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Copyright (C) 2011-2012 Vanderbilt University Permission is hereby granted, free of charge, to any person obtaining a copy of this data, including any software or models in source or binary form, as ...
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/*Copyright (C) 2010-2012 Institute for Software Integrated Systems (ISIS) This software was developed by the Institute for Software Integrated Systems (ISIS) at Vanderbilt University, Tennessee, USA for the Transformative Apps program under DARPA, Contract # HR011-10-C-0175. The United States Government has unlimited rights to this software. The US government has the right to use, modify, reproduce, release, perform, display, or disclose computer software or computer software documentation in whole or in part, in any manner and for any purpose whatsoever, and to have or authorize others to do so. *//*from ww w . j av a2 s .c o m*/ package edu.vu.isis.logger.util; import java.nio.Buffer; import java.nio.ByteBuffer; /** * Collection of static helper methods for use with a ByteBuffer object. * @author Nick King */ public class ByteBuffers { public static final char BEG_OF_TEXT_CHAR = (char) 0x00000010; public static final String BEG_OF_TEXT_STR = Character.toString(BEG_OF_TEXT_CHAR); public static final char END_OF_TEXT_CHAR = (char) 0x00000011; public static final String END_OF_TEXT_STR = Character.toString(END_OF_TEXT_CHAR); // Hide the default constructor to prevent instantiation private ByteBuffers() { } // ///////////////////////////////////////////////////////////// // STATIC HELPER METHODS // ///////////////////////////////////////////////////////////// public static String readForwardToNewline(ByteBuffer buffer) { StringBuilder sb = new StringBuilder(); if (getBufferPosition(buffer) == getBufferLimit(buffer)) return END_OF_TEXT_STR; char next = (char) buffer.get(); while (isNotBreak(next) && !isBufferUnderflow(buffer)) { sb.append(next); next = (char) buffer.get(); } if (getBufferPosition(buffer) == getBufferLimit(buffer)) { // Signal the end of the file if it is reached sb.append(END_OF_TEXT_CHAR); } return sb.toString(); } public static int getBufferLimit(ByteBuffer buffer) { return buffer.limit(); } public static String readBackwardToNewline(ByteBuffer buffer) { StringBuilder sb = new StringBuilder(); // Return if we are already at the beginning of the buffer if (getBufferPosition(buffer) == 0) return BEG_OF_TEXT_STR; char next = (char) buffer.get(getBufferPosition(buffer)); decrementBufferPosition(buffer); // We have to stop at position 1 to avoid decrementing the buffer // position to -1 while (isNotBreak(next) && getBufferPosition(buffer) >= 1) { sb.append(next); next = (char) buffer.get(getBufferPosition(buffer)); decrementBufferPosition(buffer); } if (getBufferPosition(buffer) == 0) { // The char at position 1 was not appended because we reached // position 0, so we append it if it's not a newline char if (next != '\n') { sb.append(next); } // Add the first char in the file if we reached the beginning // and it is not a newline next = (char) buffer.get(0); if(next != '\n') { sb.append(next); } // Signal the beginning of the file sb.append(BEG_OF_TEXT_CHAR); } return sb.reverse().toString(); } static boolean isNotBreak(char ch) { return ch != '\n' && ch != '\r'; } public static int getBufferPosition(Buffer buffer) { return buffer.position(); } public static void setBufferPosition(Buffer buffer, int newPosition) { buffer.position(newPosition); } public static void decrementBufferPosition(Buffer buffer) { setBufferPosition(buffer, getBufferPosition(buffer) - 1); } /** * Moves the buffer forward a given number of lines * * @param buffer * -- the buffer to use * @param numLines * -- the number of lines to skip forward * @return -- true if the given number of lines were skipped, false if not */ public static boolean skipForward(ByteBuffer buffer, int numLines) { if (getBufferPosition(buffer) == getBufferLimit(buffer)) return false; // Waste no time if we were given a dumb argument if (numLines <= 0) return true; int numSkipped = 0; for (; numSkipped < numLines; numSkipped++) { char next = (char) buffer.get(); while (isNotBreak(next) && !isBufferUnderflow(buffer)) { next = (char) buffer.get(); } if (isBufferUnderflow(buffer)) { // We reached the end of the buffer, so we need to determine // whether or not we read all of the lines requested return numSkipped + 1 == numLines; } } return numSkipped == numLines; } /** * Moves the buffer backward a given number of lines * * @param buffer * -- the buffer to use * @param numLines * -- the number of lines to skip backward * @return -- true if the given number of lines were skipped, false if not */ public static boolean skipBackward(ByteBuffer buffer, int numLines) { // Return if we are already at the beginning of the buffer if (getBufferPosition(buffer) == 0) return false; // Waste no time if we were given a dumb argument if (numLines <= 0) return true; int numSkipped = 0; for (; numSkipped < numLines; numSkipped++) { char next = (char) buffer.get(getBufferPosition(buffer)); decrementBufferPosition(buffer); // We have to stop at position 1 to avoid decrementing the buffer // position to -1 while (isNotBreak(next) && getBufferPosition(buffer) >= 1) { next = (char) buffer.get(getBufferPosition(buffer)); decrementBufferPosition(buffer); } if (getBufferPosition(buffer) == 0) { // We reached the beginning of the buffer, so we need to // determine // whether or not we read all of the lines requested return numSkipped + 1 == numLines; } } return numSkipped == numLines; } /** * Checks if the buffer is currently in an underflow state * * @param buffer * -- the buffer to check * @return -- whether the buffer's position is not smaller than its limit */ public static boolean isBufferUnderflow(ByteBuffer buffer) { return !(getBufferPosition(buffer) < getBufferLimit(buffer)); } static boolean isEOF(String str) { return str.endsWith(END_OF_TEXT_STR); } static boolean isBOF(String str) { return str.startsWith(BEG_OF_TEXT_STR); } public static int countLinesBetween(ByteBuffer buffer, int startPos, int endPos) { setBufferPosition(buffer, startPos); int numBetween = 0; while (skipForward(buffer, 1)) { if (getBufferPosition(buffer) < endPos) { numBetween++; } else { break; } } return numBetween; } }