Utils

[Utils - JDK] 2 Files

This class consists exclusively of static methods that operate on files, directories, or other types of files...

Posted by Mr.Vincent on 2020-09-13
Estimated Reading Time 20 Minutes
Words 3.9k In Total
Viewed Times

概述

JDK1.7引入了新的IO操作类。java.nio 包下定义了一些操作文件和文件系统的接口和类。java.nio.file.Files 类具有对文件、目录和其他类型的文件进行操作的静态实用程序方法。在这篇文章中，我们将学习 java.nio 文件 API。Files 类在 java.nio.file 包下。这篇文章将介绍有关文件操作的 NIO Files 类。

Java NIO Paths

在 java.nio.file 包下有一个 Path 类，这个类用于来表示文件路径和文件。在 JDK 1.7 中 Path 类取代了 File 类。NIO Files 类中的 API 就通过 Path 类来工作。

构造 Path 的方法（Java 8）

  • get(String first, String... more)：将路径字符串或联接后形成路径字符串的字符串序列转换为路径。

  • Path get(URI uri)：将给定的URI转换为路径对象。

例：

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@Test
public void path() {
    Path path = Paths.get("/Users/vincent/IDEA_Project/my_project/IO/sample-file.txt");
    System.out.println(path.getFileName());

    Path path2 = Paths.get("/Users", "/vincent", "/IDEA_Project", "/my_project/IO/sample-file.txt");
    System.out.println(path2.getFileName());
}

或者另一种创建路径的方法是通过创建一个 URI。

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Path path3 = Paths.get(URI.create("file:///Users/vincent/IDEA_Project/my_project/IO/sample-file.txt"));
System.out.println(path3.getFileName());

从 Java 11 开始，Paths.get() 不建议使用。取而代之的，推荐用 Path接口中的 static of() 方法来创建。它和 Paths.get() 方法没有区别。

例：

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Path path = Path.of("/Users/vincent/IDEA_Project/my_project/IO/sample-file.txt");
Path path = Path.of("/Users", "/vincent", "/IDEA_Project", "/my_project/IO/sample-file.txt");
Path path = Path.of(URI.create("file:///Users/vincent/IDEA_Project/my_project/IO/sample-file.txt"));

Path 部分方法

  • toFile()：获取文件。
  • getFileName()：获取文件名。
  • toUri()：获取 URI（例：file:///Users/vincent/IDEA_Project/my_project/IO/sample-file.txt）。
  • getParent()：获取父路径。
  • getRoot()：获取根路径。
  • toString()：该路径的字符串形式。
  • isAbsolute()：是否是绝对路径。

例：

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@Test
public void path(){
    Path path = Paths.get("/Users/vincent/IDEA_Project/my_project/IO/sample-file.txt");

    File file = path.toFile();
    System.out.println(file);

    Path fileName = path.getFileName();
    System.out.println(fileName);

    URI uri = path.toUri();
    System.out.println(uri);

    Path parent = path.getParent();
    System.out.println(parent);

    Path root = path.getRoot();
    System.out.println(root);

    boolean absolute = path.isAbsolute();
    System.out.println(absolute);
}

Java NIO Files

常用方法

  • exists(Path path, LinkOption... options)：是否存在。
  • notExists(Path path, LinkOption... options)：是否不存在。
  • isDirectory(Path path, LinkOption... options)：是否是目录。
  • isSymbolicLink(Path path)：是否是象征链接。
  • isWritable(Path path)：是否可写。
  • isExecutable(Path path)：是否可执行。
  • isReadable(Path path)：是否可读。
  • isHidden(Path path)：是否是隐藏。
  • getPosixFilePermissions(Path path, LinkOption... options)：获取具体的权限。
  • getOwner(Path path, LinkOption... options)：
  • getLastModifiedTime(Path path, LinkOption... options)：获取最后修改时间。
  • size(Path path)：获取大小。
  • newInputStream(Path path, OpenOption... options)：返回输入流。
  • newOutputStream(Path path, OpenOption... options)：返回输出流。

