Populace

Populace is flexible library for walking and populating object graphs. It is often used to facilitate solid test coverage of serialisation mechanisms where complex domain models are used and full object graphs need to be populated.

Populace supports integration points to allow the behaviour of how the object graph is walked, how new entities are instantiated, and how existing fields are mutated. This allows Populace to be fully customised to match both the domain model and the needs of your project.

Usage

Populace is comprised of two core features:

1. Graph walking - GraphWalker allows a user supplied fieldVisitor and elementVisitor to visit all of the fields and, in the case of container types such as List or Set, any child elements on an object, and all of the fields and elements of objects referenced by that object, in a recursive manner. The walk can be customised by installing different FieldFilters, to control what fields are included or excluded from the walk, and by installing Inspectors, to control what fields an instance exposes, or, in the case of collection types, what child elements the field exposes.
2. Graph population - GraphPopulator walks the object graph, performing customisable operations on each field, such as ensuring the field is not null or empty, or mutating any existing value. This process can be customised by way installing Mutators, which control how field values are changed and InstanceFactorys, which control how new instances of different types are instantiated.

Additional modules provide specialised extensions to the core Populace library:

1. JaxB Annotations support - provides support for the applicable subset of JaxB annotations. For example, it provides an InstanceFactory that recognises the @XmlJavaTypeAdapter annotation, which is commonly used to link interfaces to concrete types. The factory can then instantiate the appropriate concrete implementation when a interface field is encountered. See the read me for more info

Examples

The examples below use the following simple domain model:

public class Contacts {
    private List<Person> people = new ArrayList<>();

    public List<Person> getPeople() {
        return people;
    }
}

public class Person {
    private final String name;
    private final Address address;

    public Person(final String name, final Address address) {
        this.name = name;
        this.address = address;
    }

    public String getName() {
        return name;
    }

    public Address getAddress() {
        return address;
    }

    // Used by Populace.
    private Person() {
        name = null;
        address = null;
    }
}

public class Address {
    private final List<String> lines;

    public Address(List<String> lines) {
        this.lines = Collections.unmodifiableList(new ArrayList<>(lines));
    }

    public List<String> getLines() {
        return lines;
    }

    // Used by Populace
    private Address() {
        lines = null;
    }
}

Walk example

You can walk all the fields of a populated Contacts list as follows, (NB: Without the SetAccessibleFieldVisitor visitor the code would throw a IllegalAccessException as the fields are private).

Contacts contacts = createPopulatedContacts();
GraphWalker walker = GraphWalker.newBuilder().build();

FieldVisitor fieldVisitor = FieldVisitors.chain(
    SetAccessibleFieldVisitor.INSTANCE,
    field -> System.out.println(field.toIndentedString() + "=" + field.getValue()));

ElementVisitor elementVisitor =
    element -> System.out.println(element.toIndentedString() + "=" + element.getValue());

walker.walk(contacts, fieldVisitor, elementVisitor);

The fieldVisitor will be called back on all fields encountered while walking and the elementVisitor would be called back on for all child elements of container types, such as the Address lines.

Populate example

You can create a populated instance of Contacts with the following code:

GraphPopulator populator = GraphPopulator.newBuilder().build();
Contacts contacts = populator.populate(Contacts.class);

Or you can populate an existing instance of Contacts with the following code:

GraphPopulator populator = GraphPopulator.newBuilder().build();
Contacts contacts = populator.populate(new Contacts());

More information on the configuration and use of the core Populace graph walking and mutation can be found here.

Known limitations

Collection fields

Due to the restrictions of the Collection API it is not possible to mutate collections of immutable types, (i.e. types where the mutator returns a new instance, rather than mutating the existing element). This is because there is no reliable way to replace a single element in a Collection.

By default Populace will log a warning when immutable Collection elements are encountered.

Most standard library sub-types of Collection, such as List and Set are supported, through their own specialised types. If your code contains collection types, or those of third-party libraries not supported by Populace, you can implement you own custom Inspector to handle the type.

Null Object fields

There is not enough type information to populate fields that have a null value and are of type Object, or types that are equivalent to Object at runtime such as WildcardTypes without upper bounds or unresolvable TypeVariables,

• what object should be created?

By default, Populace will just log a warning when a null Object field is encountered. However, this is customisable: you can install your own NullObjectStrategy into the InstanceFactories collection used by Populace.

Download

Populace is available from maven central.

Maven

If you're using Maven, then add the following to your pom.xml:

<dependencies>
  <dependency>
      <groupId>com.github.datalorax.populace</groupId>
      <artifactId>populace-core</artifactId>
      <version>1.1.1</version>
  </dependency>
</dependencies>

Gradle

If you're using Gradle, then add the following to your build.gradle:

dependencies {
    compile 'com.github.datalorax.populace:populace-core:1.1.1'
}

SBT

If you're using SBT, then add the following to your project:

libraryDependencies += "com.github.datalorax.populace" % "populace-core" % "1.1.1"

Javadocs

Javadocs for each release can be pulled down from maven central and are available here.

License

Populace is licensed under the Apache License, Version 2.0.

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

How to build

Prerequisites

Before building the code you'll need:

• JDK 1.8 or above
• To clone this repo.

How to: Compile and run the tests.

Run the following command from the root directory of the project:

gradlew

The script automatically downloads the correct Gradle version, so you won't have to do anything else. Gradle will then compile the project, run the tests, generate the java docs and build the project jars. If everything runs successfully, each module's jar will be located under its build/libs directory.

To see a full list of tasks available run:

gradlew tasks

How to: Create Intellij project files

Gradle includes a task that creates all files required to develop populace in Intellij. Run the following command:

gradlew idea

Then import the project into your workspace or open the root populace.ipr project file.

How to: Create Eclipse project files

Gradle includes a task that creates all files required to develop populace in Eclipse. Run the following command:

gradlew eclipse

Then import the project into your workspace.

Contributing

Contributing is good! Please get stuck in, but first read notes on contributing