Java System Properties

Java maintains a Set of system properties that can be accessed in the runtime by executing programs. Each system property is a key-value pair. For example, one such system property is “java.version”=”1.7.0_09“.

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

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.

1. Java System Properties List

The following is a list of important system properties in each category.

1.1. Runtime Environment 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.

1.2. File 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.

1.3. User Properties

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

1.4. Operation 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“.

2. Get the Value of a 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).

2.1. List of all System Properties

Properties pros = System.getProperties();

pros.list(System.out);

2.2. Get a system property value by its key

System.getProperty("java.home");

3. Set a System Property

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

3.1. Using Command Line

In the 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

3.2. Using Java Code

Similar to the 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 !!