org.apache.commons.io.DirectoryWalker<T>
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java.lang.Object
public abstract class DirectoryWalker<T>
Abstract class that walks through a directory hierarchy and provides subclasses with convenient hooks to add specific behaviour.
This class operates with a FileFilter and maximum depth to
limit the files and direcories visited.
Commons IO supplies many common filter implementations in the
filefilter package.
The following sections describe:
FileCleaner implementation.FileFilter(s) with DirectoryWalker.
public class FileCleaner extends DirectoryWalker {
public FileCleaner() {
super();
}
public List clean(File startDirectory) {
List results = new ArrayList();
walk(startDirectory, results);
return results;
}
protected boolean handleDirectory(File directory, int depth, Collection results) {
// delete svn directories and then skip
if (".svn".equals(directory.getName())) {
directory.delete();
return false;
} else {
return true;
}
}
protected void handleFile(File file, int depth, Collection results) {
// delete file and add to list of deleted
file.delete();
results.add(file);
}
}
The first option is to visit all directories and files. This is achieved via the no-args constructor.
The second constructor option is to supply a single FileFilter
that describes the files and directories to visit. Care must be taken
with this option as the same filter is used for both directories
and files.
For example, if you wanted all directories which are not hidden and files which end in ".txt":
public class FooDirectoryWalker extends DirectoryWalker {
public FooDirectoryWalker(FileFilter filter) {
super(filter, -1);
}
}
// Build up the filters and create the walker
// Create a filter for Non-hidden directories
IOFileFilter fooDirFilter =
FileFilterUtils.andFileFilter(FileFilterUtils.directoryFileFilter,
HiddenFileFilter.VISIBLE);
// Create a filter for Files ending in ".txt"
IOFileFilter fooFileFilter =
FileFilterUtils.andFileFilter(FileFilterUtils.fileFileFilter,
FileFilterUtils.suffixFileFilter(".txt"));
// Combine the directory and file filters using an OR condition
java.io.FileFilter fooFilter =
FileFilterUtils.orFileFilter(fooDirFilter, fooFileFilter);
// Use the filter to construct a DirectoryWalker implementation
FooDirectoryWalker walker = new FooDirectoryWalker(fooFilter);
The third constructor option is to specify separate filters, one for
directories and one for files. These are combined internally to form
the correct FileFilter, something which is very easy to
get wrong when attempted manually, particularly when trying to
express constructs like 'any file in directories named docs'.
For example, if you wanted all directories which are not hidden and files which end in ".txt":
public class FooDirectoryWalker extends DirectoryWalker {
public FooDirectoryWalker(IOFileFilter dirFilter, IOFileFilter fileFilter) {
super(dirFilter, fileFilter, -1);
}
}
// Use the filters to construct the walker
FooDirectoryWalker walker = new FooDirectoryWalker(
HiddenFileFilter.VISIBLE,
FileFilterUtils.suffixFileFilter(".txt"),
);
This is much simpler than the previous example, and is why it is the preferred
option for filtering.
What DirectoryWalker does provide for cancellation is:
DirectoryWalker.CancelException which can be thrown in any of the
lifecycle methods to stop processing.walk() method traps thrown DirectoryWalker.CancelException
and calls the handleCancelled() method, providing
a place for custom cancel processing.Implementations need to provide:
DirectoryWalker.CancelException.handleCancelled() method.
Two possible scenarios are envisaged for cancellation:
The following sections provide example implementations for these two different scenarios.
cancel() method that can be
called by another thread to stop the processing. A typical example use-case
would be a cancel button on a GUI. Calling this method sets a
volatile flag to ensure it will work properly in a multi-threaded environment.
