java.io.RandomAccessFile
is new.
java.lang.Object
public class RandomAccessFile
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 | |
|---|---|
|
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. |
|
| Method Summary | |
|---|---|
| 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
|
| 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. |
| Methods inherited from class java.lang. Object |
|---|
| clone , equals , finalize , getClass , hashCode , notify , notifyAll , toString , wait , wait , wait |
| Constructor Detail |
|---|
public 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.
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 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.
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.
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.
| Method Detail |
|---|
public final FileDescriptor getFD()
throws IOException
public final FileChannel getChannel()
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
Although RandomAccessFile is not a subclass of InputStream, this method behaves in exactly the same way as the InputStream.read() method of InputStream.
public int read(byte[] b,
int off,
int len)
throws IOException
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.
in array b at which
data is written.
- 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
Although RandomAccessFile is not a subclass of InputStream, this method behaves in exactly the same way as the InputStream.read(byte[]) method of InputStream.
- 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
public final void readFully(byte[] b,
int off,
int len)
throws IOException
public int skipBytes(int n)
throws IOException
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.
public void write(int b)
throws IOException
public void write(byte[] b)
throws IOException
public void write(byte[] b,
int off,
int len)
throws IOException
public long getFilePointer()
throws IOException
public void seek(long pos)
throws IOException
public long length()
throws IOException
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.
public void close()
throws IOException
If this file has an associated channel then the channel is closed as well.
public final boolean readBoolean()
throws IOException
public final byte readByte()
throws IOException
(byte)(b)
This method blocks until the byte is read, the end of the stream is detected, or an exception is thrown.
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.
public final short readShort()
throws IOException
(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.
public final int readUnsignedShort()
throws IOException
(b1 << 8) | b2
This method blocks until the two bytes are read, the end of the stream is detected, or an exception is thrown.
public final char readChar()
throws IOException
(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.
file, interpreted
char.
public final int readInt()
throws IOException
(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.
public final long readLong()
throws IOException
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.
public final float readFloat()
throws IOException
This method blocks until the four bytes are read, the end of the stream is detected, or an exception is thrown.
public final double readDouble()
throws IOException
This method blocks until the eight bytes are read, the end of the stream is detected, or an exception is thrown.
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.
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.
public final void writeBoolean(boolean v)
throws IOException
public final void writeByte(int v)
throws IOException
public final void writeShort(int v)
throws IOException
public final void writeChar(int v)
throws IOException
public final void writeInt(int v)
throws IOException
public final void writeLong(long v)
throws IOException
public final void writeFloat(float v)
throws IOException
public final void writeDouble(double v)
throws IOException
public final void writeBytes(String s)
throws IOException
public final void writeChars(String s)
throws IOException
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.