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Detailed explanation of Java's method of obtaining environment variables and system attributes

Author：Eve Cole Update Time：2025-04-26 05:32:01

The concept of environment variables is not unfamiliar with it, it is the environment variables of the operating system.
System variables are variables maintained by Java itself. Get it through System.getProperty.
For different operating systems, the processing of environment variables may be inconsistent, such as case insensitive, etc.

Java Get environment variables
 Java's way of getting environment variables is very simple:
System.getEnv() gets all environment variables
System.getEnv(key) Gets the value of an environment variable

 Map map = System.getenv(); Iterator it = map.entrySet().iterator(); while(it.hasNext()) { Entry entry = (Entry)it.next(); System.out.print(entry.getKey()+"="); System.out.println(entry.getValue()); }

If it is a Windows system, the printed value is the same as the environment variables seen from "My Computer".

Java gets and sets system variables
 Java's way of getting environment variables is also very simple:
System.getProperties() Gets all system variables
System.getProperty(key) Gets the value of a system variable

 Properties properties = System.getProperties(); Iterator it = properties.entrySet().iterator(); while(it.hasNext()) { Entry entry = (Entry)it.next(); System.out.print(entry.getKey()+"="); System.out.println(entry.getValue()); }

In addition to being able to obtain system variables, you can also set the system variables you need through System.setProperty(key, value).

By default, what system variables are set in java:

  • java.version Java runtime environment version
  • java.vendor Java runtime environment vendor
  • java.vendor.url The URL of the Java vendor
  • java.home Java installation directory
  • java.vm.specification.version Java Virtual Machine Specification Version
  • java.vm.specification.vendor Java Virtual Machine Specification Vendor
  • java.vm.specification.name Java virtual machine specification name
  • java.vm.version Java virtual machine implementation version
  • java.vm.vendor Java virtual machine implementation vendor
  • java.vm.name Java virtual machine implementation name
  • java.specification.version Java runtime environment specification version
  • java.specification.vendor Java Runtime Environment Specification Vendor
  • java.specification.name Java runtime environment specification name
  • java.class.version Java class format version number
  • java.class.path Java classpath
  • java.library.path List of paths searched when loading the library
  • java.io.tmpdir The default temporary file path
  • The name of the JIT compiler to use by java.compiler
  • java.ext.dirs The path to one or more extension directories
  • os.name The name of the operating system
  • os.arch operating system architecture
  • os.version operating system version
  • file.separator file separator ("/" in UNIX systems)
  • path.separator path separator (in UNIX systems it is ":")
  • line.separator line separator ("/n" in UNIX systems)
  • user.name user's account name
  • user.home user's home directory
  • user.dir The current working directory of the user

Replenish
 1. In .bat; .cmd or .sh, some variables will be set by set.
For example, weblogic's setDomainEnv.cmd
set SUN_JAVA_HOME=C:/Oracle/Middleware/jdk160_21
The environment variable is set here
2. In the log4j configuration, the generation path of the log file is sometimes configured.
For example, ${LOG_DIR}/logfile.log, the LOG_DIR here is replaced by a variable of the system attribute.
3. Take a look at the java source code. When you obtain system variables through System.getProperties(), there will be a safe check.

 public static Properties getProperties() { SecurityManager sm = getSecurityManager(); if (sm != null) { sm.checkPropertiesAccess(); } return props; }

The SecurityManager in the System is empty during a single Java application test.
When Applet runs, the permissions are checked in combination with the .policy file.

