Kotlin + Spring Boot + Apache Commons Export Data to CSV Example

 Hello everyone, today we will learn how to export and download the data as a CSV file in a Kotlin + Spring Boot project. CSV stands for Comma-Separated-Values and it's a common format for doing a bulk data transfer between systems. For creating and parsing CSV files, we will use Apache Commons' 3rd-party library. 


Project Directory:


Technologies used:

  • Kotlin
  • Spring Boot
  • Apache Commons
  • Spring Data JPA
  • H2DB
  • Maven

Maven[pom.xml]

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" 
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 
https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.3.7.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.knf.dev</groupId>
    <artifactId>kotlin_springboot_apachecommans_exportcsv</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>kotlin_springboot_apachecommans_exportcsv</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <java.version>1.8</java.version>
        <kotlin.version>1.3.72</kotlin.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.module</groupId>
            <artifactId>jackson-module-kotlin</artifactId>
        </dependency>
        <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-csv</artifactId>
            <version>1.8</version>
        </dependency>
        <dependency>
            <groupId>org.jetbrains.kotlin</groupId>
            <artifactId>kotlin-reflect</artifactId>
        </dependency>
        <dependency>
            <groupId>org.jetbrains.kotlin</groupId>
            <artifactId>kotlin-stdlib-jdk8</artifactId>
        </dependency>

        <dependency>
            <groupId>com.h2database</groupId>
            <artifactId>h2</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
            <exclusions>
                <exclusion>
                    <groupId>org.junit.vintage</groupId>
                    <artifactId>junit-vintage-engine</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
    </dependencies>

    <build>
        <sourceDirectory>${project.basedir}/src/main/kotlin</sourceDirectory>
        <testSourceDirectory>${project.basedir}/src/test/kotlin</testSourceDirectory>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
            <plugin>
                <groupId>org.jetbrains.kotlin</groupId>
                <artifactId>kotlin-maven-plugin</artifactId>
                <configuration>
                    <args>
                        <arg>-Xjsr305=strict</arg>
                    </args>
                    <compilerPlugins>
                        <plugin>spring</plugin>
                    </compilerPlugins>
                </configuration>
                <dependencies>
                    <dependency>
                        <groupId>org.jetbrains.kotlin</groupId>
                        <artifactId>kotlin-maven-allopen</artifactId>
                        <version>${kotlin.version}</version>
                    </dependency>
                </dependencies>
            </plugin>
        </plugins>
    </build>

</project>

Creating the Document

package com.knf.dev.entity

import javax.persistence.*

@Entity
@Table(name = "employee")
class Employee {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    var id: Long = 0
    var name: String? = null
    var email: String? = null
    var country: String? = null
    var age = 0
    var role: String? = null

    constructor() : super() {}
    constructor(
        name: String?, email: String?, country: String?,
        age: Int, role: String?
    ) : super() {
        this.name = name
        this.email = email
        this.country = country
        this.age = age
        this.role = role
    }
}

Creating the Repository

package com.knf.dev.repository

import com.knf.dev.entity.Employee
import org.springframework.data.jpa.repository.JpaRepository
import org.springframework.stereotype.Repository

@Repository
interface EmployeeRepository : JpaRepository<Employee, Long>

Creating the Service

package com.knf.dev.service

import java.io.ByteArrayInputStream
import com.knf.dev.entity.Employee
import com.knf.dev.helper.CSVHelper
import com.knf.dev.helper.CSVHelper.employeesToCSV
import com.knf.dev.repository.EmployeeRepository
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.stereotype.Service


@Service
class EmployeeService {
    @Autowired
    var employeeRepository: EmployeeRepository? = null
    fun fetchAll(): List<Employee> {
        return employeeRepository!!.findAll()
    }

    fun load(): ByteArrayInputStream {
        //save Dummy Data
        saveDummyEmployees()
        val employees = fetchAll()
        return CSVHelper.employeesToCSV(employees)
    }

    //save Dummy Data
    fun saveDummyEmployees() {

        val employees: MutableList<Employee> = ArrayList()

