Java System Properties

Java maintains a set of system properties for its operations. Each java system property is a key-value (String-String) pair. For example, one such system property is “java.version”=”1.7.0_09“.

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.

We can retrieve all the system properties via System.getProperties() or we can also retrieve individual property via System.getProperty(key) method.

Table of Contents

1. Java System Properties List
2. Get System Property
3. Set System Property

1. Java System Properties List

1. JRE 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. IO 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 Properties

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

4. OS 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“.

2. Getting System Property

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

Example 1: Java example to get the list of all system properties

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);
   }
}

Example 2: Java example to a system property value by its key

import java.util.Properties;
public class PrintSystemProperties 
{
   public static void main(String[] a) 
   {
      // List all System properties
      Properties pros = System.getProperties();
 
      // 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"));
   }
}

3. Set System Property

In Java, you can set a custom system property either from the command line or from the application code itself.

Example 3: How to set system property in java using command line

In given example, the application will be able to access the property with key custom_key. It’s value will be available as custom_value.

java -Dcustom_key="custom_value" application_launcher_class

Example 4: How to set system property using Java code

Similar to above example, after executing this code, the application will be able to access the property with key custom_key. It’s value will be available as custom_value.

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

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

Happy Learning !!