Java基础之IO和NIO补完

Java Stream，File，IO

关于NIO和IO的比较，参考：Java NIO系列教程（十二） Java NIO与IO

java包之java.io

参考材料：菜鸟教材

NIO

由于下面的系列教程只翻译到了13，后面的也挺简单的。主要是代码。记录在这里。
重点参考：java NIO系列教程

15 Java NIO Path

翻译自：15Java NIO Path
Java的java.nio.file.Path接口是JavaNIO 2 update的一部分，在Java6和Java7中得到更新。Java path接口在java7中被加入到Java NIO中。Path接口位于java.nio.file包中，所以Java Path接口的全名是：java.nio.file.Path。
一个Java Path接口代表了一个文件系统中的path路径。path路径可以指向文件或目录。一个路径可以是绝对路径也可以是相对路径。一个绝对路径是从文件系统根目录指向该文件或路径的全路径。一个相对路径是指相对于其他路径一个文件或目录的相对路径。相对路径可能比较费解，不用担心，我会在该文中详细介绍。
对于操作系统中的系统路径这样的环境变量不要疑惑，java Path接口跟它们没有关系。
在很多方面java.nio.file.Path和java.io.File类是类似的，在一些地方你可以使用Path接口来代替File类，但是也有一些不同。

1. 创建Path实例

你可以使用java.nio.file.Paths类的静态方法Paths.get()来创建一个java.nio.file.Path的实例:

import java.nio.file.Path;

import java.nio.file.Paths;

public class PathExample {

    public static void main(String[] args) {

        Path path = Paths.get("c:\\data\\myfile.txt");

    }

}

Paths.get()方法是创建Path实例的工厂方法。

2. 创建一个绝对路径Path实例

Windows文件系统下的绝对路径：

Path path = Paths.get("c:\\data\\myfile.txt");

类Unix操作系统下的绝对路径：

Path path = Paths.get("/home/jakobjenkov/myfile.txt");

//如果你在windows上这么使用，会表示当前系统分区下的路径，如：C:/home/jakobjenkov/myfile.txt

3. 创建一个相对路径Path实例

相对路径需要一个basepath和relativepath来创建：

Path projects = Paths.get("d:\\data", "projects");

Path file     = Paths.get("d:\\data", "projects\\a-project\\myfile.txt");

可以使用'.','..'来创建路径实例：

Path currentDir = Paths.get(".");

System.out.println(currentDir.toAbsolutePath());

4. Path.normalize()

String originalPath =

        "d:\\data\\projects\\a-project\\..\\another-project";

Path path1 = Paths.get(originalPath);

System.out.println("path1 = " + path1);

Path path2 = path1.normalize();

System.out.println("path2 = " + path2);

path1 = d:\data\projects\a-project\..\another-project

path2 = d:\data\projects\another-project

16. Java NIO Files

翻译自：16Java NIO Files
java.nio.file.Files类提供了多种方法来操作文件。

1. Files.exists()

LinkOption.NOFOLLOW_LINKS表示文件存在，但是不能是链接形式的。

Path path = Paths.get("data/logging.properties");

boolean pathExists =

        Files.exists(path,

            new LinkOption[]{ LinkOption.NOFOLLOW_LINKS});

2. Files.createDirectory()

Path path = Paths.get("data/subdir");

try {

    Path newDir = Files.createDirectory(path);

} catch(FileAlreadyExistsException e){

    // the directory already exists.

