基於java Files類和Paths類的用法(詳解)

Java7中文件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用於來表示文件路徑和文件。可以有多種方法來構造一個Path對象來表示一個文件路徑，或者一個文件：

1）首先是final類Paths的兩個static方法，如何從一個路徑字符串來構造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）創建一個文件：

 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來指定rwx權限。

5）Files.newBufferedReader讀取文件：

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

這裡如果指定的字符編碼不對，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）文件寫操作：

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

7）遍歷一個文件夾：

 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(); }

上面是遍歷單個目錄，它不會遍歷整個目錄。遍歷整個目錄需要使用：Files.walkFileTree

8）遍歷整個文件目錄：

 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; } }

將目錄下面所有符合條件的圖片刪除掉：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生成指定大小的縮略圖。 a.jpg 則生成a_1.jpg

2. 強大的java.nio.file.Files

1）創建目錄和文件：

 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();}

注意創建目錄和文件Files.createDirectories 和Files.createFile不能混用，必須先有目錄，才能在目錄中創建文件。

2）文件複製:

從文件複製到文件：Files.copy(Path source, Path target, CopyOption options);

從輸入流複製到文件：Files.copy(InputStream in, Path target, CopyOption options);

從文件複製到輸出流：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）遍歷一個目錄和文件夾上面已經介紹了：Files.newDirectoryStream ， Files.walkFileTree

4）讀取文件屬性：

 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）讀取和設置文件權限：

 Path profile = Paths.get("/home/digdeep/.profile"); PosixFileAttributes attrs = Files.readAttributes(profile, PosixFileAttributes.class);// 讀取文件的權限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); // 設置文件的權限

Files類簡直強大的一塌糊塗，幾乎所有文件和目錄的相關屬性，操作都有想要的api來支持。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(); } }}

場景是，sql server導出數據時，會將datatime 導成16進制的binary格式，形如：, CAST(0x0000A2A500FC2E4F AS DateTime))

所以上面的程序是將最後一個datatime 字段導出的, CAST(0x0000A2A500FC2E4F AS DateTime) 刪除掉，生成新的不含有datetime字段值的sql 腳本。用來導入到mysql中。

做到半途，其實有更好的方法，使用sql yog可以很靈活的將sql server中的表以及數據導入到mysql中。使用sql server自帶的導出數據的功能，反而不好處理。

以上這篇基於java Files類和Paths類的用法(詳解)就是小編分享給大家的全部內容了，希望能給大家一個參考，也希望大家多多支持武林網。