java.lang.Object java.io.RandomAccessFile
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.
RandomAccessFile(File file, String mode)
File argument. RandomAccessFile(String name, String mode)
void close()
FileChannel getChannel()
FileChannel object associated with this file. FileDescriptor getFD()
long getFilePointer()
long length()
int read()
int read(byte[] b)
b.length bytes of data from this file into an array of bytes. int read(byte[] b, int off, int len)
len bytes of data from this file into an array of bytes. boolean readBoolean()
boolean from this file. byte readByte()
char readChar()
double readDouble()
double from this file. float readFloat()
float from this file. void readFully(byte[] b)
b.length bytes from this file into the byte array, starting at the current file pointer. void readFully(byte[] b, int off, int len)
len bytes from this file into the byte array, starting at the current file pointer. int readInt()
String readLine()
long readLong()
short readShort()
int readUnsignedByte()
int readUnsignedShort()
String readUTF()
void seek(long pos)
void setLength(long newLength)
int skipBytes(int n)
n bytes of input discarding the skipped bytes. void write(byte[] b)
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)
len bytes from the specified byte array starting at offset off to this file. void write(int b)
void writeBoolean(boolean v)
boolean to the file as a one-byte value. void writeByte(int v)
byte to the file as a one-byte value. void writeBytes(String s)
void writeChar(int v)
char to the file as a two-byte value, high byte first. void writeChars(String s)
void writeDouble(double v)
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)
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)
int to the file as four bytes, high byte first. void writeLong(long v)
long to the file as eight bytes, high byte first. void writeShort(int v)
short to the file as two bytes, high byte first. void writeUTF(String str)
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait RandomAccessFile
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 filename
mode - 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 file
SecurityException - 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 file
SecurityException, 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:
The "rws" and "rwd" modes work much like theValue
Meaning
"r" Open for reading only. Invoking any of the write methods of the resulting object will cause anIOExceptionto 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 object
mode - 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 file
SecurityException - 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 file
SecurityManager.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.
FileDescriptor
public 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 of the data.
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 an I/O error occurs.
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 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 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.
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
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
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
write in interface DataOutput
b - 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 DataOutput
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.
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
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 file
IOException - If an I/O error occurs
public void close()
throws IOException
If this file has an associated channel then the channel is closed as well.
close in interface Closeable
IOException - 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 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
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
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
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
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
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
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 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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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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