RandomAccessFile (wahlweiser Dateizugriff)

Advanced Java Services

RandomAccessFile

Objekte dieser Klasse haben einen wahlfreien Zugriff auf den Inhalt einer Datei. Dagegen stellen die übrigen Dateizugriffe eine Art Einbahnstraße dar, egal ob zum Lesen oder Schreiben, man kann die Datei nur in einer Richtung durchlaufen, vom Dateianfang zum Dateiende. Mit RandomAccessFile kann man sich in einer datei beliebig vorwärts oder eben auch rückwärts bewegen. Dies geschieht mit einem Dateipositionszeiger, der frei verschiebbar ist. Mit der Methode seek(long pos) kann man den Dateipositionszeiger setzen. Der Zugriff kann lesend oder schreibend sein oder beides zugleich. Die Art des Zugriffs wird über den zweiten Parameter des Konstruktors gesteuert. Die Methoden von RandomAccessFile sind zum Teil identisch mit den Methoden aus ObjectInputStream und ObjectOutputStream, da RandomAccessFile die Interfaces und DataInput und DataOutput implementiert.

Mögliche Zugriffsmodi (zweiter Parameter des Konstruktors)

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.
"other"	RuntimeException in thread "main" java.lang.IllegalArgumentException: mode must be r, rw, rws or rwd

Auszug aus der API

Konstruktoren
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.

Wichtige Methoden
Returntyp	Name der Methode
void	close() Closes this random access file stream and releases any system resources associated with the 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.
int	read(byte[] buf, int off, int len) Reads into an array of bytes.
boolean	readBoolean() Reads in a boolean.
byte	readByte() Reads an 8 bit byte.
char	readChar() Reads a 16 bit char.
double	readDouble() Reads a 64 bit double.
float	readFloat() Reads a 32 bit float.
void	readFully(byte[] buf) Reads bytes, blocking until all bytes are read.
int	readInt() Reads a 32 bit int.
long	readLong() Reads a 64 bit long.
short	readShort() Reads a 16 bit short.
int	readUnsignedByte() Reads an unsigned 8 bit byte.
int	readUnsignedShort() Reads an unsigned 16 bit short.
String	readUTF() Reads a String in modified UTF-8 format.
void	seek(long pos) Sets the file-pointer offset, measured from the beginning of this file, at which the next read or write occurs.
String	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[] buf) Writes an array of bytes.
void	write(int val) Writes a byte.
void	writeBoolean(boolean val) Writes a boolean.
void	writeByte(int val) Writes an 8 bit byte.
void	writeBytes(String str) Writes a String as a sequence of bytes.
void	writeChar(int val) Writes a 16 bit char.
void	writeChars(String str) Writes a String as a sequence of chars.
void	writeDouble(double val) Writes a 64 bit double.
void	writeFloat(float val) Writes a 32 bit float.
void	writeInt(int val) Writes a 32 bit int.
void	writeLong(long val) Writes a 64 bit long.
void	writeShort(int val) Writes a 16 bit short.
void	writeUTF(String str) Primitive data write of this String in modified UTF-8 format.