Property Path - Simplifying access to Java Bean properties

Table of Contents

1. Overview
2. Example
3. Supported property paths
4. Transforming the result
5. Why is my method not supported
6. How to contribute
7. Migration guide

Overview

This library was build to simplify the access of transitive Java Bean properties.

Accessing properties within a tree of Java Beans with optional properties requires many null checks. Every return value of an optional property getter must be null-checked.

Assume the following relationship: Contract -has an optional company-> Company -has optional list of Addresses-> Address -has City-> String.

To access the city of the first address you would have to write something like this:

  public Optional<String> getCity_showcase_without_PropertyPath() {
    Contract contract = new Contract(...); // Assume we have a contract object
    if (nonNull(contract.getCompany())) {
      List<Address> addresses = contract.getCompany()
          .getAddresses();
      if (nonNull(addresses) && !addresses.isEmpty()) {
        Address address = addresses.get(0);
        return Optional.of(address.getCity());
      }
    }
    return Optional.empty();
  }

This library is able to shorten the above example to the following code:

    Contract contract = new Contract(...); // Assume we have a contract object
    Optional<String> firstCityOptional = Getter.newFor(Contract.class)
                                               .evaluate(c -> c.getCompany().getAddresses().get(0).getCity())
                                               .from(contract);

The property path c.getCompany().getAddresses().get(0).getCity() can be declared without writing null-checks. The property path will be evaluated by this library and all neccessary null-checks are performed. The result is provided by an Optional holding a value if available.

This is supported even for Lists and Maps.

Example

The following example demonstrates how to generate a sample instance of Person.

public class Contract {
  private String client;
  private Company company; // Optional, may be null
  // Getters, Setters, No-Args Default Constructor...
}

public class Company {
  private List<Address> addresses; // Optional, may be null or empty
  // Getters, Setters, No-Args Default Constructor...
}

public class Address {
  String street;
  String houseNumber;
  String zipCode;
  String city; // Desired value to get.
  // Getters, Setters, No-Args Default Constructor...
}


@Test
public void shouldGetCityOfFirstAddressNullSafe() {
Optional<String> firstCityOptional = Getter.newFor(Contract.class)
    .evaluate(c -> c.getCompany()
        .getAddresses()
        .get(0)
        .getCity())
    .from(contract);

// Check Optional.isEmpty() for a value and get the value with Optional.get() if present.
}

The above example will access the first address of the company's addresses if available. If any get-call returns null or operates on empty lists, the Optional-instance will be empty.

Supported property paths

When declaring a property path the following calls are supported:

• any Java Bean property conform getter
• java.util.List.get(int)
• java.util.Map.get(Object)

Transforming the result

Since version 0.0.6 the property path may specify a function that transforms the result value of the property path to a different type. Due to the fact that a property path may not perform computations, the transform function provides a way to apply computation after evaluating the property path.

Example

Assume you want to get the length of the street name for a given person you can write the following:

Optional<Integer> optStreetLength = Getter.newFor(Person.class)
    .evaluateAnd(p -> p.getAddress()
        .getStreet())
    .apply(String::length)
    .from(person);

If the property path evaluates to a non-null value, the transform function (String::length) is applied to the result and reduces the street name to the number of characters. The result can be accessed via the returned java.util.Optional.

In case the property path evaluates to a null value, the transform function will not be applied.

A transform function may return a null value. In this case an empty java.util.Optional is the result.

Why is my method not supported?

This library currently only supports the above method calls in a property path. Other methods are not implemented because this would morph this library into a mocking framework, and that is not the intent.

The method java.util.Map.getOrDefault(Object, V) seemed like a good candidate to be implemented and supported in property paths, but using complex objects as key or value in maps introduces a dependency when testing. The arguments in property paths are also checked using equals, so the test must have the exact same arguments which is considered as a strong dependecy.

How to contribute

Please refer to the project's contribution guide

Migration guide

Migration from 0.0.x to 0.1.x

Due to a JDK 8 bug related to type inference of generic exception type variables the API was restructured. You may have to change code if you used the apply-feature but the changes are minimal ;)