Lesson 2
Parsing Table Data Using Java
Introduction and Context Setting

Welcome to another lesson on parsing tables from text files with Java. In today's digital world, data is frequently stored in tabular formats, similar to spreadsheets. Text files provide a straightforward means to store this data when dealing with simple, organized datasets. Parsing, which involves reading and translating this data into usable formats, is an essential skill for data manipulation.

Consider situations where you need to process configuration files, logs, or reports exported from systems that store data in text file formats. By the end of this lesson, you will be equipped with the knowledge to parse such data into a structured format, facilitating easy manipulation in Java.

Understanding Text-Based Table Structure

Text files frequently store tabular data using simple delimiters like tabs between values. Consider the following example of a data.txt file:

Plain text
1Name    Age Occupation
2John    28  Engineer
3Alice   34  Doctor
4Bob     23  Artist

In this file, each line represents a row in a table, and each value within a line is separated by a tab, forming distinct columns. The first line acts as a header, describing the data in the lines that follow.

To effectively parse these lines into a structured format, we'll use a Person class:

Java
1static class Person {
2    public String name;
3    public int age;
4    public String occupation;
5
6    public Person(String name, int age, String occupation) {
7        this.name = name;
8        this.age = age;
9        this.occupation = occupation;
10    }
11}

The Person class will help us organize the extracted data, allowing us to map each piece of information to the respective properties: name, age, and occupation.

Reading the Table Data

To begin parsing the table data, we first need to read the text file. Java's Files.readAllLines method provides an efficient way to accomplish this, allowing us to easily access all lines in the file at once.

Java
1// Specify the input file path using a Path object
2Path filePath = Paths.get("data.txt");
3
4// Read all lines from the text file
5List<String> lines = Files.readAllLines(filePath);
6
7// Remove the header
8lines.remove(0);

In this snippet:

  • Files.readAllLines(filePath) retrieves all lines from the specified file.
  • lines.remove(0) excludes the first line, which contains the header, from further processing.

This approach sets a solid foundation for capturing all the rows of data that we need to parse, focusing only on the meaningful data entries.

Splitting Lines into Columns

Once the lines are retrieved, the next move is to convert each line into a list of values, corresponding to the columns.

Java
1// Initialize a list to store Person objects
2List<Person> people = new ArrayList<>();
3
4// Iterate over each line from the file
5for (String line : lines) {
6    // Split the current line by tab into an array of strings
7    String[] tokens = line.split("\t");
8    
9    // Create a new Person object with the extracted data and add it to the list
10    people.add(new Person(tokens[0], Integer.parseInt(tokens[1]), tokens[2]));
11}

Explanation:

  • List<Person> people = new ArrayList<>() initializes a list to store Person objects.
  • line.split("\t") divides the line into components based on the tab delimiter.
  • people.add(new Person(...)) adds each parsed person to the list.
Outputting the Parsed Data

Lastly, to verify the parsed data, we should print it out in a structured manner.

Java
1// Output the list of people to verify the result
2System.out.println("Parsed People Data:");
3for (Person person : people) {
4    System.out.println("Name: " + person.name + ", Age: " + person.age + ", Occupation: " + person.occupation);
5}

In this segment, a for loop iterates through each Person in the people list, and System.out.println is used to print each person's information.

The output confirms that each Person object is correctly populated with the corresponding data fields:

Plain text
1Parsed People Data:
2Name: John, Age: 28, Occupation: Engineer
3Name: Alice, Age: 34, Occupation: Doctor
4Name: Bob, Age: 23, Occupation: Artist
Summary, Key Takeaways, and Preparing for Practice

In this lesson, we've explored the fundamental elements of parsing a table from a text file using Java. The key takeaways include understanding how to:

  • Read a text file using Files.readAllLines.
  • Utilize the split("\t") method to divide lines into components.
  • Structure the data using collections like ArrayList<Person> in Java.

These skills are crucial for handling straightforward tabular data formats efficiently. As you progress to practice exercises, experiment with different delimiters and file structures to reinforce these concepts. Use these exercises to experiment and solidify your knowledge.

Enjoy this lesson? Now it's time to practice with Cosmo!
Practice is how you turn knowledge into actual skills.