我有以下情况
class Parent {
@SomeAnnotation(someValue)
public void someMethod(){...}
}
class Child extends Parent {
@Override
public void someMethod(){...}
}
当我引用方法@SomeAnnotation时，我需要获得Child.someMethod。
使用Child.getSuperclass()我可以获得Parent.class。此外，我找到了一个解决方案here来引用MethodHandle的{{1}}，所以我有
Parent.someMethod但是，我无法找到从MethodHandle parentMethodHandle = MethodHandles.lookup().findSpecial(
Parent.class, childSomeMethod.getName(),
MethodType.methodType(Void.class), Child.class);
到Parent.someMethod的方法parentMethodHandle的引用方法。请帮忙。
答案 0 :(得分：4)
这是一个完整的解决方案。我认为这对于所有案例都应该是正确的，除了class A extends B之类的奇怪情况，其中A和B由不同的类加载器加载。这也可能无法与其他JVM语言（如Scala）一起正常工作，其中方法可以具有相同的擦除但不会相互覆盖（如void m(List<A> l)和void m(List<B> l)，这将导致Java中的编译错误）。
正确地执行此操作会变得有点复杂，因为您必须确保两个方法实际上相互覆盖，并且目前在Java SE中没有任何方法可以做到这一点。无论如何，它都是在网站上有用的代码。
package mcve.reflect;
import java.util.*;
import java.lang.reflect.*;
import java.lang.annotation.*;
public final class MCVEReflect {
private MCVEReflect() {}
/**
* Returns the 0th element of the list returned by
* {@code getAnnotations}, or {@code null} if the
* list would be empty.
*
* @param <A> the type of the annotation to find.
* @param m the method to begin the search from.
* @param t the type of the annotation to find.
* @return the first annotation found of the specified type which
* is present on {@code m}, or present on any methods which
* {@code m} overrides.
* @throws NullPointerException if any argument is {@code null}.
* @see MCVEReflect#getAnnotations(Method, Class)
*/
public static <A extends Annotation> A getAnnotation(Method m, Class<A> t) {
List<A> list = getAnnotations(m, t);
return list.isEmpty() ? null : list.get(0);
}
/**
* Let {@code D} be the class or interface which declares the method
* {@code m}.
* <p>
* Returns a list of all of the annotations of the specified type
* which are either present on {@code m}, or present on any methods
* declared by a supertype of {@code D} which {@code m} overrides.
* <p>
* Annotations are listed in order of nearest proximity to {@code D},
* that is, assuming {@code D extends E} and {@code E extends F}, then
* the returned list would contain annotations in the order of
* {@code [D, E, F]}. A bit more formally, if {@code Sn} is the nth
* superclass of {@code D} (where {@code n} is an integer starting at 0),
* then the index of the annotation present on {@code Sn.m} is {@code n+1},
* assuming annotations are present on {@code m} for every class.
* <p>
* Annotations from methods declared by the superinterfaces of {@code D}
* appear <em>last</em> in the list, in order of their declaration,
* recursively. For example, if {@code class D implements X, Y} and
* {@code interface X extends Z}, then annotations will appear in the
* list in the order of {@code [D, X, Z, Y]}.
*
* @param <A> the type of the annotation to find.
* @param m the method to begin the search from.
* @param t the type of the annotation to find.
* @return a list of all of the annotations of the specified type
* which are either present on {@code m}, or present on any
* methods which {@code m} overrides.
* @throws NullPointerException if any argument is {@code null}.
