In this example we are going to demonstrate how to Write/Read CSV files. CSV (Comma Separated Values) is a file format for data storage which looks like a text file, contains information which is organized with one record on each line and each field is separated by comma.

A CSV file is primarily used in database migration process where we can transport data between two databases of different formats through a computer program.

There are many ways to write and read CSV files in java where we can use a native java or an open source 3rd Party tool like OpenCSV, Apache Commons CSV and Super CSV.

So, Let’s see how we can write and read a simple CSV file using the native java code.

1. POJO to map the CSV File:

We create this simple POJO to contain the student data like id, firstName, lastName, gender and age.

Student.java:

package com.jcg;

/**
 * @author ashraf
 *
 */
public class Student {
	
	private long id;
	private String firstName;
	private String lastName;
	private String gender;
	private int age;
	/**
	 * @param id
	 * @param firstName
	 * @param lastName
	 * @param gender
	 * @param age
	 */
	public Student(long id, String firstName, String lastName, String gender,
			int age) {
		super();
		this.id = id;
		this.firstName = firstName;
		this.lastName = lastName;
		this.gender = gender;
		this.age = age;
	}
	/**
	 * @return the id
	 */
	public long getId() {
		return id;
	}
	/**
	 * @param id the id to set
	 */
	public void setId(long id) {
		this.id = id;
	}
	/**
	 * @return the firstName
	 */
	public String getFirstName() {
		return firstName;
	}
	/**
	 * @param firstName the firstName to set
	 */
	public void setFirstName(String firstName) {
		this.firstName = firstName;
	}
	/**
	 * @return the lastName
	 */
	public String getLastName() {
		return lastName;
	}
	/**
	 * @param lastName the lastName to set
	 */
	public void setLastName(String lastName) {
		this.lastName = lastName;
	}
	/**
	 * @return the gender
	 */
	public String getGender() {
		return gender;
	}
	/**
	 * @param gender the gender to set
	 */
	public void setGender(String gender) {
		this.gender = gender;
	}
	/**
	 * @return the age
	 */
	public int getAge() {
		return age;
	}
	/**
	 * @param age the age to set
	 */
	public void setAge(int age) {
		this.age = age;
	}
	
	@Override
	public String toString() {
		return "Student [id=" + id + ", firstName=" + firstName
				+ ", lastName=" + lastName + ", gender=" + gender + ", age="
				+ age + "]";
	}
}

2. Write to CSV File:

CsvFileWriter creates a comma separated value format “CSV” file from a set of students data and save it in your home directory. Firstly, it writes the CSV file header, and then it writes the students data using FileWriter class.

CsvFileWriter.java:

package com.jcg;

import java.io.FileWriter;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

/**
 * @author ashraf
 * 
 */
public class CsvFileWriter {
	
	//Delimiter used in CSV file
	private static final String COMMA_DELIMITER = ",";
	private static final String NEW_LINE_SEPARATOR = "\n";
	
	//CSV file header
	private static final String FILE_HEADER = "id,firstName,lastName,gender,age";

	public static void writeCsvFile(String fileName) {
		
		//Create new students objects
		Student student1 = new Student(1, "Ahmed", "Mohamed", "M", 25);
		Student student2 = new Student(2, "Sara", "Said", "F", 23);
		Student student3 = new Student(3, "Ali", "Hassan", "M", 24);
		Student student4 = new Student(4, "Sama", "Karim", "F", 20);
		Student student5 = new Student(5, "Khaled", "Mohamed", "M", 22);
		Student student6 = new Student(6, "Ghada", "Sarhan", "F", 21);
		
		//Create a new list of student objects
		List students = new ArrayList();
		students.add(student1);
		students.add(student2);
		students.add(student3);
		students.add(student4);
		students.add(student5);
		students.add(student6);
		
		FileWriter fileWriter = null;
				
		try {
			fileWriter = new FileWriter(fileName);

			//Write the CSV file header
			fileWriter.append(FILE_HEADER.toString());
			
			//Add a new line separator after the header
			fileWriter.append(NEW_LINE_SEPARATOR);
			
			//Write a new student object list to the CSV file
			for (Student student : students) {
				fileWriter.append(String.valueOf(student.getId()));
				fileWriter.append(COMMA_DELIMITER);
				fileWriter.append(student.getFirstName());
				fileWriter.append(COMMA_DELIMITER);
				fileWriter.append(student.getLastName());
				fileWriter.append(COMMA_DELIMITER);
				fileWriter.append(student.getGender());
				fileWriter.append(COMMA_DELIMITER);
				fileWriter.append(String.valueOf(student.getAge()));
				fileWriter.append(NEW_LINE_SEPARATOR);
			}

