Java檔案IO操作應該拋棄File擁抱Paths和Files

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Java7中檔案IO發生了很大的變化，專門引入了很多新的類：

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，來取代原來的基於java.io.File的檔案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用於來表示檔案路徑和檔案。可以有多種方法來構造一個Path對象來表示一個檔案路徑，或者一個檔案：

1）首先是final類Paths的兩個static方法，如何從一個路徑字串來構造Path對象：

        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構造：

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

3）File和Path之間的轉換，File和URI之間的轉換：

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

4）建立一個檔案：

        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下不支援PosixFilePermission來指定rwx許可權。

5）Files.newBufferedReader讀取檔案：

        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 遠比原來的FileInputStream，然後BufferedReader封裝，等操作簡單的多了。

這裡如果指定的字元編碼不對，可能會拋出異常 MalformedInputException ，或者讀取到了亂碼：

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）檔案寫操作：

        try {            BufferedWriter writer = Files.newBufferedWriter(Paths.get("C:\\my2.ini"), StandardCharsets.UTF_8);            writer.write("測試檔案寫操作");            writer.flush();            writer.close();        } catch (IOException e1) {            e1.printStackTrace();        }

7）遍曆一個檔案夾：

        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){                    }

        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();        }

上面是遍曆單個目錄，它不會遍曆整個目錄。遍曆整個目錄需要使用：Files.walkFileTree

8）遍曆整個檔案目錄：

    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;        }    }

來一個實際例子：

    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;        }    }

將目錄下面所有合格圖片刪除掉：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;        }    }

 

為目錄下的所有圖片產生指定大小的縮圖。a.jpg 則產生 a_1.jpg

 

2. 強大的java.nio.file.Files

1）建立目錄和檔案：

        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();        }

注意建立目錄和檔案Files.createDirectories 和 Files.createFile不能混用，必須先有目錄，才能在目錄中建立檔案。

2）檔案複製:

從檔案複製到檔案：Files.copy(Path source, Path target, CopyOption options);

從輸入資料流複製到檔案：Files.copy(InputStream in, Path target, CopyOption options);

從檔案複製到輸出資料流：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）遍曆一個目錄和檔案夾上面已經介紹了：Files.newDirectoryStream ， Files.walkFileTree

4）讀取檔案屬性：

            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）讀取和設定檔案許可權：

            Path profile = Paths.get("/home/digdeep/.profile");            PosixFileAttributes attrs = Files.readAttributes(profile, PosixFileAttributes.class);// 讀取檔案的許可權            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);    // 設定檔案的許可權

Files類簡直強大的一塌糊塗，幾乎所有檔案和目錄的相關屬性，操作都有想要的api來支援。這裡懶得再繼續介紹了，詳細參見 jdk8 的文檔。

 

一個實際例子：

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();        }    }}

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

Java檔案IO操作應該拋棄File擁抱Paths和Files