Networking in Java ME

Extended networking features

The javax.microedition.io package only provides very basic networking possibilities. However, APIs such as Web Services, SIP, and Bluetooth have been created to allow for more extended features.

The Java ME™ Web Services specification (including JSR-172 specification (RCP) and JSR-172 specification (XML) was created in order to allow support for XML parsing and the ability to invoke Web Services. The API contains two optional packages for XML processing and Web Services. These two packages are independent and thus a device may have either one or both of them.

The Session Initiation Protocol (SIP) is an IETF signaling protocol for establishing real-time calls and conferences over Internet Protocol networks. The SIP API for Java Micro Edition (JSR-180) specification defines a Java Platform Micro Edition (Java ME) Optional Package, that enables resource limited devices (referred to as 'terminals' in the following) to send and receive SIP messages. The API is designed to be a compact and generic SIP API, which provides SIP functionality on a transaction level. The SIP API is integrated into the Generic Connection Framework defined in Connected, Limited Device Configuration (CLDC). SIP is only supported in Symbian.

SIP in itself is an application-layer control protocol that can establish, modify, and terminate communication sessions. SIP can also invite participants to already existing sessions. SIP transparently supports name mapping and redirection services, which supports personal mobility - users can maintain a single externally visible identifier regardless of their network location (see RFC 3261).

The Java APIs for Bluetooth (JSR-82) specification defines APIs that can be used to exercise certain Bluetooth protocols defined in the Bluetooth specification volume 1, and certain profiles defined in the Bluetooth specification volume 2. For more information about these profiles, see the Java APIs for Bluetooth (JSR-82) specification. The Bluetooth API is defined in such a way as to make it possible for additional and future profiles to be built on top of this API. This assumes that future changes to the Bluetooth specification remain compatible with this API.

The Bluetooth technology itself is an industrial specification for wireless personal area networks (PANs). The Bluetooth technology provides a way to connect and exchange information between devices such as personal digital assistants (PDAs), mobile devices, laptops, PCs, printers, digital cameras and video game consoles via a secure, globally unlicensed short-range radio frequency.

Networking protocols

The following table specifies the GCF Connections and the protocols used for implementing them in the Series 40 and Symbian platforms.

Support for user-selected MIDlet settings in Series 40

From Java Runtime 1.0.0 for Series 40 onwards, the user is allowed to change the Configuration Settings for each MIDlet on single-SIM devices. The sub-menu is added under the MIDlet Options menu, under the Applications Settings option. This allows the user to select from the available access point settings for different Configurations and Accounts. For more information about the Configuration Settings supported by a device, see the device's user guide.

The Nokia-MIDlet-Connectionsettings JAD attribute is used to identify the connection settings in use. If Nokia-MIDlet-Connectionsettings is set for the MIDlet, the user is not allowed to select the settings for the MIDlet.

Network prompts

Network Destination or Internet Access Point (IAP) for connection is selected using the following criteria when the MIDlet opens a network connection:

1. Use IAP Info API and Generic Connection Framework

   IAP Info API gives applications access to IAP and Network Destination related information. For more information, see IAP Info API description.

2. Use MIDlet suite default IAP if it is defined in Application Manager.

   The end user can define the Access Point manually via MIDlet suite settings in Application Manager. This Access Point is then automatically used for all network connections.

3. Use device default IAP or destination, if specified. Normally “Internet” Network Destination.

4. Prompt user for Network Destination or IAP selection.

   For further connections in the same application session the same Network Destination or IAP is used.

MIDlet default settings support setting of Network Destination ID via Application manager and using IAP Info API and GCF framework. User can also select a destination, when prompted for Access Points. The suitable IAP will be chosen by the platform based on the selected/configured Network Destination when a connection is opened.

If a network connection has been successfully opened and the operation on that opened connection fails (for example if the device is out of network coverage of the selected Internet Access Point), the user is not prompted to select Network Destination or IAP until the next connection is opened.

Caching of IAP/Network Destination by connection management is supported from Java Runtime 2.1 for Symbian onwards. During the MIDlet session, only the first connection prompts for IAP/Network Destination, then the selected Access Point is cached. Subsequent connections will not prompt for Access Point, instead the cached Access Point is used. If the connection fails (due to network being lost, or such), then the cache will be invalidated and the next connection opening will prompt the user for Access Point. Symbian^3 onwards, the first connection in home network or WLAN does not prompt, but in foreign networks the prompt is shown at the first connection.

Port Numbering

From S60 3rd Edition FP 2 onwards, port numbering for CommConnection starts from 1 instead of 0 as was the case in earlier devices. Legacy MIDlets using hard coded port number 0 receive a SecurityException when the 0 port is opened, and exit.

Output streams

Java ME utilizes two output streams, System.out() and System.err(). They have some notable characteristics:

• In Symbian, the stream output is saved on log file vmconsole.txt, which is located in directory \epoc32\WINSCW\C\logs\java. On some occasions, the directory needs to be created manually in order for the logging to function correctly.

• The log file uses UTF-8 encoding.

The Symbian platform buffers bytes written to the output stream. If your application requires that bytes written to the output stream, by sent immediately, then call the os.flush method right after the os.write method to ensure that buffered output bytes are written out.

OutputStream os;
...
os.write("hello".getBytes());
os.flush();
...

Input stream

In Symbian, InputStreamReader uses an internal buffer to make conversion from InputStream effective. It is not recommended to simultaneously read both InputStreamReader and the InputStream used in its creation, as it can lead to unexpected behavior.

Push Registry and datagram protocol

If a MIDlet registers a datagram connection, then the network connection is always on even when no MIDlets are running.

Developer's guides

The following developer's guides are available on networking in this section.

• Web Services

  The guide describes the J2ME™ Web Services Specification, which contains two optional, independent packages for XML processing and Web Services. The guide also provides an example MIDlet that uses the API.

• SIP Connections

  The guide describes the basic capabilities and the architecture of the Session Initiation Protocol (SIP). The guide also provides step-by-step instructions on how to create a MIDlet that uses the API. Support for this API was removed from S60 5th Edition and later releases.

• Bluetooth

  The guide describes the basic capabilities and the architecture of the Bluetooth protocol. The guide also provides step-by-step instructions on how to create two MIDlet examples that use the API.