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()
Example:
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);
}
}
Output: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) {
Map env = System.getenv();
for (String key : env.keySet()) {
String value = env.get(key);
System.out.println(key + " : " + value);
}
}
}
Output:
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) {
Map env = 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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