			
			
			System.out.println("CSV file was created successfully !!!");
			
		} catch (Exception e) {
			System.out.println("Error in CsvFileWriter !!!");
			e.printStackTrace();
		} finally {
			
			try {
				fileWriter.flush();
				fileWriter.close();
			} catch (IOException e) {
				System.out.println("Error while flushing/closing fileWriter !!!");
                e.printStackTrace();
			}
			
		}
	}
}

Let’s see how the generated student.csv file is organized, it contains the header and the students data below.

student.csv:

id,firstName,lastName,gender,age
1,Ahmed,Mohamed,M,25
2,Sara,Said,F,23
3,Ali,Hassan,M,24
4,Sama,Karim,F,20
5,Khaled,Mohamed,M,22
6,Ghada,Sarhan,F,21

3. Read from CSV File:

CsvFileReader reads the CSV file in java using BufferedReader class then skipping the header and starting from the second line, we split each line using String.split() function. A String.split() function splits string around matches of the given regular expression. Finally, we create a new list of student and print it.

CsvFileReader.java:

package com.jcg;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

/**
 * @author ashraf_sarhan
 *
 */
public class CsvFileReader {
	
	//Delimiter used in CSV file
	private static final String COMMA_DELIMITER = ",";
	
	//Student attributes index
	private static final int STUDENT_ID_IDX = 0;
	private static final int STUDENT_FNAME_IDX = 1;
	private static final int STUDENT_LNAME_IDX = 2;
	private static final int STUDENT_GENDER = 3; 
	private static final int STUDENT_AGE = 4;
	
	public static void readCsvFile(String fileName) {

		BufferedReader fileReader = null;
     
        try {
        	
        	//Create a new list of student to be filled by CSV file data 
        	List students = new ArrayList();
        	
            String line = "";
            
            //Create the file reader
            fileReader = new BufferedReader(new FileReader(fileName));
            
            //Read the CSV file header to skip it
            fileReader.readLine();
            
            //Read the file line by line starting from the second line
            while ((line = fileReader.readLine()) != null) {
                //Get all tokens available in line
                String[] tokens = line.split(COMMA_DELIMITER);
                if (tokens.length > 0) {
                	//Create a new student object and fill his  data
					Student student = new Student(Long.parseLong(tokens[STUDENT_ID_IDX]), tokens[STUDENT_FNAME_IDX], tokens[STUDENT_LNAME_IDX], tokens[STUDENT_GENDER], Integer.parseInt(tokens[STUDENT_AGE]));
					students.add(student);
				}
            }
            
            //Print the new student list
            for (Student student : students) {
				System.out.println(student.toString());
			}
        } 
        catch (Exception e) {
        	System.out.println("Error in CsvFileReader !!!");
            e.printStackTrace();
        } finally {
            try {
                fileReader.close();
            } catch (IOException e) {
            	System.out.println("Error while closing fileReader !!!");
                e.printStackTrace();
            }
        }

	}

}

4. Run the Example:

CsvWriteReadTest is the main class to run CsvFileWriter and CsvFileReader for the given CSV file.

CsvWriteReadTest.java:

package com.jcg;

/**
 * @author ashraf
 *
 */
public class CsvWriteReadTest {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		
		String fileName = System.getProperty("user.home")+"/student.csv";
		
		System.out.println("Write CSV file:");
		CsvFileWriter.writeCsvFile(fileName);
		
		System.out.println("\nRead CSV file:");
		CsvFileReader.readCsvFile(fileName);

	}

}

Output:

Write CSV file:
CSV file was created successfully !!!

Read CSV file:
Student [id=1, firstName=Ahmed, lastName=Mohamed, gender=M, age=25]
Student [id=2, firstName=Sara, lastName=Said, gender=F, age=23]
Student [id=3, firstName=Ali, lastName=Hassan, gender=M, age=24]
Student [id=4, firstName=Sama, lastName=Karim, gender=F, age=20]
Student [id=5, firstName=Khaled, lastName=Mohamed, gender=M, age=22]
Student [id=6, firstName=Ghada, lastName=Sarhan, gender=F, age=21]

5. Download the Source Code of this example:

This was an example of how to to Write/Read CSV files.