Kotlin - How to read/write CSV file with OpenCSV

In this tutorial, we’re gonna look at Kotlin examples that read and write CSV file using OpenCSV.

Contents

I. Dependency
II. Write Data to CSV File
III. Read Data from CSV File

I. Dependency

<groupId>org.jetbrains.kotlin</groupId>

<artifactId>kotlin-stdlib</artifactId>

</dependency>

<groupId>com.opencsv</groupId>

<artifactId>opencsv</artifactId>

</dependency>

II. Write Data to CSV File

1. From String Array

var fileWriter = FileWriter("customer.csv")

csvWriter = CSVWriter(fileWriter,

CSVWriter.DEFAULT_SEPARATOR,

CSVWriter.NO_QUOTE_CHARACTER,

CSVWriter.DEFAULT_ESCAPE_CHARACTER,

CSVWriter.DEFAULT_LINE_END)

val data = arrayOf<String>("ID","NAME","ADDRESS","AGE")

csvWriter.writeNext(data)

2. From List of Objects

val customers = Arrays.asList(...)

fileWriter = FileWriter("customerList.csv")

val mappingStrategy = ColumnPositionMappingStrategy<Customer>()

mappingStrategy.setType(Customer::class.java)

mappingStrategy.setColumnMapping("id", "name", "address", "age")

var beanToCsv = StatefulBeanToCsvBuilder<Customer>(fileWriter)

.withMappingStrategy(mappingStrategy)

.withQuotechar(CSVWriter.NO_QUOTE_CHARACTER)

.build()

beanToCsv.write(customers)

3. Practice

– Simple POJO Customer (id, name, address, age):

package com.javasampleapproach.kotlin.opencsv

class Customer {

var id: String? = null

var name: String? = null

var address: String? = null

var age: Int = 0

constructor() {}

constructor(id: String?, name: String?, address: String?, age: Int) {

this.id = id

this.name = name

this.address = address

this.age = age

}

override fun toString(): String {

return "Customer [id=" + id + ", name=" + name + ", address=" + address + ", age=" + age + "]"

}

– Write to CSV file:

package com.javasampleapproach.kotlin.opencsv

import java.io.FileWriter

import java.io.IOException

import java.util.Arrays

import com.opencsv.CSVWriter

import com.opencsv.bean.ColumnPositionMappingStrategy

import com.opencsv.bean.StatefulBeanToCsv

import com.opencsv.bean.StatefulBeanToCsvBuilder

private val CSV_HEADER = arrayOf<String>("id", "name", "address", "age")

private val customers = Arrays.asList(

Customer("1", "Jack Smith", "Massachusetts", 23),

Customer("2", "Adam Johnson", "New York", 27),

Customer("3", "Katherin Carter", "Washington DC", 26),

Customer("4", "Jack London", "Nevada", 33),

Customer("5", "Jason Bourne", "California", 36))

fun main(args: Array<String>?) {

var fileWriter: FileWriter? = null

var csvWriter: CSVWriter? = null

var beanToCsv: StatefulBeanToCsv<Customer>?

try {

fileWriter = FileWriter("customer.csv")

// write String Array

csvWriter = CSVWriter(fileWriter,

CSVWriter.DEFAULT_SEPARATOR,

CSVWriter.NO_QUOTE_CHARACTER,

CSVWriter.DEFAULT_ESCAPE_CHARACTER,

CSVWriter.DEFAULT_LINE_END)

csvWriter.writeNext(CSV_HEADER)

for (customer in customers) {

val data = arrayOf<String>(

customer.id!!,

customer.name!!,

customer.address!!,

customer.age.toString())

csvWriter.writeNext(data)

}

println("Write CSV using CSVWriter successfully!")

fileWriter = FileWriter("customerList.csv")

// write List of Objects

val mappingStrategy = ColumnPositionMappingStrategy<Customer>()

mappingStrategy.setType(Customer::class.java)

mappingStrategy.setColumnMapping("id", "name", "address", "age")

beanToCsv = StatefulBeanToCsvBuilder<Customer>(fileWriter)

.withMappingStrategy(mappingStrategy)

.withQuotechar(CSVWriter.NO_QUOTE_CHARACTER)

.build()

beanToCsv.write(customers)

println("Write CSV using BeanToCsv successfully!")

} catch (e: Exception) {

println("Writing CSV error!")

e.printStackTrace()

} finally {

try {

fileWriter!!.flush()

fileWriter.close()

csvWriter!!.close()

} catch (e: IOException) {

println("Flushing/closing error!")

e.printStackTrace()

}

– Check results:
+ customer.csv
read-write-csv-java-result

+ customerList.csv
read-write-csv-java-result-opencsv

III. Read Data from CSV File

1. As String Array

We have 2 ways:
– Line by line using csvReader.readNext()
– All lines at once using csvReader.readAll()

package com.javasampleapproach.kotlin.opencsv

import java.io.BufferedReader

import java.io.FileReader

import java.io.IOException

import com.opencsv.CSVReader

import com.opencsv.CSVReaderBuilder

fun main(args: Array<String>?) {

var fileReader: BufferedReader? = null

var csvReader: CSVReader? = null

try {

println("--- Read line by line ---")

fileReader = BufferedReader(FileReader("customer.csv"))

csvReader = CSVReader(fileReader)

var record: Array<String>?

csvReader.readNext() // skip Header

record = csvReader.readNext()

while (record != null) {

println(record[0] + " | " + record[1] + " | " + record[2] + " | " + record[3])

record = csvReader.readNext()

}

csvReader.close()

