Pieter van den Hombergh Richard van den Ham. March 13, 2018

Transcription

1 Pieter van den Hombergh Richard van den Ham Fontys Hogeschool voor Techniek en Logistiek March 13, 2018 /FHTenL March 13, /23

2 Topics /FHTenL March 13, /23

3 Figure: Taken from the Oracle/Sun Java tutorial Read or write information from different sources and types. sources: network, files, devices types: text, picture, sound Streams are FIFOs, uni-directional /FHTenL March 13, /23

4 Two basic stream types Byte Streams java.io.inputstream, java.io.outputstream read and write pdf, mp3, raw... Character Streams (16-bit Unicode) java.io.reader, java.io.writer simplifies reading and writing characters, character-arrays or Strings /FHTenL March 13, /23

5 Input Stream Overview Byte Stream Class for Input InputStream BufferedInputStream LineNumberInputStream ByteArrayInputStream (none) DataInputStream FilterInputStream PushbackInputStream PipedInputStream StringBufferInputStream (deprecated under 1.1) SequenceInputStream Char Stream Class for Input Reader BufferedReader LineNumberReader CharArrayReader InputStreamReader (none) FilterReader PushbackReader PipedReader StringReader (none) /FHTenL March 13, /23

6 Output Stream Overview Byte Stream Class for Output OutputStream BufferedOutputStream ByteArrayOutputStream DataOutputStream (none) FileOutputStream PrintStream PipedOutputStream (none) Char Stream Class for Output Writer BufferedWriter CharArrayWriter (none) OutputStreamWriter FileWriter PrintWriter PipedWriter StringWriter /FHTenL March 13, /23

7 ByteStreams - File Input and Output «interface» java.lang.autoclosable +close(): void «interface» java.io.closable +close(): void used to enable java 7 "try with resources" «interface» java.io.flushable +flush(): void java.io.inputstream + avialable(): int + mark(readlimit:int): void + marksupported: boolean + read(): int + reade(buffer: byte[]): int + read(b: byte[],off: int, len:in + reset(): void + skip(n: long): long java.io.outputstream + write(b : int): void + write(b: byte[]): void + write(b: byte[],off:int, len:int): void java.io.fileinputstream + FileInputStream(file: File) + FileInputStream(name: String) + FileInputStream(fdObj: FileDescription) # finalize(): void + getchannel(): FileChannel + getfd(): FileDescriptor java.io.fileoutputstream + FileOutputStream(file: File) + FileOutputStream(name: String) + FileOutputStream(file: File, append:boolean) + FileOutputStream(name: String, append:boolean) + FileOutputStream(fdObj: FileDescription) # finalize(): void + getchannel(): FileChannel + getfd(): FileDescriptor Both Input and Output are streams of bytes. /FHTenL March 13, /23

8 CharacterStreams - Writer and Reader «interface» java.lang.appendable + append( char c): Appendable + append(csq: CharSequence): Appe + append(csq: CharSequence csq, s «interface» java.io.flushable + flush(): void «interface» java.lang.autoclosable + close(): void «interface» java.io.closable + close(): void used to enable java 7 "try with resources" «interface» java.lang.readable + read(cb: CharBuffer): int java.io.writer +Writer() +Writer(lock: Object) + write(cbuf: char[]): Writer + write(csq : CharSequence ): Writer + write(csq : CharSequence, start: int, end: int ): Writer java.io.reader + Reader() + Reader(lock:Object) + mark(readaheadlimit:int): void + marksupported: boolean + read(): int + read(buf: char[]) : int + read(buf: char[], off: int, len: int): int + read(target: CharBuffer): int + ready(): boolean + reset(): void + skip(n: long): long Reader reads character data (text) Writer writes character data /FHTenL March 13, /23

9 Audio Stream in Servlets Idea: Use Servlet Output Stream to stream MP3s via HTTP set ContentType to audio/mpeg read MP3 files via InputStream write the bytes into the Servlet Output Stream /FHTenL March 13, /23

10 Wrapping Streams Streams can be combined Depending on source and type useful additions buffering encryption filtering... /FHTenL March 13, /23

11 Wrapping Streams - Buffering Buffered streams speed up input and output by reducing the number of reads and writes. They employ a buffered array of bytes or characters that act as a cache If no buffersize is specified, the default size is 512 bytes or characters. A buffered output stream calls the write method only when its buffer fills up or when the flush() method is called FileReader reader = new FileReader ( "/ home / hom / test. dat " ) ; BufferedReader bufferedin = new BufferedReader ( reader ) ; Useful additional function: String line = bufferedin. readline ( ) ; /FHTenL March 13, /23

12 Wrapping Streams - On-the-fly encryption Java IO streams implement the decorator design pattern new/additional behaviour can be added to an existing stream dynamically might remind you of the ISO/OSI reference model for network protocols /FHTenL March 13, /23

13 TIP: The package Since Java 1.4 there is a new java.nio package, which adds extra buffering capabilities. Since Java7 the package has been added. The you can find some very useful classes to help you with your daily file hassling code. In particular.files has many useful methods. List<String>Files.readAllLines(Path path) (since Java8 ) does what its name says. Stream<String>Files.lines(Path path) (since Java8) creates a Stream of String. Streams are a new Java 8 feature. You can do things like: public static void main ( String [] args ) throws IOException { Path path = Paths. get ("/ etc / passwd "); Files. lines ( path ). foreach ( System. out :: println ); } /FHTenL March 13, /23

