Glob with Java NIO

What is a Glob? In this Java NIO tutorial, we will go through what a glob is and how to use it with Java. This tutorial is part of the currently on going Java NIO tutorials series.

What is a Glob?

In programming, glob is a pattern using wildcards to specify filenames. For example, *.java is a simple and trivial glob. It specifies all files with extension ‘java’. Two wildcard characters that are widely used are * and ?. Asterisk * stands for “any string of characters” and question mark ? stands for “any one character”.

Glob originated from Unix operating system. Unix provided a “global command” and it got abbreviated to glob. This is similar to regular expression but simpler in representation and limited in abilities.

Glob in Java NIO

Glob was introduced in Java as part of SE7 more features for NIO. In Java glob is used in FileSystem class in PathMatcher getPathMatcher(String syntaxAndPattern) method. A glob can be passed as an argument to get a PathMatcher. Similarly in Files class glob can be used to iterate over the entries in a directory.

Following are some examples for “glob” pattern that can be used in Java NIO:

Glob	Description
*.txt	Matches all files that has extension as txt.
*.{html,htm}	Matches all files that has extension as html or htm. { } are used to group patterns and , comma is used to separate patterns.
?.txt	Matches all files that has any single charcter as name and extension as txt.
*.*	Matches all files that has . in its name.
C:\\Users\\*	Matches any files in C: ‘Users’ directory in Windows file system. Backslash is used to escape a special character.
/home/**	Matches /home/foo and /home/foo/bar on UNIX platforms. ** matches strings of characters corssing directory boundaries.
[xyz].txt	Matches a file name with single character ‘x’ or ‘y’ or ‘z’ and extension as txt. Square brackets [ ] are used to sepcify a character set.
[a-c].txt	Matches a file name with single character ‘a’ or ‘b’ or ‘c’ and extension as txt. Hypehen – is used to specify a range and used in [ ]
[!a].txt	Matches a file name with single character that is not ‘a’. ! is used for negation.

Glob Example with Java NIO

Following is an example Java program to search for a glob pattern in a given directory and its sub directories. Here in this example we are searching for all files with extension .zip in D: in windows platform. If you are in UNIX or other platforms, you need to specify the path accordingly.

List files matching a pattern

package com.javapapers.java.nio;

import java.io.IOException;
import java.nio.file.FileSystems;
import java.nio.file.FileVisitResult;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.PathMatcher;
import java.nio.file.Paths;
import java.nio.file.SimpleFileVisitor;
import java.nio.file.attribute.BasicFileAttributes;

public class FileGlobNIO {

	public static void main(String args[]) throws IOException {
		String glob = "glob:**/*.zip";
		String path = "D:/";
		match(glob, path);
	}

	public static void match(String glob, String location) throws IOException {
		
		final PathMatcher pathMatcher = FileSystems.getDefault().getPathMatcher(
				glob);
		
		Files.walkFileTree(Paths.get(location), new SimpleFileVisitor<Path>() {
			
			@Override
			public FileVisitResult visitFile(Path path,
					BasicFileAttributes attrs) throws IOException {
				if (pathMatcher.matches(path)) {
					System.out.println(path);
				}
				return FileVisitResult.CONTINUE;
			}

			@Override
			public FileVisitResult visitFileFailed(Path file, IOException exc)
					throws IOException {
				return FileVisitResult.CONTINUE;
			}
		});
	}

}

Java Files List Program Output

D:\AndroidLocation.zip
D:\Eclipse\7dec2014\eclipse-jee-kepler-R-win32-x86_64\workspace\.metadata\.mylyn\.tasks.xml.zip
D:\Eclipse\7dec2014\eclipse-jee-kepler-R-win32-x86_64\workspace\.metadata\.mylyn\repositories.xml.zip
D:\Eclipse\7dec2014\eclipse-jee-kepler-R-win32-x86_64\workspace\.metadata\.mylyn\tasks.xml.zip
D:\mysql-workbench-community-6.2.5-winx64-noinstall.zip
D:\workspace\Android\AndroidChatBubbles-master.zip
D:\workspace\Android\Google Chat\XMPPChatDemo.zip
D:\workspace\Android\Update-Android-UI-from-a-Service-master.zip
D:\workspace\Android Chat\AndroidDialog.zip
D:\workspace\Android Wear\AndroidWearPreview.zip