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1: /* RandomAccessFile.java -- Class supporting random file I/O 2: Copyright (C) 1998, 1999, 2001, 2002, 2003, 2004, 2005 Free Software Foundation, Inc. 3: 4: This file is part of GNU Classpath. 5: 6: GNU Classpath is free software; you can redistribute it and/or modify 7: it under the terms of the GNU General Public License as published by 8: the Free Software Foundation; either version 2, or (at your option) 9: any later version. 10: 11: GNU Classpath is distributed in the hope that it will be useful, but 12: WITHOUT ANY WARRANTY; without even the implied warranty of 13: MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 14: General Public License for more details. 15: 16: You should have received a copy of the GNU General Public License 17: along with GNU Classpath; see the file COPYING. If not, write to the 18: Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 19: 02110-1301 USA. 20: 21: Linking this library statically or dynamically with other modules is 22: making a combined work based on this library. Thus, the terms and 23: conditions of the GNU General Public License cover the whole 24: combination. 25: 26: As a special exception, the copyright holders of this library give you 27: permission to link this library with independent modules to produce an 28: executable, regardless of the license terms of these independent 29: modules, and to copy and distribute the resulting executable under 30: terms of your choice, provided that you also meet, for each linked 31: independent module, the terms and conditions of the license of that 32: module. An independent module is a module which is not derived from 33: or based on this library. If you modify this library, you may extend 34: this exception to your version of the library, but you are not 35: obligated to do so. If you do not wish to do so, delete this 36: exception statement from your version. */ 37: 38: 39: package java.io; 40: 41: import gnu.java.nio.FileChannelImpl; 42: 43: import java.nio.channels.FileChannel; 44: 45: /* Written using "Java Class Libraries", 2nd edition, ISBN 0-201-31002-3 46: * "The Java Language Specification", ISBN 0-201-63451-1 47: * Status: Believe complete and correct to 1.1. 48: */ 49: 50: /** 51: * This class allows reading and writing of files at random locations. 52: * Most Java I/O classes are either pure sequential input or output. This 53: * class fulfills the need to be able to read the bytes of a file in an 54: * arbitrary order. In addition, this class implements the 55: * <code>DataInput</code> and <code>DataOutput</code> interfaces to allow 56: * the reading and writing of Java primitives. 57: * 58: * @author Aaron M. Renn (arenn@urbanophile.com) 59: * @author Tom Tromey (tromey@cygnus.com) 60: */ 61: public class RandomAccessFile implements DataOutput, DataInput, Closeable 62: { 63: 64: // The underlying file. 65: private FileChannelImpl ch; 66: private FileDescriptor fd; 67: // The corresponding input and output streams. 68: private DataOutputStream out; 69: private DataInputStream in; 70: 71: 72: /** 73: * This method initializes a new instance of <code>RandomAccessFile</code> 74: * to read from the specified <code>File</code> object with the specified 75: * access mode. The access mode is either "r" for read only access or "rw" 76: * for read-write access. 77: * <p> 78: * Note that a <code>SecurityManager</code> check is made prior to 79: * opening the file to determine whether or not this file is allowed to 80: * be read or written. 81: * 82: * @param file The <code>File</code> object to read and/or write. 83: * @param mode "r" for read only or "rw" for read-write access to the file 84: * 85: * @exception IllegalArgumentException If <code>mode</code> has an 86: * illegal value 87: * @exception SecurityException If the requested access to the file 88: * is not allowed 89: * @exception FileNotFoundException If the file is a directory, or 90: * any other error occurs 91: */ 92: public RandomAccessFile (File file, String mode) 93: throws FileNotFoundException 94: { 95: int fdmode; 96: if (mode.equals("r")) 97: fdmode = FileChannelImpl.READ; 98: else if (mode.equals("rw")) 99: fdmode = FileChannelImpl.READ | FileChannelImpl.WRITE; 100: else if (mode.equals("rws")) 101: { 102: fdmode = (FileChannelImpl.READ | FileChannelImpl.WRITE 103: | FileChannelImpl.SYNC); 104: } 105: else if (mode.equals("rwd")) 106: { 107: fdmode = (FileChannelImpl.READ | FileChannelImpl.WRITE 108: | FileChannelImpl.DSYNC); 109: } 110: else 111: throw new IllegalArgumentException ("invalid mode: " + mode); 112: 113: final String fileName = file.getPath(); 114: 115: // The obligatory SecurityManager stuff 116: SecurityManager s = System.getSecurityManager(); 117: if (s != null) 118: { 119: s.checkRead(fileName); 120: 121: if ((fdmode & FileChannelImpl.WRITE) != 0) 122: s.checkWrite(fileName); 123: } 124: 125: try 126: { 127: ch = FileChannelImpl.create(file, fdmode); 128: } 129: catch (FileNotFoundException fnfe) 130: { 131: throw fnfe; 132: } 133: catch (IOException ioe) 134: { 135: FileNotFoundException fnfe = new FileNotFoundException(file.getPath()); 136: fnfe.initCause(ioe); 137: throw fnfe; 138: } 139: fd = new FileDescriptor(ch); 140: if ((fdmode & FileChannelImpl.WRITE) != 0) 141: out = new DataOutputStream (new FileOutputStream (fd)); 142: else 143: out = null; 144: in = new DataInputStream (new FileInputStream (fd)); 145: } 146: 147: /** 148: * This method initializes a new instance of <code>RandomAccessFile</code> 149: * to read from the specified file name with the specified access mode. 150: * The access mode is either "r" for read only access, "rw" for read 151: * write access, "rws" for synchronized read/write access of both 152: * content and metadata, or "rwd" for read/write access 153: * where only content is required to be synchronous. 154: * <p> 155: * Note that a <code>SecurityManager</code> check is made prior to 156: * opening the file to determine whether or not this file is allowed to 157: * be read or written. 158: * 159: * @param fileName The name of the file to read and/or write 160: * @param mode "r", "rw", "rws", or "rwd" 161: * 162: * @exception IllegalArgumentException If <code>mode</code> has an 163: * illegal value 164: * @exception SecurityException If the requested access to the file 165: * is not allowed 166: * @exception FileNotFoundException If the file is a directory or 167: * any other error occurs 168: */ 169: public RandomAccessFile (String fileName, String mode) 170: throws FileNotFoundException 171: { 172: this (new File(fileName), mode); 173: } 174: 175: /** 176: * This method closes the file and frees up all file related system 177: * resources. Since most operating systems put a limit on how many files 178: * may be opened at any given time, it is a good idea to close all files 179: * when no longer needed to avoid hitting this limit 180: */ 181: public void close () throws IOException 182: { 183: ch.close(); 184: } 185: 186: /** 187: * This method returns a <code>FileDescriptor</code> object that 188: * represents the native file handle for this file. 189: * 190: * @return The <code>FileDescriptor</code> object for this file 191: * 192: * @exception IOException If an error occurs 193: */ 194: public final FileDescriptor getFD () throws IOException 195: { 196: synchronized (this) 197: { 198: if (fd == null) 199: fd = new FileDescriptor (ch); 200: return fd; 201: } 202: } 203: 204: /** 205: * This method returns the current offset in the file at which the next 206: * read or write will occur 207: * 208: * @return The current file position 209: * 210: * @exception IOException If an error occurs 211: */ 212: public long getFilePointer () throws IOException 213: { 214: return ch.position(); 215: } 216: 217: /** 218: * This method sets the length of the file to the specified length. 219: * If the currently length of the file is longer than the specified 220: * length, then the file is truncated to the specified length (the 221: * file position is set to the end of file in this case). If the 222: * current length of the file is shorter than the specified length, 223: * the file is extended with bytes of an undefined value (the file 224: * position is unchanged in this case). 225: * <p> 226: * The file must be open for write access for this operation to succeed. 227: * 228: * @param newLen The new length of the file 229: * 230: * @exception IOException If an error occurs 231: */ 232: public void setLength (long newLen) throws IOException 233: { 234: // FIXME: Extending a file should probably be done by one method call. 235: 236: // FileChannel.truncate() can only shrink a file. 237: // To expand it we need to seek forward and write at least one byte. 238: if (newLen < length()) 239: ch.truncate (newLen); 240: else if (newLen > length()) 241: { 242: long pos = getFilePointer(); 243: seek(newLen - 1); 244: write(0); 245: seek(pos); 246: } 247: } 248: 249: /** 250: * This method returns the length of the file in bytes 251: * 252: * @return The length of the file 253: * 254: * @exception IOException If an error occurs 255: */ 256: public long length () throws IOException 257: { 258: return ch.size(); 259: } 260: 261: /** 262: * This method reads a single byte of data from the file and returns it 263: * as an integer. 264: * 265: * @return The byte read as an int, or -1 if the end of the file was reached. 