Path Interface and Files class in NIO of Java 7.0

In this blog we use a couple of new classes introduced in new IO of Java 7. Our primary focus is on Path and Files classes.

Path Interface

The Java I/O File API, as it was originally created, was not written to be extended.

Many of the methods do not throw exceptions even when an error is encountered leaving developers wondering what's happening.

The following code in Java 6.0 will not throw any exception even if the file is not found in the filesystem.

 File f = new File("c:\\test.txt");
 f.delete();

 
 Path fp = Paths.get("c:\\test.txt");   // get Path object
 Files.delete(fp);  // delete file represented by path object

output
======
Exception in thread "main" java.nio.file.NoSuchFileException: c:\test.txt

The following code shows some other new methods of Path class.

        Path p = Paths.get("c:\\jdk7.0\\bin\\javac.exe");
        System.out.println( p.getNameCount());    // 3
        System.out.println( p.getName(1));        // bin

        System.out.println( p.getFileSystem().getClass());  // display file system - sun.nio.fs.WindowsFileSystem

        File f = p.toFile();  // convert to File object

Files class

The following are the important methods of Files class.

The following example shows how to use newDirectoryStream() to get list of files from the given path. Though listFiles() method of File class provides this functionality, DirectoryStream is more scalable.

        Path path = Paths.get("c:\\jdk7.0");
       
        //  take files from jdk7.0
        try (DirectoryStream<Path>  directory =  Files.newDirectoryStream(path))   // Closes stream at the end (ARM)
        {
           for (Path file :  directory) 
              System.out.println(file.getFileName()); 
        }

         Path p = Paths.get("c:\\jdk7.0\\names.txt");
        System.out.println("Size : "  + Files.size(p));
           
        List<String> lines = Files.readAllLines(p, Charset.defaultCharset());
        for(String line : lines)
             System.out.println(line);

The following example shows how to display the list of files from the given tree in the file system. It walks through the tree that starts with c:\jdk7.0 and displays all files and folder present within jdk7.0 folder.

Method walkFileTree() takes path to start with and an object of a class that extends SimpleFileVisitor class. For each file that is visited, visitFile() method is called. Before a directory is processed, preVisitDirectory() method is called. After directory is processed, postVisitDirectory() method is called.

import java.io.IOException;
import java.nio.file.FileVisitResult;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.SimpleFileVisitor;
import java.nio.file.attribute.BasicFileAttributes;
import static java.nio.file.FileVisitResult.CONTINUE;

public class WalkTree {
    public static void main(String[] args) throws Exception 
    {
        Path p = Paths.get("c:\\jdk7.0");
        PrintFiles pf= new PrintFiles();
        Files.walkFileTree(p,pf);
    }
}

class PrintFiles extends SimpleFileVisitor<Path> {
    @Override
    public FileVisitResult visitFile(Path file, BasicFileAttributes attr) {
        System.out.println( "File :" + file.getFileName());
        return CONTINUE;
    }

    @Override
    public FileVisitResult postVisitDirectory(Path dir, IOException ioe) throws IOException {
        System.out.printf("Processed Directory: %s\n", dir.getFileName());
        return CONTINUE;
    }

    @Override
    public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes bfa) throws IOException {
        System.out.printf("About to process directory: %s\n", dir.getFileName() );
        return CONTINUE;
    }
}

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