/*
* 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.types.Parameter;
import org.apache.tools.ant.util.LineTokenizer;
/**
* Reads the first <code>n</code> lines of a stream.
* (Default is first 10 lines.)
* <p>
* Example:
* <pre><headfilter lines="3"/></pre>
* 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;
/** Whether this filter is finished */
private boolean eof;
/**
* 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</code>.
*/
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);
if (eof) {
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 HeadFilter using the passed in
* Reader for instantiation.
*
* @param rdr A Reader object providing the underlying stream.
* Must not be <code>null</code>.
*
* @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 = Long.parseLong(params[i].getValue());
continue;
}
if (SKIP_KEY.equals(params[i].getName())) {
skip = Long.parseLong(params[i].getValue());
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)) {
eof = true;
return null;
}
}
return line;
}
}