266: * 267: * @exception IOException If an error occurs 268: */ 269: public int read () throws IOException 270: { 271: return in.read(); 272: } 273: 274: /** 275: * This method reads bytes from the file into the specified array. The 276: * bytes are stored starting at the beginning of the array and up to 277: * <code>buf.length</code> bytes can be read. 278: * 279: * @param buffer The buffer to read bytes from the file into 280: * 281: * @return The actual number of bytes read or -1 if end of file 282: * 283: * @exception IOException If an error occurs 284: */ 285: public int read (byte[] buffer) throws IOException 286: { 287: return in.read (buffer); 288: } 289: 290: /** 291: * This methods reads up to <code>len</code> bytes from the file into the 292: * specified array starting at position <code>offset</code> into the array. 293: * 294: * @param buffer The array to read the bytes into 295: * @param offset The index into the array to start storing bytes 296: * @param len The requested number of bytes to read 297: * 298: * @return The actual number of bytes read, or -1 if end of file 299: * 300: * @exception IOException If an error occurs 301: */ 302: public int read (byte[] buffer, int offset, int len) throws IOException 303: { 304: return in.read (buffer, offset, len); 305: } 306: 307: /** 308: * This method reads a Java boolean value from an input stream. It does 309: * so by reading a single byte of data. If that byte is zero, then the 310: * value returned is <code>false</code> If the byte is non-zero, then 311: * the value returned is <code>true</code> 312: * <p> 313: * This method can read a <code>boolean</code> written by an object 314: * implementing the 315: * <code>writeBoolean()</code> method in the <code>DataOutput</code> 316: * interface. 317: * 318: * @return The <code>boolean</code> value read 319: * 320: * @exception EOFException If end of file is reached before reading the 321: * boolean 322: * @exception IOException If any other error occurs 323: */ 324: public final boolean readBoolean () throws IOException 325: { 326: return in.readBoolean (); 327: } 328: 329: /** 330: * This method reads a Java byte value from an input stream. The value 331: * is in the range of -128 to 127. 332: * <p> 333: * This method can read a <code>byte</code> written by an object 334: * implementing the 335: * <code>writeByte()</code> method in the <code>DataOutput</code> interface. 336: * 337: * @return The <code>byte</code> value read 338: * 339: * @exception EOFException If end of file is reached before reading the byte 340: * @exception IOException If any other error occurs 341: * 342: * @see DataOutput 343: */ 344: public final byte readByte () throws IOException 345: { 346: return in.readByte (); 347: } 348: 349: /** 350: * This method reads a Java <code>char</code> value from an input stream. 351: * It operates by reading two bytes from the stream and converting them to 352: * a single 16-bit Java <code>char</code> The two bytes are stored most 353: * significant byte first (i.e., "big endian") regardless of the native 354: * host byte ordering. 355: * <p> 356: * As an example, if <code>byte1</code> and <code>byte2</code> represent 357: * the first 358: * and second byte read from the stream respectively, they will be 359: * transformed to a <code>char</code> in the following manner: 360: * <p> 361: * <code>(char)(((byte1 & 0xFF) << 8) | (byte2 & 0xFF)</code> 362: * <p> 363: * This method can read a <code>char</code> written by an object 364: * implementing the 365: * <code>writeChar()</code> method in the <code>DataOutput</code> interface. 366: * 367: * @return The <code>char</code> value read 368: * 369: * @exception EOFException If end of file is reached before reading the char 370: * @exception IOException If any other error occurs 371: * 372: * @see DataOutput 373: */ 374: public final char readChar () throws IOException 375: { 376: return in.readChar(); 377: } 378: 379: /** 380: * This method reads a Java double value from an input stream. It operates 381: * by first reading a <code>logn</code> value from the stream by calling the 382: * <code>readLong()</code> method in this interface, then 383: * converts that <code>long</code> 384: * to a <code>double</code> using the <code>longBitsToDouble</code> 385: * method in the class <code>java.lang.Double</code> 386: * <p> 387: * This method can read a <code>double</code> written by an object 388: * implementing the 389: * <code>writeDouble()</code> method in the <code>DataOutput</code> 390: * interface. 391: * 392: * @return The <code>double</code> value read 393: * 394: * @exception EOFException If end of file is reached before reading 395: * the double 396: * @exception IOException If any other error occurs 397: * 398: * @see java.lang.Double 399: * @see DataOutput 400: */ 401: public final double readDouble () throws IOException 402: { 403: return in.readDouble (); 404: } 405: 406: /** 407: * This method reads a Java float value from an input stream. It operates 408: * by first reading an <code>int</code> value from the stream by calling the 409: * <code>readInt()</code> method in this interface, then converts 410: * that <code>int</code> 411: * to a <code>float</code> using the <code>intBitsToFloat</code> method in 412: * the class <code>java.lang.Float</code> 413: * <p> 414: * This method can read a <code>float</code> written by an object 415: * implementing the 416: * <code>writeFloat()</code> method in the <code>DataOutput</code> interface. 