tupleinput.java

berkeleyDB,强大的嵌入式数据,多个数据库的内核

/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 2000-2004
 *      Sleepycat Software.  All rights reserved.
 *
 * $Id: TupleInput.java,v 1.4 2004/09/01 14:34:20 mark Exp $
 */

package com.sleepycat.bind.tuple;

import com.sleepycat.util.FastInputStream;
import com.sleepycat.util.UtfOps;

/**
 * An <code>InputStream</code> with <code>DataInput</code>-like methods for
 * reading tuple fields.  It is used by <code>TupleBinding</code>.
 *
 * <p>This class has many methods that have the same signatures as methods in
 * the {@link java.io.DataInput} interface.  The reason this class does not
 * implement {@link java.io.DataInput} is because it would break the interface
 * contract for those methods because of data format differences.</p>
 *
 * <p>Signed numbers are stored in the buffer in MSB (most significant byte
 * first) order with their sign bit (high-order bit) inverted to cause negative
 * numbers to be sorted first when comparing values as unsigned byte arrays,
 * as done in a database.  Unsigned numbers, including characters, are stored
 * in MSB order with no change to their sign bit.</p>
 *
 * <p>Strings and character arrays are stored either as a fixed length array of
 * unicode characters, where the length must be known by the application, or as
 * a null-terminated UTF byte array.</p>
 * <ul>
 * <li>Null strings are UTF encoded as { 0xFF }, which is not allowed in a
 * standard UTF encoding.  This allows null strings, as distinct from empty or
 * zero length strings, to be represented in a tuple.  Using the default
 * comparator, null strings will be ordered last.</li>
 * <li>Zero (0x0000) character values are UTF encoded as non-zero values, and
 * therefore embedded zeros in the string are supported.  The sequence { 0xC0,
 * 0x80 } is used to encode a zero character.  This UTF encoding is the same
 * one used by native Java UTF libraries.  However, this encoding of zero does
 * impact the lexicographical ordering, and zeros will not be sorted first (the
 * natural order) or last.  For all character values other than zero, the
 * default UTF byte ordering is the same as the Unicode lexicographical
 * character ordering.</li>
 * </ul>
 *
 * <p>Floats and doubles are stored in standard Java integer-bit representation
 * (IEEE 754). Non-negative numbers are correctly ordered by numeric value.
 * However, negative numbers are not correctly ordered; therefore, if you use
 * negative floating point numbers in a key, you'll need to implement and
 * configure a custom comparator to get correct numeric ordering.</p>
 *
 * @author Mark Hayes
 */
public class TupleInput extends FastInputStream {

    /**
     * Creates a tuple input object for reading a byte array of tuple data.  A
     * reference to the byte array will be kept by this object (it will not be
     * copied) and therefore the byte array should not be modified while this
     * object is in use.
     *
     * @param buffer is the byte array to be read and should contain data in
     * tuple format.
     */
    public TupleInput(byte[] buffer) {

        super(buffer);
    }

    /**
     * Creates a tuple input object for reading a byte array of tuple data at
     * a given offset for a given length.  A reference to the byte array will
     * be kept by this object (it will not be copied) and therefore the byte
     * array should not be modified while this object is in use.
     *
     * @param buffer is the byte array to be read and should contain data in
     * tuple format.
     *
     * @param offset is the byte offset at which to begin reading.
     *
     * @param length is the number of bytes to be read.
     */
    public TupleInput(byte[] buffer, int offset, int length) {

        super(buffer, offset, length);
    }

    /**
     * Creates a tuple input object from the data contained in a tuple output
     * object.  A reference to the tuple output's byte array will be kept by
     * this object (it will not be copied) and therefore the tuple output
     * object should not be modified while this object is in use.
     *
     * @param output is the tuple output object containing the data to be read.
     */
    public TupleInput(TupleOutput output) {

        super(output.getBufferBytes(), output.getBufferOffset(),
              output.getBufferLength());
    }

