Parsing the Files.walkFileTree () utility;
Not finding anywhere sensible description in Russian, that for the beast Files.walkFileTree () , and with a creak having mastered it, as it turned out later, simple functionality, I decided to share in the framework of fixing material with examples, which I missed so much.
The walkFileTree () method allows you to bypass the tree of files and subdirectories passed to it as a parameter of the Path element ...
Two method signatures
Where
Path start is the directory whose contents are to be bypassed;
FileVisitor visitor is the instance of the class that implements the FileVisitor interface, or inherits from SimpleFileVisitor (). The latter, in my opinion, is more convenient to use when you do not need to override all FileVisitor () methods, which will be discussed below (but everything depends on the situation),
Set <\ FileVisitOption> options is a set of options that determine the behavior during traversal,
maxDepth - depth of passage subdirectories.
First, about the parameters that soon or later will be useful
maxDepth- bypass depth. If = 0, the directory will not be entered, if = MAX_VALUE, the directory will be studied to the maximum depth, respectively, if maxDepth = 3, the passage will be carried out on 3 subdirectories “down”.
FileVisitOption - enum set, which determines whether the program should follow symbolic links when crawling (in this case, the value FileVisitOption.FOLLOW_LINKS is specified).
FileVisitor is an interface that has 4 methods:
1) FileVisitResult preVisitDirectory (Tdir, BasicFileAttributes attrs) throws IOException;
includes a set of methods that should be performed before visiting the current subdirectory. For example, through attrs you can get from such data as:
lastModifiedTime (),
lastAccessTime (),
creationTime (),
isRegularFile () - true, if we have a file,
isDirectory () - true, if we have a directory,
isSymbolicLink () - true, if the object is a link,
isOther () - true, if the object in question is not a file , neither by directory nor by reference,
size () returns the size of the object and
fileKey () returns the file key or null;
If during the crawling process it is planned to count the number of directories, we should not forget that the start directory will also be taken into account in the total amount.
2) FileVisitResult visitFile (T file, BasicFileAttributes attrs) throws IOException;
a set of methods that should be performed during a visit to the current file (you can, for example, rummage through its contents and search for occurrences of the search string, or again find out the date of the last visit, change the file or fold the size of all files to crawl the directory size)
Example
In this example, when traversing the file tree, each file is checked for the simultaneous execution of 2 events - whether the file name contains the desired entry and whether the body of the file contains the occurrence of the required string. When both conditions are met, the file is added to the result sheet, after which the crawl continues;
Or another example of overloading the visitFile method.
A program during a tree traversal when visiting a file, in case it is a zip or rar archive, adds its address (path) as a string to the list of archive files;
3) FileVisitResult visitFileFailed (T file, IOException exc) throws IOException;
This method can be useful in case of file access error + it “can” throw Exception. The rest can be taught through the Override annotation. For example, count the number of files that could not be accessed;
Example
In the case of an unsuccessful attempt to access the path, the given path as a string is added to the failed sheet for it like it, and the program continues bypassing without visiting its subdirectory;
4) FileVisitResult postVisitDirectory (T dir, IOException exc) throws IOException;
Everything that needs to be done after visiting the directory should be listed as part of the overload of this method. For example, having gone through the directory and destroying all the files in it, you can destroy it by this method (we remember that Files.delete (Path dir) deletes the directory only if it is empty and does not contain files).
Example
All the above methods finish working, returning the “visit results” (FileVisitResult) of an object that belong to the enum set and can take the following values:
The walkFileTree () method allows you to bypass the tree of files and subdirectories passed to it as a parameter of the Path element ...
Two method signatures
Files.walkFileTree(Path start, FileVisitor<? super Path> visitor);
Files.walkFileTree(Path start, Set<FileVisitOption> options, int maxDepth, FileVisitor<? super Path> visitor);Where
Path start is the directory whose contents are to be bypassed;
FileVisitor visitor is the instance of the class that implements the FileVisitor interface, or inherits from SimpleFileVisitor (). The latter, in my opinion, is more convenient to use when you do not need to override all FileVisitor () methods, which will be discussed below (but everything depends on the situation),
Set <\ FileVisitOption> options is a set of options that determine the behavior during traversal,
maxDepth - depth of passage subdirectories.
