java Files类和Paths类的用法详解

灰太狼 2021-11-13 15:22 226阅读 0赞

**http://blog.csdn.net/u010889616/article/details/52694061**

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){
                
            }
    
    // or
    
       try (Stream<Path> stream = Files.list(Paths.get("C:/"))){
                Iterator<Path> ite = stream.iterator();
                while(ite.hasNext()){
                    Path pp = ite.next();
                    System.out.println(pp.getFileName());
                }
            } catch (IOException e) {
                e.printStackTrace();
            }

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;
            }
        }

来一个实际例子：

public static void main(String[] args) throws IOException {
            Path startingDir = Paths.get("F:\\upload\\images");    // F:\\upload\\images\\2\\20141206
            List<Path> result = new LinkedList<Path>();
            Files.walkFileTree(startingDir, new FindJavaVisitor(result));
            System.out.println("result.size()=" + result.size()); 
            
            System.out.println("done.");
        }
        
        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){
                String filePath = file.toFile().getAbsolutePath();       
                if(filePath.matches(".*_[1|2]{1}\\.(?i)(jpg|jpeg|gif|bmp|png)")){
                    try {
                        Files.deleteIfExists(file);
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                  result.add(file.getFileName());
                } return FileVisitResult.CONTINUE;
            }
        }

将目录下面所有符合条件的图片删除掉：filePath.matches(".\*\_\[1|2\]\{1\}\\\\.(?i)(jpg|jpeg|gif|bmp|png)")

public static void main(String[] args) throws IOException {
            Path startingDir = Paths.get("F:\\111111\\upload\\images");    // F:\111111\\upload\\images\\2\\20141206
            List<Path> result = new LinkedList<Path>();
            Files.walkFileTree(startingDir, new FindJavaVisitor(result));
            System.out.println("result.size()=" + result.size()); 
            
            System.out.println("done.");
        }
        
        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){
                String filePath = file.toFile().getAbsolutePath();
                int width = 224;
                int height = 300;
                StringUtils.substringBeforeLast(filePath, ".");
                String newPath = StringUtils.substringBeforeLast(filePath, ".") + "_1." 
                                                + StringUtils.substringAfterLast(filePath, ".");
                try {
                    ImageUtil.zoomImage(filePath, newPath, width, height);
                } catch (IOException e) {
                    e.printStackTrace();
                    return FileVisitResult.CONTINUE;
                }
                result.add(file.getFileName());
                return FileVisitResult.CONTINUE;
            }
        }

为目录下的所有图片生成指定大小的缩略图。a.jpg 则生成 a\_1.jpg

**2. 强大的java.nio.file.Files**

1）创建目录和文件：

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 jdk7 的文档。

一个实际例子：

import java.io.BufferedReader;
    import java.io.BufferedWriter;
    import java.nio.charset.StandardCharsets;
    import java.nio.file.Files;
    import java.nio.file.Path;
    import java.nio.file.Paths;
    
    public class StringTools {
        public static void main(String[] args) {
            try {
                BufferedReader reader = Files.newBufferedReader(Paths.get("C:\\Members.sql"), StandardCharsets.UTF_8);
                BufferedWriter writer = Files.newBufferedWriter(Paths.get("C:\\Members3.txt"), StandardCharsets.UTF_8);
    
                String str = null;
                while ((str = reader.readLine()) != null) {
                    if (str != null && str.indexOf(", CAST(0x") != -1 && str.indexOf("AS DateTime)") != -1) {
                        String newStr = str.substring(0, str.indexOf(", CAST(0x")) + ")";
                        writer.write(newStr);
                        writer.newLine();
                    }
                }
                writer.flush();
                writer.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }