I found an page summing up everything they changed from 1.3.1 to 1.4.0 .
It was very long page to wade trhu all the changes , but here's what they changed concerning networking and stuff :
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New Features and Enhancements in Networking

IPv6: Internet Protocol version 6 support for TCP and UDP application (including multicast) is now included in J2SE 1.4.

HTTP Digest Authentication: The HTTP digest authentication implementation has been updated to support proxies and origin servers.

Unconnected/Unbound Socket: This allows more flexible socket creation, binding, and connection. Enables manipulation of socket options before establishing or accepting connections. In addition a timeout can be specified when establishing a connection. A new class, javax.net.ssl.SSLSocket, which is a subclass of java.net.Socket has been added to provide security for data sent through sockets through encryption.

Connected UDP Socket: The UDP protocol is a connectionless protocol, however, the DatagramSocket.connect method now establishes the address association at native level. Where supported, this allows an application to have visibility of ICMP port unreachable messages as an indication that the remote application is unavailable.

Uniform Resource Identifier (URI): The java.net.URI is new a class that allows URI construction and parsing without the presence of a protocol handler, which is not possible with the URL class.

JNDI DNS Service Provider in InetAddress: This enhancement in class java.net.InetAddress enables applications to configure a pure Java name service provider by using a DNS name service provider through JNDI.

URLEncoder and URLDecoder: These have been added to enable applications to use other character encoding/decoding schemes.

TCP Out-of-Band Data: New methods in class java.net.Socket have been added to provide limited support for TCP urgent data for support certain legacy applications. Urgent data may be sent on any TCP socket. However, only partial support for receiving urgent data is provided.

SOCKS: Full V5 and V4 TCP support with autonegotiation with the proxy of which version to use.

NetworkInterface: The java.net.NetworkInterface class allows enumeration of interfaces and addresses and can be used in applications deployed on machines with multiple network interfaces.
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Time to update . Now you can kiss your 1.3.1 goodbeye !