Annotations

Annotations based usage of the ShapeShift library.

Basic Mapping

We start by defining two classes, our source class SimpleEntity and our destination class SimpleEntityDisplay.

data class SimpleEntity(
    val name: String,
    val description: String,
    val privateData: String
)

public class SimpleEntity {
    private String name;
    private String description;
    private String privateData;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }

    public String getPrivateData() {
        return privateData;
    }

    public void setPrivateData(String privateData) {
        this.privateData = privateData;
    }
}

data class SimpleEntityDisplay(
    val name: String = "",
    val description: String = ""
)

public class SimpleEntityDisplay {
    private String name = "";
    private String description = "";

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }
}

We can now start adding our annotations to the SimpleEntity class. In this example, we want to map the name and description fields to the name and description fields of the SimpleEntityDisplay class, but not the privateData field.

To achieve this, we will use the @MappedField annotation on both of these fields. Additionally, we will define @DefaultMappingTarget on the SimpleEntity class, which will indicate that all fields annotated with @MappedField that do not specify a target should be mapped to the SimpleEntityDisplay class.

@DefaultMappingTarget(SimpleEntityDisplay::class)
data class SimpleEntity(
    @MappedField
    val name: String,
    @MappedField
    val description: String,
    val privateData: String
)

@DefaultMappingTarget(SimpleEntityDisplay.class)
public class SimpleEntity {
    @MappedField
    private String name;
    @MappedField
    private String description;
    private String privateData;
    // Getters and Setters...
}

Default Mapping Target

@DefaultMappingTarget on a class, indicates that all fields annotated with @MappedField that do not specify a target should be mapped to this class by default.

Mapping Target

The mapping target comes into play when you want to map a single source to multiple destinations. The target attribute is used to indicate to which class the field should be mapped. If no target is specified the target will be determined by the @DefaultMappingTarget on the class.

@DefaultMappingTarget(SimpleEntityDisplay::class)
data class SimpleEntity(
    @MappedField
    @MappedField(target = SimpleEntityExport::class)
    val name: String,
    @MappedField
    val description: String
)

@DefaultMappingTarget(SimpleEntityDisplay.class)
public class SimpleEntity {
    @MappedField
    @MappedField(target = SimpleEntityExport.class)
    private String name;
    @MappedField
    private String description;
    // Getters and Setters...
}

In the above code name is mapped once to the SimpleEntityDisplay class using the default mapping target, and once to the SimpleEntityExport class using the target attribute.

data class SimpleEntityDisplay(
    val name: String = "",
    val description: String = ""
)

data class SimpleEntityExport(
    val name: String = ""
)

Map To Field

By default each @MappedField is mapped to a field with the same name in the target class. To change it use the mapTo value. For example:

@DefaultMappingTarget(SimpleEntityDisplay::class)
data class SimpleEntity(
    @MappedField(mapTo = "fullName")
    val name: String
)

data class SimpleEntityDisplay(
    val fullName: String = ""
)

Map From Field

The field name to map the value from.

Field Level

When mapFrom is used at the field level, it allows for mapping of nested values.

@DefaultMappingTarget(AdvancedEntityDisplay::class)
data class AdvancedEntity(
    // This field will be mapped to the "firstChildName" field in the default target class
    @MappedField(mapFrom = "childName", mapTo = "firstChildName")
    val firstChild: AdvancedChildEntity,

    // This field will be mapped to the "secondChildName" field in the default target class
    @MappedField(mapFrom = "childName", mapTo = "secondChildName")
    val secondChild: AdvancedChildEntity
)

@DefaultMappingTarget(AdvancedEntityDisplay.class)
public class AdvancedEntity {
    // This field will be mapped to the "firstChildName" field in the default target class
    @MappedField(mapFrom = "childName", mapTo = "firstChildName")
    private AdvancedChildEntity firstChild;

    // This field will be mapped to the "secondChildName" field in the default target class
    @MappedField(mapFrom = "childName", mapTo = "secondChildName")
    private AdvancedChildEntity secondChild;
    
    // Getters and Setters...
}

As you can see above, we use the mapFrom attribute to access the childName field in AdvancedChildEntity.

data class AdvancedChildEntity(
    val childName: String
)

And we use the mapTo attribute to map the values to the appropriate fields in AdvancedEntityDisplay.

data class AdvancedEntityDisplay(
    val firstChildName: String = "",
    val secondChildName: String = ""
)

Type Level

The @MappedField annotation can also be used at the type level. When used at the type level, the mapFrom attribute is required to indicate the name of the field to use, if left empty an exception will be thrown.

