Environment Variables for Java Applications. What are Environment Variables? Environment variables are global system variables accessible by all the processes running under the Operating System (OS). Environment variables are useful to store system- wide values such as the directories to search for the executable programs (PATH) and the OS version. Examples of environment variables in Windows OS are: COMPUTENAME, USERNAME: stores the computer and current user name. Ok, so you working on Computer where you dont have Admin access. Also you want to set some Environment Variables (PATH, CLASSPATH etc). In Windows XP, you can set.OS: the operating system. System. Root: the system root directory. PATH: stores a list of directories for searching executable programs. In setting up JDK and Java applications, you will encounter these environment variables: PATH, CLASSPATH, JAVA. In short: PATH: maintains a list of directories. The OS searches the PATH entries for executable programs, such as Java Compiler (javac) and Java Runtime (java). CLASSPATH: maintain a list of directories (containing many Java class files) and JAR file (a single- file archive of Java classes). Setting Environment Variables. Using environment variables is one of the ways that Windows communicates information such as the location of system files and folders. In Windows, PATH is an environment variable that lists directories where the operating system basically looks for executable files when provided a command.
The Java Compiler and Java Runtime searches the CLASSPATH entries for Java classes referenced in your program. JAVA. Environment variables are typically named in uppercase, with words joined with underscore (. To display a particular variable, use command . For examples. COMPUTERNAME=xxxxxxx. Pay particular attention to the variable called PATH. Set/Change/Unset a Variable. To set (or change) a variable, use command . There shall be no spaces before and after the '=' sign. To unset an environment variable, use . Set an Environment Variable. To set an environment variable permanently in Windows (so that it is available to all the Windows' processes), start the . For example, you can use the echo command to print the value of a variable in the form . Global environment variables (available to ALL processes) are named in uppercase, with words joined with underscore (. Local variables (available to the current process only) are in lowercase. Most of the Unixes (Ubuntu and Mac OS X) use the so- called Bash shell. Under bash shell: To list all the environment variables, use the command . You could use . Enclosed the value with double quotes if it contains spaces. To set a local variable, use the command . Local variable is available within this process only. To unset a local variable, use command . Take note that files beginning with dot (.) is hidden by default. To display hidden files, use command . For example. export CLASSPATH=.: /usr/local/tomcat/lib/servlet- api. Take note that Bash shell uses colon (: ) as the path separator; while windows use semi- colon (; ). To refresh the bash shell, issue a . In other words, PATH maintains a list of directories for searching executable programs. PATH (For Windows) When you launch an executable program (with file extension of . If the program cannot be found in these directories, you will get the following error. But as PATH is frequently used, a dedicated command called path is provided. In other words, the current working directory is searched first, before searching the other entries specified in PATH, in a the order specified. For Windows users, you could set the PATH permanently to include JDK's . DO NOT remove any existing entry; otherwise, some programs may not run. PATH (For Mac and Ubuntu)Most of the Unixes and Mac use the so- called Bash Shell in the . When you launch an executable program (with file permission of executable) in a Bash shell, the system searches the program in ALL the directories listed in the PATH. If the program cannot be found, you will get the following error. To list the current PATH, issue command. PATHTo add a directory (e. PATH (referenced as $PATH) permanently, you can add the following line at the end of the . As a result, you have to enter . It is recommended to include the current directory in the PATH by adding this line at the end of the . To use a third- party Java package, you need to place the distributed JAR file in a location that is available to the Java Compiler and Java Runtime. How Classes are Found? Java Compiler (. You can print its contents via System. System. get. Property(. IDE (such as Eclipse/Net. Beans) manages - cp (- classpath) for each of the applications and does not rely on the CLASSPATH environment. Cannot Find Classes. If the Java Runtime (. If CLASSPATH is not set, it is defaulted to the current directory. If you set the CLASSPATH, it is important to include the current working directory (.). Otherwise, the current directory will not be searched. A common problem in running hello- world program is: CLASSPATH is set but does not include the current working directory. The current directory is therefore not searched, which results in . You can simply remove the CLASSPATH, and leave the class path defaulted to the current directory. For a beginner, no explicit CLASSPATH setting is required. Read JDK documents . Make sure that the current directory '.' is included as the first entry. To create CLASSPATH . Make sure that the current directory '.' is included as the first entry. CLASSPATH (for Mac and Ubuntu)To set the CLASSPATH for the current session, issue this command. CLASSPATH=.: /usr/local/tomcat/bin/servlet- api. Use colon ': ' as the path separator (instead of semi- colon '; ' in Windows). To set the CLASSPATH permanently, place the above export command in the bash shell initialization script (. Unixes (Mac OS/Ubuntu)Java is platform independent. Java classes run in Windows as well as Unixes - binary compatible. Unixes have many shells, such as the newer bash and the older csh, ksh. Windows have two shells: the newer cmd. Each shell come with its own set of commands, utilities, and its own scripting programming language. Unix's variable name is denoted as $varname, e. CLASSPATH. Windows uses %varname%, e,g., %CLASSPATH%. Unix uses command . Windows uses command . Windows' PATH is set permanently via Control Panel . The current directory is NOT included in the Unix's PATH implicitly. To run a program in the current directory, you need to issue . It is recommended to include the current directory (.) in the PATH explicitly. On the other hand, current directory is included in Windows' PATH implicitly. A Windows' path includes a drive letter and directories. Each drive has a root directory. It uses back- slash '\' as directory separator (e. Linux's paths do not have drive letter. There is a single root. Unix uses forward slash '/' as the directory separator (e.
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