        // create dummy employees
        employees.add(
            Employee(
                "Dummy-1", "dummy1@example.com",
                "India", 35, "Lead Tester"
            )
        )
        employees.add(
            Employee(
                "Dummy-2", "dummy2@srovoki.me",
                "USA", 25, "Tester"
            )
        )
        employees.add(
            Employee(
                "Dummy-3", "dummy3@gmail.com",
                "Japan", 29, "Sr.Tester"
            )
        )
        employees.add(
            Employee(
                "Dummy-1", "dummy1@example.com",
                "India", 35, "Lead Tester"
            )
        )
        employees.add(
            Employee(
                "Dummy-2", "dummy2@srovoki.me",
                "USA", 25, "Tester"
            )
        )
        employees.add(
            Employee(
                "Dummy-3", "dummy3@gmail.com",
                "Japan", 29, "Sr.Tester"
            )
        )
        employees.add(
            Employee(
                "Dummy-1", "dummy1@example.com",
                "India", 35, "Lead Tester"
            )
        )
        employees.add(
            Employee(
                "Dummy-2", "dummy2@srovoki.me",
                "USA", 25, "Tester"
            )
        )
        employees.add(
            Employee(
                "Dummy-3", "dummy3@gmail.com",
                "Japan", 29, "Sr.Tester"
            )
        )
        employees.add(
            Employee(
                "Dummy-1", "dummy1@example.com",
                "India", 35, "Lead Tester"
            )
        )
        employees.add(
            Employee(
                "Dummy-2", "dummy2@srovoki.me",
                "USA", 25, "Tester"
            )
        )
        employees.add(
            Employee(
                "Dummy-3", "dummy3@gmail.com",
                "Japan", 29, "Sr.Tester"
            )
        )
        employees.add(
            Employee(
                "Dummy-1", "dummy1@example.com",
                "India", 35, "Lead Tester"
            )
        )
        employees.add(
            Employee(
                "Dummy-2", "dummy2@srovoki.me",
                "USA", 25, "Tester"
            )
        )
        employees.add(
            Employee(
                "Dummy-3", "dummy3@gmail.com",
                "Japan", 29, "Sr.Tester"
            )
        )
        employeeRepository?.saveAll(employees)
    }
}

Creating the Helper 

package com.knf.dev.helper

import java.io.IOException
import java.io.ByteArrayInputStream
import com.knf.dev.entity.Employee
import java.io.PrintWriter
import org.apache.commons.csv.CSVPrinter
import org.apache.commons.csv.CSVFormat
import java.io.ByteArrayOutputStream
import java.util.*


object CSVHelper {
    fun employeesToCSV(employees: List<Employee>): ByteArrayInputStream {
        val format = CSVFormat.DEFAULT.withHeader("ID", "Name", "Email", 
                  "Age", "Country", "Role")
        try {
            ByteArrayOutputStream().use({ out ->
                CSVPrinter(
                    PrintWriter(out),
                    format
                ).use { csvPrinter ->
                    for (emp in employees) {
                        val data: List<String?> = Arrays.asList(
                            emp.id.toString(),
                            emp.name, emp.email,
                            java.lang.String.valueOf(emp.age), emp.country,
                            emp.role
                        )
                        csvPrinter.printRecord(data)
                    }
                    csvPrinter.flush()
                    return ByteArrayInputStream(out.toByteArray())
                }
            })
        } catch (e: IOException) {
            throw RuntimeException(
                "fail to import data to CSV file: "
                        + e.message
            )
        }
    }
}

Creating the Controller

package com.knf.dev.controller

import org.springframework.http.HttpHeaders
import org.springframework.http.ResponseEntity
import org.springframework.core.io.InputStreamResource
import javax.servlet.http.HttpServletResponse
import org.springframework.web.bind.annotation.GetMapping
import com.knf.dev.service.EmployeeService
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.http.MediaType
import org.springframework.stereotype.Controller


@Controller
class EmployeeController {
    @Autowired
    var employeeService: EmployeeService? = null
    @GetMapping("/export-employees")
    @Throws(Exception::class)
    fun exportCSV(response: HttpServletResponse?): 
              ResponseEntity<InputStreamResource> {
        val filename = "employees.csv"
        val file = InputStreamResource(employeeService!!.load())
        return ResponseEntity.ok().header(
            HttpHeaders.CONTENT_DISPOSITION,
            "attachment; filename=$filename"
        )
            .contentType(MediaType.parseMediaType("application/csv")).body(file)
    }
}

Driver

package com.knf.dev

import org.springframework.boot.autoconfigure.SpringBootApplication
import org.springframework.boot.runApplication

@SpringBootApplication
class KotlinSpringbootApachecommansExportcsvApplication

fun main(args: Array<String>) {
   runApplication<KotlinSpringbootApachecommansExportcsvApplication>(*args)
}

Run 

$ mvn spring-boot:run

Hit this URL in your local system, http://localhost:8080/export-employees

Open the downloaded CSV file


Download source code




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