Java tutorial
/** * 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.hadoop.util; import java.io.PrintWriter; import java.io.StringWriter; import java.net.InetAddress; import java.net.URI; import java.net.URISyntaxException; import java.net.UnknownHostException; import java.text.DateFormat; import java.text.DecimalFormat; import java.text.NumberFormat; import java.util.Locale; import java.util.ArrayList; import java.util.Arrays; import java.util.Date; import java.util.List; import java.util.StringTokenizer; import java.util.Collection; import org.apache.hadoop.fs.*; /** * General string utils */ public class StringUtils { private static final DecimalFormat decimalFormat; static { NumberFormat numberFormat = NumberFormat.getNumberInstance(Locale.ENGLISH); decimalFormat = (DecimalFormat) numberFormat; decimalFormat.applyPattern("#.##"); } /** * Make a string representation of the exception. * @param e The exception to stringify * @return A string with exception name and call stack. */ public static String stringifyException(Throwable e) { StringWriter stm = new StringWriter(); PrintWriter wrt = new PrintWriter(stm); e.printStackTrace(wrt); wrt.close(); return stm.toString(); } /** * Given a full hostname, return the word upto the first dot. * @param fullHostname the full hostname * @return the hostname to the first dot */ public static String simpleHostname(String fullHostname) { int offset = fullHostname.indexOf('.'); if (offset != -1) { return fullHostname.substring(0, offset); } return fullHostname; } private static DecimalFormat oneDecimal = new DecimalFormat("0.0"); /** * Given an integer, return a string that is in an approximate, but human * readable format. * It uses the bases 'k', 'm', and 'g' for 1024, 1024**2, and 1024**3. * @param number the number to format * @return a human readable form of the integer */ public static String humanReadableInt(long number) { long absNumber = Math.abs(number); double result = number; String suffix = ""; if (absNumber < 1024) { // nothing } else if (absNumber < 1024 * 1024) { result = number / 1024.0; suffix = "k"; } else if (absNumber < 1024 * 1024 * 1024) { result = number / (1024.0 * 1024); suffix = "m"; } else { result = number / (1024.0 * 1024 * 1024); suffix = "g"; } return oneDecimal.format(result) + suffix; } /** * Format a percentage for presentation to the user. * @param done the percentage to format (0.0 to 1.0) * @param digits the number of digits past the decimal point * @return a string representation of the percentage */ public static String formatPercent(double done, int digits) { DecimalFormat percentFormat = new DecimalFormat("0.00%"); double scale = Math.pow(10.0, digits + 2); double rounded = Math.floor(done * scale); percentFormat.setDecimalSeparatorAlwaysShown(false); percentFormat.setMinimumFractionDigits(digits); percentFormat.setMaximumFractionDigits(digits); return percentFormat.format(rounded / scale); } /** * Given an array of strings, return a comma-separated list of its elements. * @param strs Array of strings * @return Empty string if strs.length is 0, comma separated list of strings * otherwise */ public static String arrayToString(String[] strs) { if (strs.length == 0) { return ""; } StringBuffer sbuf = new StringBuffer(); sbuf.append(strs[0]); for (int idx = 1; idx < strs.length; idx++) { sbuf.append(","); sbuf.append(strs[idx]); } return sbuf.toString(); } /** * Given an array of bytes it will convert the bytes to a hex string * representation of the bytes * @param bytes * @param start start index, inclusively * @param end end index, exclusively * @return hex string representation of the byte array */ public static String byteToHexString(byte[] bytes, int start, int end) { if (bytes == null) { throw new IllegalArgumentException("bytes == null"); } StringBuilder s = new StringBuilder(); for (int i = start; i < end; i++) { s.append(String.format("%02x", bytes[i])); } return s.toString(); } /** Same as byteToHexString(bytes, 0, bytes.length). */ public static String byteToHexString(byte bytes[]) { return byteToHexString(bytes, 0, bytes.length); } /** * Given a hexstring this will return the byte array corresponding to the * string * @param hex the hex String array * @return a byte array that is a hex string representation of the given * string. The size of the byte array is therefore hex.length/2 */ public static byte[] hexStringToByte(String hex) { byte[] bts = new byte[hex.length() / 2]; for (int i = 0; i < bts.length; i++) { bts[i] = (byte) Integer.parseInt(hex.substring(2 * i, 2 * i + 2), 16); } return bts; } /** * * @param uris */ public static String uriToString(URI[] uris) { if (uris == null) { return null; } StringBuffer ret = new StringBuffer(uris[0].toString()); for (int i = 1; i < uris.length; i++) { ret.append(","); ret.append(uris[i].toString()); } return ret.toString(); } /** * * @param str */ public static