The flag is returned by the handleIsCancelled() method, which
will cause the walk to stop immediately. The handleCancelled()
method will be the next, and last, callback method received once cancellation
has occurred.
public class FooDirectoryWalker extends DirectoryWalker {
private volatile boolean cancelled = false;
public void cancel() {
cancelled = true;
}
private void handleIsCancelled(File file, int depth, Collection results) {
return cancelled;
}
protected void handleCancelled(File startDirectory, Collection results, CancelException cancel) {
// implement processing required when a cancellation occurs
}
}
DirectoryWalker.CancelException could be implemented
in any of the lifecycle methods.
public class BarDirectoryWalker extends DirectoryWalker {
protected boolean handleDirectory(File directory, int depth, Collection results) throws IOException {
// cancel if hidden directory
if (directory.isHidden()) {
throw new CancelException(file, depth);
}
return true;
}
protected void handleFile(File file, int depth, Collection results) throws IOException {
// cancel if read-only file
if (!file.canWrite()) {
throw new CancelException(file, depth);
}
results.add(file);
}
protected void handleCancelled(File startDirectory, Collection results, CancelException cancel) {
// implement processing required when a cancellation occurs
}
}
| Nested Class Summary | |
|---|---|
static class |
DirectoryWalker.CancelException
CancelException is thrown in DirectoryWalker to cancel the current processing. |
| Constructor Summary | |
|---|---|
protected |
DirectoryWalker()
Construct an instance with no filtering and unlimited depth. |
protected |
DirectoryWalker(FileFilter filter,
int depthLimit)
Construct an instance with a filter and limit the depth navigated to. |
protected |
DirectoryWalker(IOFileFilter directoryFilter,
IOFileFilter fileFilter,
int depthLimit)
Construct an instance with a directory and a file filter and an optional limit on the depth navigated to. |
| Method Summary | |
|---|---|
protected void |
checkIfCancelled(File file,
int depth,
Collection<T> results)
Checks whether the walk has been cancelled by calling handleIsCancelled(java.io.File, int, java.util.Collection,
throwing a CancelException if it has. |
protected File[] |
filterDirectoryContents(File directory,
int depth,
File[] files)
Overridable callback method invoked with the contents of each directory. |
protected void |
handleCancelled(File startDirectory,
Collection<T> results,
DirectoryWalker.CancelException cancel)
Overridable callback method invoked when the operation is cancelled. |
protected boolean |
handleDirectory(File directory,
int depth,
Collection<T> results)
Overridable callback method invoked to determine if a directory should be processed. |
protected void |
handleDirectoryEnd(File directory,
int depth,
Collection<T> results)
Overridable callback method invoked at the end of processing each directory. |
protected void |
handleDirectoryStart(File directory,
int depth,
Collection<T> results)
Overridable callback method invoked at the start of processing each directory. |
protected void |
handleEnd(Collection<T> results)
Overridable callback method invoked at the end of processing. |
protected void |
handleFile(File file,
int depth,
Collection<T> results)
Overridable callback method invoked for each (non-directory) file. |
protected boolean |
handleIsCancelled(File file,
int depth,
Collection<T> results)
Overridable callback method invoked to determine if the entire walk operation should be immediately cancelled. |
protected void |
handleRestricted(File directory,
int depth,
Collection<T> results)
Overridable callback method invoked for each restricted directory. |
protected void |
handleStart(File startDirectory,
Collection<T> results)
Overridable callback method invoked at the start of processing. |
protected void |
walk(File startDirectory,
Collection<T> results)
Internal method that walks the directory hierarchy in a depth-first manner. |
| Methods inherited from class java.lang.Object |
|---|
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
| Constructor Detail |
|---|
protected DirectoryWalker()
protected DirectoryWalker(FileFilter filter,
int depthLimit)
The filter controls which files and directories will be navigated to as
part of the walk. The FileFilterUtils class is useful for combining
various filters together. A null filter means that no
filtering should occur and all files and directories will be visited.
filter - the filter to apply, null means visit all filesdepthLimit - controls how deep the hierarchy is
navigated to (less than 0 means unlimited)
protected DirectoryWalker(IOFileFilter directoryFilter,
IOFileFilter fileFilter,
int depthLimit)
The filters control which files and directories will be navigated to as part
of the walk. This constructor uses FileFilterUtils.makeDirectoryOnly(IOFileFilter)
and FileFilterUtils.makeFileOnly(IOFileFilter) internally to combine the filters.
A null filter means that no filtering should occur.
directoryFilter - the filter to apply to directories, null means visit all directoriesfileFilter - the filter to apply to files, null means visit all filesdepthLimit - controls how deep the hierarchy is
navigated to (less than 0 means unlimited)| Method Detail |
|---|
protected final void walk(File startDirectory,
Collection<T> results)
throws IOException
Users of this class do not need to call this method. This method will be called automatically by another (public) method on the specific subclass.