例：

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@Test
public void files() throws IOException {
    /**
     * exists(Path path, LinkOption... options)：是否存在。
     * notExists(Path path, LinkOption... options)：是否不存在。
     * isDirectory(Path path, LinkOption... options)：是否是目录。
     * isSymbolicLink(Path path)：是否是象征链接。
     * isWritable(Path path)：是否可写。
     * isExecutable(Path path)：是否可执行。
     * isReadable(Path path)：是否可读。
     * isHidden(Path path)：是否是隐藏。
     * getPosixFilePermissions(Path path, LinkOption... options)：获取具体的权限。
     * getOwner(Path path, LinkOption... options)：获取所属者。
     * getLastModifiedTime(Path path, LinkOption... options)：获取最后修改时间。
     * size(Path path)：获取大小。
     */
    Path newFilePath2 = Paths.get("/Users/vincent/IDEA_Project/my_project/IO/new-file2.txt");

    boolean exists = Files.exists(newFilePath2);
    System.out.println("exists：：" + exists);

    boolean notExists = Files.notExists(newFilePath2);
    System.out.println("notExists：" + notExists);

    boolean directory = Files.isDirectory(newFilePath2);
    System.out.println("directory：" + directory);

    boolean symbolicLink = Files.isSymbolicLink(newFilePath2);
    System.out.println("symbolicLink：" + symbolicLink);

    boolean writable = Files.isWritable(newFilePath2);
    System.out.println("writable：" + symbolicLink);

    boolean executable = Files.isExecutable(newFilePath2);
    System.out.println("executable：" + symbolicLink);

    boolean readable = Files.isReadable(newFilePath2);
    System.out.println("readable：" + symbolicLink);

    boolean hidden = Files.isHidden(newFilePath2);
    System.out.println("hidden：" + symbolicLink);

    Set<PosixFilePermission> posixFilePermissions = Files.getPosixFilePermissions(newFilePath2);
    posixFilePermissions.forEach(System.out::println);

    UserPrincipal owner = Files.getOwner(newFilePath2);
    System.out.println("owner：" + owner);

    FileTime lastModifiedTime = Files.getLastModifiedTime(newFilePath2);
    System.out.println("lastModifiedTime：" + lastModifiedTime);

    long size = Files.size(newFilePath2);
    System.out.println("size：" + size);
}

显示结果：

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exists：：true
notExists：false
directory：false
symbolicLink：false
writable：false
executable：false
readable：false
hidden：false
OWNER_WRITE
owner：vincent
lastModifiedTime：2020-09-13T16:40:27Z
size：0

readAttributes

readAttributes：读取文件的全部属性，作为一个批次操作。

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readAttributes(Path path, Class<A> type, LinkOption... options)
readAttributes(Path path, String attributes, LinkOption... options)

例：

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@Test
public void readAttributes() throws IOException {
    /**
     * readAttributes：读取文件的全部属性，作为一个批次操作。
     *
     * readAttributes(Path path, Class<A> type, LinkOption... options)
     * readAttributes(Path path, String attributes, LinkOption... options)
     */
    Path pathFile = Paths.get("/Users/vincent/IDEA_Project/my_project/IO/new-file2.txt");
    PosixFileAttributes attrs = Files.readAttributes(pathFile, PosixFileAttributes.class);// 读取文件的权限
    Set<PosixFilePermission> posixPermissions = attrs.permissions();
    posixPermissions.clear();
    System.out.format("%s %s%n", attrs.owner().getName(), PosixFilePermissions.toString(posixPermissions));
    Files.setPosixFilePermissions(pathFile, posixPermissions);
    
    posixPermissions.add(PosixFilePermission.OWNER_READ);
    posixPermissions.add(PosixFilePermission.GROUP_READ);
    posixPermissions.add(PosixFilePermission.OTHERS_READ);
    posixPermissions.add(PosixFilePermission.OWNER_WRITE);
    // 设置文件的权限
    Files.setPosixFilePermissions(pathFile, posixPermissions);
    System.out.format("%s %s%n", attrs.owner().getName(), PosixFilePermissions.toString(attrs.permissions()));
}

createFile 和 createDirectory

createFile：创建一个新的空的文件，如果存在创建失败（抛 FileAlreadyExistsException）。

createDirectory：创建一个新的目录，如果存在创建失败（抛 FileAlreadyExistsException）。

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createDirectories(Path dir, FileAttribute<?>... attrs)
createDirectory(Path dir, FileAttribute<?>... attrs)
createFile(Path path, FileAttribute<?>... attrs)