417: * 418: * @return The <code>float</code> value read 419: * 420: * @exception EOFException If end of file is reached before reading the float 421: * @exception IOException If any other error occurs 422: * 423: * @see java.lang.Float 424: * @see DataOutput 425: */ 426: public final float readFloat () throws IOException 427: { 428: return in.readFloat(); 429: } 430: 431: /** 432: * This method reads raw bytes into the passed array until the array is 433: * full. Note that this method blocks until the data is available and 434: * throws an exception if there is not enough data left in the stream to 435: * fill the buffer 436: * 437: * @param buffer The buffer into which to read the data 438: * 439: * @exception EOFException If end of file is reached before filling the 440: * buffer 441: * @exception IOException If any other error occurs 442: */ 443: public final void readFully (byte[] buffer) throws IOException 444: { 445: in.readFully(buffer); 446: } 447: 448: /** 449: * This method reads raw bytes into the passed array <code>buf</code> 450: * starting 451: * <code>offset</code> bytes into the buffer. The number of bytes read 452: * will be 453: * exactly <code>len</code> Note that this method blocks until the data is 454: * available and throws an exception if there is not enough data left in 455: * the stream to read <code>len</code> bytes. 456: * 457: * @param buffer The buffer into which to read the data 458: * @param offset The offset into the buffer to start storing data 459: * @param count The number of bytes to read into the buffer 460: * 461: * @exception EOFException If end of file is reached before filling 462: * the buffer 463: * @exception IOException If any other error occurs 464: */ 465: public final void readFully (byte[] buffer, int offset, int count) 466: throws IOException 467: { 468: in.readFully (buffer, offset, count); 469: } 470: 471: /** 472: * This method reads a Java <code>int</code> value from an input stream 473: * It operates by reading four bytes from the stream and converting them to 474: * a single Java <code>int</code> The bytes are stored most 475: * significant byte first (i.e., "big endian") regardless of the native 476: * host byte ordering. 477: * <p> 478: * As an example, if <code>byte1</code> through <code>byte4</code> 479: * represent the first 480: * four bytes read from the stream, they will be 481: * transformed to an <code>int</code> in the following manner: 482: * <p> 483: * <code>(int)(((byte1 & 0xFF) << 24) + ((byte2 & 0xFF) << 16) + 484: * ((byte3 & 0xFF) << 8) + (byte4 & 0xFF)))</code> 485: * <p> 486: * The value returned is in the range of 0 to 65535. 487: * <p> 488: * This method can read an <code>int</code> written by an object 489: * implementing the 490: * <code>writeInt()</code> method in the <code>DataOutput</code> interface. 491: * 492: * @return The <code>int</code> value read 493: * 494: * @exception EOFException If end of file is reached before reading the int 495: * @exception IOException If any other error occurs 496: * 497: * @see DataOutput 498: */ 499: public final int readInt () throws IOException 500: { 501: return in.readInt(); 502: } 503: 504: /** 505: * This method reads the next line of text data from an input stream. 506: * It operates by reading bytes and converting those bytes to 507: * <code>char</code> 508: * values by treating the byte read as the low eight bits of the 509: * <code>char</code> 510: * and using <code>0</code> as the high eight bits. Because of this, it does 511: * not support the full 16-bit Unicode character set. 512: * <p> 513: * The reading of bytes ends when either the end of file or a line terminator 514: * is encountered. The bytes read are then returned as a <code>String</code> 515: * A line terminator is a byte sequence consisting of either 516: * <code>\r</code> <code>\n</code> or <code>\r\n</code> These 517: * termination charaters are 518: * discarded and are not returned as part of the string. 519: * <p> 520: * This method can read data that was written by an object implementing the 521: * <code>writeLine()</code> method in <code>DataOutput</code> 522: * 523: * @return The line read as a <code>String</code> 524: * 525: * @exception IOException If an error occurs 526: * 527: * @see DataOutput 528: */ 529: public final String readLine () throws IOException 530: { 531: return in.readLine (); 532: } 533: 534: /** 535: * This method reads a Java long value from an input stream 536: * It operates by reading eight bytes from the stream and converting them to 537: * a single Java <code>long</code> The bytes are stored most 538: * significant byte first (i.e., "big endian") regardless of the native 539: * host byte ordering. 