If you give an empty SecurityManager, you will find that a permission exception will be thrown.

 public static void main(String[] args) { // TODO Auto-generated method stub System.setSecurityManager(new SecurityManager()); //SecurityManager sm = System.getSecurityManager(); //System.out.println(sm); System.getSecurityManager().checkPropertiesAccess(); }
The difference between System.getEnv() and System.getProperties()
 Conceptually, system properties and environment variables are mappings between names and values. Both mechanisms can be used to pass user-defined information to Java processes. Environment variables produce more global effects because they are visible not only to Java child processes, but also to all child processes that define them. On different operating systems, their semantics vary slightly, such as case insensitive. For these reasons, environmental variables are more likely to have unexpected side effects. It is best to use system properties wherever possible. Environment variables should be used when global effects are required, or when external system interfaces require environment variables (such as PATH). The code is as follows:
 public static void main(String [] args) { Map m = System.getenv(); for ( Iterator it = m.keySet().iterator(); it.hasNext(); ) { String key = (String ) it.next(); String value = (String ) m.get(key); System.out.println(key +":" +value); } System.out.println( "--------------------------------------" ); Properties p = System.getProperties(); for ( Iterator it = p.keySet().iterator(); it.hasNext(); ) { String key = (String ) it.next(); String value = (String ) p.get(key); System.out.println(key +":" +value); } }

