Java System Properties

Java maintains a set of system properties for its operations. Each java system property is a key-value (String-String) pair such as “java.version”=”1.7.0_09“. You can retrieve all the system properties via System.getProperties() or you can also retrieve individual property via System.getProperty(key).

Please note that Access to system properties can be restricted by the Java security manager and policy file. By default, Java programs have unrestricted access to all the system properties.

Table of Contents

Important Java System Properties
Get System Property
Set System Property

Important Java System Properties

1. JRE related system properties

   java.home	JRE home directory, e.g., “C:\Program Files\Java\jdk1.7.0_09\jre“.
   java.library.path	JRE library search path for search native libraries. It is usually but not necessarily taken from the environment variable PATH.
   java.class.path	JRE classpath e.g., '.' (dot – used for current working directory).
   java.ext.dirs	JRE extension library path(s), e.g, “C:\Program Files\Java\jdk1.7.0_09\jre\lib\ext;C:\Windows\Sun\Java\lib\ext“.
   java.version	JDK version, e.g., 1.7.0_09.
   java.runtime.version	JRE version, e.g. 1.7.0_09-b05.

2. File related system properties

   file.separator	symbol for file directory separator such as 'd:\test\test.java'. The default is '\' for windows or '/' for Unix/Mac.
   path.separator	symbol for separating path entries, e.g., in PATH or CLASSPATH. The default is ';' for windows or ':' for Unix/Mac.
   line.separator	symbol for end-of-line (or new line). The default is "\r\n" for windows or "\n" for Unix/Mac OS X.

3. User related system properties

   user.name	the user’s name.
   user.home	the user’s home directory.
   user.dir	the user’s current working directory.

4. OS related system properties

   os.name	the OS’s name, e.g., “Windows 7“.
   os.version	the OS’s version, e.g., “6.1“.
   os.arch	the OS’s architecture, e.g., “x86“.

Get System Property

As discussed earlier, You can get all the system properties via System.getProperties() or also retrieve individual property via System.getProperty(key).

import java.util.Properties;
public class PrintSystemProperties 
{
   public static void main(String[] a) 
   {
      // List all System properties
      Properties pros = System.getProperties();
      pros.list(System.out);
 
      // Get a particular System property given its key
      // Return the property value or null
      System.out.println(System.getProperty("java.home"));
      System.out.println(System.getProperty("java.library.path"));
      System.out.println(System.getProperty("java.ext.dirs"));
      System.out.println(System.getProperty("java.class.path"));
   }
}

Set System Property

In java, you can set a custom system property either from command tools or from java code itself.

1. Set system property from command line (“-D” option)

   java -Dcustom_key="custom_value" application_launcher_class

2. Set system property from code using System.setProperty() method

   System.setProperty("custom_key", "custom_value");

That’s all for this basic tutorial for reading and writing system properties in java.

Happy Learning !!