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Chapter 4 Java I/O

Chapter 4 Java I/O. x.zhang@seu.edu.cn. Content. Java I/O Introduction File and Directory Byte-stream and Character-stream Bridge between b-s and c-s Random Access File Standard I/O System.in System.out java.nio Pilot. Java I/O Introduction. I/O Target File Console

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Chapter 4 Java I/O

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  1. Chapter 4 JavaI/O x.zhang@seu.edu.cn

  2. Content • Java I/OIntroduction • File and Directory • Byte-stream and Character-stream • Bridge between b-s and c-s • Random Access File • Standard I/O • System.in • System.out • java.nioPilot

  3. Java I/OIntroduction • I/OTarget • File • Console • Network Connection • I/OManner • Text-based (char) / Data-based(byte) • Sequential / Random Access CoSE Java 2009

  4. Java I/OIntroduction • java.io Package • general classes • filtered / buffered / piped streams • data streams • File • object serialization CoSE Java 2009

  5. File and Directory • java.io.File - “A Path in a file system” • File • Directory • FileConstruction CoSE Java 2009

  6. File and Directory • Example: Directory Lister • List *.log from“c:\Windows”in descending order • Think: How to code it in C++ CoSE Java 2009

  7. File and Directory • Design of Classes CoSE Java 2009

  8. CoSE Java 2009

  9. How to write DirFilter?

  10. A E C B F D Stream • The Notion of Stream • A sequence of flowing byte / char • A channel sending message in FIFO In Out

  11. Stream • Classification of Stream • Byte Stream • Byte as the unit • Used to read and write binary data • Character Stream • Char as the unit • Used to read and write text

  12. Stream • Abstract Stream Class in java.io • Byte stream • java.io.InputStream • read() //read a byte • java.io.OutputStream • write() //write an int ?? • Character stream • java.io.Reader • read() //read a char • java.io.Writer • write() //write an int ??

  13. Stream • Implemented Classes in java.io • Byte stream • FileInputStream、FileOutputStream • *PipedInputStream、PipedOutputStream • ByteArrayInputStream、 ByteArrayOutputputStream • BufferedInputStream、BufferedOutputStream • ObjectInputStream、ObjectOutputStream • Character stream • FileReader、FileWriter • *PipedReader、PipedWriter • BufferedReader、BufferedWriter • InputStreamReader、OutputStreamWriter

  14. Byte Stream • A Complex Hierarchy of Byte Stream CoSE Java 2009

  15. Byte Stream • FileInputStream • Read bytes from file system • Used to read image or data • FileOutputStream • Write bytes to file system • Used to write image or data

  16. Byte Stream • Example: • Write following data into “c:\test.dat” • Read them out • byte 97 • char ‘b’ • String “好” CoSE Java 2009

  17. CoSE Java 2009

  18. Byte Stream • Think • What is the result of this program? • If the parameter of read() and write() out of range of Byte, what will happen?

  19. Character Stream • FileReader • Read char from file • FileWriter • Write char to file • FileReaderand FileWriter use system default encoding • Use other encodings: • InputStreamReader • OutputStreamWriter CoSE Java 2009

  20. Character Stream • Example: • Write following chars • Read them out • ‘C’‘o’‘S’‘E’ • ‘软’‘件’‘学’‘院’ CoSE Java 2009

  21. CoSE Java 2009

  22. Byte Stream and Character Stream • Byte Stream • An int or byte[] can be written to an OutputStream; • An int or byte[] can be read from an InputStream; • Character Stream • An int or char[] or String can be written to an Writer; • An int or char[] or CharBuffer can be read from a Reader

  23. Byte Stream and Character Stream • Think • How to input a student information into a file? • Student ID（int） • Name（String） • Age（short） • Sex（boolean） • How to read these information from file? • How to store these information in binary or text? CoSE Java 2009

  24. Self-study • PrintStream(will be used in Chapter 11) • Inherited from OutputStream • DataInputStreamand DataOutputStream • Inherited from InputStreamand OutputStream • PrintWriter • Inherited from Writer • Scanner • java.util.Scanner CoSE Java 2009

  25. Buffered Stream • Add buffer for input and output. • To improve the efficiency, read() and write() is not invoked immediately, but after the buffer is full. • Buffer is implemented using inner array. • Usually, buffered stream is connected to other streams (such as FileInputStream) • flush() CoSE Java 2009

  26. Buffered Stream • Example: Benchmarkfollowing classes • FileInputStream vs. BufferedInputStream; • FileOutputStream vs. BufferedOutputStream; CoSE Java 2009

  27. CoSE Java 2009

  28. Bridge Between B-S and C-S • InputStreamReader • OutputStreamWriter

  29. Random Access File • java.io.RandomAccessFile • RandomAccessFileis used for fixed length records • Using seek(long postion)to locate • Nothing to do with InputStream and OutputStream • Like DataInputStreamand DataOutputStream • Often used for building index of Search Engines

  30. Standard I/O • System.in • InputStream • Input from keyboard • System.out • PrintStream ->FilterOutputStream -> OutputStream • Show information in console • System.err • PrintStream ->FilterOutputStream -> OutputStream • Show error information in console CoSE Java 2009

  31. CoSE Java 2009

  32. Best Practice • Common Programming Errors • Use FileOutputStream to write to an existing file – the existing content will be erased. • Path errors - \ and \\ • Good Programming Habits • Choose mode r for read-only for RandomAccessFile • Judge the existence of a file before using FileOuputStream • Use buffer as possible as you can • Remember to close the stream

  33. java.nioPilot • Motivation：High Speed I/O • Mapped Memory File

  34. java.nioPilot • Example: • Use MappedByteBuffer to create a 128Mfile, with each byte be a binary representation of ‘x’ • Read 6 bytes from the file CoSE Java 2009

  35. CoSE Java 2009

  36. Lab Work • Homework：Benchmark using abstract class: • Memory-mapped file vs. DataInputStream • Memory-mapped file vs. DataOutputStream • Memory-mapped file vs. RandomAccessFile • Tips： CoSE Java 2009

  37. Lab Work • Tips • DataOutputStream • DataInputStream CoSE Java 2009

  38. Lab Work • RandomAccessFile • Mapped File CoSE Java 2009

  39. Lab Work • Setup an Benchmark Environment • Design a Benchmark Case • Run and Gain the Efficient of Each I/OClass • * Evaluate and Analysis the Performance Curve CoSE Java 2009

  40. Self-study • Serializable Object • Object serialization CoSE Java 2009

  41. Self-study • Reading • The.Java.Programming.Language.4th.Edition, Chapter 20; • Thinking in Java, 3th Edition, Chapter 12. CoSE Java 2009

  42. Forecast • Arrays • Collection • ArrayList • LinkedList • Map • HashMap • Iterator CoSE Java 2009

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