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Java > Open Source Codes > org > apache > tools > ant > filters > TailFilter


1 /*
2  * Licensed to the Apache Software Foundation (ASF) under one or more
3  * contributor license agreements. See the NOTICE file distributed with
4  * this work for additional information regarding copyright ownership.
5  * The ASF licenses this file to You under the Apache License, Version 2.0
6  * (the "License"); you may not use this file except in compliance with
7  * the License. You may obtain a copy of the License at
8  *
9  * http://www.apache.org/licenses/LICENSE-2.0
10  *
11  * Unless required by applicable law or agreed to in writing, software
12  * distributed under the License is distributed on an "AS IS" BASIS,
13  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14  * See the License for the specific language governing permissions and
15  * limitations under the License.
16  *
17  */
18 package org.apache.tools.ant.filters;
19
20 import java.io.IOException JavaDoc;
21 import java.io.Reader JavaDoc;
22 import java.util.LinkedList JavaDoc;
23 import org.apache.tools.ant.types.Parameter;
24 import org.apache.tools.ant.util.LineTokenizer;
25
26 /**
27  * Reads the last <code>n</code> lines of a stream. (Default is last10 lines.)
28  *
29  * Example:
30  *
31  * <pre>&lt;tailfilter lines=&quot;3&quot;/&gt;</pre>
32  *
33  * Or:
34  *
35  * <pre>&lt;filterreader classname=&quot;org.apache.tools.ant.filters.TailFilter&quot;&gt;
36  * &lt;param name=&quot;lines&quot; value=&quot;3&quot;/&gt;
37  * &lt;/filterreader&gt;</pre>
38  *
39  */
40 public final class TailFilter extends BaseParamFilterReader
41     implements ChainableReader {
42     /** Parameter name for the number of lines to be returned. */
43     private static final String JavaDoc LINES_KEY = "lines";
44
45     /** Parameter name for the number of lines to be skipped. */
46     private static final String JavaDoc SKIP_KEY = "skip";
47
48     /** Default number of lines to show */
49     private static final int DEFAULT_NUM_LINES = 10;
50
51     /** Number of lines to be returned in the filtered stream. */
52     private long lines = DEFAULT_NUM_LINES;
53
54     /** Number of lines to be skipped. */
55     private long skip = 0;
56
57     /** Whether or not read-ahead been completed. */
58     private boolean completedReadAhead = false;
59
60     /** A line tokenizer */
61     private LineTokenizer lineTokenizer = null;
62
63     /** the current line from the input stream */
64     private String JavaDoc line = null;
65     /** the position in the current line */
66     private int linePos = 0;
67
68     private LinkedList JavaDoc lineList = new LinkedList JavaDoc();
69
70     /**
71      * Constructor for "dummy" instances.
72      *
73      * @see BaseFilterReader#BaseFilterReader()
74      */
75     public TailFilter() {
76         super();
77     }
78
79     /**
80      * Creates a new filtered reader.
81      *
82      * @param in A Reader object providing the underlying stream.
83      * Must not be <code>null</code>.
84      */
85     public TailFilter(final Reader JavaDoc in) {
86         super(in);
87         lineTokenizer = new LineTokenizer();
88         lineTokenizer.setIncludeDelims(true);
89     }
90
91     /**
92      * Returns the next character in the filtered stream. If the read-ahead
93      * has been completed, the next character in the buffer is returned.
94      * Otherwise, the stream is read to the end and buffered (with the buffer
95      * growing as necessary), then the appropriate position in the buffer is
96      * set to read from.
97      *
98      * @return the next character in the resulting stream, or -1
99      * if the end of the resulting stream has been reached
100      *
101      * @exception IOException if the underlying stream throws an IOException
102      * during reading
103      */
104     public int read() throws IOException JavaDoc {
105         if (!getInitialized()) {
106             initialize();
107             setInitialized(true);
108         }
109
110         while (line == null || line.length() == 0) {
111             line = lineTokenizer.getToken(in);
112             line = tailFilter(line);
113             if (line == null) {
114                 return -1;
115             }
116             linePos = 0;
117         }
118
119         int ch = line.charAt(linePos);
120         linePos++;
121         if (linePos == line.length()) {
122             line = null;
123         }
124         return ch;
125     }
126
127     /**
128      * Sets the number of lines to be returned in the filtered stream.
129      *
130      * @param lines the number of lines to be returned in the filtered stream
131      */
132     public void setLines(final long lines) {
133         this.lines = lines;
134     }
135
136     /**
137      * Returns the number of lines to be returned in the filtered stream.
138      *
139      * @return the number of lines to be returned in the filtered stream
140      */
141     private long getLines() {
142         return lines;
143     }
144
145     /**
146      * Sets the number of lines to be skipped in the filtered stream.
147      *
148      * @param skip the number of lines to be skipped in the filtered stream
149      */
150     public void setSkip(final long skip) {
151         this.skip = skip;
152     }
153
154     /**
155      * Returns the number of lines to be skipped in the filtered stream.
156      *
157      * @return the number of lines to be skipped in the filtered stream
158      */
159     private long getSkip() {
160         return skip;
161     }
162
163     /**
164      * Creates a new TailFilter using the passed in
165      * Reader for instantiation.
166      *
167      * @param rdr A Reader object providing the underlying stream.
168      * Must not be <code>null</code>.
169      *
170      * @return a new filter based on this configuration, but filtering
171      * the specified reader
172      */
173     public Reader JavaDoc chain(final Reader JavaDoc rdr) {
174         TailFilter newFilter = new TailFilter(rdr);
175         newFilter.setLines(getLines());
176         newFilter.setSkip(getSkip());
177         newFilter.setInitialized(true);
178         return newFilter;
179     }
180
181     /**
182      * Scans the parameters list for the "lines" parameter and uses
183      * it to set the number of lines to be returned in the filtered stream.
184      * also scan for "skip" parameter.
185      */
186     private void initialize() {
187         Parameter[] params = getParameters();
188         if (params != null) {
189             for (int i = 0; i < params.length; i++) {
190                 if (LINES_KEY.equals(params[i].getName())) {
191                     setLines(new Long JavaDoc(params[i].getValue()).longValue());
192                     continue;
193                 }
194                 if (SKIP_KEY.equals(params[i].getName())) {
195                     skip = new Long JavaDoc(params[i].getValue()).longValue();
196                     continue;
197                 }
198             }
199         }
200     }
201
202     /**
203      * implement a tail filter on a stream of lines.
204      * line = null is the end of the stream.
205      * @return "" while reading in the lines,
206      * line while outputting the lines
207      * null at the end of outputting the lines
208      */
209     private String JavaDoc tailFilter(String JavaDoc line) {
210         if (!completedReadAhead) {
211             if (line != null) {
212                 lineList.add(line);
213                 if (lines == -1) {
214                     if (lineList.size() > skip) {
215                         return (String JavaDoc) lineList.removeFirst();
216                     }
217                 } else {
218                     long linesToKeep = lines + (skip > 0 ? skip : 0);
219                     if (linesToKeep < lineList.size()) {
220                         lineList.removeFirst();
221                     }
222                 }
223                 return "";
224             }
225             completedReadAhead = true;
226             if (skip > 0) {
227                 for (int i = 0; i < skip; ++i) {
228                     lineList.removeLast();
229                 }
230             }
231             if (lines > -1) {
232                 while (lineList.size() > lines) {
233                     lineList.removeFirst();
234                 }
235             }
236         }
237         if (lineList.size() > 0) {
238             return (String JavaDoc) lineList.removeFirst();
239         }
240         return null;
241     }
242 }
243
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