Introduction

PODAM is a lightweight tool to auto-fill Java POJOs with data. This comes handy when developing unit tests. Thanks to PODAM users now have a one-liner that does all the work them.

PODAM main features:

  • Automatic introspection of your POJOs to fill all possible attributes with random data. You can customise this behaviour.
  • Extension points to customise the data strategy, fields exclusions based on names or annotations
  • Support for your custom annotations to either provide data or exclude fields
  • The option to select minimal constructors (for lightweight POJOs) or full constructors
  • Support for Java types, enumerations, arrays, collections (lists, sets, maps)
  • Support for generics
  • Support for your own factories when PODAM cannot introspect enough information to generate a type (e.g. XMLGregorianCalendar)
  • Support for arbitrary method executions when the normal lifecycle has ended

Using PODAM in your project

To see how you add PODAM to your project, please refer to the usage page.

How to use PODAM API

// Simplest scenario. Will delegate to Podam all decisions
PodamFactory factory = new PodamFactoryImpl();

// This will use constructor with minimum arguments and
// then setters to populate POJO
Pojo myPojo = factory.manufacturePojo(Pojo.class);

// This will use constructor with maximum arguments and
// then setters to populate POJO
Pojo myPojo2 = factory.manufacturePojoWithFullData(Pojo.class);

// If object instance is already available,
// Podam can fill it with random data
Pojo myPojo3 = MyFactory.getPojoInstance();
factory.populatePojo(myPojo3);

PODAM allows users to customise the way data are assigned in several ways:

  • By defining a global strategy
  • By defining strategies at the attribute level
  • For primitive and wrapper types, by customising the numeric value through annotations
  • For strings by customising the string value and length through annotation
  • To skip a certain attribute by using the @PodamExclude annotation or by name
  • By defining a collection of methods that Podam should execute while filling POJOs

Defining a global data provider strategy

The default strategy for PODAM is Random values. However users can define their own global strategy by providing an implementation of the DataProviderStrategy interface, as follows:

DataProviderStrategy strategy = new MyDataProviderStrategy();
PodamFactory factory = new PodamFactoryImpl(strategy);

Pojo myPojo = factory.manufacturePojo(Pojo.class);

Pojo myPojo2 = factory.manufacturePojoWithFullData(Pojo.class);

Please note that annotations are not required to use PODAM. The tool will automatically introspect and fill your tree of POJOs out-of-the-box. The preferred way to customise the way PODAM fills your data is through a custom DataProviderStrategy, as shown above. However one can annotate Java classes to provide custom values, as shown below. Podam also supports your own annotations.

Defining an attribute-level strategy

PODAM allows also users to define data strategies at the attribute level: this includes the capability to define custom strategies for elements and keys in collections, maps and arrays. In order to define an attribute-level strategy, users will need to:

  • Provide an implementation of the AttributeStrategy<T> interface
  • Use the @PodamStrategyValue annotation

Example:

@PodamStrategyValue(PostCodeStrategy.class)
private String postCode;

@PodamStrategyValue(MyBirthdayStrategy.class)
private Calendar myBirthday;

In this example I defined two attribute-level strategies:

  • PostCodeStrategy to create a UK-like postcode
  • MyBirthdayStrategy to create a Calendar which contains the exact time of my birth

The PostCodeStrategy class looks like the following:

/**
 * 
 */
package uk.co.jemos.podam.test.strategies;

import uk.co.jemos.podam.api.AttributeStrategy;
import uk.co.jemos.podam.exceptions.PodamMockeryException;
import uk.co.jemos.podam.test.utils.PodamTestConstants;

/**
 * A test strategy to manufacture UK-like post codes.
 * 
 * @author mtedone
 * 
 */
public class PostCodeStrategy implements AttributeStrategy<String> {
        
        /**
         * It returns an English post code.
         * <p>
         * This is just an example. More elaborated code could the implemented by
         * this method. This is just to proof the point.
         * </p>
         * 
         * {@inheritDoc}
         */
        public String getValue() throws PodamMockeryException {
                return PodamTestConstants.POST_CODE;
        }
        
}

There is nothing special about the above class: it's job is just to provide a value of the right type.

The MyBirthdayStrategy class looks like the following:

/**
 * 
 */
package uk.co.jemos.podam.test.strategies;

import java.util.Calendar;

import uk.co.jemos.podam.api.AttributeStrategy;
import uk.co.jemos.podam.exceptions.PodamMockeryException;
import uk.co.jemos.podam.test.utils.PodamTestUtils;

/**
 * An attribute strategy which returns a Calendar object set with my DOB.
 *
 * @author mtedone
 * 
 */
public class MyBirthdayStrategy implements AttributeStrategy<Calendar> {

        /**
         * It returns a {@link Calendar} object set with the exact date of my
         * birthday.
         * 
         * {@inheritDoc}
         */
        public Calendar getValue() throws PodamMockeryException {

                Calendar myBirthday = PodamTestUtils.getMyBirthday();

                return myBirthday;
        }
                
}

The capability to customise the strategy PODAM uses to fill attribute data is extended to container-like data structures, such as Collections, Maps and Arrays; however for these data structures use the @PodamCollection annotation. Please refer to The annotation page for more details.