@MappedField(target = SimpleEntityDisplay::class, mapFrom = "firstName")
@MappedField(target = SimpleEntityDisplay::class, mapFrom = "lastName")
data class SimpleEntity(
    val firstName: String,
    val lastName: String,
)

@MappedField(target = SimpleEntityDisplay.class, mapFrom = "firstName")
@MappedField(target = SimpleEntityDisplay.class, mapFrom = "lastName")
public class SimpleEntity {
    private String firstName;
    private String lastName;
    // Getters and Setters...
}

data class SimpleEntityDisplay(
    val firstName: String = "",
    val lastName: String = ""
)

Transformer

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:

Transformers

To configure a transformer for a field use the transformer attribute. The transformer attribute receives the transformer's class.

@DefaultMappingTarget(SimpleEntityDisplay::class)
data class SimpleEntity(
    @MappedField(transformer = StringToListMappingTransformer::class, mapTo = "stringList")
    val commaDelimitedString: String
)

@DefaultMappingTarget(SimpleEntityDisplay.class)
public class SimpleEntity {
    @MappedField(transformer = StringToListMappingTransformer.class, mapTo = "stringList")
    private String commaDelimitedString;
    // Getters and Setters...
}

data class SimpleEntityDisplay(
    val stringList: List<String> = emptyList()
)

Transformers must be registered to the ShapeShift instance in order to be used. More info about registering transformers is available in the transformers page.

Transformers

Auto Mapping

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

Auto mapping can be added using the @AutoMapping annotation.

@AutoMapping(SimpleEntityDisplay::class, strategy = AutoMappingStrategy.BY_NAME)
@DefaultMappingTarget(SimpleEntityDisplay::class)
data class SimpleEntity(
    val id: String,
    val name: String,
    val birthDate: Date,
    val email: String,
    val telephone: String
)

@AutoMapping(target = SimpleEntityDisplay.class, strategy = AutoMappingStrategy.BY_NAME)
@DefaultMappingTarget(SimpleEntityDisplay.class)
public class SimpleEntity {
    private String id;
    private String name;
    private Date birthDate;
    private String email;
    private String telephone;
    // Getters and Setters...
}

The @AutoMapping annotation has two attributes:

target - If no target is added then the auto mapping will be configured to any target class. It is possible to add multiple @AutoMapping annotation for multiple target classes.
strategy - The auto mapping strategy. Default value NONE.

Mapping Condition

Conditions are used to determine wether a field should be mapped according to certain logic. More info about conditions is available here:

Conditions

A condition can be added to annotation mapping using the condition attribute.

@DefaultMappingTarget(SimpleEntityDisplay::class)
data class SimpleEntity(
    @MappedField(condition = NotBlankStringCondition::class)
    val name: String
)

We mapped the name field and added a condition for the mapping.

data class SimpleEntityDisplay(
    val name: String = ""
)

The condition receives context with the original value of the field and checks that it is not null or blank.

class NotBlankStringCondition : MappingCondition<String> {
    override fun isValid(context: MappingConditionContext<String>): Boolean {
        return !context.originalValue.isNullOrBlank()
    }
}

public class NotBlankStringCondition implements MappingCondition<String> {
    @Override
    public boolean isValid(@NonNull MappingConditionContext<String> context) {
        return context.getOriginalValue() != null && !context.getOriginalValue().trim().isEmpty();
    }
}

Override Mapping Strategy

The overrideMappingStrategy attribute allows you to override the default mapping strategy configured on the ShapeShift instance.

@DefaultMappingTarget(SimpleEntityDisplay::class)
data class SimpleEntity(
    @MappedField(overrideMappingStrategy = MappingStrategy.MAP_ALL)
    val name: String
)

@DefaultMappingTarget(SimpleEntityDisplay.class)
public class SimpleEntity {
    @MappedField(overrideMappingStrategy = MappingStrategy.MAP_ALL)
    private String name;
    // Getters and Setters...
}

More info about mapping strategy is available here:

Mapping Strategy

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