URI[] stringToURI(String[] str) { if (str == null) return null; URI[] uris = new URI[str.length]; for (int i = 0; i < str.length; i++) { try { uris[i] = new URI(str[i]); } catch (URISyntaxException ur) { System.out.println("Exception in specified URI's " + StringUtils.stringifyException(ur)); //making sure its asssigned to null in case of an error uris[i] = null; } } return uris; } /** * * @param str */ public static Path[] stringToPath(String[] str) { if (str == null) { return null; } Path[] p = new Path[str.length]; for (int i = 0; i < str.length; i++) { p[i] = new Path(str[i]); } return p; } /** * * Given a finish and start time in long milliseconds, returns a * String in the format Xhrs, Ymins, Z sec, for the time difference between two times. * If finish time comes before start time then negative valeus of X, Y and Z wil return. * * @param finishTime finish time * @param startTime start time */ public static String formatTimeDiff(long finishTime, long startTime) { long timeDiff = finishTime - startTime; return formatTime(timeDiff); } /** * * Given the time in long milliseconds, returns a * String in the format Xhrs, Ymins, Z sec. * * @param timeDiff The time difference to format */ public static String formatTime(long timeDiff) { StringBuffer buf = new StringBuffer(); long hours = timeDiff / (60 * 60 * 1000); long rem = (timeDiff % (60 * 60 * 1000)); long minutes = rem / (60 * 1000); rem = rem % (60 * 1000); long seconds = rem / 1000; if (hours != 0) { buf.append(hours); buf.append("hrs, "); } if (minutes != 0) { buf.append(minutes); buf.append("mins, "); } // return "0sec if no difference buf.append(seconds); buf.append("sec"); return buf.toString(); } /** * Formats time in ms and appends difference (finishTime - startTime) * as returned by formatTimeDiff(). * If finish time is 0, empty string is returned, if start time is 0 * then difference is not appended to return value. * @param dateFormat date format to use * @param finishTime fnish time * @param startTime start time * @return formatted value. */ public static String getFormattedTimeWithDiff(DateFormat dateFormat, long finishTime, long startTime) { StringBuffer buf = new StringBuffer(); if (0 != finishTime) { buf.append(dateFormat.format(new Date(finishTime))); if (0 != startTime) { buf.append(" (" + formatTimeDiff(finishTime, startTime) + ")"); } } return buf.toString(); } /** * Returns an arraylist of strings. * @param str the comma seperated string values * @return the arraylist of the comma seperated string values */ public static String[] getStrings(String str) { Collection<String> values = getStringCollection(str); if (values.size() == 0) { return null; } return values.toArray(new String[values.size()]); } /** * Returns a collection of strings. * @param str comma seperated string values * @return an <code>ArrayList</code> of string values */ public static Collection<String> getStringCollection(String str) { List<String> values = new ArrayList<String>(); if (str == null) return values; StringTokenizer tokenizer = new StringTokenizer(str, ","); values = new ArrayList<String>(); while (tokenizer.hasMoreTokens()) { values.add(tokenizer.nextToken()); } return values; } final public static char COMMA = ','; final public static String COMMA_STR = ","; final public static char ESCAPE_CHAR = '\\'; /** * Split a string using the default separator * @param str a string that may have escaped separator * @return an array of strings */ public static String[] split(String str) { return split(str, ESCAPE_CHAR, COMMA); } /** * Split a string using the given separator * @param str a string that may have escaped separator * @param escapeChar a char that be used to escape the separator * @param separator a separator char * @return an array of strings */ public static String[] split(String str, char escapeChar, char separator) { if (str == null) { return null; } ArrayList<String> strList = new ArrayList<String>(); StringBuilder split = new StringBuilder(); int index = 0; while ((index = findNext(str, separator, escapeChar, index, split)) >= 0) { ++index; // move over the separator for next search strList.add(split.toString()); split.setLength(0); // reset the buffer } strList.add(split.toString()); // remove trailing empty split(s) int last = strList.size(); // last split while (--last >= 0 && "".equals(strList.get(last))) { strList.remove(last); } return strList.toArray(new String[strList.size()]); } /** * Finds the first occurrence of the separator character ignoring the escaped * separators starting from the index. Note the substring between the index * and the position of the separator is passed. * @param str the source string * @param separator the character to find * @param escapeChar character used to escape * @param start from where to search * @param split used to pass back the extracted string */ public static int findNext(String str, char