540: * <p> 541: * As an example, if <code>byte1</code> through <code>byte8</code> 542: * represent the first 543: * eight bytes read from the stream, they will be 544: * transformed to an <code>long</code> in the following manner: 545: * <p> 546: * <code> 547: * (long)((((long)byte1 & 0xFF) << 56) + (((long)byte2 & 0xFF) << 48) + 548: * (((long)byte3 & 0xFF) << 40) + (((long)byte4 & 0xFF) << 32) + 549: * (((long)byte5 & 0xFF) << 24) + (((long)byte6 & 0xFF) << 16) + 550: * (((long)byte7 & 0xFF) << 8) + ((long)byte9 & 0xFF)))</code> 551: * <p> 552: * The value returned is in the range of 0 to 65535. 553: * <p> 554: * This method can read an <code>long</code> written by an object 555: * implementing the 556: * <code>writeLong()</code> method in the <code>DataOutput</code> interface. 557: * 558: * @return The <code>long</code> value read 559: * 560: * @exception EOFException If end of file is reached before reading the long 561: * @exception IOException If any other error occurs 562: * 563: * @see DataOutput 564: */ 565: public final long readLong () throws IOException 566: { 567: return in.readLong(); 568: } 569: 570: /** 571: * This method reads a signed 16-bit value into a Java in from the stream. 572: * It operates by reading two bytes from the stream and converting them to 573: * a single 16-bit Java <code>short</code> The two bytes are stored most 574: * significant byte first (i.e., "big endian") regardless of the native 575: * host byte ordering. 576: * <p> 577: * As an example, if <code>byte1</code> and <code>byte2</code> 578: * represent the first 579: * and second byte read from the stream respectively, they will be 580: * transformed to a <code>short</code> in the following manner: 581: * <p> 582: * <code>(short)(((byte1 & 0xFF) << 8) | (byte2 & 0xFF)</code> 583: * <p> 584: * The value returned is in the range of -32768 to 32767. 585: * <p> 586: * This method can read a <code>short</code> written by an object 587: * implementing the 588: * <code>writeShort()</code> method in the <code>DataOutput</code> interface. 589: * 590: * @return The <code>short</code> value read 591: * 592: * @exception EOFException If end of file is reached before reading the value 593: * @exception IOException If any other error occurs 594: * 595: * @see DataOutput 596: */ 597: public final short readShort () throws IOException 598: { 599: return in.readShort(); 600: } 601: 602: /** 603: * This method reads 8 unsigned bits into a Java <code>int</code> value 604: * from the 605: * stream. The value returned is in the range of 0 to 255. 606: * <p> 607: * This method can read an unsigned byte written by an object implementing 608: * the <code>writeUnsignedByte()</code> method in the 609: * <code>DataOutput</code> interface. 610: * 611: * @return The unsigned bytes value read as a Java <code>int</code> 612: * 613: * @exception EOFException If end of file is reached before reading the value 614: * @exception IOException If any other error occurs 615: * 616: * @see DataOutput 617: */ 618: public final int readUnsignedByte () throws IOException 619: { 620: return in.readUnsignedByte(); 621: } 622: 623: /** 624: * This method reads 16 unsigned bits into a Java int value from the stream. 625: * It operates by reading two bytes from the stream and converting them to 626: * a single Java <code>int</code> The two bytes are stored most 627: * significant byte first (i.e., "big endian") regardless of the native 628: * host byte ordering. 629: * <p> 630: * As an example, if <code>byte1</code> and <code>byte2</code> 631: * represent the first 632: * and second byte read from the stream respectively, they will be 633: * transformed to an <code>int</code> in the following manner: 634: * <p> 635: * <code>(int)(((byte1 & 0xFF) << 8) + (byte2 & 0xFF))</code> 636: * <p> 637: * The value returned is in the range of 0 to 65535. 638: * <p> 639: * This method can read an unsigned short written by an object implementing 640: * the <code>writeUnsignedShort()</code> method in the 641: * <code>DataOutput</code> interface. 642: * 643: * @return The unsigned short value read as a Java <code>int</code> 644: * 645: * @exception EOFException If end of file is reached before reading the value 646: * @exception IOException If any other error occurs 647: */ 648: public final int readUnsignedShort () throws IOException 649: { 650: return in.readUnsignedShort(); 651: } 652: 653: /** 654: * This method reads a <code>String</code> from an input stream that 655: * is encoded in 656: * a modified UTF-8 format. This format has a leading two byte sequence 657: * that contains the remaining number of bytes to read. This two byte 658: * sequence is read using the <code>readUnsignedShort()</code> method of this 659: * interface. 