Chapter 4

The previous example is very condensed, but it's not as obvious and easy to read compared to the initially described methods.

Since v1.7.1, Groovy has also introduced a very powerful traverse method in the java. io.File class. In its simplest form, it does the same as eachFileRecurse:

currentDir.traverse { File file -> println file.name

}

The traverse method has an overloaded version that also accepts a Map of additional parameters, which allows you to control various aspects of directory traversing behavior.

More advanced traverse options are described in the Searching for files recipe.

See also

The following recipes contain some additional information on the topics discussed in this recipe:

ff

ff

Searching for files

The Defining code as data in Groovy recipe in Chapter 3, Using Groovy language features

Also, it's worth examining the Groovydoc for the File, FileType, and Closure classes:

ff http://groovy.codehaus.org/groovy-jdk/java/io/File.html

ff http://groovy.codehaus.org/api/groovy/io/FileType.html

ff http://groovy.codehaus.org/api/groovy/lang/Closure.html

Searching for files

In this recipe, we will show how easy it is to filter out files and folders during a search operation on the file system.

Getting ready

Let's assume that we are searching for files in a current working directory. For that, we need to define a variable of the java.io.File type that points to the . path:

def currentDir = new File('.')

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How to do it...

As we already mentioned in the Walking through a directory recursively recipe, Groovy adds a powerful traverse method for helping us with our searching task. Let's explore the options that are given by that method:

1.The simplest way to search for specific files is to apply some filtering logic within a closure that we pass to the traverse method:

currentDir.traverse { File file ->

if (file.name.endsWith('.groovy')) { println file.name

}

}

2.The traverse method has another overloaded version that accepts a Map of the parameters. One of those parameters is nameFilter, which should be of the java.util.regex.Pattern type. So, our initial code snippet can be written in the following way:

currentDir.traverse(nameFilter: ~/.*\.groovy/) { File file ->

println file.name

}

3.The traverse method has even more tricks up its sleeve. By specifying the type of the entries (you need to import the groovy.io.FileType class beforehand), we can search for the pattern of the names we want to exclude (excludeNameFilter):

import static groovy.io.FileType.*

...

currentDir.traverse( type: FILES,

nameFilter: ~/.*\.groovy/, excludeNameFilter: ~/^C.*$/) { File file ->

println file.name

}

4.A closure that is passed as a final input argument can also be passed through a visit parameter in the map:

currentDir.traverse(
type:	FILES,
nameFilter:	{ it.matches(/.*\.groovy/)	},
excludeNameFilter:	{ it.matches(/^C.*$/)	},
visit:	{ println it.name	}
)

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5.You can also filter on file attributes, other than name, by using the filter/ excludeFilter closure parameters, which are given on java.io.File objects:

def today = new Date()

currentDir.traverse( filter: {

		it.lastModified() < (today-5).time &&
		it.name.endsWith('.groovy')
	},
excludeFilter: {		it.isDirectory() },
visit:	{	println it.name }

)

6.You can prune some directory tree branches by using the preDir (or postDir) closure parameters:

import static groovy.io.FileVisitResult.*

...

currentDir.traverse(
preDir:	{
	if (it.name == '.svn') {
	return SKIP_SUBTREE
	}
	},
nameFilter:	{ it.matches(/.*\.groovy/)	},
excludeNameFilter:	{ it.matches(/^C.*$/)	},
visit:	{ println it.name	}
)

How it works...

As you can guess, the first code snippet will walk through all the subdirectories and print all Groovy (*.groovy) source file names that are found.

In the Searching strings with regular expressions recipe in Chapter 3, Using Groovy Language Features, we mentioned the ~// operator, which constructs a Pattern object. That's what we use in the second example to match the *.groovy files and print their name again.

In the third step, we add a bit more logic to the code, since we only go through normal files by specifying FileType.FILES in the type parameter. Other possible values are FileType. ANY and FileType.DIRECTORIES. The search also excludes all files starting with C with the help of a regular expression passed to the excludeNameFilter parameter.

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The fourth example is identical to the third one, except that all filtering logic is passed through named parameters in a map.

The fifth code snippet prints the names of the files having the *.groovy extension, which are older than 5 days and which are not directories.

The last code example behaves in the same way as the third snippet, but it also excludes the .svn directory and all subdirectories from searching. The closure passed to preDir

returns an instance of the groovy.io.FileVisitResult enumeration, which controls the traversing behavior. Other possible enumeration values are CONTINUE, SKIP_SIBLINGS, and TERMINATE. In general, preDir and postDir can execute any code, and it's not mandatory to return FileVisitResult.

There's more...

There are other useful options available for the traverse method:

ff maxDepth: It says how deep should we go in our search.

ff sort: It is a closure that sets the sorting order in which files and directories will be processed.

ff visitRoot: It indicates that the visit closure should also be called for the target search directory.

ff preRoot: It indicates that the preDir closure should also be called for the target search directory.

ff postRoot: It indicates that postDir closure should also be called for the target search directory.

If you just want to search in the current directory without visiting its subdirectories, you can use the eachFileMatch method instead:

currentDir.eachFileMatch(~/.*\.groovy/) { File file -> println file.name

}

There is also an eachDirMatch method, in case you only need to walk through the matching first-level directories.

See also

An initial introduction to walking through directory trees was given in the Walking through a directory recursively recipe.

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