14 Serialization Serialization is the process of converting an object into a sequence of bits. This is necessary to transport objects via streams. Serialization respectively De is also known as Mashalling/Unmarshalling (broader scope). /FHTenL March 13, /23

15 What makes an Object, data wise Quiz: If you imagine some objects you ve encountered, what is the closest data structure that describes the structure of all objects? /FHTenL March 13, /23

16 Serialization in Java Not every object is serializable (e.g. Thread, or Socket). Quiz: Why not? (Think transparency, security). In Java, the Serializable-Interface marks serializable objects The stream implementations ObjectInputStream and ObjectOutputStream can be used to serialize/deserialize serializable objects final void writeobject( Object obj ) throws IOException final Object readobject() throws ClassNotFoundException, IOException To exclude non-serializable attributes of serializable objects, transient can be used to mark these fields. All transient fields are excluded from the. /FHTenL March 13, /23

17 /Marshalling 20 p r i v a t e s t a t i c f i n a l S t r i n g O B J E C T _ S T O R E 21 = " / tmp / o b j e c t s. ser " ; p r i v a t e void m a r s h a l ( ) { 24 t r y ( O b j e c t O u t p u t S t r e a m out 25 = new O b j e c t O u t p u t S t r e a m ( 26 new F i l e O u t p u t S t r e a m ( O B J E C T _ S T O R E ) ) ; ) { 27 UserBean user1 = new UserBean ( " Uwe ", 28 " U w e P a s s " ) ; 29 UserBean user2 = new UserBean ( " Peter ", 30 " P e t e r P a s s " ) ; 31 UserBean user3 = new UserBean ( " Paula ", 32 " P a u l a P a s s " ) ; 33 user3. s e t S o c k e t ( new S o c k e t ( ) ) ; 34 S y s t e m. out. p r i n t l n ( " B e a n C o u n t e r = " 35 + UserBean. getbeancounter ( ) ) ; out. w r i t e O b j e c t ( user1 ) ; 38 out. w r i t e O b j e c t ( user2 ) ; 39 out. w r i t e O b j e c t ( user3 ) ; 40 } c a t c h ( I O E x c e p t i o n ex ) { 41 l o g g e r. log ( L e v e l. SEVERE, n u l l, ex ) ; 42 } 43 } /FHTenL March 13, /23

18 De/UnMarshalling 45 p r i v a t e void u n m a r s h a l ( ) { 46 t r y ( O b j e c t I n p u t S t r e a m in 47 = new O b j e c t I n p u t S t r e a m ( 48 new F i l e I n p u t S t r e a m ( O B J E C T _ S T O R E ) ) ; ) { f o r ( i n t i = 0 ; i < 3 ; i++ ) { 51 UserBean user = ( UserBean ) in. readobject ( ) ; 52 S y s t e m. out. p r i n t l n ( " user = " + user ) ; 53 } // UserBean newuser = new UserBean (" Richard ", " Richardpw ") ; 56 // System. out. println (" BeanCounter = "+ newuser. getbeancounter () ) ; 57 } c a t c h ( C l a s s N o t F o u n d E x c e p t i o n I O E x c e p t i o n ex ) { 58 l o g g e r. log ( L e v e l. SEVERE, n u l l, ex ) ; 59 } 60 } /FHTenL March 13, /23

19 Binary: from Java to Java, (between JVMS even across the network) Text based (modern: always UTF-8). Can be produced and consumed by different technologies (e.g. Java at server, Javascript in browser), like PHP or C# at one end, Java at the other XML often via the SOAP protocol, typically HTTP based. JSON, also typically HTTP based. Proto Buffers. Binary. PROTBUF is a modern (de) framework that has a schema. /FHTenL March 13, /23

20 NEVER DESERIALIZE A JAVA OBJECT STREAM FROM AN UNKNOWN SOURCE. De without a schema to validate the input is dangerous at best. Efective Java 3rd ed item 85. It is very easy to create a denial of service attack this way. /FHTenL March 13, /23

21 (JSON) is very popular at the moment. It is less verbose and heavy on the wire. It is easily generated and parsed (read) by programs and humans(although only for developers during development). Nowadays the format of choice for communication between apps and backend. Can be stored, but also generated from traditional tables in PostgreSQL. Has APIs that help generating (which sounds trivial) and parsing (less so) the wire format. e.g. javax.json defines some interfaces. This will be the transport format in PRJ2 this year (2017). /FHTenL March 13, /23

22 Person (de) demo with GSON Look ma, No hands p u b l i c s t a t i c v o i d main ( String [ ] args ) { Gson gson= new Gson ( ) ; Person max = new Person ( " Max ", LocalDate. of ( 1960, 04, 30 ) ) ; String jo = gson. tojson ( max ) ; System. out. println ( "jo = " + jo ) ; Person othermax = gson. fromjson ( jo, Person. c l a s s ) ; System. out. println ( " fromjson = " + othermax ) ; assert max. equals ( othermax ) ; System. out. println ( " all done " ) ; } /FHTenL March 13, /23

23 Questions and links Not all understood? Study Basic I/O Part I/O Streams. Questions? Questions or remarks? /FHTenL March 13, /23