CheckedOutputStream.java

/*
 * Copyright (c) 1996, 1999, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package java.util.zip;

import java.io.FilterOutputStream;
import java.io.OutputStream;
import java.io.IOException;

/**
 * An output stream that also maintains a checksum of the data being written.
 * The checksum can then be used to verify the integrity of the output data.
 *
 * @author David Connelly
 * @see Checksum
 * @since 1.1
 */
// 包含数据校验器的输出流，可以对写入输出流的数据进行数据校验
public class CheckedOutputStream extends FilterOutputStream {
    private Checksum cksum;  // 数据校验
    
    /**
     * Creates an output stream with the specified Checksum.
     *
     * @param out   the output stream
     * @param cksum the checksum
     */
    public CheckedOutputStream(OutputStream out, Checksum cksum) {
        super(out);
        this.cksum = cksum;
    }
    
    /**
     * Writes a byte. Will block until the byte is actually written.
     *
     * @param b the byte to be written
     *
     * @throws IOException if an I/O error has occurred
     */
    // 写入一个字节
    public void write(int b) throws IOException {
        out.write(b);
        cksum.update(b);
    }
    
    /**
     * Writes an array of bytes. Will block until the bytes are
     * actually written.
     *
     * @param b   the data to be written
     * @param off the start offset of the data
     * @param len the number of bytes to be written
     *
     * @throws IOException if an I/O error has occurred
     */
    // 写入b中off处的len个字节
    public void write(byte[] b, int off, int len) throws IOException {
        out.write(b, off, len);
        cksum.update(b, off, len);
    }
    
    /**
     * Returns the Checksum for this output stream.
     *
     * @return the Checksum
     */
    // 返回数据校验和
    public Checksum getChecksum() {
        return cksum;
    }
}