例：

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@Test
public void createFileAndDirectory() throws IOException {
    /**
     * createFile：创建一个新的空的文件，如果存在创建失败（抛 FileAlreadyExistsException）。
     * createDirectory：创建一个新的目录，如果存在创建失败（抛 FileAlreadyExistsException）。
     *
     * createDirectories(Path dir, FileAttribute<?>... attrs)
     * createDirectory(Path dir, FileAttribute<?>... attrs)
     * createFile(Path path, FileAttribute<?>... attrs)
     */
    Path newFilePath = Paths.get("/Users/vincent/IDEA_Project/my_project/IO/new-file.txt");
    Files.createFile(newFilePath);

    //设置了权限，只能写的权限。（--w-------   1 vincent  staff        0 Sep 14 00:40 new-file2.txt）
    Path newFilePath2 = Paths.get("/Users/vincent/IDEA_Project/my_project/IO/new-file2.txt");
    FileAttribute<Set<PosixFilePermission>> fileAttributes = PosixFilePermissions
            .asFileAttribute(Sets.newHashSet(PosixFilePermission.OWNER_WRITE));
    Files.createFile(newFilePath2, fileAttributes);

    //Files.createDirectory()：只是创建目录，如果它的上级目录不存在就会报错。
    Path newDirectoryPath = Paths.get("/Users/vincent/IDEA_Project/my_project/IO/newDir1");
    Files.createDirectory(newDirectoryPath);

    //Files.createDirectories()：会首先创建所有不存在的父目录来创建目录。
    Path newDirectoriesPath = Paths.get("/Users/vincent/IDEA_Project/my_project/IO/newDir2/newDir3");
    Files.createDirectories(newDirectoriesPath);
}

createTempFile 和 createTempDirectory

createTempFile：生成临时文件，支持前缀和后缀命名。

createTempDirectory：生成临时目录，支持前缀命名。

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Path directoryPath = Paths.get("/Users/JavaDeveloperCentral/data");
Path tmpDirPath = Files.createTempDirectory(directoryPath, "");
System.out.println(tmpDirPath);
tmpDirPath.toFile().deleteOnExit();

Path filePath1 = Paths.get(tmpDirPath.toString() + "/file1");
filePath1.toFile().deleteOnExit();
Files.write(filePath1, List.of("something"));

Path filePath2 = Paths.get(tmpDirPath.toString() + "/file2");
filePath2.toFile().deleteOnExit();
Files.write(filePath2, List.of("something"));
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createTempFile(Path dir, String prefix, String suffix, FileAttribute<?>... attrs)
createTempFile(String prefix, String suffix, FileAttribute<?>... attrs)
createTempDirectory(Path dir, String prefix, FileAttribute<?>... attrs)
createTempDirectory(String prefix, FileAttribute<?>... attrs)

例：

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@Test
public void createTempFileAndDirectory() throws IOException {
    /**
     * createTempFile：生成临时文件，支持前缀和后缀命名。
     * createTempDirectory：生成临时目录，支持前缀命名。
     *
     * createTempFile(Path dir, String prefix, String suffix, FileAttribute<?>... attrs)
     * createTempFile(String prefix, String suffix, FileAttribute<?>... attrs)
     * createTempDirectory(Path dir, String prefix, FileAttribute<?>... attrs)
     * createTempDirectory(String prefix, FileAttribute<?>... attrs)
     */
    Path path = Paths.get("/Users/vincent/IDEA_Project/my_project/IO/");
    Path tempFile = Files.createTempFile(path, "prefix", "suffix.txt");
    System.out.println(tempFile);

    //不指定目录，会在系统默认目录下生成。
    Path tempFile2 = Files.createTempFile("prefix", "suffix.txt");
    System.out.println(tempFile2);

    Path tempDirectory = Files.createTempDirectory(path, "prefix");
    System.out.println(tempDirectory);

