System getProperties vs getenv

System.getenv()

'System.getenv' method return the system environment properties. If the system does not support environment variables, an empty map is returned.

App.java

package com.sample.app;

import java.util.Map;

public class App {

 public static void main(String args[]) {

  Map<String, String> properties = System.getenv();

  for (String key : properties.keySet()) {
   System.out.println(key + " = " + properties.get(key));
  }
 }

}

Output

PATH = /usr/bin:/bin:/usr/sbin:/sbin
SHELL = /bin/bash
SQLITE_EXEMPT_PATH_FROM_VNODE_GUARDS = /Users/krishna/Library/WebKit/Databases
USER = krishna
JAVA_MAIN_CLASS_62467 = com.sample.app.App
APP_ICON_5033 = ../Resources/Eclipse.icns
TMPDIR = /var/folders/1c/tb7sr9q90mb62pqngbt4l56h5l9cz7/T/]
LOGNAME = krishna
XPC_SERVICE_NAME = org.eclipse.platform.ide.11092
JAVA_STARTED_ON_FIRST_THREAD_5033 = 1
HOME = /Users/Krishna

System.properties

This method return Java specific properties. You can even set new java system properties at command line while running the application.

App.java    

package com.sample.app;

import java.util.Enumeration;
import java.util.Properties;

public class App {

 public static void main(String args[]) {

  Properties properties = System.getProperties();

  Enumeration<Object> props = properties.keys();

  while (props.hasMoreElements()) {
   Object key = props.nextElement();
   Object value = properties.get(key);
   System.out.println(key + " = " + value);
  }

 }

}

Output

java.runtime.name = Java(TM) SE Runtime Environment
sun.boot.library.path = /Library/Java/JavaVirtualMachines/jdk1.8.0_221.jdk/Contents/Home/jre/lib
java.vm.version = 25.221-b11
gopherProxySet = false
java.vm.vendor = Oracle Corporation
java.vendor.url = http://java.oracle.com/
path.separator = :
java.vm.name = Java HotSpot(TM) 64-Bit Server VM
file.encoding.pkg = sun.io
user.country = IN
sun.java.launcher = SUN_STANDARD
sun.os.patch.level = unknown
java.vm.specification.name = Java Virtual Machine Specification
user.dir = /Users/krishna/eclipse-workspace/sof
java.runtime.version = 1.8.0_221-b11
java.awt.graphicsenv = sun.awt.CGraphicsEnvironment
java.endorsed.dirs = /Library/Java/JavaVirtualMachines/jdk1.8.0_221.jdk/Contents/Home/jre/lib/endorsed
os.arch = x86_64
java.io.tmpdir = /var/folders/1c/tb7sr9q90mb62pqngbt4l56h5l9cz7/T/
line.separator = 

java.vm.specification.vendor = Oracle Corporation
os.name = Mac OS X
sun.jnu.encoding = UTF-8
java.library.path = /Users/krishna/Library/Java/Extensions:/Library/Java/Extensions:/Network/Library/Java/Extensions:/System/Library/Java/Extensions:/usr/lib/java:.
java.specification.name = Java Platform API Specification
java.class.version = 52.0
sun.management.compiler = HotSpot 64-Bit Tiered Compilers
os.version = 10.14.6
user.home = /Users/krishna
user.timezone = 
java.awt.printerjob = sun.lwawt.macosx.CPrinterJob
file.encoding = UTF-8
java.specification.version = 1.8
java.class.path = /Users/krishna/eclipse-workspace/sof/target/classes:/Users/krishna/.m2/repository/com/google/code/gson/gson/2.8.6/gson-2.8.6.jar:/Users/krishna/.m2/repository/com/fasterxml/jackson/core/jackson-core/2.6.3/jackson-core-2.6.3.jar:/Users/krishna/.m2/repository/com/fasterxml/jackson/core/jackson-databind/2.6.3/jackson-databind-2.6.3.jar:/Users/krishna/.m2/repository/com/fasterxml/jackson/core/jackson-annotations/2.6.0/jackson-annotations-2.6.0.jar:/Users/krishna/.m2/repository/com/owlike/genson/1.6/genson-1.6.jar:/Users/krishna/.m2/repository/org/apache/commons/commons-lang3/3.9/commons-lang3-3.9.jar:/Users/krishna/.m2/repository/org/apache/commons/commons-text/1.8/commons-text-1.8.jar:/Users/krishna/.m2/repository/org/springframework/spring-web/5.2.2.RELEASE/spring-web-5.2.2.RELEASE.jar:/Users/krishna/.m2/repository/org/springframework/spring-beans/5.2.2.RELEASE/spring-beans-5.2.2.RELEASE.jar:/Users/krishna/.m2/repository/org/springframework/spring-core/5.2.2.RELEASE/spring-core-5.2.2.RELEASE.jar:/Users/krishna/.m2/repository/org/springframework/spring-jcl/5.2.2.RELEASE/spring-jcl-5.2.2.RELEASE.jar
user.name = krishna
java.vm.specification.version = 1.8
sun.java.command = com.sample.app.App
java.home = /Library/Java/JavaVirtualMachines/jdk1.8.0_221.jdk/Contents/Home/jre
sun.arch.data.model = 64
user.language = en
java.specification.vendor = Oracle Corporation
awt.toolkit = sun.lwawt.macosx.LWCToolkit
java.vm.info = mixed mode
java.version = 1.8.0_221
java.ext.dirs = /Users/krishna/Library/Java/Extensions:/Library/Java/JavaVirtualMachines/jdk1.8.0_221.jdk/Contents/Home/jre/lib/ext:/Library/Java/Extensions:/Network/Library/Java/Extensions:/System/Library/Java/Extensions:/usr/lib/java
sun.boot.class.path = /Library/Java/JavaVirtualMachines/jdk1.8.0_221.jdk/Contents/Home/jre/lib/resources.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_221.jdk/Contents/Home/jre/lib/rt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_221.jdk/Contents/Home/jre/lib/sunrsasign.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_221.jdk/Contents/Home/jre/lib/jsse.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_221.jdk/Contents/Home/jre/lib/jce.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_221.jdk/Contents/Home/jre/lib/charsets.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_221.jdk/Contents/Home/jre/lib/jfr.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_221.jdk/Contents/Home/jre/classes
java.vendor = Oracle Corporation
file.separator = /
java.vendor.url.bug = http://bugreport.sun.com/bugreport/
sun.io.unicode.encoding = UnicodeBig
sun.cpu.endian = little
sun.cpu.isalist =

You can even set the system properties while launching the application from command line.

Example

java -DpropertyName1=value1 -DpropertyName2=value2... {ApplicationName}

Example

java -Dname=Krishna -DnoOfThreads=20 App

App.java

public class App {

 public static void main(String args[]) {

  String noOfThreads = System.getProperty("noOfThreads");
  String name = System.getProperty("name");
  
  System.out.println("Number Of Thread : " + noOfThreads);
  System.out.println("Name : " + name);
 }

}

Compile and run the application by passing vm arguments.

$javac App.java
$java -Dname=Krishna -DnoOfThreads=20 App
Number Of Thread : 20
Name : Krishna

How to pass vm arguments in Eclipse?

Right click on Application.

Run As -> Run Configurations…

Go to Arguments tab.

Add below statement in VM arguments: tab.

-Dname=Krishna -DnoOfThreads=20

Click on Run button to run the application.

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