VIEWING THE JVM SYSTEM PROPERTIES

When testing an application, you often need to know exactly what input
is being passed to the JVM from the operating system. Is there a 
timezone
being set, is daylight savings on (a notable JVM bug on Windows NT), 
what
directory is it saying is the user's home directory?

Fortunately this is very easy to test. The operating system's 
properties
are accessible via the System.getProperties() method. Note that this is
not a direct access to the environment properties by typing the 'set'
command on a command line in UNIX and Windows, but instead it provides
access to a standard set of properties for Java, to any vendor extras 
and to
anything passed into the Java command via the -D flag.

The following is simple code to show these properties:

import java.util.Properties;

public class SysPropDump {

static public void main(String[] args) {
System.getProperties().list(System.out);
}

}

This works well for properties with short values, such as:

java.vendor=Apple Computer, Inc.

but when the value is long, it will get cut off,
for example with the classpath:

java.class.path=/System/Library/
Frameworks/JavaVM.fra...

To show all data, the SysPropDump class needs to, on its own, do the
printing of each value in the Properties object. However this is still 
a
simple proccess:

import java.util.Properties;
import java.util.Enumeration;

/**
* Invoke with either: java SysPropDump
for a quick list or
* java SysPropDump -v
for a verbose list.
*/
public class SysPropDump {

static public void main(String[] args) {
Properties props = System.getProperties();
if( (args.length > 0) && "-v".equals(args[0]) ) {

// print each property out, one at a time
Enumeration names = props.propertyNames();
System.out.println("-- listing
verbose properties --");
while(names.hasMoreElements()) {
String name = names.nextElement();
System.out.print(name);
System.out.print("=");
System.out.println(props.
getProperty(name));
}
} else {
System.getProperties().
list(System.out);
}
}

}

java.class.path is now printed as the far spammier:

java.class.path=/System/Library/Frameworks/
JavaVM.framework/Versions/1.3/Classes/
classes.jar:/System/Library/Frameworks/
JavaVM.framework/Versions/1.3/Classes/
ui.jar:.:/usr/local/javalib/BZip2.jar:/
usr/local/javalib/gnu-regexp-1.0.8.jar:/
usr/local/javalib/jdbc.jar:/
usr/local/javalib/jndi.jar:/usr/local/
javalib/jstyle.jar:/usr/local/javalib/
servlet.jar:/usr/local/javalib/tar.
jar:/usr/local/javalib/xerces.jar

Obviously this simple command line class can be taken further to
incorporate specification of the desired properties as arguments, 
sorting the
list by some logic, and outputting in other formats--XML, HTML, and CSV 
all
spring to mind.

Though the code is longer and more complex, it's stronger and will not
leave file handles and sql connections hanging around.


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