First, about the parameters that soon or later will be useful
maxDepth- bypass depth. If = 0, the directory will not be entered, if = MAX_VALUE, the directory will be studied to the maximum depth, respectively, if maxDepth = 3, the passage will be carried out on 3 subdirectories “down”.
FileVisitOption - enum set, which determines whether the program should follow symbolic links when crawling (in this case, the value FileVisitOption.FOLLOW_LINKS is specified).
FileVisitor is an interface that has 4 methods:
1) FileVisitResult preVisitDirectory (Tdir, BasicFileAttributes attrs) throws IOException;
includes a set of methods that should be performed before visiting the current subdirectory. For example, through attrs you can get from such data as:
lastModifiedTime (),
lastAccessTime (),
creationTime (),
isRegularFile () - true, if we have a file,
isDirectory () - true, if we have a directory,
isSymbolicLink () - true, if the object is a link,
isOther () - true, if the object in question is not a file , neither by directory nor by reference,
size () returns the size of the object and
fileKey () returns the file key or null;
If during the crawling process it is planned to count the number of directories, we should not forget that the start directory will also be taken into account in the total amount.
2) FileVisitResult visitFile (T file, BasicFileAttributes attrs) throws IOException;
a set of methods that should be performed during a visit to the current file (you can, for example, rummage through its contents and search for occurrences of the search string, or again find out the date of the last visit, change the file or fold the size of all files to crawl the directory size)
Example
publicclassMyFileVisitorextendsSimpleFileVisitor<Path> {
String partOfName;
String partOfContent;
@Overridepublic FileVisitResult visitFile(Path file, BasicFileAttributes attrs)throws IOException {
boolean containsName = true;
if(partOfName!=null && !file.getFileName().toString().contains(partOfName))
containsName = false;
String content = new String(Files.readAllBytes(file));
boolean containsContent = true;
if(partOfContent!=null && !content.contains(partOfContent))
containsContent = false;
if(containsName && containsContent)
foundFiles.add(file);
return FileVisitResult.CONTINUE;
}In this example, when traversing the file tree, each file is checked for the simultaneous execution of 2 events - whether the file name contains the desired entry and whether the body of the file contains the occurrence of the required string. When both conditions are met, the file is added to the result sheet, after which the crawl continues;
Or another example of overloading the visitFile method.
@Overridepublic FileVisitResult visitFile(Path path, BasicFileAttributes attrs)throws IOException {
if(path.toString().endsWith(".rar") || path.toString().endsWith(".zip"))
archived.add(path.toString());
return FileVisitResult.CONTINUE;
}A program during a tree traversal when visiting a file, in case it is a zip or rar archive, adds its address (path) as a string to the list of archive files;
3) FileVisitResult visitFileFailed (T file, IOException exc) throws IOException;
This method can be useful in case of file access error + it “can” throw Exception. The rest can be taught through the Override annotation. For example, count the number of files that could not be accessed;
Example
@Overridepublic FileVisitResult visitFileFailed(Path path, IOException exc)throws IOException {
failed.add(path.toString());
return FileVisitResult.SKIP_SUBTREE;
}In the case of an unsuccessful attempt to access the path, the given path as a string is added to the failed sheet for it like it, and the program continues bypassing without visiting its subdirectory;
4) FileVisitResult postVisitDirectory (T dir, IOException exc) throws IOException;
Everything that needs to be done after visiting the directory should be listed as part of the overload of this method. For example, having gone through the directory and destroying all the files in it, you can destroy it by this method (we remember that Files.delete (Path dir) deletes the directory only if it is empty and does not contain files).
Example
@Overridepublic FileVisitResult postVisitDirectory(Path path, IOException exc)throws IOException {
Files.delete(path);
return FileVisitResult.CONTINUE;
}All the above methods finish working, returning the “visit results” (FileVisitResult) of an object that belong to the enum set and can take the following values:
CONTINUE- continues to traverse the tree;TERMINATE- finishes tree traversal;SKIP_SUBTREE- continues to bypass, without entering this directory;SKIP_SIBLINGS- excludes from bypassing "relatives" of the file or directory;