.write in interface DataOutputb - 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
IOException - if an I/O error occurs.public 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 long length()
throws IOException
IOException - if an I/O error occurs.public 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 void close()
throws IOException
If this file has an associated channel then the channel is closed as well.
close in interface Closeableclose in interface AutoCloseableIOException - if an 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.readBoolean in interface DataInputboolean value read.EOFException - if this file has reached the end.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.
readByte in interface DataInputbyte.EOFException - if this file has reached the end.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.
readUnsignedByte in interface DataInputEOFException - if this file has reached the end.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.
readShort in interface DataInputEOFException - if this file reaches the end before reading
two bytes.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.
readUnsignedShort in interface DataInputEOFException - if this file reaches the end before reading
two bytes.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.
readChar in interface DataInputchar.EOFException - if this file reaches the end before reading
two bytes.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.
readInt in interface DataInputint.EOFException - if this file reaches the end before reading
four bytes.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.
readLong in interface DataInputlong.EOFException - if this file reaches the end before reading
eight bytes.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.
readFloat in interface DataInputfloat.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
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 DataInputdouble.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
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 DataInputIOException - 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.
readUTF in interface DataInputEOFException - 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
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 DataOutputv - 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.writeByte in interface DataOutputv - a byte value 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.writeShort in interface DataOutputv - a short 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.writeChar in interface DataOutputv - a char 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.writeInt in interface DataOutputv - 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.writeLong in interface DataOutputv - a long 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.writeFloat in interface DataOutputv - a float value to be written.IOException - if an I/O error occurs.Float.floatToIntBits(float)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.writeDouble in interface DataOutputv - a double value to be written.IOException - if an I/O error occurs.Double.doubleToLongBits(double)public final void writeBytes(String s) throws IOException
writeBytes in interface DataOutputs - a string of bytes 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.writeChars in interface DataOutputs - a String value to be written.IOException - if an I/O error occurs.writeChar(int)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.
writeUTF in interface DataOutputstr - a string to be written.IOException - if an I/O error occurs. Submit a bug or feature
For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
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