separator, char escapeChar, int start, StringBuilder split) { int numPreEscapes = 0; for (int i = start; i < str.length(); i++) { char curChar = str.charAt(i); if (numPreEscapes == 0 && curChar == separator) { // separator return i; } else { split.append(curChar); numPreEscapes = (curChar == escapeChar) ? (++numPreEscapes) % 2 : 0; } } return -1; } /** * Escape commas in the string using the default escape char * @param str a string * @return an escaped string */ public static String escapeString(String str) { return escapeString(str, ESCAPE_CHAR, COMMA); } /** * Escape <code>charToEscape</code> in the string * with the escape char <code>escapeChar</code> * * @param str string * @param escapeChar escape char * @param charToEscape the char to be escaped * @return an escaped string */ public static String escapeString(String str, char escapeChar, char charToEscape) { return escapeString(str, escapeChar, new char[] { charToEscape }); } // check if the character array has the character private static boolean hasChar(char[] chars, char character) { for (char target : chars) { if (character == target) { return true; } } return false; } /** * @param charsToEscape array of characters to be escaped */ public static String escapeString(String str, char escapeChar, char[] charsToEscape) { if (str == null) { return null; } int len = str.length(); // Let us specify good enough capacity to constructor of StringBuilder sothat // resizing would not be needed(to improve perf). StringBuilder result = new StringBuilder((int) (len * 1.5)); for (int i = 0; i < len; i++) { char curChar = str.charAt(i); if (curChar == escapeChar || hasChar(charsToEscape, curChar)) { // special char result.append(escapeChar); } result.append(curChar); } return result.toString(); } /** * Unescape commas in the string using the default escape char * @param str a string * @return an unescaped string */ public static String unEscapeString(String str) { return unEscapeString(str, ESCAPE_CHAR, COMMA); } /** * Unescape <code>charToEscape</code> in the string * with the escape char <code>escapeChar</code> * * @param str string * @param escapeChar escape char * @param charToEscape the escaped char * @return an unescaped string */ public static String unEscapeString(String str, char escapeChar, char charToEscape) { return unEscapeString(str, escapeChar, new char[] { charToEscape }); } /** * @param charsToEscape array of characters to unescape */ public static String unEscapeString(String str, char escapeChar, char[] charsToEscape) { if (str == null) { return null; } StringBuilder result = new StringBuilder(str.length()); boolean hasPreEscape = false; for (int i = 0; i < str.length(); i++) { char curChar = str.charAt(i); if (hasPreEscape) { if (curChar != escapeChar && !hasChar(charsToEscape, curChar)) { // no special char throw new IllegalArgumentException( "Illegal escaped string " + str + " unescaped " + escapeChar + " at " + (i - 1)); } // otherwise discard the escape char result.append(curChar); hasPreEscape = false; } else { if (hasChar(charsToEscape, curChar)) { throw new IllegalArgumentException( "Illegal escaped string " + str + " unescaped " + curChar + " at " + i); } else if (curChar == escapeChar) { hasPreEscape = true; } else { result.append(curChar); } } } if (hasPreEscape) { throw new IllegalArgumentException( "Illegal escaped string " + str + ", not expecting " + escapeChar + " in the end."); } return result.toString(); } /** * Return hostname without throwing exception. * @return hostname */ public static String getHostname() { try { return "" + InetAddress.getLocalHost(); } catch (UnknownHostException uhe) { return "" + uhe; } } /** * Return a message for logging. * @param prefix prefix keyword for the message * @param msg content of the message * @return a message for logging */ private static String toStartupShutdownString(String prefix, String[] msg) { StringBuffer b = new StringBuffer(prefix); b.append("\n/************************************************************"); for (String s : msg) b.append("\n" + prefix + s); b.append("\n************************************************************/"); return b.toString(); } /** * Print a log message for starting up and shutting down * @param clazz the class of the server * @param args arguments * @param LOG the target log object */ public static void startupShutdownMessage(Class<?