*/
public static <A extends Annotation> List<A> getAnnotations(Method m, Class<A> t) {
List<A> list = new ArrayList<>();
Collections.addAll(list, m.getAnnotationsByType(t));
Class<?> decl = m.getDeclaringClass();
for (Class<?> supr = decl; (supr = supr.getSuperclass()) != null;) {
addAnnotations(list, m, t, supr);
}
for (Class<?> face : getAllInterfaces(decl)) {
addAnnotations(list, m, t, face);
}
return list;
}
private static Set<Class<?>> getAllInterfaces(Class<?> c) {
Set<Class<?>> set = new LinkedHashSet<>();
do {
addAllInterfaces(set, c);
} while ((c = c.getSuperclass()) != null);
return set;
}
private static void addAllInterfaces(Set<Class<?>> set, Class<?> c) {
for (Class<?> i : c.getInterfaces()) {
if (set.add(i)) {
addAllInterfaces(set, i);
}
}
}
private static <A extends Annotation> void addAnnotations
(List<A> list, Method m, Class<A> t, Class<?> decl) {
try {
Method n = decl.getDeclaredMethod(m.getName(), m.getParameterTypes());
if (overrides(m, n)) {
Collections.addAll(list, n.getAnnotationsByType(t));
}
} catch (NoSuchMethodException x) {
}
}
/**
* @param a the method which may override {@code b}.
* @param b the method which may be overridden by {@code a}.
* @return {@code true} if {@code a} probably overrides {@code b}
* and {@code false} otherwise.
* @throws NullPointerException if any argument is {@code null}.
*/
public static boolean overrides(Method a, Method b) {
if (!a.getName().equals(b.getName()))
return false;
Class<?> classA = a.getDeclaringClass();
Class<?> classB = b.getDeclaringClass();
if (classA.equals(classB))
return false;
if (!classB.isAssignableFrom(classA))
return false;
int modsA = a.getModifiers();
int modsB = b.getModifiers();
if (Modifier.isPrivate(modsA) || Modifier.isPrivate(modsB))
return false;
if (Modifier.isStatic(modsA) || Modifier.isStatic(modsB))
return false;
if (Modifier.isFinal(modsB))
return false;
if (compareAccess(modsA, modsB) < 0)
return false;
if ((isPackageAccess(modsA) || isPackageAccess(modsB))
&& !Objects.equals(classA.getPackage(), classB.getPackage()))
return false;
if (!b.getReturnType().isAssignableFrom(a.getReturnType()))
return false;
Class<?>[] paramsA = a.getParameterTypes();
Class<?>[] paramsB = b.getParameterTypes();
if (paramsA.length != paramsB.length)
return false;
for (int i = 0; i < paramsA.length; ++i)
if (!paramsA[i].equals(paramsB[i]))
return false;
return true;
}
public static boolean isPackageAccess(int mods) {
return (mods & ACCESS_MODIFIERS) == 0;
}
private static final int ACCESS_MODIFIERS =
Modifier.PUBLIC | Modifier.PROTECTED | Modifier.PRIVATE;
private static final List<Integer> ACCESS_ORDER =
Arrays.asList(Modifier.PRIVATE,
0,
Modifier.PROTECTED,
Modifier.PUBLIC);
public static int compareAccess(int lhs, int rhs) {
return Integer.compare(ACCESS_ORDER.indexOf(lhs & ACCESS_MODIFIERS),
ACCESS_ORDER.indexOf(rhs & ACCESS_MODIFIERS));
}
}
这里也是一个JUnit 4测试：
package mcve.reflect;
import static mcve.reflect.MCVEReflect.*;
import java.lang.reflect.*;
import java.lang.annotation.*;
import java.util.*;
import static java.util.stream.Collectors.*;
import org.junit.*;
import static org.junit.Assert.*;
public class MCVEReflectTest {
public MCVEReflectTest() {
}
@Retention(RetentionPolicy.RUNTIME)
@interface AnnoContainer {
Anno[] value();
}
@Repeatable(AnnoContainer.class)
@Retention(RetentionPolicy.RUNTIME)
@interface Anno {
String value();
}
interface I {
@Anno("I.m")
void m();
}
interface J extends I {
@Anno("J.m")
@Override
void m();
}
interface K {
@Anno("K.m")
void m();
}
@Test
public void getAnnotationsTest() throws NoSuchMethodException {
try {
getAnnotations(null, Anno.class);
