private Part read() throws IOException {
StringBuffer sb = new StringBuffer();
for (int i = 0; i < PNUMLEN; i++) sb.append(raf.readChar());
String partnum = sb.toString().trim();
sb.setLength(0);
for (int i = 0; i < DESCLEN; i++) sb.append(raf.readChar());
String partdesc = sb.toString().trim();
int qty = raf.readInt();
int ucost = raf.readInt();
return new Part(partnum, partdesc, qty, ucost);
}
/** {@inheritDoc} */
public char readChar() throws IOException {
fileSize -= 1;
if (fileSize < 0) {
throw new EOFException();
}
return dataInput.readChar();
}
public static void main(String args[]) {
try {
String fname = "d:\\q.txt";
String mode;
// mode = "r";//r : file must exist
mode = "rw"; // rw : file will be created or opened
// open the file
RandomAccessFile raf = new RandomAccessFile(fname, mode);
/*
//seek and write demo
raf.seek(10);//position file r/w pointer at index 10 wrt BOF
//a seek beyond file size causes file to grow upto the seek value
raf.write(65);//raf.write('A');
*/
// r/w java datatypes
int i1, i2;
float f1, f2;
char c1, c2;
String s1, s2;
i1 = -10;
f1 = 1234.5678F;
c1 = 'q';
s1 = "hello files";
raf.seek(0); // reach BOF
raf.writeInt(i1);
raf.writeFloat(f1);
raf.writeChar(c1);
raf.writeUTF(s1);
raf.seek(0); // reach BOF
i2 = raf.readInt();
f2 = raf.readFloat();
c2 = raf.readChar();
s2 = raf.readUTF();
System.out.println(i2);
System.out.println(f2);
System.out.println(c2);
System.out.println(s2);
// close the file
raf.close();
} catch (IOException ex) {
System.out.println(ex); // ex converts into ex.toString()
}
} // main
/**
* Create a new DBWriter according to the input file name.
*
* @param fileName the name of the file
* @exception FileNotFoundException from library call
* @exception IOException from library call or if file is corrupted
*/
public DBWriter(String fileName) throws IOException {
outStream = new RandomAccessFile(fileName, "rw");
lastPosition = outStream.length();
// case this is a new database
if (lastPosition == 0) {
wroteColumnNames = false;
headerSize = 0;
numRows = 0;
CRC = 0;
needReposition = false;
}
// case this might be an old database
else if (lastPosition > MIN_DATA_OFFSET) {
// check that we have a valid database here
checkID();
wroteColumnNames = true;
// read header data
outStream.seek(HEAD_SIZE_OFFSET);
headerSize = outStream.readLong();
numRows = outStream.readLong();
numColumns = outStream.readLong();
// read description
outStream.seek(headerSize - DESCRIPTION_SIZE - ID_SIZE - CRC_SIZE);
description = "";
for (int i = 0; i < DESCRIPTION_LENGTH; i++) description += outStream.readChar();
description = description.trim();
// read CRC
outStream.seek(headerSize - CRC_SIZE);
CRC = outStream.readInt();
// by default we append to an existing database
needReposition = true;
}
// case this is not a database
else throw new IOException("Attempting to load invalid database");
}
/** This reads a binary char from the file. */
public char readBinaryChar(int col, int row) throws IOException {
raf.seek(row * nBytesPerRow + columnStartAt[col]);
return raf.readChar();
}
// call this method to check the existence of the ID
// the file pointer must be already positioned
private void checkID() throws IOException {
for (int i = 0; i < ID.length(); i++)
if (outStream.readChar() != ID.charAt(i))
throw new IOException("Attempting to load invalid database");
}
/* @see java.io.DataInput.readChar() */
public char readChar() throws IOException {
return raf.readChar();
}
