Java文件IO操作应该抛弃File拥抱Paths和Files-白红宇

Java文件IO操作应该抛弃File拥抱Paths和Files

阅读量：4990 次

发布时间：2019-06-12

本文共 10907 字，大约阅读时间需要 36 分钟。

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
     
       perms = PosixFilePermissions.fromString("rw-rw-rw-");//      FileAttribute
      
       
        > 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
     
       stream = Files.newDirectoryStream(dir)){            for(Path e : stream){                System.out.println(e.getFileName());            }        }catch(IOException e){                    }

try (Stream
     
       stream = Files.list(Paths.get("C:/"))){            Iterator
      
        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
     
       result = new LinkedList
      
       ();        Files.walkFileTree(startingDir, new FindJavaVisitor(result));        System.out.println("result.size()=" + result.size());            }        private static class FindJavaVisitor extends SimpleFileVisitor
       
        {        private List
        
          result;        public FindJavaVisitor(List
         
           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
     
       result = new LinkedList
      
       ();        Files.walkFileTree(startingDir, new FindJavaVisitor(result));        System.out.println("result.size()=" + result.size());                 System.out.println("done.");    }        private static class FindJavaVisitor extends SimpleFileVisitor
       
        {        private List
        
          result;        public FindJavaVisitor(List
         
           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
     
       result = new LinkedList
      
       ();        Files.walkFileTree(startingDir, new FindJavaVisitor(result));        System.out.println("result.size()=" + result.size());                 System.out.println("done.");    }        private static class FindJavaVisitor extends SimpleFileVisitor
       
        {        private List
        
          result;        public FindJavaVisitor(List
         
           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：

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
     
       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。

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();        }    }}

转自：https://www.cnblogs.com/digdeep/p/4478734.html

转载于:https://www.cnblogs.com/yixiu868/p/8004397.html

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