Java – Convert CSV File to/from JSON (String/File) – using Commons-CSV + Jackson

In the tutorial, Grokonez shows how to convert CSV File to JSON String or JSON File and vice versa with Java language by examples.

I. Dependencies

	org.apache.commons
	commons-csv
	1.5


	com.fasterxml.jackson.core
	jackson-databind
	2.8.5

II. CSV to JSON

CSV File to JSON String

We do 2 steps:
– Step 1: Read CSV File into Java List Objects
– Step 2: Convert Java List Objects to JSON String

-> CSV File:

Customer.java:

package com.ozenero.convertcsv2json;

public class Customer {
	private String id;
	private String name;
	private String address;
	private int age;
 
	public Customer() {
	}
 
	public Customer(String id, String name, String address, int age) {
		this.id = id;
		this.name = name;
		this.address = address;
		this.age = age;
	}
 
	public String getId() {
		return id;
	}
 
	public void setId(String id) {
		this.id = id;
	}
 
	public String getName() {
		return name;
	}
 
	public void setName(String name) {
		this.name = name;
	}
 
	public String getAddress() {
		return address;
	}
 
	public void setAddress(String address) {
		this.address = address;
	}
 
	public int getAge() {
		return age;
	}
 
	public void setAge(int age) {
		this.age = age;
	}
 
	@Override
	public String toString() {
		return "Customer [id=" + id + ", name=" + name + ", address=" + address + ", age=" + age + "]";
	}
 
}

-> Converting Implementation:

package com.ozenero.convertcsv2json;

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

import org.apache.commons.csv.CSVFormat;
import org.apache.commons.csv.CSVParser;
import org.apache.commons.csv.CSVRecord;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;

public class ConvertCsv2Json {
	
    public static void main(String[] args) {
    	List customers = readCsvFile("customers.csv");
    	String jsonString = convertJavaObject2JsonString(customers);
    	System.out.println(jsonString);
    }

    /**
     * 
     * Read CSV File into Memory
     * @param filePath
     * @return
     */
    private static List readCsvFile(String filePath) {
		BufferedReader fileReader = null;
		CSVParser csvParser = null;

		List customers = new ArrayList();
		
		try {
			fileReader = new BufferedReader(new FileReader(filePath));
			csvParser = new CSVParser(fileReader,
					CSVFormat.DEFAULT.withFirstRecordAsHeader().withIgnoreHeaderCase().withTrim());
 
			Iterable csvRecords = csvParser.getRecords();
			
			for (CSVRecord csvRecord : csvRecords) {
				Customer customer = new Customer(
						csvRecord.get("id"),
						csvRecord.get("name"),
						csvRecord.get("address"),
						Integer.parseInt(csvRecord.get("age"))  
						);
				
				customers.add(customer);
			}
 
		} catch (Exception e) {
			System.out.println("Reading CSV Error!");
			e.printStackTrace();
		} finally {
			try {
				fileReader.close();
				csvParser.close();
			} catch (IOException e) {
				System.out.println("Closing fileReader/csvParser Error!");
				e.printStackTrace();
			}
		}
		
		return customers;
	}
 
    /**
     * 
     * Convert Java Object to JSON String
     * 
     * @param customers
     * @return
     */
    private static String convertJavaObject2JsonString(List customers) {
    	ObjectMapper mapper = new ObjectMapper();
    	String jsonString = "";
    	
    	try {
    		jsonString = mapper.writeValueAsString(customers);
    	} catch (JsonProcessingException e) {
    		e.printStackTrace();
    	}
    	
    	return jsonString; 
    }
}

-> Output:

[{"id":"1","name":"Jack Smith","address":"Massachusetts","age":23},{"id":"2","name":"Adam Johnson","address":"New York","age":27},{"id":"3","name":"Katherin Carter","address":"Washington DC","age":26},{"id":"4","name":"Jack London","address":"Nevada","age":33},{"id":"5","name":"Jason Bourne","address":"California","age":36}]

-> Pretty Format:

[
   {
      "id":"1",
      "name":"Jack Smith",
      "address":"Massachusetts",
      "age":23
   },
   {
      "id":"2",
      "name":"Adam Johnson",
      "address":"New York",
      "age":27
   },
   {
      "id":"3",
      "name":"Katherin Carter",
      "address":"Washington DC",
      "age":26
   },
   {
      "id":"4",
      "name":"Jack London",
      "address":"Nevada",
      "age":33
   },
   {
      "id":"5",
      "name":"Jason Bourne",
      "address":"California",
      "age":36
   }
]

CSV File to JSON File

We do 2 steps:
– Step 1: Read CSV File into Java List Objects
– Step 2: Convert Java List Objects to JSON File

-> Implementation:

package com.ozenero.convertcsv2json;

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

import org.apache.commons.csv.CSVFormat;
import org.apache.commons.csv.CSVParser;
import org.apache.commons.csv.CSVRecord;

import com.fasterxml.jackson.databind.ObjectMapper;

public class ConvertCsv2Json {
	
    public static void main(String[] args) {
    	// Step 1: Read CSV File into Java List Objects
    	List customers = readCsvFile("customers.csv");
    	
    	// Step 2: Convert Java List Objects to JSON File
    	convertJavaObject2JsonFile(customers, "customers.json");
    }

    /**
     * 
     * Read CSV File into Memory
     * @param filePath
     * @return
     */
    private static List readCsvFile(String filePath) {
		BufferedReader fileReader = null;
		CSVParser csvParser = null;

		List customers = new ArrayList();
		
		try {
			fileReader = new BufferedReader(new FileReader(filePath));
			csvParser = new CSVParser(fileReader,
					CSVFormat.DEFAULT.withFirstRecordAsHeader().withIgnoreHeaderCase().withTrim());
 
			Iterable csvRecords = csvParser.getRecords();
			
			for (CSVRecord csvRecord : csvRecords) {
				Customer customer = new Customer(
						csvRecord.get("id"),
						csvRecord.get("name"),
						csvRecord.get("address"),
						Integer.parseInt(csvRecord.get("age"))  
						);
				
				customers.add(customer);
			}
 
		} catch (Exception e) {
			System.out.println("Reading CSV Error!");
			e.printStackTrace();
		} finally {
			try {
				fileReader.close();
				csvParser.close();
			} catch (IOException e) {
				System.out.println("Closing fileReader/csvParser Error!");
				e.printStackTrace();
			}
		}
		
		return customers;
	}
 
    /**
     * Convert Java Object to JSON File
     * @param customers
     * @param pathFile
     */
    private static void convertJavaObject2JsonFile(List customers, String pathFile) {
        ObjectMapper mapper = new ObjectMapper();

        File file = new File(pathFile);
        try {
            // Serialize Java object info JSON file.
            mapper.writeValue(file, customers);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

III. JSON to CSV

JSON String to CSV File

We do 2 steps:
– Convert JSON String to Java List Objects
– Write Java List Objects to CSV File

-> Implementation:

package com.ozenero.convertcsv2json;

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

import org.apache.commons.csv.CSVFormat;
import org.apache.commons.csv.CSVPrinter;

import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;

public class ConvertJson2Csv {
	
	public static void main(String[] args) {
		// Step 1: Read JSON File to List Objects
		String jsonStr = "[{\"id\":\"1\",\"name\":\"Jack Smith\",\"address\":\"Massachusetts\",\"age\":23},{\"id\":\"2\",\"name\":\"Adam Johnson\",\"address\":\"New York\",\"age\":27},{\"id\":\"3\",\"name\":\"Katherin Carter\",\"address\":\"Washington DC\",\"age\":26},{\"id\":\"4\",\"name\":\"Jack London\",\"address\":\"Nevada\",\"age\":33},{\"id\":\"5\",\"name\":\"Jason Bourne\",\"address\":\"California\",\"age\":36}]";
		
		List customers = convertJsonString2Objects(jsonStr);
		