660: * <p> 661: * After the number of remaining bytes have been determined, these bytes 662: * are read an transformed into <code>char</code> values. 663: * These <code>char</code> values 664: * are encoded in the stream using either a one, two, or three byte format. 665: * The particular format in use can be determined by examining the first 666: * byte read. 667: * <p> 668: * If the first byte has a high order bit of 0 then 669: * that character consists on only one byte. This character value consists 670: * of seven bits that are at positions 0 through 6 of the byte. As an 671: * example, if <code>byte1</code> is the byte read from the stream, it would 672: * be converted to a <code>char</code> like so: 673: * <p> 674: * <code>(char)byte1</code> 675: * <p> 676: * If the first byte has <code>110</code> as its high order bits, then the 677: * character consists of two bytes. The bits that make up the character 678: * value are in positions 0 through 4 of the first byte and bit positions 679: * 0 through 5 of the second byte. (The second byte should have 680: * 10 as its high order bits). These values are in most significant 681: * byte first (i.e., "big endian") order. 682: * <p> 683: * As an example, if <code>byte1</code> and <code>byte2</code> 684: * are the first two bytes 685: * read respectively, and the high order bits of them match the patterns 686: * which indicate a two byte character encoding, then they would be 687: * converted to a Java <code>char</code> like so: 688: * <p> 689: * <code>(char)(((byte1 & 0x1F) << 6) | (byte2 & 0x3F))</code> 690: * <p> 691: * If the first byte has a <code>1110</code> as its high order bits, then the 692: * character consists of three bytes. The bits that make up the character 693: * value are in positions 0 through 3 of the first byte and bit positions 694: * 0 through 5 of the other two bytes. (The second and third bytes should 695: * have <code>10</code> as their high order bits). These values are in most 696: * significant byte first (i.e., "big endian") order. 697: * <p> 698: * As an example, if <code>byte1</code> <code>byte2</code> 699: * and <code>byte3</code> are the 700: * three bytes read, and the high order bits of them match the patterns 701: * which indicate a three byte character encoding, then they would be 702: * converted to a Java <code>char</code> like so: 703: * <p> 704: * <code>(char)(((byte1 & 0x0F) << 12) | ((byte2 & 0x3F) << 6) | 705: * (byte3 & 0x3F))</code> 706: * <p> 707: * Note that all characters are encoded in the method that requires the 708: * fewest number of bytes with the exception of the character with the 709: * value of <code>\u0000</code> which is encoded as two bytes. This is 710: * a modification of the UTF standard used to prevent C language style 711: * <code>NUL</code> values from appearing in the byte stream. 712: * <p> 713: * This method can read data that was written by an object implementing the 714: * <code>writeUTF()</code> method in <code>DataOutput</code> 715: * 716: * @return The <code>String</code> read 717: * 718: * @exception EOFException If end of file is reached before reading the 719: * String 720: * @exception UTFDataFormatException If the data is not in UTF-8 format 721: * @exception IOException If any other error occurs 722: * 723: * @see DataOutput 724: */ 725: public final String readUTF () throws IOException 726: { 727: return in.readUTF(); 728: } 729: 730: /** 731: * This method sets the current file position to the specified offset 732: * from the beginning of the file. Note that some operating systems will 733: * allow the file pointer to be set past the current end of the file. 734: * 735: * @param pos The offset from the beginning of the file at which to set 736: * the file pointer 737: * 738: * @exception IOException If an error occurs 739: */ 740: public void seek (long pos) throws IOException 741: { 742: ch.position(pos); 743: } 744: 745: /** 746: * This method attempts to skip and discard the specified number of bytes 747: * in the input stream. It may actually skip fewer bytes than requested. 748: * The actual number of bytes skipped is returned. This method will not 749: * skip any bytes if passed a negative number of bytes to skip. 750: * 751: * @param numBytes The requested number of bytes to skip. 752: * 753: * @return The number of bytes actually skipped. 754: * 755: * @exception IOException If an error occurs. 