Java traverse files

Methods

1. java.io.File.listFiles - old java IO
2. java.nio.Files.newDirectoryStream - NIO & NIO2 - new java IO
3. org.apache.commons.io.FileUtils.iterateFiles and org.apache.commons.io.FileUtils.iterateFilesAndDirs (commons-io:2.6) - uses jdk7 but File.listFiles
4. com.google.common.io.Files.fileTreeTraverser (guava:26.0) uses jdk7 but File.listFiles
5. com.google.common.io.Files.fileTraverser - https://google.github.io/guava/releases/snapshot/api/docs/com/google/common/io/Files.html#fileTraverser--
6. java.nio.Files.walk - uses newDirectoryStream and returns a Stream
7. java.nio.Files.walkFileTree - uses newDirectoryStream by using a java.nio.file.FileVisitor

More resources

• See how a Finder is implemented at https://docs.oracle.com/javase/tutorial/displayCode.html?code=https://docs.oracle.com/javase/tutorial/essential/io/examples/Find.java
• https://docs.oracle.com/javase/tutorial/essential/io/walk.html
• manually iterate using Files.newDirectoryStream - https://examples.javacodegeeks.com/core-java/nio/java-nio-iterate-files-directory/
• parallel iterate using Files.walkFileTree - https://stackoverflow.com/questions/17732819/parallel-version-of-files-walkfiletree-java-or-scala
• File.listFiles is also an option but is using old java IO library.
• walkFileTree example - https://www.concretepage.com/java/jdk7/traverse-directory-structure-using-files-walkfiletree-java-nio2
• com.google.common.io.Files.fileTreeTraverser is uses File.listFiles but also the deprecated com.google.common.collect.TreeTraverser (better com.google.common.graph.Traverser) that is a generic way to traverse a tree.
• https://stackoverflow.com/questions/20987214/recursively-list-all-files-within-a-directory-using-nio-file-directorystream

Sequence diagram

Comparison of how to traverse files in jdk7 using Files.walk, Files.walkFileTree and Files.newDirectoryStream. All of them call Files.newDirectoryStream which is implemented natively by JVM. This lists all entries in a directory.

sequenceDiagram
  Client->>+Files:walk => Stream<Path>
  Files->>FileTreeIterator: create
  FileTreeIterator->>FileTreeWalker: create
  Note right of DirectoryStream: lists only a directory
  FileTreeWalker->>DirectoryStream:create
  Files->>FileTreeIterator: iterate
  FileTreeIterator->>FileTreeWalker: walk => Event
  FileTreeWalker->>DirectoryStream:create | walk | next
  Client->>Files:newDirectoryStream
  Files->>DirectoryStream: create
  Note right of DirectoryStream:stream inside a directory
  Client->>Files:walkFileTree(visitor:FileVisitor<Path>)
  Files->>FileTreeWalker:create
  Files->>Files:iterate
  Files->>FileTreeWalker:walk => Event
  FileTreeWalker->>DirectoryStream:create | walk | next

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