注释处理器是否有可能访问在前一轮中生成的类型？

Question

package tmp;

@MyAnnotation
public class Foo {
  private Foo me;
  private FooId myId;
}

@SupportedAnnotationTypes("tmp.proc.MyAnnotation")
@SupportedSourceVersion(SourceVersion.RELEASE_7)
public class CreateIdProcessor extends AbstractProcessor {
  @Override
  public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {
    for (Element elem : roundEnv.getElementsAnnotatedWith(MyAnnotation.class)) {
      System.out.println("Writing ID for " + elem.getSimpleName());
      try {
        Writer file = processingEnv.getFiler().createSourceFile(elem + "Id").openWriter();
        file.write(String.format("package tmp; public class %sId {}", elem.getSimpleName()));
        file.close();
      } catch (IOException e) {
        throw new RuntimeException(e);
      }
    }
    return false;
  }
}

@SupportedAnnotationTypes("tmp.proc.MyAnnotation")
@SupportedSourceVersion(SourceVersion.RELEASE_7)
public class CheckIdProcessor extends AbstractProcessor {
  @Override
  public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {
    for (Element elem : roundEnv.getElementsAnnotatedWith(MyAnnotation.class)) {
      for (Element element : elem.getEnclosedElements()) {
        System.out.printf("%s = %s (%s)\n", element.getSimpleName(), element.asType(), element.asType().getKind());
      }
    }
    return false;
  }
}

Writing ID for Foo
<init> = ()void (EXECUTABLE)
me = tmp.Foo (DECLARED)
myId = FooId (ERROR)

编译一切都很好，但是第二个处理器将myid类型视为错误，即使它是由第一个处理器生成的（而且FooId类确实在输出jar中）。这阻止了注释处理器分析fooid，例如找出它所属的包以便导入它。这个问题有什么解决办法吗？

Answer 1

Java注释过程以轮为单位执行其工作。在每一轮中，它将运行所有适用的注释处理器，然后编译输出。注释处理器API还跟踪处理了哪些类，并且只处理一次。您遇到的问题是，createidprocessor生成类的过程与checkidprocessor查找类的过程相同。因为fooid在checkidProcessory运行之前没有编译，所以调用getEncellseDelements()返回的元素是error元素。

简而言之，第二个处理器将fooid字段类型视为错误，因为fooid的源代码已经生成，但尚未编译。

你可以做一个实验。这个注释处理器将打印出在给定轮中处理的所有新类。fooid显示在round:1下，而foo显示在round:0下：

Round: 0
Foo = tmp.Foo (DECLARED)
<init> = ()void (EXECUTABLE)
me = tmp.Foo (DECLARED)
myId = FooId (ERROR)
Writing ID for Foo
Round: 1
FooId = tmp.FooId (DECLARED)
Round: 2
Round: 3

@SupportedAnnotationTypes("*")
@SupportedSourceVersion(SourceVersion.RELEASE_6)
public class OutputRoundProcessor extends AbstractProcessor {
  private int round = 0;
  @Override
  public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {
    System.out.println("Round: " + round);
    for (Element element : roundEnv.getRootElements()) {
      System.out.printf("%s = %s (%s)\n", element.getSimpleName(), element.asType(), element.asType().getKind());
    }
    round++;
    return false;
  }
}