How to generate tons of random CSV files in Java

This post was originally posted on my blog

The CSV format is a simple but commonly used format for exchanging data. Many applications support the import and export of information as CSV files. Due to the popularity of this format, there is a requirement for developers to generate large amounts of CSV files for testing. This is where my latest open source project SDGen comes into play.

SDGen is a Java library that helps developers generate randomized data files for testing purposes. It supports CSV and Fixed Width formats, with more formats such as JSON planned for the future.

This guide will show you how to generate a simple CSV file using SDGen and Faker. Faker will be used to assist creating random values.

Maven

For a Maven project, we can add the required libraries by inserting the following xml into the pom.xml file of a project.

<dependencies>
    <dependency>
        <groupId>au.com.anthonybruno</groupId>
        <artifactId>SdGen</artifactId>
        <version>0.3.0</version>
    </dependency>
    <dependency>
        <groupId>com.github.javafaker</groupId>
        <artifactId>javafaker</artifactId>
        <version>0.14</version>
    </dependency>
</dependencies>

Instructions

Firstly, we need to get the Faker instance by writing:

    Faker faker = Faker.instance();

We can then use the faker instance to generate values such as URLs faker.internet().url() and planet names faker.space().planet().

Next, we'll use SDGen's fluent builder to create the schema for the CSV file we want to create. To begin, we write:

    Gen.start()

We can then add fields (aka columns) using the addField method. addField takes 2 parameters: A String name, which will be to identify the field in the produced file and a Generator. A Generator is a simple interface with a single method generate. This is the way that random values are created and added to a field.

We are going to make a simple CSV file of people. To do that, we will add a 'First Name' and a 'Last Name' column using the corresponding Faker methods to generate values for these:

    Gen.start()
        .addField("First Name", () -> faker.name().firstName())
        .addField("Last Name", () -> faker.name().lastName())

Note: Using lambdas (e.g. () -> faker.name().firstName() is the equivalent of writing:

new Generator() {
    @Override
    public Object generate() {
        return faker.name().firstName();
    }
}

We also want to add an 'Age' field. To do this, we can use SDGen's inbuilt IntGenerator. We can give it a sensible minimum and maximum value to limit the range of numbers it will generate. SDGen provides generators for all primitive types.

Gen.start()
    .addField("First Name", () -> faker.name().firstName())
    .addField("Last Name", () -> faker.name().lastName())
    .addField("Age", new IntGenerator(18, 80))

Next, we specify how many rows to generate by using the generate method. We also want to select the format of the generated data. We will be using asCsv to generate the data in CSV format. SDGen also supports the Fixed Width format and will support other data formats such as JSON in the future.

Gen.start()
    .addField("First Name", () -> faker.name().firstName())
    .addField("Last Name", () -> faker.name().lastName())
    .addField("Age", new IntGenerator(18, 80))
    .generate(1000) //1000 rows will be generated
    .asCsv()

Finally, we specify how the data will be output. We will use the toFile method to put the information into a file.

Gen.start()
    .addField("First Name", () -> faker.name().firstName())
    .addField("Last Name", () -> faker.name().lastName())
    .addField("Age", new IntGenerator(18, 80))
    .generate(1000)
    .asCsv()
    .toFile("people.csv");

And that's it! Running the code will produce a CSV file in the project's working directory. Here is some data that was produced when I ran it:

First Name,Last Name,Age
Corrine,Berge,78
Gerald,Carter,63
Enid,Padberg,66
Eleanora,Murray,79
Coy,Okuneva,76
Jovan,Reynolds,77
Lane,Haag,48

For more information about SDGen, please visit it on Github.

Details

• Faker: Github
• SDGen: Github