// -------------------------------------------

println("\n--- Read all at once ---")

fileReader = BufferedReader(FileReader("customer.csv"))

csvReader = CSVReaderBuilder(fileReader).withSkipLines(1).build()

val records = csvReader.readAll()

for (_record in records) {

println(_record[0] + " | " + _record[1] + " | " + _record[2] + " | " + _record[3])

}

} catch (e: Exception) {

println("Reading CSV Error!")

e.printStackTrace()

} finally {

try {

fileReader!!.close()

csvReader!!.close()

} catch (e: IOException) {

println("Closing fileReader/csvParser Error!")

e.printStackTrace()

}

– Check result in Console:

--- Read line by line ---

1 | Jack Smith | Massachusetts | 23

2 | Adam Johnson | New York | 27

3 | Katherin Carter | Washington DC | 26

4 | Jack London | Nevada | 33

5 | Jason Bourne | California | 36

--- Read all at once ---

1 | Jack Smith | Massachusetts | 23

2 | Adam Johnson | New York | 27

3 | Katherin Carter | Washington DC | 26

4 | Jack London | Nevada | 33

5 | Jason Bourne | California | 36

2. As Java Object using Annotation

– We can use @CsvBindByName annotation for mapping between the CSV columns and the class fields:

package com.javasampleapproach.kotlin.opencsv

import com.opencsv.bean.CsvBindByName

class AnnoCustomer {

@CsvBindByName

var id: String? = null

@CsvBindByName

var name: String? = null

@CsvBindByName

var address: String? = null

@CsvBindByName

var age: Int = 0

constructor() {}

constructor(id: String?, name: String?, address: String?, age: Int) {

this.id = id

this.name = name

this.address = address

this.age = age

}

override fun toString(): String {

return "Customer [id=" + id + ", name=" + name + ", address=" + address + ", age=" + age + "]"

}

– Run the Test Class:

package com.javasampleapproach.kotlin.opencsv

import java.io.BufferedReader

import java.io.FileReader

import java.io.IOException

import com.opencsv.bean.CsvToBean

import com.opencsv.bean.CsvToBeanBuilder

fun main(args: Array<String>?) {

var fileReader: BufferedReader? = null

var csvToBean: CsvToBean<AnnoCustomer>?

try {

fileReader = BufferedReader(FileReader("customer.csv"))

csvToBean = CsvToBeanBuilder<AnnoCustomer>(fileReader)

.withType(AnnoCustomer::class.java)

.withIgnoreLeadingWhiteSpace(true)

.build()

val customers = csvToBean.parse()

for (customer in customers) {

println(customer)

}

} catch (e: Exception) {

println("Reading CSV Error!")

e.printStackTrace()

} finally {

try {

fileReader!!.close()

} catch (e: IOException) {

println("Closing fileReader/csvParser Error!")

e.printStackTrace()

}

– Check Result in Console:

Customer [id=1, name=Jack Smith, address=Massachusetts, age=23]

Customer [id=2, name=Adam Johnson, address=New York, age=27]

Customer [id=3, name=Katherin Carter, address=Washington DC, age=26]

Customer [id=4, name=Jack London, address=Nevada, age=33]

Customer [id=5, name=Jason Bourne, address=California, age=36]

3. As simple Java Object

– Simple POJO Customer (id, name, address, age):

package com.javasampleapproach.kotlin.opencsv

class Customer {

var id: String? = null

var name: String? = null

var address: String? = null

var age: Int = 0

constructor() {}

constructor(id: String?, name: String?, address: String?, age: Int) {

this.id = id

this.name = name

this.address = address

this.age = age

}

override fun toString(): String {

return "Customer [id=" + id + ", name=" + name + ", address=" + address + ", age=" + age + "]"

}

– Run the Test Class:

package com.javasampleapproach.kotlin.opencsv

import java.io.BufferedReader

import java.io.FileReader

import java.io.IOException

import com.opencsv.bean.ColumnPositionMappingStrategy

import com.opencsv.bean.CsvToBean

import com.opencsv.bean.CsvToBeanBuilder

fun main(args: Array<String>?) {

var fileReader: BufferedReader? = null

var csvToBean: CsvToBean<Customer>?

try {

fileReader = BufferedReader(FileReader("customer.csv"))

val mappingStrategy = ColumnPositionMappingStrategy<Customer>()

mappingStrategy.setType(Customer::class.java)

mappingStrategy.setColumnMapping("id", "name", "address", "age")

csvToBean = CsvToBeanBuilder<Customer>(fileReader)

.withMappingStrategy(mappingStrategy)

.withSkipLines(1)

.withIgnoreLeadingWhiteSpace(true)

.build()

val customers = csvToBean.parse()

for (customer in customers) {

println(customer)

}

} catch (e: Exception) {

println("Reading CSV Error!")

e.printStackTrace()

} finally {

try {

fileReader!!.close()

} catch (e: IOException) {

println("Closing fileReader/csvParser Error!")

e.printStackTrace()

}

– Check Result in Console:

Customer [id=1, name=Jack Smith, address=Massachusetts, age=23]

Customer [id=2, name=Adam Johnson, address=New York, age=27]

Customer [id=3, name=Katherin Carter, address=Washington DC, age=26]

Customer [id=4, name=Jack London, address=Nevada, age=33]

Customer [id=5, name=Jason Bourne, address=California, age=36]

By grokonez | February 25, 2018.

Kotlin – How to read/write CSV file with OpenCSV

I. Dependency

II. Write Data to CSV File

1. From String Array

2. From List of Objects

3. Practice

III. Read Data from CSV File

1. As String Array

2. As Java Object using Annotation

3. As simple Java Object

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I. Dependency

II. Write Data to CSV File

1. From String Array

2. From List of Objects

3. Practice

III. Read Data from CSV File

1. As String Array

2. As Java Object using Annotation

3. As simple Java Object

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