Server-Side Java - Java - page 665

Discussion
Getting the debug output from a desktop client is fairly easy on most operating systems. But
if the program you want to debug is running in a “container” like a servlet engine or an EJB
server, it can be difficult to obtain debugging output, particularly if the container is running
on a remote computer. It would be convenient if you could have your program send mes-
sages back to a program on your desktop machine for immediate display. Needless to say, it's
not that hard to do this with Java's socket mechanism.
Many logging APIs can handle this:
▪ Java has had for years a standard logging API (discussed in Network Logging with
java.util.logging ) that talks to various logging mechanisms including Unix syslog .
▪ The Apache Logging Services Project produces log4j , which is used in many open
source projects that require logging (see Network Logging with log4j ) .
▪ The Apache Jakart Commons Logging (JCL) . Not discussed here; similar to the others.
▪ SLF4J (Simple Logging Facade For Java, see Network Logging with SLF4J ) is the new-
est and, as the name implies, a facade that can use the others.
▪ And, before these became widely used, I wrote a small, simple API to handle this type of
logging function. My netlog is not discussed here because it is preferable to use one of
the standard logging mechanisms; its code is in the logging subdirectory of the javasrc
repo if you want to exhume it.
The JDK logging API, log4j , and SFL4J are more fully fleshed out and can write to such
destinations as a file, an OutputStream or Writer , or a remote log4j , Unix syslog , or Win-
dows Event Log server.
The program being debugged is the “client” from the logging API's point of view—even
though it may be running in a server-side container such as a web server or application serv-
er—because the “network client” is the program that initiates the connection. The program
that runs on your desktop machine is the “server” program for sockets because it waits for a
connection to come along.
If you want to run any network-based logger reachable from any public network, you need to
be more aware of security issues. One common form of attack is a simple denial-of-service
(DoS), during which the attacker makes a lot of connections to your server in order to slow it
down. If you are writing the logto disk, for example, the attacker could fill up your disk by