Converting an CSV file to a JSON object in Java

Question

Is there an open source java library to convert a CSV (or XLS) file to a JSON object?

I tried using json.cdl, but somehow it does not seem to work for large CSV stri

Answer 1

If you're using Java 8, you can do something like this. No Libraries or complicated logic required.

Firstly, create a POJO representing your new JSON object. In my example it's called 'YourJSONObject' and has a constructor taking two strings.

What the code does is initially reads the file, then creates a stream of String based lines. ( a line is equivalent to a line in your CSV file).

We then pass the line in to the map function which splits it on a comma and then creates the YourJSONObject.

All of these objects are then collected to a list which we pass in to the JSONArray constructor.

You now have an Array of JSONObjects. You can then call toString() on this object if you want to see the text representation of this.

        JSONArray objects = new JSONArray(Files.readAllLines(Paths.get("src/main/resources/your_csv_file.csv"))
            .stream()
            .map(s -> new YourJSONObject(s.split(",")[0], s.split(",")[1]))
            .collect(toList()));

Answer 2

@Mouscellaneous basically answered this for you so please give him the credit.

Here is what I came up with:

package edu.apollogrp.csvtojson;

import au.com.bytecode.opencsv.bean.CsvToBean;
import au.com.bytecode.opencsv.bean.HeaderColumnNameMappingStrategy;
import org.codehaus.jackson.map.ObjectMapper;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.List;

public class ConvertCsvToJson {
    public static void main(String[] args) throws IOException, ClassNotFoundException {
        if (args.length > 1) {
            String pathToCsvFile = args[0];
            String javaBeanClassName = "edu.apollogrp.csvtojson.bean." + args[1];
            final File file = new File(pathToCsvFile);
            if (!file.exists()) {
                System.out.println("The file you specified does not exist. path=" + pathToCsvFile);
            }
            Class<?> type = null;
            try {
                type = Class.forName(javaBeanClassName);
            } catch (ClassNotFoundException e) {
                System.out.println("The java bean you specified does not exist. className=" + javaBeanClassName);
            }

            HeaderColumnNameMappingStrategy strat = new HeaderColumnNameMappingStrategy();
            strat.setType(type);

            CsvToBean csv = new CsvToBean();
            List list = csv.parse(strat, new InputStreamReader(new FileInputStream(file)));
            System.out.println(new ObjectMapper().writeValueAsString(list));
        } else {
            System.out.println("Please specify the path to the csv file.");
        }
    }
}

I used maven to include the dependencies, but you could also download them manually and include them in your classpath.

<dependency>
    <groupId>net.sf.opencsv</groupId>
    <artifactId>opencsv</artifactId>
    <version>2.0</version>
</dependency>

<dependency>
    <groupId>org.codehaus.jackson</groupId>
    <artifactId>jackson-mapper-asl</artifactId>
    <version>1.9.12</version>
</dependency>
<dependency>
    <groupId>org.codehaus.jackson</groupId>
    <artifactId>jackson-core-asl</artifactId>
    <version>1.9.12</version>
</dependency>

Answer 3

With Java 8, writing JSON is at hand.

You didn't specify what JSON API you want, so I assume by "JSON object" you mean a string with a serialized JSON object.

What I did in the CSV Cruncher project:

1. Load the CSV using HSQLDB. That's a relatively small (~2 MB) library, which actually implements a SQL 2008 database.
2. Query that database using JDBC.
3. Build a JDK JSON object (javax.json.JsonObject) and serialize it.

Here's how to do it:

static void convertResultToJson(ResultSet resultSet, Path destFile, boolean printAsArray) 
{
            OutputStream outS = new BufferedOutputStream(new FileOutputStream(destFile.toFile()));
            Writer outW = new OutputStreamWriter(outS, StandardCharsets.UTF_8);

            // javax.json way
            JsonObjectBuilder builder = Json.createObjectBuilder();
            // Columns
            for (int colIndex = 1; colIndex <= metaData.getColumnCount(); colIndex++) {
                addTheRightTypeToJavaxJsonBuilder(resultSet, colIndex, builder);
            }
            JsonObject jsonObject = builder.build();
            JsonWriter writer = Json.createWriter(outW);
            writer.writeObject(jsonObject);

The whole impl is here. (Originally I wrote my own CSV parsing and JSON writing, but figured out both are complicated enough to reach for a tested out-of-the-shelf library.)