    Path tempDirectory2 = Files.createTempDirectory("prefix");
    System.out.println(tempDirectory2);
}

readAllBytes、readAllLines、readString、lines、list

readAllBytes：读取文件，返回字节。

readAllLines：读取文件的所以行，返回 List<String>。

readString：读取文件，返回字符串。（Java 11）

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//This method was added in Java 11
String data = Files.readString(filePath);
System.out.println(data);

data = Files.readString(filePath, StandardCharsets.UTF_8);
System.out.println(data);

lines：从文件中读取所有行作为 Stream 。

list：返回一个懒惰的填充 Stream ，其元素是 Stream 中的条目。

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readAllBytes(Path path)
readAllLines(Path path)
readAllLines(Path path, Charset cs)
readString(Path path)	
readString(Path path, Charset cs)
lines(Path path)
lines(Path path, Charset cs)
list(Path dir)

例：

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@Test
public void readXxx() throws IOException {
    /**
     * readAllBytes：读取文件，返回字节。
     * readAllLines：读取文件的所以行，返回 List<String>。
     * readString：读取文件，返回字符串。（Java 11）
     * lines：从文件中读取所有行作为 Stream 。
     * list：返回一个懒惰的填充 Stream ，其元素是 Stream 中的条目。
     *
     * readAllBytes(Path path)
     * readAllLines(Path path)
     * readAllLines(Path path, Charset cs)
     * readString(Path path)（Java 11）
     * readString(Path path, Charset cs)（Java 11）
     * lines(Path path)
     * lines(Path path, Charset cs)
     * list(Path dir)
     */
    Path filePath = Paths.get("/Users/vincent/IDEA_Project/my_project/IO/sample-file.txt");
    byte[] bytes = Files.readAllBytes(filePath);
    System.out.println(new String(bytes));
    System.out.println();

    List<String> readAllLines = Files.readAllLines(filePath, StandardCharsets.UTF_8);
    readAllLines.forEach(System.out::println);
    System.out.println();

    try (Stream<String> lines = Files.lines(filePath)) {
        lines.forEach(System.out::println);
    }
    System.out.println();

    Path directoryPath = Paths.get("/Users/vincent/IDEA_Project/my_project/IO");
    try (Stream<Path> list = Files.list(directoryPath)) {
        list.forEach(System.out::println);
    }
}

显示结果：

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1-Will-90
2-James-87
3-Kyle-67

1-Will-90
2-James-87
3-Kyle-67

1-Will-90
2-James-87
3-Kyle-67

/Users/vincent/IDEA_Project/my_project/IO/copyFile.png
/Users/vincent/IDEA_Project/my_project/IO/new-file2.txt
/Users/vincent/IDEA_Project/my_project/IO/sample-output-file.txt
/Users/vincent/IDEA_Project/my_project/IO/IO.iml
/Users/vincent/IDEA_Project/my_project/IO/reader.txt
/Users/vincent/IDEA_Project/my_project/IO/touch
/Users/vincent/IDEA_Project/my_project/IO/target
/Users/vincent/IDEA_Project/my_project/IO/io.png
/Users/vincent/IDEA_Project/my_project/IO/pom.xml
/Users/vincent/IDEA_Project/my_project/IO/writer.txt
/Users/vincent/IDEA_Project/my_project/IO/readerAndWriter.txt
/Users/vincent/IDEA_Project/my_project/IO/touch.txt
/Users/vincent/IDEA_Project/my_project/IO/new-file.txt
/Users/vincent/IDEA_Project/my_project/IO/outputStreamReader.txt
/Users/vincent/IDEA_Project/my_project/IO/inputStreamReader.txt
/Users/vincent/IDEA_Project/my_project/IO/a.txt
/Users/vincent/IDEA_Project/my_project/IO/.gitignore
/Users/vincent/IDEA_Project/my_project/IO/write.txt
/Users/vincent/IDEA_Project/my_project/IO/sample-file.txt
/Users/vincent/IDEA_Project/my_project/IO/io3.png
/Users/vincent/IDEA_Project/my_project/IO/io2.png
/Users/vincent/IDEA_Project/my_project/IO/inputStream.txt
/Users/vincent/IDEA_Project/my_project/IO/fileutils
/Users/vincent/IDEA_Project/my_project/IO/.git
/Users/vincent/IDEA_Project/my_project/IO/copyFile2.png
/Users/vincent/IDEA_Project/my_project/IO/.idea
/Users/vincent/IDEA_Project/my_project/IO/src

write、writeString

write：将内容写入文件。

writeString：将字符写入文件。（Java 11）

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//This method was added in Java 11
//File exists - Append to it
Files.writeString(filePath, data, StandardOpenOption.WRITE, StandardOpenOption.APPEND);