		// Step 2: Write List Objects to CSV File
		writeListObjects2CsvFile(customers, "customers.csv");
	}
	
	/**
	 * 
	 * Convert JSON String to List Java Objects
	 * 
	 * @param pathFile
	 * @return
	 */
	private static List convertJsonString2Objects(String jsonString){
		List customers = null;
		
		try {
			customers = new ObjectMapper().readValue(jsonString, new TypeReference>(){});
		} catch (JsonParseException e) {
			e.printStackTrace();
		} catch (JsonMappingException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		}
		
		return customers;
	}
	
	/**
	 * Write List Objects to CSV File
	 * 
	 * @param customers
	 */
	private static void writeListObjects2CsvFile(List customers, String pathFile) {
		final String[] CSV_HEADER = { "id", "name", "address", "age" };
		
		FileWriter fileWriter = null;
		CSVPrinter csvPrinter = null;
 
		try {
			fileWriter = new FileWriter(pathFile);
			csvPrinter = new CSVPrinter(fileWriter, CSVFormat.DEFAULT.withHeader(CSV_HEADER));
 
			for (Customer customer : customers) {
				List data = Arrays.asList(
						customer.getId(),
						customer.getName(),
						customer.getAddress(),
						String.valueOf(customer.getAge()));
				
				csvPrinter.printRecord(data);
			}
		} catch (Exception e) {
			System.out.println("Writing CSV error!");
			e.printStackTrace();
		} finally {
			try {
				fileWriter.flush();
				fileWriter.close();
				csvPrinter.close();
			} catch (IOException e) {
				System.out.println("Flushing/closing error!");
				e.printStackTrace();
			}
		}
	}		
}

JSON File to CSV File

We do 2 steps:
– Read JSON File to Java List Objects
– Write Java List Objects to CSV File

-> Implementation:

package com.ozenero.convertcsv2json;

import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStream;
import java.util.Arrays;
import java.util.List;

import org.apache.commons.csv.CSVFormat;
import org.apache.commons.csv.CSVPrinter;

import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;

public class ConvertJson2Csv {
	
	public static void main(String[] args) {
		// Step 1: Read JSON File to List Objects
		List customers = readJSONFile2ListObjects("customers.json");
		
		// Step 2: Write List Objects to CSV File
		writeListObjects2CsvFile(customers, "customers.csv");
	}
	
	/**
	 * 
	 * Read JSON File to List Java Objects
	 * 
	 * @param pathFile
	 * @return
	 */
	private static List readJSONFile2ListObjects(String pathFile) {
		
		InputStream inJson = Customer.class.getResourceAsStream(pathFile);
		List customers = null;
		
		try {
			customers = new ObjectMapper().readValue(inJson, new TypeReference>(){});
		} catch (JsonParseException e) {
			e.printStackTrace();
		} catch (JsonMappingException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		}
		
		return customers;
	}
	
	/**
	 * Write List Objects to CSV File
	 * 
	 * @param customers
	 */
	private static void writeListObjects2CsvFile(List customers, String pathFile) {
		final String[] CSV_HEADER = { "id", "name", "address", "age" };
		
		FileWriter fileWriter = null;
		CSVPrinter csvPrinter = null;
 
		try {
			fileWriter = new FileWriter(pathFile);
			csvPrinter = new CSVPrinter(fileWriter, CSVFormat.DEFAULT.withHeader(CSV_HEADER));
 
			for (Customer customer : customers) {
				List data = Arrays.asList(
						customer.getId(),
						customer.getName(),
						customer.getAddress(),
						String.valueOf(customer.getAge()));
				
				csvPrinter.printRecord(data);
			}
		} catch (Exception e) {
			System.out.println("Writing CSV error!");
			e.printStackTrace();
		} finally {
			try {
				fileWriter.flush();
				fileWriter.close();
				csvPrinter.close();
			} catch (IOException e) {
				System.out.println("Flushing/closing error!");
				e.printStackTrace();
			}
		}
	}		
}