Configuring path for java

Java NIO Path (with Examples)

The Path class, introduced in the Java SE 7 release, is one of the primary entry points of the java.nio.file package. If our application uses Java New IO, we should learn more about the powerful features available in this class.

In this Java tutorial, we are learning 6 ways to create a Path .

Table of Contents 1. Building the absolute path 2. Building path relative to file store root 3. Building path relative to the current working directory 4. Building path from URI scheme 5. Building path using file system defaults 6. Building path using System.getProperty()

Prerequisite: I am building path for a file in location – “ C:/Lokesh/Setup/workspace/NIOExamples/src/sample.txt “. I have created this file beforehand and will create Path to this file in all examples.

An absolute path always contains the root element and the complete directory hierarchy required to locate the file. There is no more information required further to access the file or path.

To create an absolute path to a file, use getPath() method.

/** * Converts a path string, or a sequence of strings that when joined form a path string, * to a Path. If more does not specify any elements then the value of the first parameter * is the path string to convert. If more specifies one or more elements then each non-empty * string, including first, is considered to be a sequence of name elements and is * joined to form a path string. */ public static Path get(String first, String. more);

Example 1: Create an absolute Path to a file in Java NIO

In all given examples, we are creating the absolute path for the same file, in different ways.

//Starts with file store root or drive Path absolutePath1 = Paths.get("C:/Lokesh/Setup/workspace/NIOExamples/src", "sample.txt"); Path absolutePath2 = Paths.get("C:/Lokesh/Setup/workspace", "NIOExamples/src", "sample.txt"); Path absolutePath3 = Paths.get("C:/Lokesh", "Setup/workspace", "NIOExamples/src", "sample.txt");

2. Building path relative to file store root

Path relative to file store root starts with a forward-slash (“/”) character.

Example 2: Create relative Path to a given file

//How to define path relative to file store root (in windows it is c:/) Path relativePath1 = FileSystems .getDefault() .getPath("/Lokesh/Setup/workspace/NIOExamples/src", "sample.txt"); Path relativePath2 = FileSystems .getDefault() .getPath("/Lokesh", "Setup/workspace/NIOExamples/src", "sample.txt");

3. Building path relative to current working directory

To define the path relative to the current working directory, do not use either file system root (c:/ in windows) or slash (“/”).

Example 3: Create relative Path to current working directory

In given example, the current working directory is NIOExamples .

//How to define path relative to current working directory Path relativePath1 = Paths.get("src", "sample.txt");

4. Building path from URI scheme

Not frequently, but at times we might face a situation where we would like to convert a file path in format “file:///src/someFile.txt” to NIO path.

Example 4: Get the absolute path of a file using file URI in Java NIO

//Writing c:/ is optional //URI uri = URI.create("file:///c:/Lokesh/Setup/workspace/NIOExamples/src/sample.txt"); URI uri = URI.create("file:///Lokesh/Setup/workspace/NIOExamples/src/sample.txt"); String scheme = uri.getScheme(); if (scheme == null) throw new IllegalArgumentException("Missing scheme"); //Check for default provider to avoid loading of installed providers if (scheme.equalsIgnoreCase("file")) < String absPath = FileSystems.getDefault() .provider() .getPath(uri) .toAbsolutePath() .toString(); System.out.println(absPath); >//If you do not know scheme then use this code. //This code check file scheme as well if available. for (FileSystemProvider provider: FileSystemProvider.installedProviders()) < if (provider.getScheme().equalsIgnoreCase(scheme)) < String absPath = provider.getPath(uri) .toAbsolutePath() .toString(); System.out.println(absPath); >>

5. Building path using file system default

This is another variation of above examples where instead of using Paths.get() , we can use FileSystems.getDefault().getPath() method.

The rules for absolute and relatives paths are the same as the above methods.

Example 5: Get absolute path of a file using system defaults

FileSystem fs = FileSystems.getDefault(); //relative path Path path1 = fs.getPath("src/sample.txt"); //absolute path Path path2 = fs.getPath("C:/Lokesh/Setup/workspace/NIOExamples/src", "sample.txt");

6. Building path using System.getProperty()

Well, this is off the course, but good to know. We can use system-specific System.getProperty() also to build Path for specific files.

Example 6: Get path of a file in the system download folder

Path path1 = FileSystems.getDefault() .getPath(System.getProperty("user.home"), "downloads", "somefile.txt");

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PATH and CLASSPATH

This section explains how to use the PATH and CLASSPATH environment variables on Microsoft Windows, Solaris, and Linux. Consult the installation instructions included with your installation of the Java Development Kit (JDK) software bundle for current information.

After installing the software, the JDK directory will have the structure shown below.

The bin directory contains both the compiler and the launcher.

Update the PATH Environment Variable (Microsoft Windows)

You can run Java applications just fine without setting the PATH environment variable. Or, you can optionally set it as a convenience.

