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