Get path environment variable in java

How to Get Environment Variable in Java?

The very common way of getting the Environment variable in Java is by using the System class. The system class provides a method name System.getenv() , which takes an optional String argument and can be used to get the value of an environment variable set in the current system.

The System.getEnv() method is an overloaded method API that returns a String map that contains all the environment variables and their values. We can give a String argument to get the value of the particular value as follows:

The variable has a key-value pair and on passing a key to the System.getEnv() method returns the value of the environment variable.

Another method of getting Environment Variable in Java is by using System Properties. But they have only a limited set of predefined environment variables like java.classpath, java.username, etc.

What is Environment Variable in Java?

An environment variable is a dynamic value used by the operating system and other applications to identify information related to a particular machine. An environment variable is a key value pair. Environment variable values are set outside the program, usually by the operating system through inbuilt functionality.

Various Examples to Get Environment Variables in Java

Let us see a few examples to understand how to get Environment the variable in Java:

Example 1: Getting specific environment variable

The above syntax can be used to store the value of the environment variable in a String for later use. To get the value of the specific variable a String argument is passed.

Let us now see an example to print the classpath for the java program.

The above example returns values for two variables Class Path and OS.

Example 2: Printing all the Environment Variables

Let us take another example to display all the environment variables of the system.

It returns a map of key-value pairs both being of String type. We can store it in the map for later use. Here we do not pass the String argument.

As we can see, all the variables are listed. As the optional argument String isn’t passed, the System.getenv() method returns a map having key-value pair both of type string. This map contains all the variables present. We are printing them using the System.out.format method to format the output.

Example 3: Getting Environment Variables using System Property

Another method of getting environment variables is using System Property.

It is similar to System.getenv() method. The System.getProperty() has values for only selected properties/variable.

Let us use various properties in an example using the System Property of the System class.

If no such property exists then the system returns null as in the case of home and name. The System.getProperty returns the properties of the specified fields.

Note: Similarly, we can also fetch various properties altogether using System.getProperties .

Learn More

If you found this interesting, you may also like to learn about Java IO Streams

Conclusion

• To get environment variables we can use either System.getenv() or System.getProperty() methods of the System class.
• Environment variables are key-value pairs storing system information for the machine used by the operating system and other applications.
• Methods System.getenv() and System.getProperty() can be used to fetch values of a particular property as well as the list of all the properties.

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Java Reading Environment Variable — System.getEnv() Examples

A quick programmatic guide to read or get environment variable values in java. Java API has System class with getEnv(String key) and getEnv() methods to system env variables.

1. Introduction

In this tutorial, We will learn how to read System environment variables programmatically in java. We do set the PATH or JAVA_HOME values in system-level and now we want to retrieve them in java for further usage.

Java API has System class and has two methods to work with environment variables. The following are the methods and both are defined as static methods so which can be accessed directly with the class name.

getEnv(String keyName)
getEnv()

String value = System.getEnv("PATH");

2. Java Program to read PATH, JAVA_HOME and TEMP Environment Variables

In the following program, we are going to retrieve PATH, JAVA_HOME, Temporary directory and SHELL from mac os env variables. Just need to call the getenv() method and pass the env variable name to it. All these env vars are OS-dependent.

package com.java.w3schools.blog.java.program.to.system.env; /** * * java Program to read system environment variables in Java * * @author JavaProgramTo.com * */ public class ReadEnvVar < public static void main(String[] args) < String shellValue = System.getenv("SHELL"); System.out.println("SHELL value : " + shellValue); String tempDir = System.getenv("TMPDIR"); System.out.println("TMPDIR value : " + tempDir); String pathValue = System.getenv("PATH"); System.out.println("PATH value : " + pathValue); String JavaHomeValue = System.getenv("JAVA_HOME"); System.out.println("Java_home value : " + JavaHomeValue); >>

SHELL value : /bin/bash TMPDIR value : /var/folders/g0/0x5m1w1950z18h3m6z6h1_000000gn/T/ PATH value : /usr/bin:/bin:/usr/sbin:/sbin Java_home value : /usr/bin/java

3. Reading all Env Variables in Java

Along with the getting value for a specific env var, System class has another method to fetch all keys and values in the OS. All are retrieved with System.getEnv() method. getEnv() method returns a Map and the iterating map will return key/value pairs.

package com.java.w3schools.blog.java.program.to.system.env; import java.util.Map; public class ReadAllEnv < public static void main(String[] args) < Mapenv = System.getenv(); for (String key : env.keySet()) < String value = env.get(key); System.out.println(key + " : " + value); >> > 

PATH : /usr/bin:/bin:/usr/sbin:/sbin SHELL : /bin/bash SQLITE_EXEMPT_PATH_FROM_VNODE_GUARDS : /Users/javaprogramto/Library/WebKit/Databases SECURITYSESSIONID : 186aa USER : javaprogramto APP_ICON_340 : ../Resources/Eclipse.icns COMMAND_MODE : unix2003 TMPDIR : /var/folders/g0/0x5m1w1950z18h3m6z6h1_000000gn/T/ SSH_AUTH_SOCK : /private/tmp/com.apple.launchd.M0QVWzoZa9/Listeners JAVA_MAIN_CLASS_24103 : com.java.w3schools.blog.java.program.to.system.env.ReadAllEnv XPC_FLAGS : 0x0 __CF_USER_TEXT_ENCODING : 0x1F5:0x0:0x0 Apple_PubSub_Socket_Render : /private/tmp/com.apple.launchd.m7YJcjjT4h/Render JAVA_STARTED_ON_FIRST_THREAD_340 : 1 LOGNAME : javaprogramto XPC_SERVICE_NAME : com.apple.xpc.launchd.oneshot.0x10000003.eclipse HOME : /Users/javaprogramto

5. Using Java 8 forEach

The above program can be iterated using Java 8 API forEach() method and will produce the same output as the above program.

import java.util.Map; public class ReadAllEnvJava8 < public static void main(String[] args) < Mapenv = System.getenv(); // using java 8 forEach env.forEach((key, value) -> System.out.println(key + " : " + value)); > > 

5. Conclusion

In this short article, We have seen how to read environment variable value programmatically in java. System class has two utility methods getEnv(String key) which returns the corresponding value and getEnv() method returns all key, value pairs from OS.

Shown the example programs on these two methods.

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A quick programmatic guide to read or get environment variable values in java. Java API has System class with getEnv(String key) and getEnv() methods to system env variables.

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