Although Java is an object oriented language, you will often separate our data and your actual business logic. You will write POJOs, entities, domain models and DTOs which you will pass to services, repositories and controllers. If you do so, you will properly need test data for those objects. Often, the data you pass will be very important as it represents the state of your application and business process. You must design it carefully to get the test results you are looking for. However, there are also some cases where the data isn’t so important – it must just be there! You need an object, filled with random data. That’s it.
Java’s reflection mechanism offers an easy method to create POJOs filled with random data. Here is a basic code snippet which will take a class, instantiate it and fills its fields with random data. Maybe it makes your test setup easier.
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import java.lang.reflect.Field; import java.math.BigInteger; import java.util.Random; import java.util.UUID; public class RandomObjectFiller { private Random random = new Random(); public <T> T createAndFill(Class<T> clazz) throws Exception { T instance = clazz.newInstance(); for(Field field: clazz.getDeclaredFields()) { field.setAccessible(true); Object value = getRandomValueForField(field); field.set(instance, value); } return instance; } private Object getRandomValueForField(Field field) throws Exception { Class<?> type = field.getType(); // Note that we must handle the different types here! This is just an // example, so this list is not complete! Adapt this to your needs! if(type.isEnum()) { Object[] enumValues = type.getEnumConstants(); return enumValues[random.nextInt(enumValues.length)]; } else if(type.equals(Integer.TYPE) || type.equals(Integer.class)) { return random.nextInt(); } else if(type.equals(Long.TYPE) || type.equals(Long.class)) { return random.nextLong(); } else if(type.equals(Double.TYPE) || type.equals(Double.class)) { return random.nextDouble(); } else if(type.equals(Float.TYPE) || type.equals(Float.class)) { return random.nextFloat(); } else if(type.equals(String.class)) { return UUID.randomUUID().toString(); } else if(type.equals(BigInteger.class)){ return BigInteger.valueOf(random.nextInt()); } return createAndFill(type); } } |
Best regards,
Thomas
Note that JFairy is quite good for this. Particularly if you can use it’s pre-supplied data types, like Peson or Company. See https://github.com/Codearte/jfairy
You can find various libraries in order to fill in data for your tests. One example is Podam, another one is javafaker
Correct me if I am wrong, but javafaker can do just predefined objects or you can use its RandomService, but that is overkill, I cannot use it for generation of random instances of custom objects.
But Podam is really a hammer for fake data generation. Thanks for this whole post and references here
Thanks very usefull 🙂
Why code it when it already exists
A library that is taking a similar path to what you describe in this article is called MockNeat.
It can generate randomised objects and fill them up with data through reflection or lambda tricks. It can also randomize java collections.
I mainly use it to generate some JSON files (from Pojo classes), but it can be used in other scenarios.