Set the PATH environment variable if you want to be able to conveniently run the executables ( javac.exe , java.exe , javadoc.exe , and so on) from any directory without having to type the full path of the command. If you do not set the PATH variable, you need to specify the full path to the executable every time you run it, such as:

C:\Java\jdk1.7.0\bin\javac MyClass.java

The PATH environment variable is a series of directories separated by semicolons ( ; ). Microsoft Windows looks for programs in the PATH directories in order, from left to right. You should have only one bin directory for the JDK in the path at a time (those following the first are ignored), so if one is already present, you can update that particular entry.

The following is an example of a PATH environment variable:

C:\Java\jdk1.7.0\bin;C:\Windows\System32\;C:\Windows\;C:\Windows\System32\Wbem

It is useful to set the PATH environment variable permanently so it will persist after rebooting. To make a permanent change to the PATH variable, use the System icon in the Control Panel. The precise procedure varies depending on the version of Windows:

1. Select Start, select Control Panel. double click System, and select the Advanced tab.
2. Click Environment Variables. In the section System Variables, find the PATH environment variable and select it. Click Edit. If the PATH environment variable does not exist, click New .
3. In the Edit System Variable (or New System Variable) window, specify the value of the PATH environment variable. Click OK. Close all remaining windows by clicking OK.

1. From the desktop, right click the My Computer icon.
2. Choose Properties from the context menu.
3. Click the Advanced tab (Advanced system settings link in Vista).
4. Click Environment Variables. In the section System Variables, find the PATH environment variable and select it. Click Edit. If the PATH environment variable does not exist, click New .
5. In the Edit System Variable (or New System Variable) window, specify the value of the PATH environment variable. Click OK. Close all remaining windows by clicking OK.

1. From the desktop, right click the Computer icon.
2. Choose Properties from the context menu.
3. Click the Advanced system settings link.
4. Click Environment Variables. In the section System Variables, find the PATH environment variable and select it. Click Edit. If the PATH environment variable does not exist, click New .
5. In the Edit System Variable (or New System Variable) window, specify the value of the PATH environment variable. Click OK. Close all remaining windows by clicking OK.

Note: You may see a PATH environment variable similar to the following when editing it from the Control Panel:

%JAVA_HOME%\bin;%SystemRoot%\system32;%SystemRoot%;%SystemRoot%\System32\Wbem

Variables enclosed in percentage signs ( % ) are existing environment variables. If one of these variables is listed in the Environment Variables window from the Control Panel (such as JAVA_HOME ), then you can edit its value. If it does not appear, then it is a special environment variable that the operating system has defined. For example, SystemRoot is the location of the Microsoft Windows system folder. To obtain the value of a environment variable, enter the following at a command prompt. (This example obtains the value of the SystemRoot environment variable):

Update the PATH Variable (Solaris and Linux)

You can run the JDK just fine without setting the PATH variable, or you can optionally set it as a convenience. However, you should set the path variable if you want to be able to run the executables ( javac , java , javadoc , and so on) from any directory without having to type the full path of the command. If you do not set the PATH variable, you need to specify the full path to the executable every time you run it, such as:

% /usr/local/jdk1.7.0/bin/javac MyClass.java

To find out if the path is properly set, execute:

This will print the version of the java tool, if it can find it. If the version is old or you get the error java: Command not found, then the path is not properly set.

To set the path permanently, set the path in your startup file.

For C shell ( csh ), edit the startup file (~/.cshrc ):

set path=(/usr/local/jdk1.7.0/bin $path)

For bash , edit the startup file ( ~/.bashrc ):

PATH=/usr/local/jdk1.7.0/bin:$PATH export PATH

For ksh , the startup file is named by the environment variable, ENV . To set the path:

PATH=/usr/local/jdk1.7.0/bin:$PATH export PATH

For sh , edit the profile file ( ~/.profile ):

PATH=/usr/local/jdk1.7.0/bin:$PATH export PATH

Then load the startup file and verify that the path is set by repeating the java command:

% source ~/.cshrc % java -version

Checking the CLASSPATH variable (All platforms)

The CLASSPATH variable is one way to tell applications, including the JDK tools, where to look for user classes. (Classes that are part of the JRE, JDK platform, and extensions should be defined through other means, such as the bootstrap class path or the extensions directory.)

The preferred way to specify the class path is by using the -cp command line switch. This allows the CLASSPATH to be set individually for each application without affecting other applications. Setting the CLASSPATH can be tricky and should be performed with care.

The default value of the class path is «.», meaning that only the current directory is searched. Specifying either the CLASSPATH variable or the -cp command line switch overrides this value.

To check whether CLASSPATH is set on Microsoft Windows NT/2000/XP, execute the following:

On Solaris or Linux, execute the following:

If CLASSPATH is not set you will get a CLASSPATH: Undefined variable error (Solaris or Linux) or simply %CLASSPATH% (Microsoft Windows NT/2000/XP).

To modify the CLASSPATH , use the same procedure you used for the PATH variable.

Class path wildcards allow you to include an entire directory of .jar files in the class path without explicitly naming them individually. For more information, including an explanation of class path wildcards, and a detailed description on how to clean up the CLASSPATH environment variable, see the Setting the Class Path technical note.

Previous page: Miscellaneous Methods in System
Next page: Questions and Exercises: The Platform Environment

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