//File exists - Truncate existing data
Files.writeString(filePath, data, StandardOpenOption.WRITE, StandardOpenOption.TRUNCATE_EXISTING);

//File does not exist, create a new one and write
Files.writeString(filePath, data, StandardOpenOption.CREATE_NEW);

//Create file if it does not exist and Append to it
Files.writeString(filePath, data, StandardOpenOption.CREATE, StandardOpenOption.APPEND);

//Create file if it does not exist - Truncate existing data
Files.writeString(filePath, data, StandardOpenOption.CREATE, StandardOpenOption.TRUNCATE_EXISTING);
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write(Path path, byte[] bytes, OpenOption... options)
write(Path path, Iterable<? extends CharSequence> lines, Charset cs, OpenOption... options)
write(Path path, Iterable<? extends CharSequence> lines, OpenOption... options)
writeString(Path path, CharSequence csq, Charset cs, OpenOption... options)	（Java 11）
writeString(Path path, CharSequence csq, OpenOption... options)（Java 11）

例：

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@Test
public void writeXxx() throws IOException {
    /**
     * write：将内容写入文件。
     * writeString：将字符写入文件。（Java 11）
     *
     * write(Path path, byte[] bytes, OpenOption... options)
     * write(Path path, Iterable<? extends CharSequence> lines, Charset cs, OpenOption... options)
     * write(Path path, Iterable<? extends CharSequence> lines, OpenOption... options)
     * writeString(Path path, CharSequence csq, Charset cs, OpenOption... options)	（Java 11）
     * writeString(Path path, CharSequence csq, OpenOption... options)（Java 11）
     */
    Path filePath = Paths.get("/Users/vincent/IDEA_Project/my_project/IO/sample-file.txt");
    Path filePath2 = Paths.get("/Users/vincent/IDEA_Project/my_project/IO/sample-output-file.txt");
    Path write = Files.write(filePath2, Files.readAllBytes(filePath));

    //StandardOpenOption.APPEND：追加在原文件内容后。
    Path write2 = Files.write(filePath2, Lists.newArrayList("a", "b", "c"), StandardCharsets.UTF_8, StandardOpenOption.APPEND);
}

copy

copy：复制文件或目录。

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copy(InputStream in, Path target, CopyOption... options)	
copy(Path source, OutputStream out)	
copy(Path source, Path target, CopyOption... options)

例：

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    @Test
    public void copy() throws IOException {
        /**
         * copy：复制文件或目录。
         *
         * copy(InputStream in, Path target, CopyOption... options)	
         * copy(Path source, OutputStream out)	
         * copy(Path source, Path target, CopyOption... options)
         */
        Path sourceFilePath = Paths.get("/Users/vincent/IDEA_Project/my_project/IO/source.txt");
        Path destinationFilePath = Paths.get("/Users/vincent/IDEA_Project/my_project/IO/destination.txt");

        //StandardCopyOption.REPLACE_EXISTING：如果存在，则替换。
        Files.copy(sourceFilePath, destinationFilePath, StandardCopyOption.REPLACE_EXISTING);

//        Files.copy(sourceFilePath, new FileOutputStream(destinationFilePath.toFile()));
        Files.copy(sourceFilePath, Files.newOutputStream(destinationFilePath, StandardOpenOption.WRITE));

//        Files.copy(IOUtils.toInputStream("Vincent is so handsome!!!", StandardCharsets.UTF_8), destinationFilePath, StandardCopyOption.REPLACE_EXISTING);
        Files.copy(Files.newInputStream(sourceFilePath), destinationFilePath, StandardCopyOption.REPLACE_EXISTING);
    }

move、delete、deleteIfExists

move：移动或重命名文件到目标文件；移动或重命名目录（注：被移动或重命名的目录必须为空目录）。

delete：删除文件。

deleteIfExists：如果存在删除文件。

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move(Path source, Path target, CopyOption... options)
delete(Path path)
deleteIfExists(Path path)

