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Modern Programming Language
Lesson 5
TCP/IP connection
Java stream, filters, java.io
TCP/IP communication
Simple protocolls
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Using streams in Java
• Stream: An I/O Stream represents an input source or an
output destination. A stream can represent many
different kinds of sources and destinations, including disk
files, devices, other programs, and memory arrays.
• The java.io package contains the necessary classes
• Life cycle of a stream:
– Open
Instantiation of the appropriate stream class.
– Read/write
Using the methods of the stream object.
– Close
Using the close() method of the stream object.
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Stream types
Main stream classes
• Byte streams
(descended from InputStream/OutputStream)
To perform input and output of 8-bit bytes.
• Character streamek
(descended from Reader/Writer)
The Java platform stores character values using Unicode
conventions. Character stream I/O automatically
translates this internal format to and from the local
character set. In Western locales, the local character set
is usually an 8-bit superset of ASCII.
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Communication using streams
• The base class definies the read/write methods
• Byte stream (OutputStream)
– write(int a) throws IOException
– write(byte b[]) throws IOException
– write(byte b[], int off, int len) throws IOException
• Character stream (Writer)
–
–
–
–
write(int c) throws IOException
write(char c[]) throws IOException
write(char c[], int off, int len) throws IOException
write(String s)
• Clear buffer
– Using the flush() method
– Closing the stream
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Read/write using streams
• Byte stream (InputStream)
– int read() throws IOException
– int read(byte c[]) throws IOException
– int read(byte c[], int off, int len) throws IOException
Result is the number
of readed bytes
• Character stream (Reader)
– int read() throws IOException
– int read(char c[]) throws IOException
– int read(char c[], int off, int len) throws IOException
Állapot
Visszatérési érték
New data
Code of the data item (byte/character)
End of data flow
-1
No data
Stream is waiting
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Stream example
Copy using streams
public static void copy(InputStream in, OutputStream out) {
try {
int b;
while (b = in.read() != -1) out.write(b);
out.flush();
} catch (IOException e) {
System.out.println(e.getMessage());
}
}
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Mapping to physical streams
• File handling classes
– Character: FileReader/FileWriter
– Byte: FileInputReader/FileOutputStream
• Available constructors
– FileReader(String filename) throws FileNotFoundException
– FileReader(File file) throws FileNotFoundException
– FileReader(FileDescriptor fd)
• Pipe streams
– PipedInputStream/PipedOutputStream
– PipedReader/PipedWriter
• Array streams
– pl. CharArrayWriter etc.
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Filters
• Filters are connected to an already existing stream (not
directly to the physical medium)
• Filters are desendants from streams classes, therefore
they can be used as channels
(we can connect more than one filter to a stream)



A
BFilter
C
Reader
Reader
Writer
Writer

BA
CAB Filter
A
B
C

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Using filters
• Generally, we define the original stream in the
constructor of the filter
FileOutputStream fout = new FileOutputStream(”...”);
DataOutputStream dos = new DataOutputStream(fout);
• We can connect a filter to an other filter too.
• In case of connected filters, do not use the stream
directly
dos.writeFloat(...);
• It is enough to close the filter
dos.close();
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Read/write of Java basic types
• Using DataOutputStream filter (connected to a byte
stream)
– public void writeInt(int v) throws IOException
– public void writeFloat(float v) throws IOException
– public void writeChar(char v) throws IOException
...
• Using DataInputStream filter (connected to a byte
stream)
– public int readInt() throws IOException
– public float readFloat() throws IOException
– public char readChar() throws IOException
...
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Write textual data
• Using the PrintWriter filter (connected to a character
stream)
• Write out data + enter:
– public void println(int v) throws IOException
– public void println(float v) throws IOException
– public void println(String v) throws IOException
...
Write out data:
– public void print(int v) throws IOException
– public void print(float v) throws IOException
– public void print(String v) throws IOException
...
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Reading and parsing textual data
• We can use the BufferedReader filter (connected to
character streams)
– public char read () throws IOException
Reads one character
– public string readLine() throws IOException
Reads a line
• We can use the LineNumberReader to count the line
numbers (connected to a character stream)
– public int getLineNumber()
It counts the readed line numbers-
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Further filters
• Convert a byte stream into a character stream
InputStreamReader/OutputStreamWriter
The constructor gets a byte stream. The object itself is a
character stream.
• Archiving
ZipInputStream/ZipOutputStream
GZIPInputStream/GZIPOutputStream
• Checked data transfer
CheckedInputStream/CheckedOutputStream
• Encription
CipherInputStream/CipherOutputStream
• Object transfer
ObjectInputStream/ObjectOutputStream
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TCP/IP connection
• TCP connection is based on sockets. A socket = IP
number + port number
• The server and the client is the same. The only
difference is the connection mode (the client requests
the connection, the server receive the request)
• There are the same Socket objects in booth side.
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TCP connection
• The java.net package contains
– URL handling
– TCP connection handling
– UDP connection handling (not discussed)
• We can start a TCP based connection using the Socket
class
There are input and output stream in booth side. The
server and the client can comminucate via these.
Server
IP:15.6.8.6
port: 4520
port: 6621
port: 4521
port: 6622
port: 4522
port: 6623
Socket
port: 4523
InputStream
InputStream
OutputStream
OutputStream
Client
IP:12.2.6.5
Socket
port: 6624
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Socket class
• Calling the constring initiates the connection
– public Socket(String host, int port)
throws UnknownHostException, IOException
Host format: ”192.168.0.5” or ”www.bmf.hu”
Port format: a number between 1 and 65535
• In case of valid connection, we can access the streams
using the following methods:
– public InputStream getInputStream() throws IOException
– public OutputStream getOutputStream() throws IOException
• Closing the connection
– public void close() throws IOException
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Client side communication
Client example
try {
Socket s = new Socket("ultra.obuda.kando.hu", 7);
InputStream is = s.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
OutputStream os = s.getOutputStream();
PrintWriter pw = new PrintWriter(os);
pw.println("ECHO"); pw.flush();
String answer = br.readLine(); System.out.println(answer);
s.close();
} catch (Exception e) {
System.out.println(e.getMessage());
}
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ServerSocket class
• The ServerSocket constructor needs the following
parameters:
– public ServerSocket(int port) throws IOException
The port parameters is the number of the listening port.
If the port number is 0, the server will choose a free port automatically.
– public ServerSocket(int port, int backlog) throws IOException
the backlog paramters contains the size of the back log.
• Closing the ServerSocket object
– public void close() throws IOException
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Listening with ServerSocket
• We have to call the following method to put the ServerSocket
object into listening phase:
– public Socket accept() throws IOException
• This will block the program execution, until a new connection
request arrives.
• If a new connection request apperars, the program will run
forward. The result of the accept() method is a Socket object,
connected to the client.
• After the request handling, we have to call the accept()
method agait to listen to the next requets.
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Server side communication
Example: echo protocoll
try {
ServerSocket ss = new ServerSocket(7);
while (true) {
Socket s = ss.accept();
InputStream is = s.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
OutputStream os = s.getOutputStream();
PrintWriter bos = new PrintWriter(os);
String question = br.readLine();
bos.println(question); bos.flush();
s.close();
}
} catch (Exception e) {
System.out.println(e.getMessage());
}
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