Java Cookbook

Threaded Network Server

Problem

You want a network server to be multithreaded.

Solution

Either create a thread when you accept a connection, or pre-create a pool of threads and have each wait on the accept( ) call.

Discussion

Networking (see Chapter 15 through Chapter 17) and threads are two very powerful APIs that are a standard part of the Java platform. Used alone, each can increase the reach of your Java programming skills. A common paradigm is a threaded network server, which can either preallocate a certain number of threads, or can start a new thread each time a client connects. The big advantage is that each thread can block on read, without causing other client threads to delay.

One example of a threaded socket server was discussed in Section 16.5; another is shown here. It seems to be some kind of rite (or wrong) of passage for Java folk to write a web server entirely in Java. This one is fairly small and simple; if you want a full-bodied flavor, check out the Apache Foundation’s Apache (written in C) and Tomcat (pure Java) servers, or the World Wide Web Consortium’s jigsaw server. The main program of mine constructs one instance of class Httpd. This creates a socket and waits for incoming clients in the accept( ) method. Each time there is a return from accept( ), we have another client, so we create a new thread to process that client. This happens in the main( ) and runserver( ) methods, which are near the beginning of Example 24-11.

Example 24-11. Httpd.java

/** * ...