dbfheader.java

实现如何用java读dbase库的

/*	
 DBFHeader
 Class for reading the metadata assuming that the given
 InputStream carries DBF data.

 This file is part of JavaDBF packege.

 Author: [e-mail]
 License: LGPL (http://www.gnu.org/copyleft/lesser.html)

 $Id$
*/	

package com.linuxense.javadbf;

import java.io.*;
import java.util.*;

class DBFHeader {

	static final byte SIG_DBASE_III = (byte)0x03;
	/* DBF structure start here */
	
	byte signature;              /* 0 */
	byte year;                   /* 1 */
	byte month;                  /* 2 */
	byte day;                    /* 3 */
	int numberOfRecords;         /* 4-7 */
	short headerLength;          /* 8-9 */
	short recordLength;          /* 10-11 */
	short reserv1;               /* 12-13 */
	byte incompleteTransaction;  /* 14 */
	byte encryptionFlag;         /* 15 */
	int freeRecordThread;        /* 16-19 */
	int reserv2;                 /* 20-23 */
	int reserv3;                 /* 24-27 */
	byte mdxFlag;                /* 28 */
	byte languageDriver;         /* 29 */
	short reserv4;               /* 30-31 */
	DBFField []fieldArray;       /* each 32 bytes */	
	byte terminator1;            /* n+1 */

	//byte[] databaseContainer; /* 263 bytes */
	/* DBF structure ends here */

	DBFHeader() {

		this.signature = SIG_DBASE_III;
		this.terminator1 = 0x0D;
	}
	
	void read( DataInput dataInput) throws IOException {

		signature = dataInput.readByte(); /* 0 */
		year = dataInput.readByte();      /* 1 */
		month = dataInput.readByte();     /* 2 */
		day = dataInput.readByte();       /* 3 */
		numberOfRecords = Utils.readLittleEndianInt( dataInput); /* 4-7 */

		headerLength = Utils.readLittleEndianShort( dataInput); /* 8-9 */
		recordLength = Utils.readLittleEndianShort( dataInput); /* 10-11 */

		reserv1 = Utils.readLittleEndianShort( dataInput);      /* 12-13 */
		incompleteTransaction = dataInput.readByte();           /* 14 */
		encryptionFlag = dataInput.readByte();                  /* 15 */
		freeRecordThread = Utils.readLittleEndianInt( dataInput); /* 16-19 */
		reserv2 = dataInput.readInt();                            /* 20-23 */
		reserv3 = dataInput.readInt();                            /* 24-27 */
		mdxFlag = dataInput.readByte();                           /* 28 */
		languageDriver = dataInput.readByte();                    /* 29 */
		reserv4 = Utils.readLittleEndianShort( dataInput);        /* 30-31 */

		Vector v_fields = new Vector();
		
		DBFField field = DBFField.createField( dataInput); /* 32 each */
		while( field != null) {

			v_fields.addElement( field);
			field = DBFField.createField( dataInput);
		}

		fieldArray = new DBFField[ v_fields.size()];
		
		for( int i=0; i<fieldArray.length; i++) {

			fieldArray[ i] = (DBFField)v_fields.elementAt( i);
		}	
		//System.out.println( "Number of fields: " + fieldArray.length);

	}

	void write( DataOutput dataOutput) throws IOException {

		dataOutput.writeByte( signature);                       /* 0 */

		GregorianCalendar calendar = new GregorianCalendar();
		year = (byte)( calendar.get( Calendar.YEAR) - 1900);
		month = (byte)( calendar.get( Calendar.MONTH)+1);
		day = (byte)( calendar.get( Calendar.DAY_OF_MONTH));

		dataOutput.writeByte( year);  /* 1 */
		dataOutput.writeByte( month); /* 2 */
		dataOutput.writeByte( day);   /* 3 */

		//System.out.println( "Number of records in O/S: " + numberOfRecords);
		numberOfRecords = Utils.littleEndian( numberOfRecords);
		dataOutput.writeInt( numberOfRecords); /* 4-7 */

		headerLength = findHeaderLength();
		dataOutput.writeShort( Utils.littleEndian( headerLength)); /* 8-9 */

		recordLength = findRecordLength(); 
		dataOutput.writeShort( Utils.littleEndian( recordLength)); /* 10-11 */

		dataOutput.writeShort( Utils.littleEndian( reserv1)); /* 12-13 */
		dataOutput.writeByte( incompleteTransaction); /* 14 */
		dataOutput.writeByte( encryptionFlag); /* 15 */
		dataOutput.writeInt( Utils.littleEndian( freeRecordThread));/* 16-19 */
		dataOutput.writeInt( Utils.littleEndian( reserv2)); /* 20-23 */
		dataOutput.writeInt( Utils.littleEndian( reserv3)); /* 24-27 */

		dataOutput.writeByte( mdxFlag); /* 28 */
		dataOutput.writeByte( languageDriver); /* 29 */
		dataOutput.writeShort( Utils.littleEndian( reserv4)); /* 30-31 */

		for( int i=0; i<fieldArray.length; i++) {

							//System.out.println( "Length: " + fieldArray[i].getFieldLength());
			fieldArray[i].write( dataOutput);
		}

		dataOutput.writeByte( terminator1); /* n+1 */
	}

	private short findHeaderLength() {

		return (short)(
		1+
		3+
		4+
		2+
		2+
		2+
		1+
		1+
		4+
		4+
		4+
		1+
		1+
		2+
		(32*fieldArray.length)+
		1
		);
	}

	private short findRecordLength() {

		int recordLength = 0;
		for( int i=0; i<fieldArray.length; i++) {

			recordLength += fieldArray[i].getFieldLength();
		}

		return (short)(recordLength + 1);
	}
}