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The Apache Cassandra Project develops a highly scalable second-generation distributed database, bringing together Dynamo's fully distributed design and Bigtable's ColumnFamily-based data model.
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/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.apache.cassandra.utils;

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class Hex
{
    private static final Constructor stringConstructor = getProtectedConstructor(String.class, int.class, int.class, char[].class);
    private final static byte[] charToByte = new byte[256];
    private static final Logger logger = LoggerFactory.getLogger(Hex.class);

    // package protected for use by ByteBufferUtil. 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 (InvocationTargetException ite) {
                // The underlying constructor failed. Unwrapping the exception.
                Throwable cause = ite.getCause();
                logger.error("Underlying string constructor threw an error: {}",
                    cause == null ? ite.getMessage() : cause.getMessage());
            }
            catch (Exception e)
            {
                JVMStabilityInspector.inspectThrowable(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;
        }
    }
}