core/src/main/java/org/apache/calcite/util/ConversionUtil.java

/*
 * 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.calcite.util;

import java.nio.ByteOrder;
import java.text.NumberFormat;
import java.util.Locale;

import static org.apache.calcite.util.Static.RESOURCE;

/**
 * Utility functions for converting from one type to another.
 */
public class ConversionUtil {
  private ConversionUtil() {}

  //~ Static fields/initializers ---------------------------------------------

  public static final String NATIVE_UTF16_CHARSET_NAME =
      (ByteOrder.nativeOrder() == ByteOrder.BIG_ENDIAN) ? "UTF-16BE"
          : "UTF-16LE";

  /**
   * A constant string which can be used wherever a Java string containing
   * Unicode characters is needed in a test. It spells 'anthropos' in Greek.
   */
  public static final String TEST_UNICODE_STRING =
      "\u03B1\u03BD\u03B8\u03C1\u03C9\u03C0\u03BF\u03C2";

  /**
   * A constant string which can be used wherever a SQL literal containing
   * Unicode escape characters is needed in a test. It spells 'anthropos' in
   * Greek. The escape character is the SQL default (backslash); note that the
   * backslash-doubling here is for Java only, so by the time the SQL parser
   * gets it, there is only one backslash.
   */
  public static final String TEST_UNICODE_SQL_ESCAPED_LITERAL =
      "\\03B1\\03BD\\03B8\\03C1\\03C9\\03C0\\03BF\\03C2";

  //~ Methods ----------------------------------------------------------------

  /**
   * Converts a byte array into a bit string or a hex string.
   *
   * <p>For example, <code>toStringFromByteArray(new byte[] {0xAB, 0xCD},
   * 16)</code> returns <code>ABCD</code>.
   */
  public static String toStringFromByteArray(
      byte[] value,
      int radix) {
    assert (2 == radix) || (16 == radix)
        : "Make sure that the algorithm below works for your radix";
    if (0 == value.length) {
      return "";
    }

    int trick = radix * radix;
    StringBuilder ret = new StringBuilder();
    for (byte b : value) {
      ret.append(Integer.toString(trick | (0x0ff & b), radix).substring(1));
    }

    return ret.toString().toUpperCase(Locale.ROOT);
  }

  /**
   * Converts a string into a byte array. The inverse of
   * {@link #toStringFromByteArray(byte[], int)}.
   */
  public static byte[] toByteArrayFromString(
      String value,
      int radix) {
    assert 16 == radix
        : "Specified string to byte array conversion not supported yet";
    assert (value.length() % 2) == 0
        : "Hex binary string must contain even number of characters";

    byte[] ret = new byte[value.length() / 2];
    for (int i = 0; i < ret.length; i++) {
      int digit1 =
          Character.digit(
              value.charAt(i * 2),
              radix);
      int digit2 =
          Character.digit(
              value.charAt((i * 2) + 1),
              radix);
      assert (digit1 != -1) && (digit2 != -1)
          : "String could not be converted to byte array";
      ret[i] = (byte) ((digit1 * radix) + digit2);
    }
    return ret;
  }

  /**
   * Converts an approximate value into a string, following the SQL 2003
   * standard.
   */
  public static String toStringFromApprox(double d, boolean isFloat) {
    NumberFormat nf = NumberUtil.getApproxFormatter(isFloat);
    return nf.format(d);
  }

  /**
   * Converts a string into a BOOLEAN.
   */
  public static Boolean toBoolean(String str) {
    if (str == null) {
      return null;
    }
    str = str.trim();
    if (str.equalsIgnoreCase("TRUE")) {
      return Boolean.TRUE;
    } else if (str.equalsIgnoreCase("FALSE")) {
      return Boolean.FALSE;
    } else if (str.equalsIgnoreCase("UNKNOWN")) {
      return null;
    } else {
      throw RESOURCE.invalidBoolean(str).ex();
    }
  }
}