inputstorage.java

有关j2me的很好的例子可以研究一下

/*
 *  @(#)InputStorage.java	1.3 01/08/10
 * 
 *  Copyright (c) 2001 Sun Microsystems, Inc., 901 San Antonio Road,
 *  Palo Alto, CA 94303, U.S.A.  All Rights Reserved.
 *
 *  Sun Microsystems, Inc. has intellectual property rights relating
 *  to the technology embodied in this software.  In particular, and
 *  without limitation, these intellectual property rights may include
 *  one or more U.S. patents, foreign patents, or pending
 *  applications.  Sun, Sun Microsystems, the Sun logo, Java, KJava,
 *  and all Sun-based and Java-based marks are trademarks or
 *  registered trademarks of Sun Microsystems, Inc.  in the United
 *  States and other countries.
 *
 *  This software is distributed under licenses restricting its use,
 *  copying, distribution, and decompilation.  No part of this
 *  software may be reproduced in any form by any means without prior
 *  written authorization of Sun and its licensors, if any.
 *
 *  FEDERAL ACQUISITIONS:  Commercial Software -- Government Users
 *  Subject to Standard License Terms and Conditions
 */
package com.sun.midp.publickeystore;

import java.io.*;

/**
 * Retieves stored fields from an InputStream.
 * Since Java Microedition has no serialization, this is a simple substitute.
 */
class InputStorage extends Storage {
    /** stream to read from */
    private DataInputStream in;

    /**
     * Constructs an InputStorage for an InputStream.
     * @param input the input storage input stream.
     * @exception IOException if the storage version cannot be read
     */
    InputStorage(InputStream input) throws IOException {
        in = new DataInputStream(input);

        // skip past the version number.
        in.readByte();
    }

    /**
     * Reads a field that was stored as tag, type, value set.
     * @param tag byte array of one byte to hold the tag of the field that
     *            was read
     * @return value of field that was stored, or null if there are no more
     *         fields
     * @exception IOException if the input storage was corrupted
     */
    Object readValue(byte[] tag) throws IOException {
        byte type;

        try {
            in.readFully(tag, 0, 1);
        } catch (EOFException e) {
            // this just means there are no more fields in storage
            return null;
        }

        type = in.readByte();
        if (type == BINARY_TYPE) {
            int len;
            byte[] value;

            /*
             * must read the length first, because DataOutputStream does not
             * handle handle byte arrays.
             */
            len = in.readUnsignedShort();
            if (len < 0) {
                throw new IOException("input storage corrupted");
            }

            value = new byte[len];
            in.readFully(value);
            return value;
        }

        if (type == STRING_TYPE) {
            return in.readUTF();
        }

        if (type == LONG_TYPE) {
            return new Long(in.readLong());
        }

        throw new IOException("input storage corrupted");
    }
}