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[Java教程]Java文件IO操作应该抛弃File拥抱Path和Files


Java7中文件IO发生了很大的变化,专门引入了很多新的类:

import java.nio.file.DirectoryStream;
import java.nio.file.FileSystem;
import java.nio.file.FileSystems;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.attribute.FileAttribute;
import java.nio.file.attribute.PosixFilePermission;
import java.nio.file.attribute.PosixFilePermissions;

......等等,来取代原来的基于java.io.File的文件IO操作方式.

1. Path就是取代File的

A Path represents a path that is hierarchical and composed of a sequence of directory and file name elements separated by a special separator or delimiter.

Path用于来表示文件路径和文件。可以有多种方法来构造一个Path对象来表示一个文件路径,或者一个文件:

1)首先是final类Paths的两个static方法,如何从一个路径字符串来构造Path对象:

    Path path = Paths.get("C:/", "Xmp");    Path path2 = Paths.get("C:/Xmp");        URI u = URI.create("file:///C:/Xmp/dd");        Path p = Paths.get(u);

2)FileSystems构造:

Path path3 = FileSystems.getDefault().getPath("C:/", "access.log");

3)File和Path之间的转换,File和URI之间的转换:

    File file = new File("C:/my.ini");    Path p1 = file.toPath();    p1.toFile();    file.toURI();

4)创建一个文件:

    Path target2 = Paths.get("C:\\mystuff.txt");//   Set<PosixFilePermission> perms = PosixFilePermissions.fromString("rw-rw-rw-");//   FileAttribute<Set<PosixFilePermission>> attrs = PosixFilePermissions.asFileAttribute(perms);    try {      if(!Files.exists(target2))        Files.createFile(target2);    } catch (IOException e) {      e.printStackTrace();    }

windows下不支持PosixFilePermission来指定rwx权限。

5)Files.newBufferedReader读取文件:

    try {//      Charset.forName("GBK")      BufferedReader reader = Files.newBufferedReader(Paths.get("C:\\my.ini"), StandardCharsets.UTF_8);      String str = null;      while((str = reader.readLine()) != null){        System.out.println(str);      }    } catch (IOException e) {      e.printStackTrace();    }

可以看到使用 Files.newBufferedReader 远比原来的FileInputStream,然后BufferedReader包装,等操作简单的多了。

这里如果指定的字符编码不对,可能会抛出异常 MalformedInputException ,或者读取到了乱码:

java.nio.charset.MalformedInputException: Input length = 1  at java.nio.charset.CoderResult.throwException(CoderResult.java:281)  at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:339)  at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:178)  at java.io.InputStreamReader.read(InputStreamReader.java:184)  at java.io.BufferedReader.fill(BufferedReader.java:161)  at java.io.BufferedReader.readLine(BufferedReader.java:324)  at java.io.BufferedReader.readLine(BufferedReader.java:389)  at com.coin.Test.main(Test.java:79)

6)文件写操作:

    try {      BufferedWriter writer = Files.newBufferedWriter(Paths.get("C:\\my2.ini"), StandardCharsets.UTF_8);      writer.write("测试文件写操作");      writer.flush();      writer.close();    } catch (IOException e1) {      e1.printStackTrace();    }

7)遍历一个文件夹:

    Path dir = Paths.get("D:\\webworkspace");    try(DirectoryStream<Path> stream = Files.newDirectoryStream(dir)){      for(Path e : stream){        System.out.println(e.getFileName());      }    }catch(IOException e){          }

上面是遍历单个目录,它不会遍历整个目录。遍历整个目录需要使用:Files.walkFileTree

8)遍历整个文件目录:

  public static void main(String[] args) throws IOException{    Path startingDir = Paths.get("C:\\apache-tomcat-8.0.21");    List<Path> result = new LinkedList<Path>();    Files.walkFileTree(startingDir, new FindJavaVisitor(result));    System.out.println("result.size()=" + result.size());      }    private static class FindJavaVisitor extends SimpleFileVisitor<Path>{    private List<Path> result;    public FindJavaVisitor(List<Path> result){      this.result = result;    }    @Override    public FileVisitResult visitFile(Path file, BasicFileAttributes attrs){      if(file.toString().endsWith(".java")){        result.add(file.getFileName());      }      return FileVisitResult.CONTINUE;    }  }

2. 强大的java.nio.file.Files

1)创建目录和文件:

    try {      Files.createDirectories(Paths.get("C://TEST"));      if(!Files.exists(Paths.get("C://TEST")))          Files.createFile(Paths.get("C://TEST/test.txt"));//      Files.createDirectories(Paths.get("C://TEST/test2.txt"));    } catch (IOException e) {      e.printStackTrace();    }

注意创建目录和文件Files.createDirectories 和 Files.createFile不能混用,必须先有目录,才能在目录中创建文件。

2)文件复制:

从文件复制到文件:Files.copy(Path source, Path target, CopyOption options);

从输入流复制到文件:Files.copy(InputStream in, Path target, CopyOption options);

从文件复制到输出流:Files.copy(Path source, OutputStream out);

    try {      Files.createDirectories(Paths.get("C://TEST"));      if(!Files.exists(Paths.get("C://TEST")))          Files.createFile(Paths.get("C://TEST/test.txt"));//     Files.createDirectories(Paths.get("C://TEST/test2.txt"));      Files.copy(Paths.get("C://my.ini"), System.out);      Files.copy(Paths.get("C://my.ini"), Paths.get("C://my2.ini"), StandardCopyOption.REPLACE_EXISTING);      Files.copy(System.in, Paths.get("C://my3.ini"), StandardCopyOption.REPLACE_EXISTING);    } catch (IOException e) {      e.printStackTrace();    }

3)遍历一个目录和文件夹上面已经介绍了:Files.newDirectoryStream , Files.walkFileTree

4)读取文件属性:

      Path zip = Paths.get(uri);      System.out.println(Files.getLastModifiedTime(zip));      System.out.println(Files.size(zip));      System.out.println(Files.isSymbolicLink(zip));      System.out.println(Files.isDirectory(zip));      System.out.println(Files.readAttributes(zip, "*"));

5)读取和设置文件权限:

      Path profile = Paths.get("/home/digdeep/.profile");      PosixFileAttributes attrs = Files.readAttributes(profile, PosixFileAttributes.class);// 读取文件的权限      Set<PosixFilePermission> posixPermissions = attrs.permissions();      posixPermissions.clear();      String owner = attrs.owner().getName();      String perms = PosixFilePermissions.toString(posixPermissions);      System.out.format("%s %s%n", owner, perms);            posixPermissions.add(PosixFilePermission.OWNER_READ);      posixPermissions.add(PosixFilePermission.GROUP_READ);      posixPermissions.add(PosixFilePermission.OTHERS_READ);      posixPermissions.add(PosixFilePermission.OWNER_WRITE);            Files.setPosixFilePermissions(profile, posixPermissions);  // 设置文件的权限

Files类简直强大的一塌糊涂,几乎所有文件和目录的相关属性,操作都有想要的api来支持。这里懒得再继续介绍了,详细参见 jdk8 的文档。