> clazz, String[] args, final org.apache.commons.logging.Log LOG) { final String hostname = getHostname(); final String classname = clazz.getSimpleName(); LOG.info(toStartupShutdownString("STARTUP_MSG: ", new String[] { "Starting " + classname, " host = " + hostname, " args = " + Arrays.asList(args), " version = " + VersionInfo.getVersion(), " build = " + VersionInfo.getUrl() + " -r " + VersionInfo.getRevision() + "; compiled by '" + VersionInfo.getUser() + "' on " + VersionInfo.getDate() })); Runtime.getRuntime().addShutdownHook(new Thread() { public void run() { LOG.info(toStartupShutdownString("SHUTDOWN_MSG: ", new String[] { "Shutting down " + classname + " at " + hostname })); } }); } /** * The traditional binary prefixes, kilo, mega, ..., exa, * which can be represented by a 64-bit integer. * TraditionalBinaryPrefix symbol are case insensitive. */ public static enum TraditionalBinaryPrefix { KILO(1024), MEGA(KILO.value << 10), GIGA(MEGA.value << 10), TERA(GIGA.value << 10), PETA( TERA.value << 10), EXA(PETA.value << 10); public final long value; public final char symbol; TraditionalBinaryPrefix(long value) { this.value = value; this.symbol = toString().charAt(0); } /** * @return The TraditionalBinaryPrefix object corresponding to the symbol. */ public static TraditionalBinaryPrefix valueOf(char symbol) { symbol = Character.toUpperCase(symbol); for (TraditionalBinaryPrefix prefix : TraditionalBinaryPrefix.values()) { if (symbol == prefix.symbol) { return prefix; } } throw new IllegalArgumentException("Unknown symbol '" + symbol + "'"); } /** * Convert a string to long. * The input string is first be trimmed * and then it is parsed with traditional binary prefix. * * For example, * "-1230k" will be converted to -1230 * 1024 = -1259520; * "891g" will be converted to 891 * 1024^3 = 956703965184; * * @param s input string * @return a long value represented by the input string. */ public static long string2long(String s) { s = s.trim(); final int lastpos = s.length() - 1; final char lastchar = s.charAt(lastpos); if (Character.isDigit(lastchar)) return Long.parseLong(s); else { long prefix = TraditionalBinaryPrefix.valueOf(lastchar).value; long num = Long.parseLong(s.substring(0, lastpos)); if (num > (Long.MAX_VALUE / prefix) || num < (Long.MIN_VALUE / prefix)) { throw new IllegalArgumentException(s + " does not fit in a Long"); } return num * prefix; } } } /** * Escapes HTML Special characters present in the string. * @param string * @return HTML Escaped String representation */ public static String escapeHTML(String string) { if (string == null) { return null; } StringBuffer sb = new StringBuffer(); boolean lastCharacterWasSpace = false; char[] chars = string.toCharArray(); for (char c : chars) { if (c == ' ') { if (lastCharacterWasSpace) { lastCharacterWasSpace = false; sb.append(" "); } else { lastCharacterWasSpace = true; sb.append(" "); } } else { lastCharacterWasSpace = false; switch (c) { case '<': sb.append("<"); break; case '>': sb.append(">"); break; case '&': sb.append("&"); break; case '"': sb.append("""); break; default: sb.append(c); break; } } } return sb.toString(); } /** * Return an abbreviated English-language desc of the byte length */ public static String byteDesc(long len) { double val = 0.0; String ending = ""; if (len < 1024 * 1024) { val = (1.0 * len) / 1024; ending = " KB"; } else if (len < 1024 * 1024 * 1024) { val = (1.0 * len) / (1024 * 1024); ending = " MB"; } else if (len < 1024L * 1024 * 1024 * 1024) { val = (1.0 * len) / (1024 * 1024 * 1024); ending = " GB"; } else if (len < 1024L * 1024 * 1024 * 1024 * 1024) { val = (1.0 * len) / (1024L * 1024 * 1024 * 1024); ending = " TB"; } else { val = (1.0 * len) / (1024L * 1024 * 1024 * 1024 * 1024); ending = " PB"; } return limitDecimalTo2(val) + ending; } public static synchronized String limitDecimalTo2(double d) { return decimalFormat.format(d); } /** * Concatenates strings, using a separator. * * @param separator Separator to join with. * @param strings Strings to join. * @return the joined string */ public static String join(CharSequence separator, Iterable<String> strings) { StringBuilder sb = new StringBuilder(); boolean first = true; for (String s : strings) { if (first) { first = false; } else { sb.append(separator); } sb.append(s); } return sb.toString(); } /** * Concatenates strings, using a separator. * * @param separator to join with * @param strings to join * @return the joined string */ public static String join(CharSequence separator, String[] strings) { // Ideally we don't have to duplicate the code here if array is iterable. StringBuilder sb = new StringBuilder(); boolean first = true; for (String s : strings) { if (first) { first = false; } else { sb.append(separator); } sb.append(s); } return sb.toString(); } /** * Capitalize a word * * @param s the input string * @return capitalized string */ public static String capitalize(String s) { int len = s.length(); if (len == 0) return s; return new StringBuilder(len).append(Character.toTitleCase(s.charAt(0))).append(s.substring(1)).toString(); } /** * Convert SOME_STUFF to SomeStuff * * @param s input string * @return camelized string */ public static String camelize(String s) { StringBuilder sb = new StringBuilder(); String[] words = split(s.toLowerCase(Locale.US), ESCAPE_CHAR, '_'); for (String word : words) sb.append(capitalize(word)); return sb.toString(); } }