How can I get current working directory?

By I Wayan Saryada in Core API, IO 0 Comment

A system properties named user.dir can be used if you want to find the current working directory of your Java program.

package org.kodejava.io;

public class CurrentDirectoryExample {
    public static void main(String[] args) {
        // System property key to get current working directory.
        String USER_DIR_KEY = "user.dir";
        String currentDir = System.getProperty(USER_DIR_KEY);

        System.out.println("Working Directory: " + currentDir);
    }
}

Result example:

Working Directory: F:\Wayan\Kodejava\kodejava-example

How can I change file attribute to writable?

By I Wayan Saryada in Core API, IO 0 Comment

Prior to Java 1.6 the java.io.File class doesn’t include a method to change a read only file attribute and make it writable. To do this on the old days we have to utilize or called operating system specific command. In Java 1.6 a new method named setWritable() was introduced to do exactly what the method name says.

package org.kodejava.io;

import java.io.File;

public class WritableExample {
    public static void main(String[] args) throws Exception {
        File file = new File("Writable.txt");

        // Create a file only if it doesn't exist.
        boolean created = file.createNewFile();

        // Set file attribute to read only so that it cannot be written
        boolean succeeded = file.setReadOnly();

        // We are using the canWrite() method to check whether we can
        // modified file content.
        if (file.canWrite()) {
            System.out.println("File is writable!");
        } else {
            System.out.println("File is in read only mode!");
        }

        // Now make our file writable
        succeeded = file.setWritable(true);

        // re-check the read-write status of file
        if (file.canWrite()) {
            System.out.println("File is writable!");
        } else {
            System.out.println("File is in read only mode!");
        }
    }
}

And here are the result of the code snippet above:

File is in read only mode!
File is writable!

How can I change file attribute to read only?

By I Wayan Saryada in Core API, IO 0 Comment

This code demonstrate how we can modify file attribute to be read only. File class has a setReadOnly() method to make file read only and a canWrite() method to know whether it is writable or not.

package org.kodejava.io;

import java.io.File;

public class FileReadOnlyExample {
    public static void main(String[] args) throws Exception {
        File file = new File("ReadOnly.txt");

        // Create a file only if it doesn't exist.
        boolean created = file.createNewFile();

        // Set file attribute to read only so that it cannot be written
        boolean succeeded = file.setReadOnly();

        // We are using the canWrite() method to check whether we can
        // modified file content.
        if (file.canWrite()) {
            System.out.println("File is writable!");
        } else {
            System.out.println("File is in read only mode!");
        }
    }
}

This code snippet print the following output:

File is in read only mode!

How do I append data to a text file?

By I Wayan Saryada in Core API, IO 0 Comment

One of the common task related to a text file is to append or add some contents to the file. It’s really simple to do this in Java using a FileWriter class. This class has a constructor that accept a boolean parameter call append. By setting this value to true a new data will be appended at the end of the file when we write a new data to it.

Let’s see an example.

package org.kodejava.io;

import java.io.File;
import java.io.FileWriter;
import java.io.IOException;

public class AppendFileExample {
    public static void main(String[] args) {
        File file = new File("user.txt");

        try (FileWriter writer = new FileWriter(file, true)) {
            writer.write("username=kodejava;password=secret" + System.lineSeparator());
            writer.flush();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

How do I use LineNumberReader class to read file?

By I Wayan Saryada in Core API, IO 0 Comment

In this example we use LineNumberReader class to read file contents. What we try to do here is to get the line number of the read data. Instead of introducing another variable; an integer for instance; to keep track the line number we can utilize the LineNumberReader class. This class offers the getLineNumber() method to know the current line of the data that is read.

package org.kodejava.io;

import java.io.FileReader;
import java.io.LineNumberReader;
import java.util.Objects;

public class LineNumberReaderExample {
    public static void main(String[] args) throws Exception {
        // We'll read a file called student.csv that contains our
        // student information data.
        String filename = Objects.requireNonNull(Thread.currentThread().getContextClassLoader()
                .getResource("student.csv")).getFile();

        // To create the FileReader we can pass in our student data
        // file to the reader. Next we pass the reader into our
        // LineNumberReader class.
        try (FileReader fileReader = new FileReader(filename);
             LineNumberReader lineNumberReader = new LineNumberReader(fileReader)) {
            // If we set the line number of the LineNumberReader here
            // we'll got the line number start from the defined line
            // number + 1

            //lineNumberReader.setLineNumber(400);

            String line;
            while ((line = lineNumberReader.readLine()) != null) {
                // We print out the student data and show what line
                // is currently read by our program.
                System.out.printf("Line Number %s: %s%n", lineNumberReader.getLineNumber(), line);
            }
        }
    }
}

The /resources/student.csv file:

Alice, 7
Bob, 8
Carol, 5
Doe, 6
Earl, 6
Malory, 8

And here is the result of our code snippet above:

Line Number 1: Alice, 7
Line Number 2: Bob, 8
Line Number 3: Carol, 5
Line Number 4: Doe, 6
Line Number 5: Earl, 6
Line Number 6: Malory, 8