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DatagramConnection.java API Doc J2ME CLDC 1.1 8003 Wed Feb 05 15:56:00 GMT 2003 javax.microedition.io

DatagramConnection

public interface DatagramConnection implements Connection

This interface defines the capabilities that a datagram connection must have.

Reminder: Since the CLDC Specification does not define any actual network protocol implementations, the syntax for datagram addressing is not defined in the CLDC Specification. Rather, syntax definition takes place at the level of J2ME profiles such as MIDP.

In the sample implementation that is provided as part of the CLDC reference implementation, the following addressing scheme is used:

The parameter string describing the target of a connection in the CLDC reference implementation takes the following form:

{protocol}://[{host}]:[{port}]

A datagram connection can be opened in a "client" mode or "server" mode. If the "//{host}" part is missing then the connection is opened as a "server" (by "server", we mean that a client application initiates communication). When the "//{host}" part is specified, the connection is opened as a "client".

Examples:

A datagram connection for accepting datagrams
datagram://:1234

A datagram connection for sending to a server:
datagram://123.456.789.12:1234

Note that the port number in "server mode" (unspecified host name) is that of the receiving port. The port number in "client mode" (host name specified) is that of the target port. The reply-to port in both cases is never unspecified. In "server mode", the same port number is used for both receiving and sending. In "client mode", the reply-to port is always dynamically allocated.

Also note that the allocation of datagram objects is done in a more abstract way than in Java 2 Standard Edition (J2SE). Instead of providing a concrete DatagramPacket class, an abstract Datagram interface is provided. This is to allow a single platform to support several different datagram interfaces simultaneously. Datagram objects must be allocated by calling the newDatagram methods of the DatagramConnection object. The resulting object is defined using another interface type called javax.microedition.io.Datagram.

author: Brian Modra
author: Nik Shaylor
version: 12/17/01 (CLDC 1.1)
since: CLDC 1.0

Fields Summary
Constructors Summary
Methods Summary
public int getMaximumLength()
Get the maximum length a datagram can be. Maximum length determines the maximum size of the datagram that can be created using the newDatagram method, and the maximum size of the datagram that can be sent or received.
return
The maximum length of a datagram.
exception
IOException If an I/O error occurs.
public int getNominalLength()
Get the nominal length of a datagram. Nominal length refers to the size of the datagram that is stored into the data buffer. Nominal length may be equal or less than the maximum length of the datagram.
return
The nominal length of a datagram.
exception
IOException If an I/O error occurs.
public Datagram newDatagram(int size)
Create a new datagram object.
param
size The size of the buffer needed for the datagram
return
A new datagram
exception
IOException If an I/O error occurs.
exception
IllegalArgumentException if the size is negative or larger than the maximum size
public Datagram newDatagram(int size, java.lang.String addr)
Create a new datagram object.
param
size The size of the buffer needed for the datagram
param
addr The I/O address to which the datagram will be sent
return
A new datagram
exception
IOException If an I/O error occurs.
exception
IllegalArgumentException if the size is negative or larger than the maximum size, or if the address parameter is invalid
public Datagram newDatagram(byte[] buf, int size)
Create a new datagram object.
param
buf The buffer to be used for the datagram
param
size The size of the buffer needed for the datagram
return
A new datagram
exception
IOException If an I/O error occurs.
exception
IllegalArgumentException if the size is negative or larger than the maximum size or the given buffer's length, or if the buffer parameter is invalid
public Datagram newDatagram(byte[] buf, int size, java.lang.String addr)
Make a new datagram object.
param
buf The buffer to be used for the datagram
param
size The size of the buffer needed for the datagram
param
addr The I/O address to which the datagram will be sent
return
A new datagram
exception
IOException If an I/O error occurs.
exception
IllegalArgumentException if the size is negative or larger than the maximum size or the given buffer's length, or if the address or buffer parameter is invalid
public void receive(Datagram dgram)
Receive a datagram. When this method returns, the internal buffer in the Datagram object is filled with the data received, starting at the location determined by the offset state variable, and the data is ready to be read using the methods of the DataInput interface.
This method blocks until a datagram is received. The internal length state variable in the Datagram object contains the length of the received datagram. If the received data is longer than the length of the internal buffer minus offset, data is truncated.
This method does not change the internal read/write state variable of the Datagram object. Use method Datagram.reset to change the pointer before reading if necessary.
param
dgram A datagram.
exception
IOException If an I/O error occurs.
exception
InterruptedIOException Timeout or interrupt occurred.
public void send(Datagram dgram)
Send a datagram. The Datagram object includes the information indicating the data to be sent, its length, and the address of the receiver. The method sends length bytes starting at the current offset of the Datagram object, where length and offset are internal state variables of the Datagram object.
param
dgram A datagram.
exception
IOException If an I/O error occurs.
exception
InterruptedIOException Timeout or interrupt occurred.