How are sockets implemented in JVM?

Question

I want to know, how sockets are implemented in the Java Virtual Machine.

• Is there a native library included?
• And if, is it a C library?

Where can I find information about this topic? The offical Java tutorial on networking does not help me there.

Some interesting links would help.

Update: Are there any official information provided by Sun?

Thanks in advance!

Edit I found a proof, I mark my answer as the correct one. Thanks to Oscar, that was the perfect hint for me!!! THANKS!

Answer 1

Probably using the system-V socket calls exposed by the underlying platform, e.g. system-V under Unix, WinSock under Windows. The specification only dictates how a virtual machine must behave, so implementers are free to do as they wish.

Answer 2

Java is open source, so you can grab the source code for a self paced deep examination of the class.

As an start and quick answer to your question here's what I've found in a very quick scan:

private native void socketConnect(InetAddress address, int port, int timeout)

So yeap, a native lib is included and my guess it is a C++ library.

There are a number of implementations ( SSLSocket, PlainSocket etc. )

The online source of JDK7 is here :S _{Not sure how up to date it is}

I've used my IDE to navigate the source code that comes with every JDK installation.

IDE screenshot showing the source of Socket http://img83.imageshack.us/img83/5358/socketimpfv3.png

Answer 3

In the network guide of Java 1.4.2, an interesting piece of information is provided:

The implementation details...

...that you don't need to know, unless you subclass SocketImpl/DatagramSocketImpl. Every *Socket object has an underlying SocketImpl/DatagramSocketImpl that interfaces to native code. The Impl classes implement two methods to support options:

void setOption(int optID, Object val) throws SocketException; Object getOption(int optID) throws SocketException;

that look much like C. These methods act as glue to the native methods, and ensure type safety before native methods are invoked.

So I think it's proofed: Java uses native libraries for sockets.