Writers of subclasses should call this method to start the directory walk.
Once called, this method will emit events as it walks the hierarchy.
The event methods have the prefix handle.
startDirectory - the directory to start from, not nullresults - the collection of result objects, may be updated
NullPointerException - if the start directory is null
IOException - if an I/O Error occurs
protected final void checkIfCancelled(File file,
int depth,
Collection<T> results)
throws IOException
handleIsCancelled(java.io.File, int, java.util.Collection) ,
throwing a CancelException if it has.
Writers of subclasses should not normally call this method as it is called
automatically by the walk of the tree. However, sometimes a single method,
typically handleFile(java.io.File, int, java.util.Collection, may take a long time to run. In that case,
you may wish to check for cancellation by calling this method.
file - the current file being processeddepth - the current file level (starting directory = 0)results - the collection of result objects, may be updated
IOException - if an I/O Error occurs
protected boolean handleIsCancelled(File file,
int depth,
Collection<T> results)
throws IOException
This method should be implemented by those subclasses that want to
provide a public cancel() method available from another
thread. The design pattern for the subclass should be as follows:
public class FooDirectoryWalker extends DirectoryWalker {
private volatile boolean cancelled = false;
public void cancel() {
cancelled = true;
}
private void handleIsCancelled(File file, int depth, Collection results) {
return cancelled;
}
protected void handleCancelled(File startDirectory,
Collection results, CancelException cancel) {
// implement processing required when a cancellation occurs
}
}
If this method returns true, then the directory walk is immediately
cancelled. The next callback method will be handleCancelled(java.io.File, java.util.Collection.
This implementation returns false.
file - the file or directory being processeddepth - the current directory level (starting directory = 0)results - the collection of result objects, may be updated
IOException - if an I/O Error occurs
protected void handleCancelled(File startDirectory,
Collection<T> results,
DirectoryWalker.CancelException cancel)
throws IOException
This implementation just re-throws the DirectoryWalker.CancelException.
startDirectory - the directory that the walk started fromresults - the collection of result objects, may be updatedcancel - the exception throw to cancel further processing
containing details at the point of cancellation.
IOException - if an I/O Error occurs
protected void handleStart(File startDirectory,
Collection<T> results)
throws IOException
This implementation does nothing.
startDirectory - the directory to start fromresults - the collection of result objects, may be updated
IOException - if an I/O Error occurs
protected boolean handleDirectory(File directory,
int depth,
Collection<T> results)
throws IOException
This method returns a boolean to indicate if the directory should be examined or not. If you return false, the entire directory and any subdirectories will be skipped. Note that this functionality is in addition to the filtering by file filter.
This implementation does nothing and returns true.
directory - the current directory being processeddepth - the current directory level (starting directory = 0)results - the collection of result objects, may be updated
IOException - if an I/O Error occurs
protected void handleDirectoryStart(File directory,
int depth,
Collection<T> results)
throws IOException
This implementation does nothing.
directory - the current directory being processeddepth - the current directory level (starting directory = 0)results - the collection of result objects, may be updated
IOException - if an I/O Error occurs
protected File[] filterDirectoryContents(File directory,
int depth,
File[] files)
throws IOException
This implementation returns the files unchanged
directory - the current directory being processeddepth - the current directory level (starting directory = 0)files - the files (possibly filtered) in the directory
IOException - if an I/O Error occurs
protected void handleFile(File file,
int depth,
Collection<T> results)
throws IOException
This implementation does nothing.
file - the current file being processeddepth - the current directory level (starting directory = 0)results - the collection of result objects, may be updated
IOException - if an I/O Error occurs
protected void handleRestricted(File directory,
int depth,
Collection<T> results)
throws IOException
This implementation does nothing.
directory - the restricted directorydepth - the current directory level (starting directory = 0)results - the collection of result objects, may be updated
IOException - if an I/O Error occurs
protected void handleDirectoryEnd(File directory,
int depth,
Collection<T> results)
throws IOException
This implementation does nothing.
directory - the directory being processeddepth - the current directory level (starting directory = 0)results - the collection of result objects, may be updated
IOException - if an I/O Error occurs
protected void handleEnd(Collection<T> results)
throws IOException
This implementation does nothing.
results - the collection of result objects, may be updated
IOException - if an I/O Error occurs
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