Java Glossary : Filter

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Filter

A filter lets you display a list of files with some of the files filtered out.

String[] fileNames = file. list( someFilter );

will get list of files in this directory. Wildcards won't work. Note it returns an array of Strings, not including the directory, not File objects. Files are not in any particular order. They include the subdirectories, but not the . or .. entries.

Your FilenameFilter needs at a minimum to filter with File.isDirectory().

You can also use FileDialog.setFilenameFilter(java.io.FilenameFilter) to restrict which files are displayed in a File choosing dialog.

I have written 10 FilenameFilters with source. All are trivial except for the MultiFilter that lets you combine other filters in various ways.

They come with Java source. The collection is mainly for newbies trying to get some ideas on how FilenameFilters work and how you could write them.

FilenameFilters
Name	Purpose
AllDirectoriesFilter	gets all directories
AllFilesFilter	gets all files
ClamFilter	simple wildcard
EverythingFilter	gets everything
FileLengthFilter	gets short or long files
FileNameLengthFilter	gets short or long filenames
ListFilter	gets a list of files
MultiFilter	combines other Filters with "consider", "must" and "never".
RecentFilter	filters based on lastModified date
RegexFilter	filters with Regex expressions.

You can cascade (combine) FileNameFilters by having one ask advice of another, or write a mother filter that asks the advice of several child filters and &&'s or ||'s the results of their accept methods. MultiFilter makes that task easy.

If you are selecting files to display in Swing, the classes of interest are: javax.swing.filechooser.FileFilter, javax.swing.JFileChooser, javax.swing.plaf.BasicFileChooserUI, javax.swing.plaf.multi.MultiFileChooserUI.

In the context of Servlets, javax.servlet.Filter is an interface to allow a transaction to be processed in an assembly line. Each Filter does some of the work and passes on the input or output to the next filter in the chain, and decides on who is next.

File ¤ Servlet ¤ wildcard filters

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