gsonpath.util.TypeHandler.kt Maven / Gradle / Ivy

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An annotation processor which generates Type Adapters for the Google Gson library
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package gsonpath.util

import com.squareup.javapoet.ClassName
import com.squareup.javapoet.TypeName
import javax.annotation.processing.ProcessingEnvironment
import javax.lang.model.element.Element
import javax.lang.model.element.ElementKind
import javax.lang.model.element.Modifier
import javax.lang.model.element.TypeElement
import javax.lang.model.type.DeclaredType
import javax.lang.model.type.ExecutableType
import javax.lang.model.type.TypeMirror

interface TypeHandler {
    fun getTypeName(typeMirror: TypeMirror): TypeName?
    fun getClassName(typeMirror: TypeMirror): TypeName?
    fun isSubtype(t1: TypeMirror, t2: TypeMirror): Boolean
    fun asElement(t: TypeMirror): Element?
    fun getAllMembers(typeElement: TypeElement): List
    fun getFields(typeElement: TypeElement, filterFunc: ((Element) -> Boolean)): List
    fun getMethods(typeElement: TypeElement): List
    fun isMirrorOfCollectionType(typeMirror: TypeMirror): Boolean
}

data class FieldElementContent(
        val element: Element,
        val generifiedElement: TypeMirror
)

data class MethodElementContent(
        val element: Element,
        val generifiedElement: ExecutableType
)

class ProcessorTypeHandler(private val processingEnv: ProcessingEnvironment) : TypeHandler {
    override fun getTypeName(typeMirror: TypeMirror): TypeName? = TypeName.get(typeMirror)

    override fun getClassName(typeMirror: TypeMirror): TypeName? = ClassName.get(typeMirror)

    override fun asElement(t: TypeMirror): Element? {
        return processingEnv.typeUtils.asElement(t)
    }

    override fun isSubtype(t1: TypeMirror, t2: TypeMirror): Boolean {
        return processingEnv.typeUtils.isSubtype(t1, t2)
    }

    override fun getAllMembers(typeElement: TypeElement): List {
        return processingEnv.elementUtils.getAllMembers(typeElement)
    }

    override fun getFields(typeElement: TypeElement, filterFunc: (Element) -> Boolean): List {
        return getAllMembers(typeElement)
                .asSequence()
                .filter {
                    // Ignore modelElement that are not fields.
                    it.kind == ElementKind.FIELD
                }
                .filter(filterFunc)
                .map { FieldElementContent(it, getGenerifiedTypeMirror(typeElement, it)) }
                .toList()
    }

    override fun getMethods(typeElement: TypeElement): List {
        return getAllMembers(typeElement)
                .asSequence()
                .filter {
                    // Ignore methods from the base Object class
                    TypeName.get(it.enclosingElement.asType()) != TypeName.OBJECT
                }
                .filter {
                    it.kind == ElementKind.METHOD
                }
                .filter {
                    // Ignore Java 8 default/static interface methods.
                    !it.modifiers.contains(Modifier.DEFAULT) &&
                            !it.modifiers.contains(Modifier.STATIC)
                }
                .map { MethodElementContent(it, getGenerifiedTypeMirror(typeElement, it) as ExecutableType) }
                .toList()
    }

    override fun isMirrorOfCollectionType(typeMirror: TypeMirror): Boolean {
        val rawType: TypeMirror = when (typeMirror) {
            is DeclaredType -> typeMirror.typeArguments.first()

            else -> return false
        }

        val collectionTypeElement = processingEnv.elementUtils.getTypeElement(Collection::class.java.name)
        val collectionType = processingEnv.typeUtils.getDeclaredType(collectionTypeElement, rawType)

        return processingEnv.typeUtils.isSubtype(typeMirror, collectionType)
    }

    private fun getGenerifiedTypeMirror(containing: TypeElement, element: Element): TypeMirror {
        return processingEnv.typeUtils.asMemberOf(containing.asType() as DeclaredType, element)
    }
}