Ant example source code file (TailFilter.java)

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Java - Ant tags/keywords

baseparamfilterreader, chainablereader, default_num_lines, io, lines_key, linetokenizer, linetokenizer, linkedlist, reader, reader, skip_key, string, string, tailfilter, tailfilter, util

The TailFilter.java source code

/*
 *  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.tools.ant.filters;

import java.io.IOException;
import java.io.Reader;
import java.util.LinkedList;
import org.apache.tools.ant.types.Parameter;
import org.apache.tools.ant.util.LineTokenizer;

/**
 * Reads the last <code>n lines of a stream. (Default is last10 lines.)
 *
 * Example:
 *
 * <pre><tailfilter lines="3"/>

* * Or: * * <pre><filterreader classname="org.apache.tools.ant.filters.TailFilter"> * <param name="lines" value="3"/> * </filterreader></pre> * */ public final class TailFilter extends BaseParamFilterReader implements ChainableReader { /** Parameter name for the number of lines to be returned. */ private static final String LINES_KEY = "lines"; /** Parameter name for the number of lines to be skipped. */ private static final String SKIP_KEY = "skip"; /** Default number of lines to show */ private static final int DEFAULT_NUM_LINES = 10; /** Number of lines to be returned in the filtered stream. */ private long lines = DEFAULT_NUM_LINES; /** Number of lines to be skipped. */ private long skip = 0; /** Whether or not read-ahead been completed. */ private boolean completedReadAhead = false; /** A line tokenizer */ private LineTokenizer lineTokenizer = null; /** the current line from the input stream */ private String line = null; /** the position in the current line */ private int linePos = 0; private LinkedList lineList = new LinkedList(); /** * Constructor for "dummy" instances. * * @see BaseFilterReader#BaseFilterReader() */ public TailFilter() { super(); } /** * Creates a new filtered reader. * * @param in A Reader object providing the underlying stream. * Must not be <code>null. */ public TailFilter(final Reader in) { super(in); lineTokenizer = new LineTokenizer(); lineTokenizer.setIncludeDelims(true); } /** * Returns the next character in the filtered stream. If the read-ahead * has been completed, the next character in the buffer is returned. * Otherwise, the stream is read to the end and buffered (with the buffer * growing as necessary), then the appropriate position in the buffer is * set to read from. * * @return the next character in the resulting stream, or -1 * if the end of the resulting stream has been reached * * @exception IOException if the underlying stream throws an IOException * during reading */ public int read() throws IOException { if (!getInitialized()) { initialize(); setInitialized(true); } while (line == null || line.length() == 0) { line = lineTokenizer.getToken(in); line = tailFilter(line); if (line == null) { return -1; } linePos = 0; } int ch = line.charAt(linePos); linePos++; if (linePos == line.length()) { line = null; } return ch; } /** * Sets the number of lines to be returned in the filtered stream. * * @param lines the number of lines to be returned in the filtered stream */ public void setLines(final long lines) { this.lines = lines; } /** * Returns the number of lines to be returned in the filtered stream. * * @return the number of lines to be returned in the filtered stream */ private long getLines() { return lines; } /** * Sets the number of lines to be skipped in the filtered stream. * * @param skip the number of lines to be skipped in the filtered stream */ public void setSkip(final long skip) { this.skip = skip; } /** * Returns the number of lines to be skipped in the filtered stream. * * @return the number of lines to be skipped in the filtered stream */ private long getSkip() { return skip; } /** * Creates a new TailFilter using the passed in * Reader for instantiation. * * @param rdr A Reader object providing the underlying stream. * Must not be <code>null. * * @return a new filter based on this configuration, but filtering * the specified reader */ public Reader chain(final Reader rdr) { TailFilter newFilter = new TailFilter(rdr); newFilter.setLines(getLines()); newFilter.setSkip(getSkip()); newFilter.setInitialized(true); return newFilter; } /** * Scans the parameters list for the "lines" parameter and uses * it to set the number of lines to be returned in the filtered stream. * also scan for "skip" parameter. */ private void initialize() { Parameter[] params = getParameters(); if (params != null) { for (int i = 0; i < params.length; i++) { if (LINES_KEY.equals(params[i].getName())) { setLines(new Long(params[i].getValue()).longValue()); continue; } if (SKIP_KEY.equals(params[i].getName())) { skip = new Long(params[i].getValue()).longValue(); continue; } } } } /** * implement a tail filter on a stream of lines. * line = null is the end of the stream. * @return "" while reading in the lines, * line while outputting the lines * null at the end of outputting the lines */ private String tailFilter(String line) { if (!completedReadAhead) { if (line != null) { lineList.add(line); if (lines == -1) { if (lineList.size() > skip) { return (String) lineList.removeFirst(); } } else { long linesToKeep = lines + (skip > 0 ? skip : 0); if (linesToKeep < lineList.size()) { lineList.removeFirst(); } } return ""; } completedReadAhead = true; if (skip > 0) { for (int i = 0; i < skip; ++i) { lineList.removeLast(); } } if (lines > -1) { while (lineList.size() > lines) { lineList.removeFirst(); } } } if (lineList.size() > 0) { return (String) lineList.removeFirst(); } return null; } }