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.
You can download the full source code of this example here: Write/Read CSV Files Example Code
Now try it with data containing newlines and embedded commas.
Thanks for your blog. It helped me a lot. Can you help me to solve the problem of parsing a CSV cell which contains multiple comma(,)?
where file will get store after writing successfully .
thanks
where file will get store after writing successfully .
I’m facing Type mismatch error
for(Student student : students)i’m facing the same issue
same here
List<Student> students =new
ArrayList();This will work