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Java System properties


How to read Java System Properties? In the following example we show how to read single System property, list all, and use default when property is not defined.


java.lang.System has a couple of methods that help to read System properties. They are:

  • Properties getProperties() Loads all system properties.
  • String getProperty(String key) Returns value of specified system property or null.
  • String getProperty(String key, String def) Returns value of specified system property or default value when not found.

All three methods are demonstrated in the following example:


import java.util.Map.Entry;

public class SystemGetProperties {

    public static void main(String[] args) {
        // Get property value or null:
        System.out.println("Java version: "
                + System.getProperty("java.version"));

        System.out.println("Unknown property: "
                + System.getProperty(""));

        // Use default if not found:
        System.out.println("\nConfig location: "
                + System.getProperty("config.location", "/tmp/config"));

        // List all system properties:
        System.out.println("\nSystem properties:");
        for (Entry<Object,Object> property : System.getProperties().entrySet()) {
            System.out.printf("%s: %s%n", property.getKey(), property.getValue());

Truncated result of running the above example:

Java version: 1.8.0_45
Unknown property: null

Config location: /tmp/config

System properties: Java(TM) SE Runtime Environment
sun.boot.library.path: /usr/lib/jvm/java-8-oracle/jre/lib/amd64
java.vm.version: 25.45-b02
java.vm.vendor: Oracle Corporation
path.separator: :
idea.launcher.port: 7533 Java HotSpot(TM) 64-Bit Server VM

In the following posts we’ll dig dipper into Properties, so stay tuned! :-)

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