} catch (IOException e) {

    //something else went wrong

    e.printStackTrace();

}

3. Files.copy()

Path sourcePath      = Paths.get("data/logging.properties");

Path destinationPath = Paths.get("data/logging-copy.properties");

try {

    Files.copy(sourcePath, destinationPath);

} catch(FileAlreadyExistsException e) {

    //destination file already exists

} catch (IOException e) {

    //something else went wrong

    e.printStackTrace();

}

4. Overwriting Existing Files

通过复制选项来覆盖已经存在的Files

Path sourcePath      = Paths.get("data/logging.properties");

Path destinationPath = Paths.get("data/logging-copy.properties");

try {

    Files.copy(sourcePath, destinationPath,

            StandardCopyOption.REPLACE_EXISTING);

} catch(FileAlreadyExistsException e) {

    //destination file already exists

} catch (IOException e) {

    //something else went wrong

    e.printStackTrace();

}

5. Files.move()

java.io.File 有方法 renameTo() ,Files可以Files.move()

Path sourcePath      = Paths.get("data/logging-copy.properties");

Path destinationPath = Paths.get("data/subdir/logging-moved.properties");

try {

    Files.move(sourcePath, destinationPath,

            StandardCopyOption.REPLACE_EXISTING);

} catch (IOException e) {

    //moving file failed.

    e.printStackTrace();

}

6. Files.delete()

Path path = Paths.get("data/subdir/logging-moved.properties");

try {

    Files.delete(path);

} catch (IOException e) {

    //deleting file failed

    e.printStackTrace();

}

7. Files.walkFileTree()

Files.walkFileTree()用来递归遍历文件目录，有Path实例和FileVisitor来做参数。
FileVisitor接口有如下形式：

public interface FileVisitor {

    public FileVisitResult preVisitDirectory(

        Path dir, BasicFileAttributes attrs) throws IOException;

    public FileVisitResult visitFile(

        Path file, BasicFileAttributes attrs) throws IOException;

    public FileVisitResult visitFileFailed(

        Path file, IOException exc) throws IOException;

    public FileVisitResult postVisitDirectory(

        Path dir, IOException exc) throws IOException {

}

FileVisitor有一个简单实现SimpleFileVisitor类：

Files.walkFileTree(path, new FileVisitor<Path>() {

  @Override

  public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs) throws IOException {

    System.out.println("pre visit dir:" + dir);

    return FileVisitResult.CONTINUE;

  }

  @Override

  public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {

    System.out.println("visit file: " + file);

    return FileVisitResult.CONTINUE;

  }

  @Override

  public FileVisitResult visitFileFailed(Path file, IOException exc) throws IOException {

    System.out.println("visit file failed: " + file);

    return FileVisitResult.CONTINUE;

  }

  @Override

  public FileVisitResult postVisitDirectory(Path dir, IOException exc) throws IOException {

    System.out.println("post visit directory: " + dir);

    return FileVisitResult.CONTINUE;

  }

});

- FileVisitResult的集合有：

CONTINUE 表示继续

TERMINATE 表示停止

SKIP_SIBLINGS 表示继续但是不再便利兄弟目录

SKIP_SUBTREE 表示继续但是不再便利子目录

8. Searching For Files

下面可以实现SimpleFileVisitor来查找文件：

Path rootPath = Paths.get("data");

String fileToFind = File.separator + "README.txt";

try {

  Files.walkFileTree(rootPath, new SimpleFileVisitor<Path>() {

    @Override

    public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {

      String fileString = file.toAbsolutePath().toString();

      //System.out.println("pathString = " + fileString);

      if(fileString.endsWith(fileToFind)){

        System.out.println("file found at path: " + file.toAbsolutePath());

        return FileVisitResult.TERMINATE;

      }

      return FileVisitResult.CONTINUE;

    }

  });

} catch(IOException e){

    e.printStackTrace();

}

9. Deleting Directories Recursively

Path rootPath = Paths.get("data/to-delete");

try {

  Files.walkFileTree(rootPath, new SimpleFileVisitor<Path>() {

    @Override

    public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {

      System.out.println("delete file: " + file.toString());

      Files.delete(file);

      return FileVisitResult.CONTINUE;

    }

    @Override

    public FileVisitResult postVisitDirectory(Path dir, IOException exc) throws IOException {

      Files.delete(dir);

      System.out.println("delete dir: " + dir.toString());

      return FileVisitResult.CONTINUE;

    }

  });

} catch(IOException e){

  e.printStackTrace();

