Files 需要关闭吗 files.

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智能开发者 2024-03-22 14:53:24

文章标签 Files 需要关闭吗 java System List 文章分类 架构后端开发

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

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){
            
        }

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：

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

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

3.path的join和resolve

1.连接路径：path.join([path1][, path2][, ...])

path.join()方法可以连接任意多个路径字符串。要连接的多个路径可做为参数传入。path.join()方法在接边路径的同时也会对路径进行规范化。例如：

var path = require('path');
//合法的字符串连接
path.join('/foo', 'bar', 'baz/asdf', 'quux', '..')
// 连接后
'/foo/bar/baz/asdf'

//不合法的字符串将抛出异常
path.join('foo', {}, 'bar')
// 抛出的异常
TypeError: Arguments to path.join must be strings'

var path = require('path');
//合法的字符串连接
path.join('/foo', 'bar', 'baz/asdf', 'quux', '..')
// 连接后
'/foo/bar/baz/asdf'

//不合法的字符串将抛出异常
path.join('foo', {}, 'bar')
// 抛出的异常
TypeError: Arguments to path.join must be strings'

2.路径解析：path.resolve([from ...], to)

path.resolve()方法可以将多个路径解析为一个规范化的绝对路径。其处理方式类似于对这些路径逐一进行cd操作，与cd操作不同的是，这引起路径可以是文件，并且可不必实际存在（resolve()方法不会利用底层的文件系统判断路径是否存在，而只是进行路径字符串操作）。例如：

path.resolve('foo/bar', '/tmp/file/', '..', 'a/../subfile') 相当于

cd foo/bar
cd /tmp/file/
cd ..
cd a/../subfile
pwd

例子：

path.resolve('/foo/bar', './baz')
// 输出结果为
'/foo/bar/baz'
path.resolve('/foo/bar', '/tmp/file/')
// 输出结果为
'/tmp/file'

path.resolve('wwwroot', 'static_files/png/', '../gif/image.gif')
// 当前的工作路径是 /home/itbilu/node，则输出结果为
'/home/itbilu/node/wwwroot/static_files/gif/image.gif' 

path.resolve('/foo/bar', './baz')
// 输出结果为
'/foo/bar/baz'
path.resolve('/foo/bar', '/tmp/file/')
// 输出结果为
'/tmp/file'

path.resolve('wwwroot', 'static_files/png/', '../gif/image.gif')
// 当前的工作路径是 /home/itbilu/node，则输出结果为
'/home/itbilu/node/wwwroot/static_files/gif/image.gif'

3.对比

const path = require('path');
let myPath = path.join(__dirname,'/img/so');
let myPath2 = path.join(__dirname,'./img/so');
let myPath3 = path.resolve(__dirname,'/img/so');
let myPath4 = path.resolve(__dirname,'./img/so');
console.log(__dirname);           //D:\myProgram\test
console.log(myPath);     //D:\myProgram\test\img\so
console.log(myPath2);   //D:\myProgram\test\img\so
console.log(myPath3);   //D:\img\so<br>
console.log(myPath4);   //D:\myProgram\test\img\so
const path = require('path');
let myPath = path.join(__dirname,'/img/so');
let myPath2 = path.join(__dirname,'./img/so');
let myPath3 = path.resolve(__dirname,'/img/so');
let myPath4 = path.resolve(__dirname,'./img/so');
console.log(__dirname);           //D:\myProgram\test
console.log(myPath);     //D:\myProgram\test\img\so
console.log(myPath2);   //D:\myProgram\test\img\so
console.log(myPath3);   //D:\img\so<br>
console.log(myPath4);   //D:\myProgram\test\img\so

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