例：

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@Test
public void moveAndDelete() throws IOException {
    /**
     * move：移动或重命名文件到目标文件；移动或重命名目录（注：被移动或重命名的目录必须为空目录）。
     * delete：删除文件。
     * deleteIfExists：如果存在删除文件。
     *
     * move(Path source, Path target, CopyOption... options)
     * delete(Path path)
     * deleteIfExists(Path path)
     */
    Path sourceFilePath = Paths.get("/Users/vincent/IDEA_Project/my_project/IO/source.txt");
    Path destinationFilePath = Paths.get("/Users/vincent/IDEA_Project/my_project/IO/new_source.txt");
    Files.move(sourceFilePath, destinationFilePath, StandardCopyOption.REPLACE_EXISTING);

    Path path1 = Paths.get("/Users/vincent/IDEA_Project/my_project/IO/newData");
    Path path2 = Paths.get("/Users/vincent/IDEA_Project/my_project/IO/dir1/dir2");
    //Works only if on the same filestore - else use walkFileTree
    Files.move(path1, path2);

    Path filePathToDelete = Paths.get("/Users/vincent/IDEA_Project/my_project/IO/a.txt");
    Files.delete(filePathToDelete);

    //deletes only if it exists
    Files.deleteIfExists(filePathToDelete);
}

newDirectoryStream

newDirectoryStream：遍历当前目录（仅当前目录）下的所以条目（但不做递归遍历）。

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newDirectoryStream(Path dir)
newDirectoryStream(Path dir, DirectoryStream.Filter<? super Path> filter)
newDirectoryStream(Path dir, String glob)

例：

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@Test
public void newDirectoryStream() throws IOException {
    /**
     * newDirectoryStream：遍历当前目录（仅当前目录）下的所以条目（但不做递归遍历）。
     * 这里有个目录，目录结构如下：
     * |-- data
     *     |-- file1.txt
     *     |-- file2.txt
     *     |-- SomeClass.java
     *     |-- dir1
     *         |-- dir2
     *             |-- file1InDir2.txt
     *     |-- file3.txt
     *
     * 调用 newDirectoryStream(Path dir) 后，输出打印：
     *     file1.txt
     *     file2.txt
     *     SomeClass.java
     *     dir1
     *     file3.txt
     *
     * newDirectoryStream(Path dir)
     * newDirectoryStream(Path dir, DirectoryStream.Filter<? super Path> filter)
     * newDirectoryStream(Path dir, String glob)
     */
    Path directoryPath = Paths.get("/Users/vincent/IDEA_Project/my_project/IO/fileutils");
    try (DirectoryStream<Path> directoryStream = Files.newDirectoryStream(directoryPath)) {
        directoryStream.forEach(System.out::println);
    }
    System.out.println();

    try (DirectoryStream<Path> directoryStream = Files.newDirectoryStream(directoryPath, path -> path.toFile().isFile())) {
        directoryStream.forEach(System.out::println);
    }
    System.out.println();

    try (DirectoryStream<Path> directoryStream = Files.newDirectoryStream(directoryPath, "*.txt")) {
        directoryStream.forEach(System.out::println);
    }
}

显示结果：

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file1.txt
file2.txt
SomeClass.java
dir1
file3.txt

file1.txt
file2.txt
SomeClass.java
file3.txt

file1.txt
file2.txt
file3.txt

walk 和 walkFileTree

walk：遍历整个文件目录（递归）。

walkFileTree：遍历整个文件目录（递归）。

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walk(Path start, FileVisitOption... options)
walk(Path start, int maxDepth, FileVisitOption... options)
walkFileTree(Path start, FileVisitor<? super Path> visitor)
walkFileTree(Path start, Set<FileVisitOption> options, int maxDepth, FileVisitor<? super Path> visitor)

例：

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@Test
public void walkAndWalkFileTree() throws IOException {
    /**
     * walk：遍历整个文件目录（递归）。
     * walkFileTree：遍历整个文件目录（递归）。
     *
     * walk(Path start, FileVisitOption... options)
     * walk(Path start, int maxDepth, FileVisitOption... options)
     * walkFileTree(Path start, FileVisitor<? super Path> visitor)
     * walkFileTree(Path start, Set<FileVisitOption> options, int maxDepth, FileVisitor<? super Path> visitor)
     */
    Path directoryPath = Paths.get("/Users/vincent/IDEA_Project/my_project/IO/fileutils");
    try (Stream<Path> walk = Files.walk(directoryPath, 1)) {
        walk.forEach(System.out::println);
    }
    System.out.println();


