• A filter lets you display a list of files with some of the files filtered out. If works with File.list and FilnameFilter.
• File.list just gives you the unqualified filename. If you want a filtered list of File OBjects containing the full path, you use File. listFiles and a FilenameFilter alternatively a FilenameFilter .
• If you are selecting files to display in Swing with a JFilechooser, and want to filter our various files from consideration, 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.
• There are pair classes you can override to intervene on the processing of an i/o stream to modify it, collect statistics or monitor progress. You override FilterInputStream or FilterOutputStream and insert than in the chain of processors in the same way you insert BufferedInputStream.

Filtering File.list

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

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.

Here is how to write a simple class that implements the FilenameFilter interface:

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.

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.

FileInputStream

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