StringUtil.java

/*
 * Copyright 2012 The Netty Project
 *
 * The Netty Project 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.jboss.netty.util.internal;

import java.util.ArrayList;
import java.util.Formatter;
import java.util.List;

/**
 * String utility class.
 */
public final class StringUtil {

    private StringUtil() {
        // Unused.
    }

    public static final String NEWLINE;

    static {
        String newLine;

        try {
            newLine = new Formatter().format("%n").toString();
        } catch (Exception e) {
            newLine = "\n";
        }

        NEWLINE = newLine;
    }

    /**
     * Strip an Object of it's ISO control characters.
     *
     * @param value
     *          The Object that should be stripped. This objects toString method will
     *          called and the result passed to {@link #stripControlCharacters(String)}.
     * @return {@code String}
     *          A new String instance with its hexadecimal control characters replaced
     *          by a space. Or the unmodified String if it does not contain any ISO
     *          control characters.
     */
    public static String stripControlCharacters(Object value) {
        if (value == null) {
            return null;
        }

        return stripControlCharacters(value.toString());
    }

    /**
     * Strip a String of it's ISO control characters.
     *
     * @param value
     *          The String that should be stripped.
     * @return {@code String}
     *          A new String instance with its hexadecimal control characters replaced
     *          by a space. Or the unmodified String if it does not contain any ISO
     *          control characters.
     */
    public static String stripControlCharacters(String value) {
        if (value == null) {
            return null;
        }

        boolean hasControlChars = false;
        for (int i = value.length() - 1; i >= 0; i --) {
            if (Character.isISOControl(value.charAt(i))) {
                hasControlChars = true;
                break;
            }
        }

        if (!hasControlChars) {
            return value;
        }

        StringBuilder buf = new StringBuilder(value.length());
        int i = 0;

        // Skip initial control characters (i.e. left trim)
        for (; i < value.length(); i ++) {
            if (!Character.isISOControl(value.charAt(i))) {
                break;
            }
        }

        // Copy non control characters and substitute control characters with
        // a space.  The last control characters are trimmed.
        boolean suppressingControlChars = false;
        for (; i < value.length(); i ++) {
            if (Character.isISOControl(value.charAt(i))) {
                suppressingControlChars = true;
                continue;
            } else {
                if (suppressingControlChars) {
                    suppressingControlChars = false;
                    buf.append(' ');
                }
                buf.append(value.charAt(i));
            }
        }

        return buf.toString();
    }

    private static final String EMPTY_STRING = "";

    /**
     * Splits the specified {@link String} with the specified delimiter.  This operation is a simplified and optimized
     * version of {@link String#split(String)}.
     */
    public static String[] split(String value, char delim) {
        final int end = value.length();
        final List<String> res = new ArrayList<String>();

        int start = 0;
        for (int i = 0; i < end; i ++) {
            if (value.charAt(i) == delim) {
                if (start == i) {
                    res.add(EMPTY_STRING);
                } else {
                    res.add(value.substring(start, i));
                }
                start = i + 1;
            }
        }

        if (start == 0) { // If no delimiter was found in the value
            res.add(value);
        } else {
            if (start != end) {
                // Add the last element if it's not empty.
                res.add(value.substring(start, end));
            } else {
                // Truncate trailing empty elements.
                for (int i = res.size() - 1; i >= 0; i --) {
                    if (res.get(i).length() == 0) {
                        res.remove(i);
                    } else {
                        break;
                    }
                }
            }
        }

        return res.toArray(new String[res.size()]);
    }
}