Example on how to use PODAM custom attribute strategy to fill collection elements:

@PodamCollection(nbrElements = 2, collectionElementStrategy = MyBirthdayStrategy.class)
private List<Calendar> myBirthdays = new ArrayList<Calendar>();

Example on how to use PODAM custom attribute strategy to fill Map keys and elements. Please note that @PodamCollection offers also the possibility to define a strategy to set the values for keys in a Map, through the mapKeyStrategy attribute:

@PodamCollection(nbrElements = 2, mapElementStrategy = MyBirthdayStrategy.class)
private Map<String, Calendar> myBirthdaysMap = new HashMap<String, Calendar>();

Example on how to use PODAM custom attribute strategy to fill array elements:

@PodamCollection(nbrElements = 2, collectionElementStrategy = MyBirthdayStrategy.class)
private Calendar[] myBirthdaysArray;

PODAM will use the MyBirthdayStrategy to set the value for the two array elements.

Customising PODAM behaviour for primitives and wrapper types

Primitive and Wrapper type values can be customised through annotations.

@PodamDoubleValue(minValue = PodamTestConstants.NUMBER_DOUBLE_MIN_VALUE, maxValue = PodamTestConstants.NUMBER_DOUBLE_MAX_VALUE)
private double doubleFieldWithMinAndMaxValue;

Please note that by contract (DataProviderStrategy) min and max values are inclusive.

For a full list of supported annotations, please refer to the Annotations page.

To know more about how PODAM works, please refer to the The walk-through example page or to the Corner Cases page on the left menu.

A simple example to manufacture collections

You can use PODAM to fill in generic collections with dummy data.

PodamFactory podam = new PodamFactoryImpl();

// Annotation required to remove warning because of type erasure although it would work without
@SuppressWarnings("unchecked")
List<String> list = podam.manufacturePojo(ArrayList.class, String.class);

Defining an attribute-level strategy with DataProviderStrategy

Assuming we are filling the class

public static class Pojo {
        private String randomString;
        private String postCode;
        private URL url;

        public String getRandomString() { return randomString; }

        public void setRandomString(String randomString) { this.randomString = randomString; }

        public String getUrl() { return url.toString(); }

        public void setUrl(String url) throws MalformedURLException { this.url = new URL(url); }

        public String getPostCode() { return postCode; }

        public void setPostCode(String postCode) { this.postCode = postCode; }
}

Define custom TypeManufacturer, which will be producing string values depending on attribute name

public class CustomStringManufacturer extends StringTypeManufacturerImpl() {

        @Override
        public String getType(DataProviderStrategy strategy,
                        AttributeMetadata attributeMetadata,
                        Map<String, Type> genericTypesArgumentsMap) {

                if (Pojo.class.isAssignableFrom(attributeMetadata.getPojoClass())) {

                        if ("url".equals(attributeMetadata.getAttributeName())) {
                                return "http://wikipedia.org";
                        } else if ("postCode".equals(attributeMetadata.getAttributeName())) {
                                return "00100";
                        }
                }
                return super.getType(strategy, attributeMetadata, genericTypesArgumentsMap);
        };
}

Intantiate POJO with PodamFactory

CustomStringManufacturer customStringManufacturer = new CustomStringManufacturer();
PodamFactory factory = new PodamFactoryImpl();
factory.getStrategy().addOrReplaceTypeManufacturer(String.class, customStringManufacturer);

Result:

{
  "randomString":"rP_yOK2EtR",
  "postCode":"00100",
  "url":"http://wikipedia.org"
}

Specifing factories for POJOs

DataProviderStrategy can be extended to hint Podam with factory classes to initialize POJOs.

RandomDataProviderStrategy strategy = (RandomDataProviderStrategy) factory.getStrategy();
strategy.addOrReplaceFactory(
        javax.xml.transform.Transformer.class,
        javax.xml.transform.TransformerFactory.class);
Transformer pojo = factory.manufacturePojo(javax.xml.transform.Transformer.class);

Manufacturing generic types

Sometimes you may want to manufacture a generic type directly without a wrapper class or a subclass.

As you should have noticed, the manufacturePojo method of the PodamFactory interface can take some additional parameters through varargs. This is a way to allow the definition of the generic types for a given class.

