**Course Title:** Comprehensive Java Programming: From Basics to Advanced Concepts **Section Title:** File I/O and Working with External Data **Topic:** Working with data formats: Text, CSV, and JSON **Introduction** In the previous topic, we learned about reading and writing files using FileReader, FileWriter, and BufferedReader. However, in real-world applications, we often deal with different data formats such as text, CSV, and JSON. In this topic, we will learn how to work with these data formats in Java. **Working with Text Files** Text files are the simplest form of data storage. We can read and write text files using the FileReader and FileWriter classes. However, when working with large text files, we can use the BufferedReader and BufferedWriter classes for efficient reading and writing. Here's an example of reading a text file: ```java import java.io.BufferedReader; import java.io.FileReader; import java.io.IOException; public class ReadTextFile { public static void main(String[] args) { try (BufferedReader reader = new BufferedReader(new FileReader("example.txt"))) { String line; while ((line = reader.readLine()) != null) { System.out.println(line); } } catch (IOException e) { System.err.println("Error reading file: " + e.getMessage()); } } } ``` And here's an example of writing to a text file: ```java import java.io.BufferedWriter; import java.io.FileWriter; import java.io.IOException; public class WriteTextFile { public static void main(String[] args) { try (BufferedWriter writer = new BufferedWriter(new FileWriter("example.txt"))) { writer.write("Hello, World!"); } catch (IOException e) { System.err.println("Error writing to file: " + e.getMessage()); } } } ``` **Working with CSV Files** CSV (Comma Separated Values) files are used to store tabular data. In Java, we can use the OpenCSV library [https://opencsv.sourceforge.io/](https://opencsv.sourceforge.io/) to read and write CSV files. Here's an example of reading a CSV file: ```java import com.opencsv.CSVReader; import com.opencsv.CSVReaderBuilder; import java.io.FileReader; import java.io.IOException; public class ReadCSVFile { public static void main(String[] args) { try (CSVReader reader = new CSVReaderBuilder(new FileReader("example.csv")).build()) { String[] row; while ((row = reader.readNext()) != null) { for (String cell : row) { System.out.print(cell + " "); } System.out.println(); } } catch (IOException e) { System.err.println("Error reading file: " + e.getMessage()); } } } ``` And here's an example of writing to a CSV file: ```java import com.opencsv.CSVWriter; import com.opencsv.CSVWriterBuilder; import java.io.FileWriter; import java.io.IOException; public class WriteCSVFile { public static void main(String[] args) { try (CSVWriter writer = new CSVWriterBuilder(new FileWriter("example.csv")).build()) { writer.writeNext(new String[] {"Name", "Age", "City"}); writer.writeNext(new String[] {"John Doe", "30", "New York"}); } catch (IOException e) { System.err.println("Error writing to file: " + e.getMessage()); } } } ``` **Working with JSON Files** JSON (JavaScript Object Notation) files are used to store data in a lightweight, human-readable format. In Java, we can use the Jackson library [https://github.com/FasterXML/jackson](https://github.com/FasterXML/jackson) to read and write JSON files. Here's an example of reading a JSON file: ```java import com.fasterxml.jackson.databind.ObjectMapper; import java.io.File; import java.io.IOException; public class ReadJSONFile { public static void main(String[] args) { try { ObjectMapper mapper = new ObjectMapper(); Person person = mapper.readValue(new File("example.json"), Person.class); System.out.println(person); } catch (IOException e) { System.err.println("Error reading file: " + e.getMessage()); } } } class Person { private String name; private int age; private String city; // Getters and setters } ``` And here's an example of writing to a JSON file: ```java import com.fasterxml.jackson.databind.ObjectMapper; import java.io.File; import java.io.IOException; public class WriteJSONFile { public static void main(String[] args) { try { ObjectMapper mapper = new ObjectMapper(); Person person = new Person("John Doe", 30, "New York"); mapper.writeValue(new File("example.json"), person); } catch (IOException e) { System.err.println("Error writing to file: " + e.getMessage()); } } } class Person { private String name; private int age; private String city; // Getters and setters } ``` **Conclusion** In this topic, we learned how to work with different data formats in Java, including text, CSV, and JSON. We saw examples of reading and writing files using various libraries and APIs. By understanding how to work with these data formats, you can handle a wide range of data in your Java applications. **Practice Problems** 1. Write a Java program to read a text file and display its contents on the console. 2. Write a Java program to write data to a CSV file using the OpenCSV library. 3. Write a Java program to read a JSON file using the Jackson library and display its contents on the console. **What to Do Next** In the next topic, we will learn about Java's `java.nio` and `java.io` packages for file handling. **Comments and Questions** Please leave a comment below if you have any questions or need further clarification on any of the concepts covered in this topic.