File Source: ReverseFileReader.java
/*
P/P * Method: com.dmdirc.addons.logging.ReverseFileReader__static_init
*/
1 /*
2 * Copyright (c) 2006-2009 Chris Smith, Shane Mc Cormack, Gregory Holmes
3 *
4 * Permission is hereby granted, free of charge, to any person obtaining a copy
5 * of this software and associated documentation files (the "Software"), to deal
6 * in the Software without restriction, including without limitation the rights
7 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
8 * copies of the Software, and to permit persons to whom the Software is
9 * furnished to do so, subject to the following conditions:
10 *
11 * The above copyright notice and this permission notice shall be included in
12 * all copies or substantial portions of the Software.
13 *
14 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
15 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
16 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
17 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
18 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
19 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
20 * SOFTWARE.
21 */
22
23 package com.dmdirc.addons.logging;
24
25 import java.io.File;
26 import java.io.FileNotFoundException;
27 import java.io.RandomAccessFile;
28 import java.io.IOException;
29 import java.io.EOFException;
30 import java.nio.charset.Charset;
31 import java.util.Stack;
32 import java.util.ArrayList;
33
34 /**
35 * Reads a file in reverse.
36 *
37 * @author Shane 'Dataforce' McCormack
38 */
39 public class ReverseFileReader {
40 /** File to manipulate. */
41 private RandomAccessFile file;
42 /** Number of bytes to skip backwards at a time. */
43 private byte seekLength = 50;
44
45 /**
46 * Create a new ReverseFileReader.
47 *
48 * @param filename File to open.
49 * @throws FileNotFoundException If the file is not a regular file.
50 * @throws SecurityException If a security manager exists and its checkRead method denies read access to the file.
51 * @throws IOException If there is an error seeking to the end of the file.
52 */
/*
P/P * Method: void com.dmdirc.addons.logging.ReverseFileReader(String)
*
* Postconditions:
* this.file == &new RandomAccessFile(ReverseFileReader#1)
* this.seekLength == 50
* new RandomAccessFile(ReverseFileReader#1) num objects == 1
*/
53 public ReverseFileReader(String filename) throws FileNotFoundException, SecurityException, IOException {
54 file = new RandomAccessFile(filename, "r");
55 reset();
56 }
57
58 /**
59 * Create a new ReverseFileReader.
60 *
61 * @param myFile Existing file to use.
62 * @throws FileNotFoundException If the file is not a regular file.
63 * @throws SecurityException If a security manager exists and its checkRead method denies read access to the file.
64 * @throws IOException If there is an error seeking to the end of the file.
65 */
/*
P/P * Method: void com.dmdirc.addons.logging.ReverseFileReader(File)
*
* Postconditions:
* this.file == &new RandomAccessFile(ReverseFileReader#1)
* this.seekLength == 50
* new RandomAccessFile(ReverseFileReader#1) num objects == 1
*/
66 public ReverseFileReader(File myFile) throws FileNotFoundException, SecurityException, IOException {
67 file = new RandomAccessFile(myFile, "r");
68 reset();
69 }
70
71 /**
72 * Reset the file pointer to the end of the file.
73 *
74 * @throws IOException If there is an error seeking, or the file is closed.
75 */
76 public void reset() throws IOException {
/*
P/P * Method: void reset()
*
* Preconditions:
* this.file != null
*/
77 if (file == null) { throw new IOException("File has been closed."); }
78 file.seek(file.length());
79 }
80
81 /**
82 * Get the current seekLength.
83 *
84 * @return current seekLength
85 */
86 public byte getSeekLength() {
/*
P/P * Method: byte getSeekLength()
*
* Preconditions:
* init'ed(this.seekLength)
*
* Postconditions:
* return_value == this.seekLength
* init'ed(return_value)
*/
87 return seekLength;
88 }
89
90 /**
91 * Set the seekLength.
92 *
93 * @param newValue New value for seekLength
94 */
95 public void setSeekLength(final byte newValue) {
/*
P/P * Method: void setSeekLength(byte)
*
* Postconditions:
* this.seekLength == newValue
* init'ed(this.seekLength)
*/
96 seekLength = newValue;
97 }
98
99 /**
100 * Close the file pointer.
101 * This should be called before removing the reference to this object
102 *
103 * @throws IOException If there is an error closing the file, or if it has been closed already.
104 */
105 public void close() throws IOException {
/*
P/P * Method: void close()
*
* Preconditions:
* this.file != null
*
* Postconditions:
* this.file == null
*/
106 if (file == null) { throw new IOException("File has been closed."); }
107 file.close();
108 file = null;
109 }
110
111 /**
112 * Get the next full line.
113 *
114 * @return The next full line.
115 * @throws EOFException If there is no more lines.
116 * @throws IOException If an error reading or seeking occured, or if the fiel is closed.
117 */
118 public String getNextLine() throws EOFException, IOException {
/*
P/P * Method: String getNextLine()
*
* Preconditions:
* this.file != null
* init'ed(this.seekLength)
*
* Presumptions:
* java.io.RandomAccessFile:getFilePointer(...)@134 != 0
* java.io.RandomAccessFile:getFilePointer(...)@145 >= -231
* java.io.RandomAccessFile:getFilePointer(...)@145 - this.seekLength in {-2_147_483_903..264-1}
* java.util.ArrayList:get(...)@205 != null
* java.util.ArrayList:size(...)@204 >= 1
* ...
