我有一个注释处理器,它接受一个带注释的类并尝试创建它的一个子类:
package test;
import com.squareup.javapoet.ClassName;
import com.squareup.javapoet.JavaFile;
import com.squareup.javapoet.TypeSpec;
import java.io.IOException;
import java.util.Set;
import javax.annotation.processing.AbstractProcessor;
import javax.annotation.processing.ProcessingEnvironment;
import javax.annotation.processing.RoundEnvironment;
import javax.annotation.processing.SupportedAnnotationTypes;
import javax.annotation.processing.SupportedSourceVersion;
import javax.lang.model.SourceVersion;
import javax.lang.model.element.Element;
import javax.lang.model.element.Modifier;
import javax.lang.model.element.TypeElement;
@SupportedAnnotationTypes("java.lang.SuppressWarnings")
@SupportedSourceVersion(SourceVersion.RELEASE_7)
public class BSProcessor extends AbstractProcessor {
@Override
public synchronized void init(ProcessingEnvironment processingEnv) {
super.init(processingEnv);
}
@Override
public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnvironment) {
for (TypeElement baseClassAnnotation : annotations) {
for (Element annotatedElement : roundEnvironment.getElementsAnnotatedWith(baseClassAnnotation)) {
handleAnnotatedTypeElement((TypeElement) annotatedElement);
}
}
return true;
}
private void handleAnnotatedTypeElement(TypeElement annotatedTypeElement) {
try {
javaFile(annotatedTypeElement).writeTo(System.out);
} catch (IOException e) {
e.printStackTrace();
}
}
private JavaFile javaFile(TypeElement annotatedTypeElement) {
return JavaFile.builder(packageName(annotatedTypeElement), typeSpec(annotatedTypeElement))
.build();
}
private TypeSpec typeSpec(TypeElement annotatedTypeElement) {
return TypeSpec.classBuilder(className(annotatedTypeElement))
.addModifiers(Modifier.PUBLIC, Modifier.ABSTRACT)
.build();
}
private ClassName className(TypeElement annotatedTypeElement) {
return ClassName.get(packageName(annotatedTypeElement), String.format("AutoGenerated_%s",
annotatedTypeElement.getSimpleName()));
}
private String packageName(TypeElement annotatedTypeElement) {
return annotatedTypeElement.getEnclosingElement().toString();
}
}
这适用于没有类型参数的类,但我不确定如何使用它们。对类型变量执行 toString
只会给出变量名,而不是边界。关于如何执行此操作的任何想法?
最佳答案
TypeElement
的类型参数可以通过调用 getTypeParameters()
获取,它们的边界可以通过调用 getBounds()
获得 TypeParameterElement
s。我假设您对以下步骤感到困扰 — 应将哪些具体类型传递给那些类型参数以满足这些界限。
不幸的是,这是一个问题,对于任意 类型(这似乎是您所追求的)无法轻松解决。例如,看看这个类型:
public abstract class Recursive<UU extends Callable<UU>> {
}
你可能会凭直觉得出结论,它可以通过这样的类来实现:
public class Solution extends Recursive<Solution> implements Callable<Solution> {
@Override
public Solution call() throws Exception {
return new Solution();
}
}
但这对于自动化来说并非易事,而且您(可能)不想在您的代码中包含所需的机制。
与其尝试自己解决该问题,我建议您利用类型删除并让编译器为您解决问题:
// returns something like "Map<K, V>", this is NOT what you want!
DeclaredType classType = (DeclaredType) typeElement.asType();
Types types = processingEnvironment.getTypeUtils();
Elements elements = processingEnvironment.getElementUtils();
// this obtains raw type (plain "Map"), with all methods type-erased,
// the compiler is much better at solving type riddles than you!
DeclaredType rawType = types.getDeclaredType(typeElement);
final Collection<? extends ExecutableElement> methods =
ElementFilter.methodsIn(elements.getAllMembers(typeElement));
// To create a MethodSpec, suitable for the raw type, you should
// call 3-parameter MethodSpec#overriding with type-erased raw class type
// as second parameter and javax.lang.model.util.Types instance as third
MethodSpec newMethod = MethodSpec.overriding(methods.get(0), rawType, types);
因此,您的特定问题的答案是“不要将任何类型参数传递给 JavaPoet,使用原始类型”。
关于java - 如何找到 TypeMirror 的边界并将它们转换为 JavaPoet TypeSpec?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/40586423/