JAVA IO and NIO.

java.io.file

• path interface
• get(String, String)
• getFileName()
• getName(int)
• getNameCount()
• getParent(), getRoot()
• toAbsolutePath()
• toFile()
• paths class
• exists(path)
• notExists(path)
• isReadable(path)
• isWritable(path)
• isDirectory(path)
• isRegularFile(path)
• size(path)
• newDirectoryStream(path)
• createFile(path)
• createDirectory(path)
• createDirectories(path)
• files class
• Exceptions
• IOException
• EOFException
• FileNotFoundException
• FileAlreadyExistsException
• DirectoryNotEmptyException

import java.io.*;
import java.nio.file.*;

Path myp = Paths.get("./mydir");

String dir = "./src/db/files";
String filename = "db.txt";
Path dirPath = Paths.get(dir);
Path fPath = Paths.get(dir, filename);
File fName = fPath.toFile();

if (Files.notExists(fPath)) {
    Files.createDirectories(fPath);
}

// fPath.getFileName() -> return String
// fPath.toAbsolutePath() -> return String
// Files.isWritable(fPath) -> return boolean
// Files.exists(dirPath) -> return boolean
// Files.isDirectory (dirPath) -> return boolean

DirectoryStream dirs = Files.newDirectoryStream(dirPath);
for (Path p: dirs) {
    if (Files.isRegularFile (p) {
        System.out.println (" " + 
            p.getFileName());
    }
}

// Write data to file
// layered approach to get an object using constructor
try (PrintWriter out = new PrintWriter (
                       new BufferedWriter (
                       new FileWriter (productsFile))))
{
    out.println ("printout line");
}
catch (IOException e)
{
    System.out.println(e);
}

//Read data from the file
try (BufferedReader in = new BufferedReader(
                         new FileReader(myFile)))
{
    String line = in.readLine();
    while (line != null)
    {
        System.out.println(line);
        line = in.readLine();
        String[] columns = line.split("\t");
        String name = columns[0];
        String value = columns[1];
        int type = Integer.parseInteger(columns[2]);
        System.out.println(type);
    }
}
catch (IOException e)
{
    System.out.println(e);
}
// flush the buffer and close the input stream
in.close();

// Code that handles I/O exceptions
Path productsPath = Paths.get("products.txt");
if (Files.exists(productsPath)){  //defensive prog.
    //prevent the FileNotFoundeException
    File productsFile = productsPath.toFile();
    try (BufferedReader in = new BufferedReader(
                             new FileReader(productsFile)))
    {
        String line = in.readLine();
        //prevent EOFException
        while(line != null){
            System.out.println(line);
            line = in.readLine();
        }
    }
    catch (IOException e){
        System.out.println(e);
    }
} else{
    System.out.println(
              productsPath.toAbsolutePath() + " doesn't exist");
}

// ProductDAO interface
public interface ProductDAO
          extends ProductReader, ProductWriter,
          ProductConstants {}

import java.util.ArrayList;
public interface ProductReader
{
    Product getProduct(String code);
    ArrayList getProducts();
}

//The ProductWriter interface
public interface ProductWriter
{
    boolean addProduct(Product p);
    boolean updateProduct(Product p);
    boolean deleteProduct(Product p);
}
//The ProductConstants interface
public interface ProductConstants
{
    int CODE_SIZE = 4;
    int DESCRIPTION_SIZE = 40;
}

java.nio.file (JDK 1.7+)

• Threads and NIO