    // --- begin DataInput compatible methods ---

    /**
     * Reads a null-terminated UTF string from the data buffer and converts
     * the data from UTF to Unicode.
     * Reads values that were written using {@link
     * TupleOutput#writeString(String)}.
     *
     * @return the converted string.
     *
     * @throws IndexOutOfBoundsException if no null terminating byte is found
     * in the buffer.
     *
     * @throws IllegalArgumentException malformed UTF data is encountered.
     */
    public final String readString()
        throws IndexOutOfBoundsException, IllegalArgumentException  {

        byte[] buf = getBufferBytes();
        int off = getBufferOffset();
        if (available() >= 2 &&
            buf[off] == TupleOutput.NULL_STRING_UTF_VALUE &&
            buf[off + 1] == 0) {
            skip(2);
            return null;
        } else {
            int byteLen = UtfOps.getZeroTerminatedByteLength(buf, off);
            skip(byteLen + 1);
            return UtfOps.bytesToString(buf, off, byteLen);
        }
    }

    /**
     * Reads a char (two byte) unsigned value from the buffer.
     * Reads values that were written using {@link TupleOutput#writeChar}.
     *
     * @return the value read from the buffer.
     *
     * @throws IndexOutOfBoundsException if not enough bytes are available in
     * the buffer.
     */
    public final char readChar() throws IndexOutOfBoundsException {

        return (char) readUnsignedShort();
    }

    /**
     * Reads a boolean (one byte) unsigned value from the buffer and returns
     * true if it is non-zero and false if it is zero.
     * Reads values that were written using {@link TupleOutput#writeBoolean}.
     *
     * @return the value read from the buffer.
     *
     * @throws IndexOutOfBoundsException if not enough bytes are available in
     * the buffer.
     */
    public final boolean readBoolean() throws IndexOutOfBoundsException {

        int c = readFast();
        if (c < 0) {
            throw new IndexOutOfBoundsException();
        }
        return (c != 0);
    }

    /**
     * Reads a signed byte (one byte) value from the buffer.
     * Reads values that were written using {@link TupleOutput#writeByte}.
     *
     * @return the value read from the buffer.
     *
     * @throws IndexOutOfBoundsException if not enough bytes are available in
     * the buffer.
     */
    public final byte readByte() throws IndexOutOfBoundsException {

        return (byte) (readUnsignedByte() ^ 0x80);
    }

    /**
     * Reads a signed short (two byte) value from the buffer.
     * Reads values that were written using {@link TupleOutput#writeShort}.
     *
     * @return the value read from the buffer.
     *
     * @throws IndexOutOfBoundsException if not enough bytes are available in
     * the buffer.
     */
    public final short readShort() throws IndexOutOfBoundsException {

        return (short) (readUnsignedShort() ^ 0x8000);
    }

    /**
     * Reads a signed int (four byte) value from the buffer.
     * Reads values that were written using {@link TupleOutput#writeInt}.
     *
     * @return the value read from the buffer.
     *
     * @throws IndexOutOfBoundsException if not enough bytes are available in
     * the buffer.
     */
    public final int readInt() throws IndexOutOfBoundsException {

        return (int) (readUnsignedInt() ^ 0x80000000);
    }

    /**
     * Reads a signed long (eight byte) value from the buffer.
     * Reads values that were written using {@link TupleOutput#writeLong}.
     *
     * @return the value read from the buffer.
     *
     * @throws IndexOutOfBoundsException if not enough bytes are available in
     * the buffer.
     */
    public final long readLong() throws IndexOutOfBoundsException {

        return readUnsignedLong() ^ 0x8000000000000000L;
    }

    /**
     * Reads a signed float (four byte) value from the buffer.
     * Reads values that were written using {@link TupleOutput#writeFloat}.
     * <code>Float.intBitsToFloat</code> is used to convert the signed int
     * value.
     *
     * @return the value read from the buffer.
     *
     * @throws IndexOutOfBoundsException if not enough bytes are available in
     * the buffer.
     */
    public final float readFloat() throws IndexOutOfBoundsException {

        return Float.intBitsToFloat((int) readUnsignedInt());
    }

    /**
     * Reads a signed double (eight byte) value from the buffer.