    /**
     * walkFileTree(Path start, Set<FileVisitOption> options, int maxDepth, FileVisitor<? super Path> visitor)：
     * 参数：
     *      1. java.nio.file.Path start：遍历的起始路径。
     *      2. Set<java.nio.file.FileVisitOption> options：遍历选项。
     *      3. int maxDepth：遍历深度。
     *      4. java.nio.file.FileVisitor<? super Path> visitor：遍历过程中的行为控制器。
     *
     * FileVisitor<Path>：
     *      1. preVisitDirectory：访问一个目录，在进入之前调用。
     *      2. postVisitDirectory：一个目录的所有节点都被访问后调用。遍历时跳过同级目录或有错误发生，Exception 会传递给这个方法。
     *      3. visitFile：文件被访问时被调用。该文件的文件属性被传递给这个方法。
     *      4. visitFileFailed：当文件不能被访问时，此方法被调用。Exception 被传递给这个方法。
     * FileVisitResult：
     *      1. CONTINUE：继续遍历。
     *      2. SKIP_SIBLINGS：继续遍历，但忽略当前节点的所有兄弟节点直接返回上一层继续遍历。
     *      3. SKIP_SUBTREE：继续遍历，但是忽略子目录，但是子文件还是会访问。
     *      4. TERMINATE：终止遍历。
     *
     */
    Files.walkFileTree(directoryPath, new MySimpleFileVisitorImpl());
    System.out.println();

    Files.walkFileTree(directoryPath, Sets.newHashSet(FileVisitOption.FOLLOW_LINKS), 1, new SimpleFileVisitor<Path>() {
        @Override
        public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {
            System.out.println("visitFile " + file);
            return super.visitFile(file, attrs);
        }
    });

}

public class MySimpleFileVisitorImpl implements FileVisitor<Path> {
    @Override
    public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs) throws IOException {
        System.out.println("preVisitDirectory " + dir);
        return FileVisitResult.CONTINUE;
    }

    @Override
    public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {
        System.out.println("visitFile " + file);
        return FileVisitResult.CONTINUE;
    }

    @Override
    public FileVisitResult visitFileFailed(Path file, IOException exc) throws IOException {
        System.out.println("visitFileFailed " + file);
        return FileVisitResult.CONTINUE;
    }

    @Override
    public FileVisitResult postVisitDirectory(Path dir, IOException exc) throws IOException {
        System.out.println("postVisitDirectory " + dir);
        return FileVisitResult.CONTINUE;
    }
}

显示结果：

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/Users/vincent/IDEA_Project/my_project/IO/fileutils
/Users/vincent/IDEA_Project/my_project/IO/fileutils/abc
/Users/vincent/IDEA_Project/my_project/IO/fileutils/io.png
/Users/vincent/IDEA_Project/my_project/IO/fileutils/a.txt

preVisitDirectory /Users/vincent/IDEA_Project/my_project/IO/fileutils
preVisitDirectory /Users/vincent/IDEA_Project/my_project/IO/fileutils/abc
visitFile /Users/vincent/IDEA_Project/my_project/IO/fileutils/abc/abc.txt
visitFile /Users/vincent/IDEA_Project/my_project/IO/fileutils/abc/a.txt
visitFile /Users/vincent/IDEA_Project/my_project/IO/fileutils/abc/abcd.txt
postVisitDirectory /Users/vincent/IDEA_Project/my_project/IO/fileutils/abc
visitFile /Users/vincent/IDEA_Project/my_project/IO/fileutils/io.png
visitFile /Users/vincent/IDEA_Project/my_project/IO/fileutils/a.txt
postVisitDirectory /Users/vincent/IDEA_Project/my_project/IO/fileutils

visitFile /Users/vincent/IDEA_Project/my_project/IO/fileutils/abc
visitFile /Users/vincent/IDEA_Project/my_project/IO/fileutils/io.png
visitFile /Users/vincent/IDEA_Project/my_project/IO/fileutils/a.txt

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