Mapping CSV to JavaBeans using OpenCSV

CSV files are basically plain text files that store data in comma-separated columns. OpenCSV is the library for parsing these CSV files, which are otherwise difficult to process. It is a very easy-to-use library that supports multiple functions such as reading and writing CSV files with headers.

In this article, we will discuss the process of mapping CSV files to JavaBeans through OpenCSV. Additionally, OpenCSV is a helpful tool in this process.

Mapping CSV to JavaBean

The OpenCSV library provides some classes and mapping strategies for mapping CSV files to Java Beans. One of the classes is CSVToBean, which is used to map CSV files to JavaBeans. To parse these CSV files, the CSVToBean class needs a mapping strategy defined and passed to the CSVToBean class. One of the popular mapping strategies is HeaderColumnNameTranslateMappingStrategy, which maps column IDs to Java Bean properties.

grammar

The mapping of CSV files to Beans is completed through a series of steps. However, the syntax for creating a HashMap with a mapping between column IDs and beam properties is as follows -

HashMap map = new HashMap();
map.put("column_id", "bean_property");

First, we create a hashmap, and then use the put() function of HashMap to map the column id with the corresponding Java bean property.

algorithm

• Step One - First add OpenCSV to your Java project using the following dependencies.

For Maven projects, add the following dependencies to the java project -

<dependency>
   <groupId>com.opencsv</groupId>
   <artifactId>opencsv</artifactId>
   <version>4.1</version>
</dependency>

For a Gradle project, you need to add the following dependencies -

compile group: 'com.opencsv', name: 'opencsv', version: '4.1'

• Step 2 - Now, let’s start the basic steps of mapping csv file to Java Bean.

• Step 3 - Create a HashMap with a mapping between column IDs and bean properties.

• Step 4 - Add all the column ids of the csv file corresponding to the bean properties.

• Step 5 − Create HeaderColumnNameTranslateMappingStrategy object.

• Step 6 - Now, pass the mapped hashmap to the setColumnMapping() method.

• Step 7 - Call objects of CSVToBean and CSVReader classes.

• Step 8 - Now, we will call the parse method of the CSVToBean class and pass it the HeaderColumnNameTranslateMappingStrategy and CSVReader objects.

• Step 9 - Print the details of the Bean object.

method

Now, let us use OpenCSV to map the contents of the Employee.csv file to JavaBeans. The Employee.csv file contains data such as employee name, department, and salary.

The contents of the Employee.csv file are as follows:

Employee_Name, Department, Salary
Naman, Human Resource, 45000
Nikita, Sales, 35000
Rocky, IT, 50000
Raman, Human Resource, 42000

Now, let us first create the Employee class and then create the main method that maps the contents of that csv file to JavaBeans.

Example: Employee.java

public class Employee {
   private static final long serialVersionUID = 1L;
 
   public String emp_name, department, salary;
 
    public String getName() {
      return emp_name;
   }
 
   public void setName(String n) {
      emp_name  = n;
   }
 
   public String getSalary() {
      return salary;
   }
 
   public void setSalary(String s) {
      salary = s;
   }
 
   public String getDepartment() {
      return department;
   }
 
   public void setDepartment(String d) {
      d = department;
   }
   public String toString() {
      return "Employee [Name=" + emp_name + ", Department= " + department +",
         Salary = " + salary+ "]";
   }
}

The following is the program code of the CsvToBean.java file.

Example

import java.util.*;
import com.opencsv.CSVReader;
import com.opencsv.bean.CsvToBean;
import com.opencsv.bean.HeaderColumnNameTranslateMappingStrategy;

public class csvtobean {
   public static void main(String[] args) {
      Map<String, String> map = new HashMap<>();
      map.put("Employee_Name", "emp_name");
      map.put("Department", "department");
      map.put("Salary", "salary");
      HeaderColumnNameTranslateMappingStrategy<Employee> s =
         new HeaderColumnNameTranslateMappingStrategy<>();
      s.setType(Employee.class);
      s.setColumnMapping(map);
      CSVReader csvReader = null;
      try {
         csvReader = new CSVReader(new FileReader
         ("D:\CSVFiles\Employee.csv"));
      }
      catch (FileNotFoundException e) {
         e.printStackTrace();
      }
      CsvToBean csvToBean = new CsvToBean();
      List<Employee> l = csvToBean.parse(s, csvReader);
      for (Employee x : l) {
         System.out.println(x);
      }
   }
}

Output

Employee [Name=Naman, Department=Human Resource, Salary=45000]
Employee [Name=Nikita, Department=Sales, Salary=35000]
Employee [Name=Rocky, Department=IT, Salary=50000]
Employee [Name=Raman, Department=Human Resource, Salary=42000]

As you can see in the above program code, we first create a hash map that maps column IDs to corresponding bean properties. We then implemented the HeaderColumnNameTranslateMappingStrategy strategy for the Employee class and passed it to the parse method of the CsvToBean class to map the CSV to JavaBean using OpenCSV.

in conclusion

In this article, we looked at how to map CSV files to JavaBeans using OpenCSV. The simple technique discussed to do this is to use the CsvToBean class and a mapping strategy for the objects passed to the CsvToBean class. We discussed the steps and program code to parse employee data in csv format into JavaBeans using OpenCSV.

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