Java File Read via ByteBuffer readZipComment(File file)

Description

read Zip Comment

License

Open Source License

Declaration

public static String readZipComment(File file) throws IOException 

Method Source Code

//package com.java2s;
//License from project: Open Source License 

import java.io.*;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.util.Arrays;

public class Main {
    private static final byte[] COMMENT_SIGN = new byte[] { 99, 104, 97, 110, 110, 101, 108 };

    public static String readZipComment(File file) throws IOException {
        RandomAccessFile raf = null;
        try {//from w ww.j  a  va  2  s .c  o m
            raf = new RandomAccessFile(file, "r");
            long index = raf.length();
            byte[] buffer = new byte[COMMENT_SIGN.length];
            index -= COMMENT_SIGN.length;
            // read sign bytes
            raf.seek(index);
            raf.readFully(buffer);
            // if sign bytes matched
            if (Arrays.equals(buffer, COMMENT_SIGN)) {
                index -= 2;
                raf.seek(index);
                // read content length field
                int length = readShort(raf);
                if (length > 0) {
                    index -= length;
                    raf.seek(index);
                    // read content bytes
                    byte[] bytesComment = new byte[length];
                    raf.readFully(bytesComment);
                    return new String(bytesComment, "utf-8");
                } else {
                    throw new IOException("Zip comment content not found");
                }
            } else {
                throw new IOException("Zip comment sign bytes not found");
            }
        } finally {
            if (raf != null) {
                raf.close();
            }
        }
    }

    private static short readShort(DataInput input) throws IOException {
        byte[] buf = new byte[2];
        input.readFully(buf);
        ByteBuffer bb = ByteBuffer.wrap(buf).order(ByteOrder.LITTLE_ENDIAN);
        return bb.getShort(0);
    }
}

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