Hex.java

// Copyright 2017 JanusGraph Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package org.janusgraph.diskstorage.util;

import java.lang.reflect.Constructor;

/**
 * Utility methods for hexadecimal representation of bytes
 *
 */
public class Hex {
    private static final Constructor<String> stringConstructor = getProtectedConstructor(String.class, int.class, int.class, char[].class);
    private final static byte[] charToByte = new byte[256];

    // package protected for use by BufferUtil. Do not modify this array !!
    static final char[] byteToChar = new char[16];

    static {
        for (char c = 0; c < charToByte.length; ++c) {
            if (c >= '0' && c <= '9')
                charToByte[c] = (byte) (c - '0');
            else if (c >= 'A' && c <= 'F')
                charToByte[c] = (byte) (c - 'A' + 10);
            else if (c >= 'a' && c <= 'f')
                charToByte[c] = (byte) (c - 'a' + 10);
            else
                charToByte[c] = (byte) -1;
        }

        for (int i = 0; i < 16; ++i) {
            byteToChar[i] = Integer.toHexString(i).charAt(0);
        }
    }

    public static byte[] hexToBytes(String str) {
        if (str.length() % 2 == 1)
            throw new NumberFormatException("An hex string representing bytes must have an even length");

        byte[] bytes = new byte[str.length() / 2];
        for (int i = 0; i < bytes.length; i++) {
            byte halfByte1 = charToByte[str.charAt(i * 2)];
            byte halfByte2 = charToByte[str.charAt(i * 2 + 1)];
            if (halfByte1 == -1 || halfByte2 == -1)
                throw new NumberFormatException("Non-hex characters in " + str);
            bytes[i] = (byte) ((halfByte1 << 4) | halfByte2);
        }
        return bytes;
    }

    public static String bytesToHex(byte... bytes) {
        char[] c = new char[bytes.length * 2];
        for (int i = 0; i < bytes.length; i++) {
            int bint = bytes[i];
            c[i * 2] = byteToChar[(bint & 0xf0) >> 4];
            c[1 + i * 2] = byteToChar[bint & 0x0f];
        }

        return wrapCharArray(c);
    }

    /**
     * Create a String from a char array with zero-copy (if available), using reflection to access a package-protected constructor of String.
     */
    public static String wrapCharArray(char[] c) {
        if (c == null)
            return null;

        String s = null;

        if (stringConstructor != null) {
            try {
                s = stringConstructor.newInstance(0, c.length, c);
            } catch (Exception e) {
                // Swallowing as we'll just use a copying constructor
            }
        }
        return s == null ? new String(c) : s;
    }

    /**
     * Used to get access to protected/private constructor of the specified class
     *
     * @param klass      - name of the class
     * @param paramTypes - types of the constructor parameters
     * @return Constructor if successful, null if the constructor cannot be
     *         accessed
     */
    public static Constructor getProtectedConstructor(Class klass, Class... paramTypes) {
        Constructor c;
        try {
            c = klass.getDeclaredConstructor(paramTypes);
            c.setAccessible(true);
            return c;
        } catch (Exception e) {
            return null;
        }
    }
}