}

10. Additional Methods in the Files Class

Files类有很多其他方法，如 creating symbolic links, determining the file size, setting file permissions 等。参考java文档。

17. Java NIO AsynchronousFileChannel

java7中AsynchronousFileChannel加入到了java NIO的包中。AsynchronousFileChannels使得异步读写文件实现。

1. Creating an AsynchronousFileChannel

Path path = Paths.get("data/test.xml");

AsynchronousFileChannel fileChannel =

    AsynchronousFileChannel.open(path, StandardOpenOption.READ);

2. Reading Data

Reading Data Via a Future

Future<Integer> operation = fileChannel.read(buffer, 0);

AsynchronousFileChannel fileChannel =

    AsynchronousFileChannel.open(path, StandardOpenOption.READ);

ByteBuffer buffer = ByteBuffer.allocate(1024);

long position = 0;

Future<Integer> operation = fileChannel.read(buffer, position);

// Of course, this is not a very efficient use of the CPU - but somehow you need to wait until the read operation has completed.

while(!operation.isDone());

buffer.flip();

byte[] data = new byte[buffer.limit()];

buffer.get(data);

System.out.println(new String(data));

buffer.clear();

Reading Data Via a CompletionHandler

fileChannel.read(buffer, position, buffer, new CompletionHandler<Integer, ByteBuffer>() {

//Once the read operation finishes the CompletionHandler's completed() method will be called.

    @Override

    public void completed(Integer result, ByteBuffer attachment) {

        System.out.println("result = " + result);

        attachment.flip();

        byte[] data = new byte[attachment.limit()];

        attachment.get(data);

        System.out.println(new String(data));

        attachment.clear();

    }

//If the read operation fails, the failed() method of the CompletionHandler will get called instead.

    @Override

    public void failed(Throwable exc, ByteBuffer attachment) {

    }

});

3. Writing Data

Writing Data Via a Future



Path path = Paths.get("data/test-write.txt");

//If the file does not exist the write() method will throw a java.nio.file.NoSuchFileException .

if(!Files.exists(path)){

    Files.createFile(path);

}

AsynchronousFileChannel fileChannel =

    AsynchronousFileChannel.open(path, StandardOpenOption.WRITE);

ByteBuffer buffer = ByteBuffer.allocate(1024);

long position = 0;

buffer.put("test data".getBytes());

buffer.flip();

Future<Integer> operation = fileChannel.write(buffer, position);

buffer.clear();

while(!operation.isDone());

System.out.println("Write done");

Writing Data Via a CompletionHandler

Path path = Paths.get("data/test-write.txt");

if(!Files.exists(path)){

    Files.createFile(path);

}

AsynchronousFileChannel fileChannel =

    AsynchronousFileChannel.open(path, StandardOpenOption.WRITE);

ByteBuffer buffer = ByteBuffer.allocate(1024);

long position = 0;

buffer.put("test data".getBytes());

buffer.flip();

fileChannel.write(buffer, position, buffer, new CompletionHandler<Integer, ByteBuffer>() {

    @Override

    public void completed(Integer result, ByteBuffer attachment) {

        System.out.println("bytes written: " + result);

    }

    @Override

    public void failed(Throwable exc, ByteBuffer attachment) {

        System.out.println("Write failed");

        exc.printStackTrace();

    }

});

via

Java基础之IO和NIO补完

Java Stream，File，IO

java包之java.io

NIO

15 Java NIO Path

1. 创建Path实例

2. 创建一个绝对路径Path实例

3. 创建一个相对路径Path实例

4. Path.normalize()

16. Java NIO Files

1. Files.exists()

2. Files.createDirectory()

3. Files.copy()

4. Overwriting Existing Files

5. Files.move()

6. Files.delete()

7. Files.walkFileTree()

8. Searching For Files

9. Deleting Directories Recursively

10. Additional Methods in the Files Class

17. Java NIO AsynchronousFileChannel

1. Creating an AsynchronousFileChannel

2. Reading Data

3. Writing Data