The System class in Java maintains a set of properties. These properties are stored in the form of key/value pairs. Both keys and values are Strings that define traits or attributes of the current working environment.
There are two methods that you can use to read the system properties: getProperty() and getProperties().
Table of Contents
Getting All System Properties in Java
System.getProperties() returns an Enumeration of all the system properties. The following code prints all the system properties on the console.
import java.util.Enumeration;
import java.util.Properties;
public class Main {
public static void main(String[] args)
{
Properties p = System.getProperties();
Enumeration keys = p.keys();
while (keys.hasMoreElements()) {
String key = (String)keys.nextElement();
String value = (String)p.get(key);
System.out.println(key + ": " + value);
}
}
}
The Output in text form:
gopherProxySet: false awt.toolkit: sun.lwawt.macosx.LWCToolkit java.specification.version: 11 sun.cpu.isalist: sun.jnu.encoding: UTF-8 java.class.path: /Users/jayant/Desktop/java/JD1/out/production/JD1 java.vm.vendor: Oracle Corporation sun.arch.data.model: 64 java.vendor.url: http://java.oracle.com/ user.timezone: os.name: Mac OS X java.vm.specification.version: 11 sun.java.launcher: SUN_STANDARD user.country: GB sun.boot.library.path: /Library/Java/JavaVirtualMachines/jdk-11.0.2.jdk/Contents/Home/lib sun.java.command: Main http.nonProxyHosts: local|*.local|169.254/16|*.169.254/16 jdk.debug: release sun.cpu.endian: little user.home: /Users/jayant user.language: en java.specification.vendor: Oracle Corporation java.version.date: 2018-10-16 java.home: /Library/Java/JavaVirtualMachines/jdk-11.0.2.jdk/Contents/Home file.separator: / java.vm.compressedOopsMode: Zero based line.separator: java.specification.name: Java Platform API Specification java.vm.specification.vendor: Oracle Corporation java.awt.graphicsenv: sun.awt.CGraphicsEnvironment sun.management.compiler: HotSpot 64-Bit Tiered Compilers ftp.nonProxyHosts: local|*.local|169.254/16|*.169.254/16 java.runtime.version: 11.0.2+7-LTS user.name: jayant path.separator: : os.version: 10.14.2 java.runtime.name: Java(TM) SE Runtime Environment file.encoding: UTF-8 java.vm.name: Java HotSpot(TM) 64-Bit Server VM java.vendor.version: 18.9 java.vendor.url.bug: http://bugreport.java.com/bugreport/ java.io.tmpdir: /var/folders/56/fc29wjz520x_21fmrl9r2jgc0000gn/T/ java.version: 11.0.2 user.dir: /Users/jayant/Desktop/java/JD1 os.arch: x86_64 java.vm.specification.name: Java Virtual Machine Specification java.awt.printerjob: sun.lwawt.macosx.CPrinterJob sun.os.patch.level: unknown java.library.path: /Users/jayant/Library/Java/Extensions:/Library/Java/Extensions:/Network/Library/Java/Extensions:/System/Library/Java/Extensions:/usr/lib/java:. java.vendor: Oracle Corporation java.vm.info: mixed mode java.vm.version: 11.0.2+7-LTS sun.io.unicode.encoding: UnicodeBig java.class.version: 55.0 socksNonProxyHosts: local|*.local|169.254/16|*.169.254/16 Process finished with exit code 0
Important System Properties
Some of the important system properties are:
| “file.separator” | File separator (for example, “/”) |
| “java.class.path” | Java classpath |
| “java.class.version” | Java class version number |
| “java.home” | Java installation directory |
| “java.vendor” | Java vendor-specific string |
| “java.vendor.url” | Java vendor URL |
| “java.version” | Java version number |
| “line.separator” | Line separator |
| “os.arch” | Operating system architecture |
| “os.name” | Operating system name |
| “os.version” | Operating system version |
| “path.separator” | Path separator (for example, “:”) |
| “user.language” | Language used by User |
| “user.dir” | User’s current working directory |
| “user.home” | User home directory |
| “user.name” | User account name |
Getting a Specific System Property
To get a particular property from the list use System.Property(key). Where key is the name of the property you want to retrieve. The output is returned as a string. If the property key doesn’t match then null is returned.
public class Main {
public static void main(String[] args)
{
System.out.println(System.getProperty("java.class.path"));
System.out.println(System.getProperty("os.name"));
System.out.println(System.getProperty("user.name"));
}
}
/Users/jayant/Desktop/java/JD1/out/production/JD1 Mac OS X jayant
The three properties have been printed out.
There is another variation that lets you specify what has to be printed in case the property name doesn’t match. Observe the difference in the fourth and fifth line in the following :
public class Main {
public static void main(String[] args)
{
System.out.println(System.getProperty("java.class.path"));
System.out.println(System.getProperty("os.name"));
System.out.println(System.getProperty("user.name"));
System.out.println(System.getProperty("hello"));
System.out.println(System.getProperty("hello","property not found"));
}
}
/Users/jayant/Desktop/java/JD1/out/production/JD1 Mac OS X jayant null property not found
The fourth line returns null, since “hello” doesn’t match with any property name. The fifth line returns the line we mentioned in the code “property not found”.
Conclusion
We can retrieve system properties using the above-mentioned methods. Information such as the version of Java in use, home directory, name of Java vendor can be retrieved from the System properties.