The following class is an example of a generic POJO:

public class GenericPojo<F, S> {

        private F firstValue;
        private S secondValue;
        @PodamCollection(nbrElements = 2)
        private List<F> firstList;
        @PodamCollection(nbrElements = 2)
        private S[] secondArray;
        @PodamCollection(nbrElements = 2)
        private Map<F, S> firstSecondMap;
        
        ... getter, setters and toString
}

Now imagine that you want an instance of this class defining F and S as Double and String respectively. This is how it should be done:

GenericPojo pojo = factory.manufacturePojo(GenericPojo.class, Double.class, String.class);

As you can see, the first class is the POJO to be manufactured (GenericPojo), and the subsequent classes are the type parameters to be used for this GenericPojo instance.

This is the result of the call above:

GenericPojo [
    firstValue=0.03181392348712919,
    secondValue=L4OicBAhKY,
    firstList=[0.770082469177622, 0.7924208229673068],
    secondArray=[8EsGFHtwwE, Zqz8B_4oAr],
    firstSecondMap={0.778926356384843=sl4FxQIEYe, 0.2909259461070528=j8mlZshNsv}
]

It is also possible to specify some complex nested generic types like GenericPojo<GenericPojo<String, Long>, Map<Integer, List<Boolean>>> using the uk.co.jemos.podam.api.PodamParameterizedType class as in the following example:

ParameterizedType stringLongGenericPojoType =
                new PodamParameterizedType(GenericPojo.class, String.class, Long.class);

ParameterizedType IntegerBooleanListMapType =
                new PodamParameterizedType(Map.class,
                                Integer.class,
                                new PodamParameterizedType(List.class, Boolean.class));

GenericPojo<GenericPojo<String, Long>, Map<Integer, List<Boolean>>> pojo =
                factory.manufacturePojo(GenericPojo.class, stringLongGenericPojoType, IntegerBooleanListMapType);

Running the code above the following result is produced:

GenericPojo [
    firstValue=GenericPojo [
        firstValue=e0NI7ZnKfW,
        secondValue=1340165351073,
        firstList=[2UlUwNJdOS, bZ7X0KZWtV],
        secondArray=[1340165351073, 1340165351073],
        firstSecondMap={QiB36seL99=1340165351072, Dk_KwHCGOq=1340165351072}
    ],
    secondValue={2081811337=[true]},
    firstList=[
        GenericPojo [
            firstValue=ECNfFuF6WM,
            secondValue=1340165351067,
            firstList=[QfZXnqOk1N, HDAGfxdat0],
            secondArray=[1340165351067, 1340165351067],
            firstSecondMap={UgJ4VNvro_=1340165351067, 5NGtW0hH0h=1340165351067}
        ],
        GenericPojo [
            firstValue=kHryFVavEn,
            secondValue=1340165351070,
            firstList=[wAKe40d3zO, OH8q03P9Cw],
            secondArray=[1340165351070, 1340165351070],
            firstSecondMap={LhRoWR2DNX=1340165351068, zg0IAN4ZZ5=1340165351068}
        ]
    ],
    secondArray=[{2115657799=[true, true], -1507554610=[true, true]}, {1990372468=[true, true], -340173617=[true, true]}],
    firstSecondMap={
        GenericPojo [
            firstValue=WeEDkbr2pc,
            secondValue=1340165351058,
            firstList=[0TRSKWur8n, vbIptzObXA],
            secondArray=[1340165351057, 1340165351057],
            firstSecondMap={49wLsEiuip=1340165351056, LGIUi7CptX=1340165351056}
        ] = {1126207473=[true, true], -1973087621=[true, true]},
        GenericPojo [
            firstValue=2RtNOrjgjZ,
            secondValue=1340165351064,
            firstList=[l1S7URCgFT, ntoKQnI1Kj],
            secondArray=[1340165351064, 1340165351064],
            firstSecondMap={F0gqzGJMZL=1340165351061, vXdlU9NCfR=1340165351061}
        ] = {-485029362=[true, true], 609129754=[true, true]}
    }
]

Tweaking PODAM for performance

Building huge graphs of nested objects may take time. Podam has a memoization option which is the default. When enabled, Podam will only create a unique object for each class and reuse it. This reduces algorithmic complexity in scenarios where distinct random data is not needed. To disable memoization, you can do the following:

PodamFactory podam = new PodamFactoryImpl();
podam.getStrategy().setMemoizationEnabled(false);

Executing arbitrary methods after POJO instantiation

Class info strategy can be instructed to execute arbitrary methods after POJO creation and hydation.

For example, the class

public class MyPojo {

    private String strValue;
    private Integer intValue;

    public void init(String strValue, Integer intValue) {
        this.strValue = strValue;
        this.intValue = intValue;
    }
}

One needs to specify POJO class, method name and list of method parameter types.

DefaultClassInfoStrategy classInfoStrategy = DefaultClassInfoStrategy.getInstance();
classInfoStrategy.addExtraMethod(MyPojo.class, "init", String.class, Integer.class);

Then instantiation will look like:

PodamFactory podam = new PodamFactoryImpl();
Pojo myPojo = factory.manufacturePojo(Pojo.class);

PODAM will use values provided by DataProviderStrategy as parameters to call the methods.