Enter as follows:
 ANT_HOME:D:/program/devel/antPROCESSOR_ARCHITECTURE:x86LOGONSERVER://RJ-WEIJIANJUNHOMEDRIVE:C:CATALINA_HOME:D:/program/server/Tomcat5.5DXSDK_DIR:d:/Program Files/Microsoft DirectX SDK (August 2008)/VS80COMNTOOLS:C:/Program Files/Microsoft Visual Studio 8/Common7/Tools/SESSIONNAME:ConsoleHOMEPATH:/Documents and Settings/AdministratorTMP:C:/DOCUME~1/ADMINI~1/LOCALS~1/Tempwindir:C:/WINDOWSPROCESSOR_IDENTIFIER:x86 Family 6 Model 15 Stepping 13, GenuineIntelVS90COMNTOOLS:e:/Program Files/Microsoft Visual Studio 9.0/Common7/Tools/SystemDrive:C:USERPROFILE:C:/Documents and Settings/AdministratorPATHEXT:.COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSHCommonProgramFiles:C:/Program Files/Common FilesNUMBER_OF_PROCESSORS:2ComSpec:C:/WINDOWS/system32/cmd.exeCOMPUTERNAME:RJ-WEIJIANJUNOS:Windows_NTUSERNAME:AdministratorCLIENTNAME:ConsoleTEMP:C:/DOCUME~1/ADMINI~1/LOCALS~1/TempUSERDOMAIN:RJ-WEIJIANJUNALLUSERSPROFILE:C:/Documents and Settings/All Userslib:C:/Program Files/SQLXML 4.0/bin/PROCESSOR_LEVEL:6SystemRoot:C:/WINDOWSClusterLog:C:/WINDOWS/Cluster/cluster.logAPPDATA:C:/Documents and Settings/Administrator/Application DataPath:C:/WINDOWS/system32;C:/WINDOWS;C:/WINDOWS/System32/Wbem;C:/Program Files/Microsoft SQL Server/80/Tools/Binn/;C:/Program Files/Microsoft SQL Server/90/DTS/Binn/;C:/Program Files/Microsoft SQL Server/90/Tools/binn/;C:/Program Files/Microsoft SQL Server/90/Tools/Binn/VSShell/Common7/IDE/;C:/Program Files/Microsoft Visual Studio 8/Common7/IDE/PrivateAssemblies/;D:/program/devel/flex_sdk2/bin;D:/program/devel/ant/bin;C:/Program Files/Java/jdk1.6.0_07/bin;%JONAS_ROOT%/bin/nt;d:/program/devel/ant/binJAVA_HOME:C:/Program Files/Java/jdk1.6.0_07FP_NO_HOST_CHECK:NOPROCESSOR_REVISION:0f0dProgramFiles:C:/Program Files
Here is the output of the property:
 --------------------------------------java.runtime.name:Java(TM) 2 Runtime Environment, Standard Editionsun.boot.library.path:D:/Program Files/MyEclipse 6.5/jre/binjava.vm.version:1.5.0_11-b03java.vm.vendor:Sun Microsystems Inc.java.vendor.url:http://java.sun.com/path.separator:;java.vm.name:Java HotSpot(TM) Client VMfile.encoding.pkg:sun.iosun.java.launcher:SUN_STANDARDuser.country:CNsun.os.patch.level:Service Pack 2java.vm.specification.name:Java Virtual Machine Specificationuser.dir:D:/dev/eclipse/mye65/workspace/jmxjava.runtime.version:1.5.0_11-b03java.awt.graphicsenv:sun.awt.Win32GraphicsEnvironmentjava.endorsed.dirs:D:/Program Files/MyEclipse 6.5/jre/lib/endorsedos.arch:x86java.io.tmpdir:C:/DOCUME~1/ADMINI~1/LOCALS~1/Temp/line.separator: java.vm.specification.vendor:Sun Microsystems Inc.user.variant:os.name:Windows 2003sun.jnu.encoding:GBKjava.library.path:D:/Program Files/MyEclipse 6.5/jre/bin;.;C:/WINDOWS/system32;C:/WINDOWS;C:/WINDOWS/system32;C:/WINDOWS;C:/WINDOWS/System32/Wbem;C:/Program Files/Microsoft SQL Server/80/Tools/Binn/;C:/Program Files/Microsoft SQL Server/90/DTS/Binn/;C:/Program Files/Microsoft SQL Server/90/Tools/binn/;C:/Program Files/Microsoft SQL Server/90/Tools/binn/;C:/Program Files/Microsoft SQL Server/90/Tools/Binn/VSShell/Common7/IDE/;C:/Program Files/Microsoft Visual Studio 8/Common7/IDE/PrivateAssemblies/;D:/program/devel/flex_sdk2/bin;D:/program/devel/ant/bin;C:/Program Files/Java/jdk1.6.0_07/bin;%JONAS_ROOT%/bin/nt;d:/program/devel/ant/binjava.specification.name:Java Platform API Specificationjava.class.version:49.0sun.management.compiler:HotSpot Client Compileros.version:5.2user.home:C:/Documents and Settings/Administratoruser.timezone:Asia/Shanghaijava.awt.printerjob:sun.awt.windows.WPrinterJobfile.encoding:GBKjava.specification.version:1.5java.class.path:D:/dev/eclipse/mye65/workspace/jmx/bin;D:/program/li b/jmx/jmxtools.jar;D:/program/lib/log/commons-logging-1.1.1.jar;D:/program/lib/log/log4j-1.2.15.jar;D:/program/lib/registry/registry.jaruser.name:Administratorjava.vm.specification.version:1.0java.home:D:/Program Files/MyEclipse 6.5/jresun.arch.data.model:32user.language:zhjava.specification.vendor:Sun Microsystems Inc.awt.toolkit:sun.awt.windows.WToolkitjava.vm.info:mixed modejava.version:1.5.0_11java.ext.dirs:D:/Program Files/MyEclipse 6.5/jre/lib/extsun.boot.class.path:D:/Program Files/MyEclipse 6.5/jre/lib/rt.jar;D:/Program Files/MyEclipse 6.5/jre/lib/i18n.jar;D:/Program Files/MyEclipse 6.5/jre/lib/sunrasign.jar;D:/Program Files/MyEclipse 6.5/jre/lib/jsse.jar;D:/Program Files/MyEclipse 6.5/jre/lib/jce.jar;D:/Program Files/MyEclipse 6.5/jre/lib/charsets.jar;D:/Program Files/MyEclipse 6.5/jre/lib/charsets.jar;D:/Program Files/MyEclipse 6.5/jre/classesjava.vendor:Sun Microsystems Inc.file.separator:/java.vendor.url.bug:http://java.sun.com/cgi-bin/bugreport.cgisun.io.unicode.encoding:UnicodeLittlesun.cpu.endian:littlesun.desktop:windowsun.cpu.isalist:pentium_pro+mmx pentium_pro pentium+mmx pentium i486 i386 i86
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