*
* Postconditions:
* return_value == &new String(getNextLine#4)
* new String(getNextLine#4) num objects == 1
*
* Test Vectors:
* bytes[i]@162: {13}, {10}, {-128..9, 11,12, 14..255}
* java.io.RandomAccessFile:getFilePointer(...)@145 - this.seekLength: {1..264-1}, {-2_147_483_903..-1}
*/
119 if (file == null) { throw new IOException("File has been closed."); }
120 // Used to store result to output.
121 // StringBuilder line = new StringBuilder();
122 final ArrayList<Byte> line = new ArrayList<Byte>(seekLength);
123 // Used to store position in file pre-read
124 long fp = 0;
125 // Used to store position in file when this is called
126 long startfp = 0;
127 // Used to store read bytes
128 byte[] bytes;
129 // Distance seeked
130 int seekDistance = 0;
131
132 // Check current position, if 0 we are at the start of the file
133 // and should throw an exception.
134 startfp = file.getFilePointer();
135 if (startfp == 0) {
136 throw new EOFException("Reached Start of file");
137 }
138
139 // Keep looping untill we get a full line, or the end of the file
140 boolean keepLooping = true;
141 boolean gotNewLine;
142 while (keepLooping) {
143 gotNewLine = false;
144 // Get Current Position
145 fp = file.getFilePointer();
146
147 // Check how far to seek backwards (seekLength or to the start of the file)
148 if (fp < seekLength) {
149 // Seek to the start of the file;
150 seekDistance = (int)fp;
151 fp = 0;
152 } else {
153 // Seek to position current-seekLength
154 seekDistance = seekLength;
155 fp = fp - seekDistance;
156 }
157 // Seek!
158 file.seek(fp);
159
160 bytes = new byte[seekDistance];
161 // Read into the bytes array
162 file.read(bytes);
163
164 // And loop looking for data
165 // This uses seekDistance so that only wanted data is checked.
166 for (int i = seekDistance-1; i >= 0; --i) {
167 // Check for New line Character, or a non carraige-return char
168 if (bytes[i] == '\n') {
169 // Seek to the location of this character and exit this loop.
170 file.seek(fp+i);
171 gotNewLine = true;
172 break;
173 } else if (bytes[i] != '\r') {
174 // Add to the result, the loop will continue going.
175 line.add(0, bytes[i]);
176 }
177 }
178
179 // We have now processed the data we read (Either added it all to the
180 // buffer, or found a newline character.)
181
182 if (fp == 0 && !gotNewLine) {
183 // This part of the loop started from the start of the file, but didn't
184 // find a new line anywhere. no more loops are posssible, so Treat
185 // this as "got new line"
186 gotNewLine = true;
187 file.seek(0);
188 }
189
190 // Do we need to continue?
191 if (gotNewLine) {
192 // We have found a new line somewhere, thus we don't need
193 // to read any more bytes, so exit the while loop!
194 keepLooping = false;
195 } else {
196 // We have not found a new line anywhere,
197 // Seek to the pre-read position, and repeat.
198 file.seek(fp);
199 }
200
201 }
202
203 // Return the data obtained.
204 byte[] result = new byte[line.size()];
205 for (int i = 0; i < line.size(); ++i) { result[i] = line.get(i); }
206 return new String(result, Charset.forName("UTF-8"));
207 }
208
209 /**
210 * Try and get x number of lines.
211 * If the file is closed, an empty stack will be returned.
212 *
213 * @param numLines Number of lines to try and get.
214 * @return The requested lines
215 */
216 public Stack<String> getLines(final int numLines) {
/*
P/P * Method: Stack getLines(int)
*
* Preconditions:
* (soft) this.file != null
* (soft) init'ed(this.seekLength)
*
* Postconditions:
* return_value == &new Stack(getLines#1)
* new Stack(getLines#1) num objects == 1
*/
217 final Stack<String> result = new Stack<String>();
218 for (int i = 0; i < numLines; ++i) {
219 try {
220 result.push(getNextLine());
221 } catch (IOException e) {
222 break;
223 }
224 }
225 return result;
226 }
227
228 /**
229 * Try and get x number of lines and return a \n delimited String.
230 * If the file is closed, an empty string will be returned.
231 *
232 * @param numLines Number of lines to try and get.
233 * @return The requested lines
234 */
235 public String getLinesAsString(final int numLines) {
/*
P/P * Method: String getLinesAsString(int)
*
* Preconditions:
* (soft) this.file != null
* (soft) init'ed(this.seekLength)
*
* Postconditions:
* java.lang.StringBuilder:toString(...)._tainted == 0
* return_value == &java.lang.StringBuilder:toString(...)
*
* Test Vectors:
* java.lang.StringBuilder:charAt(...)@245: {0..9, 11..216-1}, {10}
*/
236 final StringBuilder result = new StringBuilder();
237 for (int i = 0; i < numLines; ++i) {
238 try {
239 result.insert(0, "\n");
240 result.insert(0, getNextLine());
241 } catch (IOException e) {
242 break;
243 }
244 }
245 if (result.charAt(0) == '\n') {
246 result.deleteCharAt(0);
247 }
248 return result.toString();
249 }
250 }
SofCheck Inspector Build Version : 2.17854
| ReverseFileReader.java |
2009-Jun-25 01:54:24 |
| ReverseFileReader.class |
2009-Sep-02 17:04:15 |