756: */ 757: public int skipBytes (int numBytes) throws IOException 758: { 759: if (numBytes < 0) 760: throw new IllegalArgumentException ("Can't skip negative bytes: " + 761: numBytes); 762: 763: if (numBytes == 0) 764: return 0; 765: 766: long oldPos = ch.position(); 767: long newPos = oldPos + numBytes; 768: long size = ch.size(); 769: if (newPos > size) 770: newPos = size; 771: ch.position(newPos); 772: return (int) (ch.position() - oldPos); 773: } 774: 775: /** 776: * This method writes a single byte of data to the file. The file must 777: * be open for read-write in order for this operation to succeed. 778: * 779: * @param oneByte The byte of data to write, passed as an int. 780: * 781: * @exception IOException If an error occurs 782: */ 783: public void write (int oneByte) throws IOException 784: { 785: if (out == null) 786: throw new IOException("Bad file descriptor"); 787: 788: out.write(oneByte); 789: } 790: 791: /** 792: * This method writes all the bytes in the specified array to the file. 793: * The file must be open read-write in order for this operation to succeed. 794: * 795: * @param buffer The array of bytes to write to the file 796: */ 797: public void write (byte[] buffer) throws IOException 798: { 799: if (out == null) 800: throw new IOException("Bad file descriptor"); 801: 802: out.write(buffer); 803: } 804: 805: /** 806: * This method writes <code>len</code> bytes to the file from the specified 807: * array starting at index <code>offset</code> into the array. 808: * 809: * @param buffer The array of bytes to write to the file 810: * @param offset The index into the array to start writing file 811: * @param len The number of bytes to write 812: * 813: * @exception IOException If an error occurs 814: */ 815: public void write (byte[] buffer, int offset, int len) throws IOException 816: { 817: if (out == null) 818: throw new IOException("Bad file descriptor"); 819: 820: out.write (buffer, offset, len); 821: } 822: 823: /** 824: * This method writes a Java <code>boolean</code> to the underlying output 825: * stream. For a value of <code>true</code>, 1 is written to the stream. 826: * For a value of <code>false</code>, 0 is written. 827: * 828: * @param val The <code>boolean</code> value to write to the stream 829: * 830: * @exception IOException If an error occurs 831: */ 832: public final void writeBoolean (boolean val) throws IOException 833: { 834: if (out == null) 835: throw new IOException("Bad file descriptor"); 836: 837: out.writeBoolean(val); 838: } 839: 840: /** 841: * This method writes a Java <code>byte</code> value to the underlying 842: * output stream. 843: * 844: * @param val The <code>byte</code> to write to the stream, passed 845: * as an <code>int</code>. 846: * 847: * @exception IOException If an error occurs 848: */ 849: public final void writeByte (int val) throws IOException 850: { 851: if (out == null) 852: throw new IOException("Bad file descriptor"); 853: 854: out.writeByte(val); 855: } 856: 857: /** 858: * This method writes a Java <code>short</code> to the stream, high byte 859: * first. This method requires two bytes to encode the value. 860: * 861: * @param val The <code>short</code> value to write to the stream, 862: * passed as an <code>int</code>. 863: * 864: * @exception IOException If an error occurs 865: */ 866: public final void writeShort (int val) throws IOException 867: { 868: if (out == null) 869: throw new IOException("Bad file descriptor"); 870: 871: out.writeShort(val); 872: } 873: 874: /** 875: * This method writes a single <code>char</code> value to the stream, 876: * high byte first. 877: * 878: * @param val The <code>char</code> value to write, passed as 879: * an <code>int</code>. 880: * 881: * @exception IOException If an error occurs 882: */ 883: public final void writeChar (int val) throws IOException 884: { 885: if (out == null) 886: throw new IOException("Bad file descriptor"); 887: 888: out.writeChar(val); 889: } 890: 891: /** 892: * This method writes a Java <code>int</code> to the stream, high bytes 893: * first. This method requires four bytes to encode the value. 894: * 895: * @param val The <code>int</code> value to write to the stream. 896: * 897: * @exception IOException If an error occurs 898: */ 899: public final void writeInt (int val) throws IOException 900: { 901: if (out == null) 902: throw new IOException("Bad file descriptor"); 903: 904: out.writeInt(val); 905: } 906: 907: /** 908: * This method writes a Java <code>long</code> to the stream, high bytes 909: * first. This method requires eight bytes to encode the value. 910: * 911: * @param val The <code>long</code> value to write to the stream. 912: * 913: * @exception IOException If an error occurs 914: */ 915: public final void writeLong (long val) throws IOException 916: { 917: if (out == null) 918: throw new IOException("Bad file descriptor"); 919: 920: out.writeLong(val); 921: } 922: 923: /** 924: * This method writes a Java <code>float</code> value to the stream. This 925: * value is written by first calling the method 926: * <code>Float.floatToIntBits</code> 927: * to retrieve an <code>int</code> representing the floating point number, 928: * then writing this <code>int</code> value to the stream exactly the same 929: * as the <code>writeInt()</code> method does. 930: * 931: * @param val The floating point number to write to the stream. 