Ant example source code file (HeadFilter.java)

This example Ant source code file (HeadFilter.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Ant tags/keywords

baseparamfilterreader, chainablereader, default_num_lines, headfilter, headfilter, io, lines_key, linetokenizer, linetokenizer, parameter, reader, reader, skip_key, string, string

The HeadFilter.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 org.apache.tools.ant.util.LineTokenizer;
import org.apache.tools.ant.types.Parameter;

/**
 * Reads the first <code>n lines of a stream.
 * (Default is first 10 lines.)
 * <p>
 * Example:
 * <pre><headfilter lines="3"/>

* Or: * <pre><filterreader classname="org.apache.tools.ant.filters.HeadFilter"> * <param name="lines" value="3"/> * </filterreader></pre> * */ public final class HeadFilter 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"; /** Number of lines currently read in. */ private long linesRead = 0; /** 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; /** 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; /** * Constructor for "dummy" instances. * * @see BaseFilterReader#BaseFilterReader() */ public HeadFilter() { super(); } /** * Creates a new filtered reader. * * @param in A Reader object providing the underlying stream. * Must not be <code>null. */ public HeadFilter(final Reader in) { super(in); lineTokenizer = new LineTokenizer(); lineTokenizer.setIncludeDelims(true); } /** * Returns the next character in the filtered stream. If the desired * number of lines have already been read, the resulting stream is * effectively at an end. Otherwise, the next character from the * underlying stream is read and returned. * * @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); if (line == null) { return -1; } line = headFilter(line); 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 HeadFilter 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) { HeadFilter newFilter = new HeadFilter(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())) { lines = new Long(params[i].getValue()).longValue(); continue; } if (SKIP_KEY.equals(params[i].getName())) { skip = new Long(params[i].getValue()).longValue(); continue; } } } } /** * implements a head filter on the input stream */ private String headFilter(String line) { linesRead++; if (skip > 0) { if ((linesRead - 1) < skip) { return null; } } if (lines > 0) { if (linesRead > (lines + skip)) { return null; } } return line; } }