Java builder based usage of the ShapeShift library.
Basic Mapping
We start by defining two classes, our source class SimpleEntity and our destination class SimpleEntityDisplay.
public class SimpleEntity {
private String name;
private String description;
private String privateData;
public SimpleEntity() {
}
public SimpleEntity(String name, String description, String privateData) {
this.name = name;
this.description = description;
this.privateData = privateData;
}
// Getters and Setters...
}
public class SimpleEntityDisplay {
private String name;
private String description;
public SimpleEntityDisplay() {
}
// Getters and Setters...
}
We can now create a simple mapper. In this example, we want to map the name and description fields of SimpleEntity to the name and description fields of the SimpleEntityDisplay class, but not the privateData field.
In the example above we did basic mapping between fields. But what if we want to map from/to deep fields of child classes?
In order to access child classes we can use the full path of a field. Let's look at the following example:
public class From {
private Child child = new Child();
// Getters and Setters...
class Child {
private String value;
// Getters and Setters...
}
}
public class To {
private String childValue;
// Getters and Setters...
}
We want to map the value field in Child class inside the From class to the childValue field in the To class. We will use the full path of value which is child.value.
MappingDefinition mappingDefinition = new MappingDefinitionBuilder(From.class, To.class)
.mapField("child.value", "childValue")
.build();
The full path is supported in both source and destination fields, it also supports multi level depth (e.g. x.y.z).
Transformers
Field transformers are a way to transform a field from one type to another when mapping it to a destination class. More about the ins-and-outs of transformers is available here:
The withTransformer function has 2 options to use transformers. Let's look at the following classes.
public class SimpleEntity {
private String commaDelimitedString;
public SimpleEntity() {
}
public SimpleEntity(String commaDelimitedString) {
this.commaDelimitedString = commaDelimitedString;
}
// Getters and Setters...
}
public class SimpleEntityDisplay {
private List<String> stringList;
public SimpleEntityDisplay() {
}
// Getters and Setters...
}
We want to map the commaDelimitedString field to the stringList field and change the field type from String to List<String> while doing so. To accomplish that we will use a transformer.
Class Transformer
Our first option is to create a transformer class, StringToListMappingTransformer;
public class StringToListMappingTransformer implements MappingTransformer<String, List<String>> {
@Nullable
@Override
public List<String> transform(@NonNull MappingTransformerContext<? extends String> context) {
return context.getOriginalValue() != null
? Arrays.asList(context.getOriginalValue().split(","))
: null;
}
}
All we need to do to use our transformer is to pass it to the withTransformer function.
MappingDefinition mappingDefinition = new MappingDefinitionBuilder(SimpleEntity.class, SimpleEntityDisplay.class)
.mapField("commaDelimitedString", "stringList")
.withTransformer(StringToListMappingTransformer.class)
.build();
Inline Transformer
Our second option is to use an inline transformer. When we don't need to reuse a transformer we can just add its logic to the builder.
Auto mapping is used to reduce the amount of boiler-place code required to configure mapping between two classes. More info about auto mapping is available here:
Auto mapping can be added using the autoMap function.
MappingDefinition mappingDefinition = new MappingDefinitionBuilder(SimpleEntity.class, SimpleEntityDisplay.class)
.autoMap(AutoMappingStrategy.BY_NAME)
.mapField("name", "fullName")
.build();
Mapping Condition
Conditions are used to determine wether a field should be mapped according to certain logic. More info about conditions is available here:
Let's look at the following classes.
public class SimpleEntity {
private String name;
public SimpleEntity() {
}
// Getters and Setters...
}
public class SimpleEntityDisplay {
private String name;
public SimpleEntityDisplay() {
}
// Getters and Setters...
}
We want to map the name field only if it's not null or blank. The withCondition function has 2 options to add conditions.
Class Condition
Our first option is to create a condition class. The condition receives context with the original value of the field and checks that it is not null or blank.
public class NotBlankStringCondition implements MappingCondition<String> {
@Override
public boolean isValid(@NonNull MappingConditionContext<String> context) {
return context.getOriginalValue() != null && !context.getOriginalValue().trim().isEmpty();
}
}
We will create our mapper and add the condition.
MappingDefinition mappingDefinition = new MappingDefinitionBuilder(SimpleEntity.class, SimpleEntityDisplay.class)
.mapField("name", "name")
.withCondition(NotBlankStringCondition.class)
.build();
Inline Condition
Our second option is to use an inline condition. When we don't need to reuse a condition we can just add its logic to the builder.
Decorators allow to add additional logic to the mapping operation. More info about conditions is available here:
Let's look at the following classes.
public class User {
private String firstName;
private String lastName;
// Getters and Setters...
}
public class UserDisplay {
private String firstName;
private String lastName;
private String fullName;
// Getters and Setters...
}
We want to merge the firstName and lastName fields to the fullName field in addition to mapping them to their respectable fields.
Decorators can be added inline or as a separate class.
Class Decorators
To create a decorator class implement the MappingDecorator interface.
public class UserUserDisplayDecorator implements MappingDecorator<User, UserDisplay> {
@Override
public void decorate(@NonNull MappingDecoratorContext<User, UserDisplay> mappingDecoratorContext) {
User from = mappingDecoratorContext.getFrom();
UserDisplay to = mappingDecoratorContext.getTo();
to.setFullName(from.getFirstName() + " " + from.getLastName());
}
}a
And register it to the ShapeShift instance.
ShapeShift shapeShift = new ShapeShiftBuilder()
.withDecorator(User.class, UserDisplay.class, new UserUserDisplayDecorator())
.build();
Inline Decorators
It is also possible to add the decorator logic inline.
ShapeShift shapeShift = new ShapeShiftBuilder()
.withDecorator(User.class, UserDisplay.class, mappingDecoratorContext -> {
User from = mappingDecoratorContext.getFrom();
UserDisplay to = mappingDecoratorContext.getTo();
to.setFullName(from.getFirstName() + " " + from.getLastName());
})
.build();
Object Suppliers
Due to the fact that ShapeShift uses reflection behind the scenes, destination classes need a no arg constructor. But in some cases you have no control over the destination classes and cannot modify them to add a no arg constructor. This is where Object Suppliers comes into play, you can register object suppliers to the ShapeShift instance to add your own logic for instance generation.
More info about Object Suppliers is available here:
Override Mapping Strategy
The overrideStrategy function allows you to override the default mapping strategy configured on the ShapeShift instance.
MappingDefinition mappingDefinition = new MappingDefinitionBuilder(SimpleEntity.class, SimpleEntityDisplay.class)
.mapField("name", "name").withMappingStrategy(MappingStrategy.MAP_ALL)
.build();
More info about mapping strategy is available here:
