Utility class for parsing and formatting hex strings to / from byte arrays.

HexUtil.java

/*
 * Copyright 2015 Jesper de Jong
 *
 * 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 com.jesperdj.sandbox;

import java.io.ByteArrayOutputStream;

public final class HexUtil {

    private HexUtil() {
    }

    public static byte[] parseHex(String hex) {
        final int len = hex.length();
        final ByteArrayOutputStream buffer = new ByteArrayOutputStream(len / 2);
        for (int i = 0; i < len; i += 2) {
            buffer.write((charToHexDigit(hex.charAt(i)) << 4) | charToHexDigit(hex.charAt(i + 1)));
        }

        return buffer.toByteArray();
    }

    public static String formatHex(byte[] bytes) {
        final StringBuilder sb = new StringBuilder(bytes.length * 2);
        for (byte b : bytes) {
            sb.append(hexDigitToChar((b >> 4) & 0xF)).append(hexDigitToChar(b & 0xF));
        }

        return sb.toString();
    }

    private static int charToHexDigit(char c) {
        return c - (c >= 'a' ? 'W' : c >= 'A' ? '7' : '0');
    }

    private static char hexDigitToChar(int d) {
        return (char) (d + (d >= 10 ? '7' : '0'));
    }
}

HexUtilTest.java

/*
 * Copyright 2015 Jesper de Jong
 *
 * 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 com.jesperdj.sandbox;

import org.junit.Test;

import static com.jesperdj.sandbox.HexUtil.formatHex;
import static com.jesperdj.sandbox.HexUtil.parseHex;
import static org.hamcrest.CoreMatchers.is;
import static org.junit.Assert.assertThat;

public class HexUtilTest {

    @Test
    public void testParseHexZeroLength() {
        assertThat(parseHex(""), is(new byte[0]));
    }

    @Test
    public void testParseHexSingleByte() {
        for (int b = Byte.MIN_VALUE; b <= Byte.MAX_VALUE; b++) {
            assertThat(parseHex(String.format("%02X", b & 0xFF)), is(new byte[]{(byte) b}));
        }
    }

    @Test
    public void testParseHexMultipleBytes() {
        assertThat(parseHex("0123456789ABCDEF"),
                is(new byte[]{0x01, 0x23, 0x45, 0x67, (byte) 0x89, (byte) 0xAB, (byte) 0xCD, (byte) 0xEF}));
    }

    @Test
    public void testFormatHexZeroLength() {
        assertThat(formatHex(new byte[0]), is(""));
    }

    @Test
    public void testFormatHexSingleByte() {
        for (int b = Byte.MIN_VALUE; b <= Byte.MAX_VALUE; b++) {
            assertThat(formatHex(new byte[]{(byte) b}), is(String.format("%02X", b & 0xFF)));
        }
    }

    @Test
    public void testFormatHexMultipleBytes() {
        assertThat(formatHex(new byte[]{0x01, 0x23, 0x45, 0x67, (byte) 0x89, (byte) 0xAB, (byte) 0xCD, (byte) 0xEF}),
                is("0123456789ABCDEF"));
    }
}