Interface CommConnection

All Superinterfaces:
javax.microedition.io.Connection, javax.microedition.io.InputConnection, javax.microedition.io.OutputConnection, javax.microedition.io.StreamConnection

public interface CommConnection
extends javax.microedition.io.StreamConnection

This interface defines a logical serial port connection. A "logical" serial port is defined as a logical connection through which bytes are transferring serially. The logical serial port is defined within the underlying operating system and may not necessarily correspond to a physical RS-232 serial port. For instance, IrDA IRCOMM ports can commonly be configured as a logical serial port within the operating system so that it can act as a "logical" serial port.

A comm port is accessed using a Generic Connection Framework string with an explicit port identifier and embedded configuration parameters, each separated with a semi-colon (;).

Only one application may be connected to a particular serial port at a given time. An java.io.IOException is thrown, if an attempt is made to open the serial port with Connector.open() and the connection is already open.

A URI with the type and parameters is used to open the connection. The scheme (defined in [RFC3986]) must be :
comm:<port identifier>[<optional parameters>]

The first parameter must be a port identifier, which is a logical device name. These identifiers are most likely device specific and should be used with care.

The implementation MAY provide access to serial ports through the CommConnection interface. Which serial ports are available to MIDlets is implementation-specific. The valid identifiers for the ports can be queried through the method System.getProperty() using the key "microedition.commports". A comma separated list of ports is returned which can be combined with a comm: prefix as the URL string to be used to open a serial port connection. (See port naming convention below.)

Every serial port name included in the String value returned by the method System.getProperty ("microedition.commports") MUST be accessible via the javax.microedition.io.CommConnection interface.

Any additional parameters must be separated by a semi-colon (;) and spaces are not allowed in the string. If a particular optional parameter is not applicable to a particular port, the parameter MAY be ignored. The port identifier MUST NOT contain a semi-colon (;).

Legal parameters are defined by the definition of the parameters below. Illegal or unrecognized parameters cause an IllegalArgumentException. If the value of a parameter is supported by the device, it must be honored. If the value of a parameter is not supported a java.io.IOException is thrown. If a baudrate parameter is requested, it is treated in the same way that the setBaudRate method handles baudrates. e.g., if the baudrate requested is not supported the system MAY substitute a valid baudrate, which can be discovered using the getBaudRate method.

Optional Parameters

Parameter Default Description
baudrate platform dependent The speed of the port.
bitsperchar 8 The number bits per character(7 or 8).
stopbits 1 The number of stop bits per char(1 or 2)
parity none The parity can be odd, even, or none.
blocking on If on, wait for a full buffer when reading.
autocts on If on, wait for the CTS line to be on before writing.
autorts on If on, turn on the RTS line when the input buffer is not full. If off, the RTS line is always on.

BNF Format for Connector.open() string

The URI must conform to the BNF syntax specified below. If the URI does not conform to this syntax, an IllegalArgumentException is thrown.

<comm_connection_string> ::= "comm:"<port_id>[<options_list>] ;
<port_id> ::= string of alphanumeric characters
<options_list> ::= *(<baud_rate_string>| <bitsperchar>| <stopbits>| <parity>| <blocking>| <autocts>| <autorts>) ;
; if an option duplicates a previous option in the
; option list, that option overrides the previous
; option
<baud_rate_string> ::= ";baudrate="<baud_rate>
<baud_rate> ::= string of digits
<bitsperchar> ::= ";bitsperchar="<bit_value>
<bit_value> ::= "7" | "8"
<stopbits> ::= ";stopbits="<stop_value>
<stop_value> ::= "1" | "2"
<parity> ::= ";parity="<parity_value>
<parity_value> ::= "even" | "odd" | "none"
<blocking> ::= ";blocking="<on_off>
<autocts> ::= ";autocts="<on_off>
<autorts> ::= ";autorts="<on_off>
<on_off> ::= "on" | "off"


Access to serial ports is restricted to prevent unauthorized transmission or reception of data. The security model applied to the serial port connection is defined in the implementing profile. The security model may be applied on the invocation of the Connector.open() method with a valid serial port connection string. Should the application not be granted access to the serial port through the profile authorization scheme, a java.lang.SecurityException will be thrown from the Connector.open() method. The security model MAY also be applied during execution, specifically when the methods openInputStream(), openDataInputStream(), openOutputStream(), and openDataOutputStream() are invoked.


The following example shows how a CommConnection would be used to access a simple loopback program.

 CommConnection cc = (CommConnection) Connector.open("comm:COM1;baudrate=19200"); 
 int baudrate = cc.getBaudRate();
 InputStream is = cc.openInputStream(); 
 OutputStream os = cc.openOutputStream(); 
 int ch = 0; 
 while(ch != 'Z') { 
   ch = is.read(); 

The following example shows how a CommConnection would be used to discover available comm ports.

 String port1; 
 String ports = System.getProperty("microedition.commports");
 int comma = ports.indexOf(','); 
 if (comma > 0) { 
   // Parse the first port from the available ports list. 
   port1 = ports.substring(0, comma); 
 } else { 
   // Only one serial port available. 
   port1 =ports; 

Port Naming Requirements:

Ports have to be named consistently among the implementations of this class. Therefore, VM implementations MUST follow the following convention: Port names MUST contain a text abbreviation indicating port capabilities followed by a sequential number for the port. Port numbering MUST start from 1 without any leading zeros, and numbering MUST be sequential (without any gaps). The following device name types MUST be used:

This naming scheme allows API users to generally determine the type of port to use. For example, if an application needs to beam a piece of data, the application could look for IR# ports for opening the connection. The alternative is a trial-and-error approach with all available ports. If the implementation cannot determine a port type, the same naming convention as for an RS-232 port MUST be used.

MIDP 2.0

Method Summary
 int getBaudRate()
          Gets the baudrate for the serial port connection.
 int setBaudRate(int baudrate)
          Sets the baudrate for the serial port connection.
Methods inherited from interface javax.microedition.io.InputConnection
openDataInputStream, openInputStream
Methods inherited from interface javax.microedition.io.Connection
Methods inherited from interface javax.microedition.io.OutputConnection
openDataOutputStream, openOutputStream
Methods inherited from interface javax.microedition.io.Connection

Method Detail


int getBaudRate()
Gets the baudrate for the serial port connection.

the baudrate of the connection
See Also:


int setBaudRate(int baudrate)
Sets the baudrate for the serial port connection. If the requested baudrate is not supported on the platform, then the system MAY use an alternate valid setting. The alternate value can be accessed using the getBaudRate method.

baudrate - the baudrate for the connection
the previous baudrate of the connection
See Also:


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