What is the java -D command-line option good for?

[Peter Heide]

One of the SCJA Exam Objectives is:

demonstrate the proper use of the "java" command including the command-line option -D

The java jdk documentation specifies:

-Dproperty=value
Set a system property value. If value is a string that contains spaces, you must enclose the string in double quotes:
java -Dfoo="some string" SomeClass

My question is: How can I access this property value in the code. Does someone have an example?

[Paul Anil]

-D is an important switch that allows you to set environment properties.

You can call the following from anywhere in the code to read the properties given on the command line:

String value = System.getProperty("key", "defaultvalue");

[Cameron Wallace McKenzie]

A JVM runs with a number of system properties. You can configure system properties by using the -D option, pronounced with an upper case 'D'

All you have to do i suse the -D flag, and provide the system prperty name immediately following the D, and equals sign, and then the value to be assigned to the property. For example, to set the file.encoding property of the Java runtime to utf-8, you could set the following property:

java -Dfile.encoding=utf-8

You can then grab the value programatically as follows:

System.getProperty("file.encoding"); /*this method is overloaded, as per previous post*/

System geProperty JavaDoc

Don't confuse the -D switch with the -d switch. Both are tested on the SCJA exam, but both do different things. Casing is important!

Some of the default properties that are supposed to have already been set include: file.encoding, file.separator, java.home and java.version.


Cheers!

-Cameron McKenzie

[ November 05, 2006: Message edited by: Cameron W. McKenzie ]
[ November 05, 2006: Message edited by: Cameron W. McKenzie ]

[Peter Heide]

I used the following class:

public class hello {
public static void main (String[] args) {
String property = "hello";
String value = System.getProperty(property);
System.out.println(property + "=" + value);
}
}

Then I tried:

javac hello.java
java -Dhello=world hello

The output was:

hello=world

So the solution of Paul and Cameron worked well.

[a haksdjf]

Peter Heide wrote:One of the SCJA Exam Objectives is:

demonstrate the proper use of the "java" command including the command-line option -D

The java jdk documentation specifies:

-Dproperty=value
Set a system property value. If value is a string that contains spaces, you must enclose the string in double quotes:
java -Dfoo="some string" SomeClass

My question is: How can I access this property value in the code. Does someone have an example?

Can someone let me know how I and specify multiple key/value pairs?

Thanks,

[Olivier Fresse]

a haksdjf wrote:

Can someone let me know how I and specify multiple key/value pairs?

Thanks,

Use several -D arguments

java -Darg1=foo1 -Darg2=foo2  -Darg3=foo3 com.MyClass

Basically, it's text. You can also do something like :

java -Darg=key:val,key2:val2,key3:val3 com.MyClass

then you need to analyze the string key:val,key2:val2,key3:val3
to split it and get the key:val strings.
And you can split these again to get key and val.
String tokenizer is your friend Or regexp :-)