932: * 933: * @exception IOException If an error occurs 934: * 935: * @see #writeInt(int) 936: */ 937: public final void writeFloat (float val) throws IOException 938: { 939: if (out == null) 940: throw new IOException("Bad file descriptor"); 941: 942: out.writeFloat(val); 943: } 944: 945: /** 946: * This method writes a Java <code>double</code> value to the stream. This 947: * value is written by first calling the method 948: * <code>Double.doubleToLongBits</code> 949: * to retrieve an <code>long</code> representing the floating point number, 950: * then writing this <code>long</code> value to the stream exactly the same 951: * as the <code>writeLong()</code> method does. 952: * 953: * @param val The double precision floating point number to write to the 954: * stream. 955: * 956: * @exception IOException If an error occurs 957: * 958: * @see #writeLong(long) 959: */ 960: public final void writeDouble (double val) throws IOException 961: { 962: if (out == null) 963: throw new IOException("Bad file descriptor"); 964: 965: out.writeDouble(val); 966: } 967: 968: /** 969: * This method writes all the bytes in a <code>String</code> out to the 970: * stream. One byte is written for each character in the <code>String</code>. 971: * The high eight bits of each character are discarded. 972: * 973: * @param val The <code>String</code> to write to the stream 974: * 975: * @exception IOException If an error occurs 976: */ 977: public final void writeBytes (String val) throws IOException 978: { 979: if (out == null) 980: throw new IOException("Bad file descriptor"); 981: 982: out.writeBytes(val); 983: } 984: 985: /** 986: * This method writes all the characters in a <code>String</code> to the 987: * stream. There will be two bytes for each character value. The high 988: * byte of the character will be written first. 989: * 990: * @param val The <code>String</code> to write to the stream. 991: * 992: * @exception IOException If an error occurs 993: */ 994: public final void writeChars (String val) throws IOException 995: { 996: if (out == null) 997: throw new IOException("Bad file descriptor"); 998: 999: out.writeChars(val); 1000: } 1001: 1002: /** 1003: * This method writes a Java <code>String</code> to the stream in a modified 1004: * UTF-8 format. First, two bytes are written to the stream indicating the 1005: * number of bytes to follow. Note that this is the number of bytes in the 1006: * encoded <code>String</code> not the <code>String</code> length. Next 1007: * come the encoded characters. Each character in the <code>String</code> 1008: * is encoded as either one, two or three bytes. For characters in the 1009: * range of <code>\u0001</code> to <code>\u007F</code>, 1010: * one byte is used. The character 1011: * value goes into bits 0-7 and bit eight is 0. For characters in the range 1012: * of <code>\u0080</code> to <code>\u007FF</code>, two 1013: * bytes are used. Bits 1014: * 6-10 of the character value are encoded bits 0-4 of the first byte, with 1015: * the high bytes having a value of "110". Bits 0-5 of the character value 1016: * are stored in bits 0-5 of the second byte, with the high bits set to 1017: * "10". This type of encoding is also done for the null character 1018: * <code>\u0000</code>. This eliminates any C style NUL character values 1019: * in the output. All remaining characters are stored as three bytes. 1020: * Bits 12-15 of the character value are stored in bits 0-3 of the first 1021: * byte. The high bits of the first bytes are set to "1110". Bits 6-11 1022: * of the character value are stored in bits 0-5 of the second byte. The 1023: * high bits of the second byte are set to "10". And bits 0-5 of the 1024: * character value are stored in bits 0-5 of byte three, with the high bits 1025: * of that byte set to "10". 1026: * 1027: * @param val The <code>String</code> to write to the output in UTF format 1028: * 1029: * @exception IOException If an error occurs 1030: */ 1031: public final void writeUTF (String val) throws IOException 1032: { 1033: if (out == null) 1034: throw new IOException("Bad file descriptor"); 1035: 1036: out.writeUTF(val); 1037: } 1038: 1039: /** 1040: * This method creates a java.nio.channels.FileChannel. 1041: * Nio does not allow one to create a file channel directly. 1042: * A file channel must be created by first creating an instance of 1043: * Input/Output/RandomAccessFile and invoking the getChannel() method on it. 1044: */ 1045: public final synchronized FileChannel getChannel () 1046: { 1047: return ch; 1048: } 1049: }
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