fail();
} catch (NullPointerException x) {
}
try {
getAnnotations(List.class.getMethod("size"), null);
fail();
} catch (NullPointerException x) {
}
class A {
@Anno("A.m")
void m() {}
@Anno("A.m(int)")
void m(int a) {}
}
class B extends A implements K {
@Anno("B.m 1")
@Anno("B.m 2")
@Override
public void m() {}
}
class C extends B implements J {
@Anno("C.m")
@Override
public void m() {}
}
System.out.println(Arrays.toString(B.class.getInterfaces()));
List<Anno> annos;
List<String> expect;
List<String> actual;
annos = getAnnotations(A.class.getDeclaredMethod("m"), Anno.class);
expect = Arrays.asList("A.m");
actual = annos.stream().map(Anno::value).collect(toList());
assertEquals(expect, actual);
annos = getAnnotations(B.class.getDeclaredMethod("m"), Anno.class);
expect = Arrays.asList("B.m 1", "B.m 2", "A.m", "K.m");
actual = annos.stream().map(Anno::value).collect(toList());
assertEquals(expect, actual);
annos = getAnnotations(C.class.getDeclaredMethod("m"), Anno.class);
expect = Arrays.asList("C.m", "B.m 1", "B.m 2", "A.m", "J.m", "I.m", "K.m");
actual = annos.stream().map(Anno::value).collect(toList());
assertEquals(expect, actual);
annos = getAnnotations(J.class.getDeclaredMethod("m"), Anno.class);
expect = Arrays.asList("J.m", "I.m");
actual = annos.stream().map(Anno::value).collect(toList());
assertEquals(expect, actual);
annos = getAnnotations(Object.class.getMethod("toString"), Anno.class);
assertEquals(Collections.emptyList(), annos);
}
private boolean overrides(Method a, Method b) {
return MCVEReflect.overrides(a, b);
}
private boolean overrides(Class<?> classA, String nameA,
Class<?> classB, String nameB)
throws NoSuchMethodException {
return MCVEReflect.overrides(classA.getDeclaredMethod(nameA),
classB.getDeclaredMethod(nameB));
}
private boolean overrides(Class<?> classA, Class<?> classB, String name)
throws NoSuchMethodException {
return overrides(classA, name, classB, name);
}
@Test
public void overridesTest() throws NoSuchMethodException {
try {
overrides(null, List.class.getMethod("size"));
fail();
} catch (NullPointerException x) {
}
try {
overrides(List.class.getMethod("size"), null);
fail();
} catch (NullPointerException x) {
}
assertTrue("this is an override", overrides(ArrayList.class, "size", List.class, "size"));
assertFalse("same method", overrides(List.class, "size", List.class, "size"));
assertFalse("different methods", overrides(ArrayList.class, "clear", List.class, "size"));
class A { private void m() {} }
class B extends A { private void m() {} }
assertFalse("private methods", overrides(B.class, "m", A.class, "m"));
class C { public void m() {} }
class D { public void m() {} }
assertFalse("no inheritance", overrides(D.class, "m", C.class, "m"));
class E { public void m() {} }
class F { public void m() {} }
class G extends F { @Override public void m() {} }
assertTrue("yes inheritance", overrides(G.class, "m", F.class, "m"));
assertFalse("no inheritance", overrides(G.class, "m", E.class, "m"));
class H {
public void m(char a) {}
public void m(long a) {}
}
class I extends H {
@Override public void m(char a) {}
@Override public void m(long a) {}
}
assertTrue("same parameters",
overrides(I.class.getDeclaredMethod("m", char.class),
H.class.getDeclaredMethod("m", char.class)));
assertFalse("different parameters",
overrides(I.class.getDeclaredMethod("m", char.class),
H.class.getDeclaredMethod("m", long.class)));
class SubHashMap extends HashMap<Object, Object> {
void reinitialize() {
}
}
String reinitialize = "reinitialize";
// if this throws, find another method as a replacement
Method m = HashMap.class.getDeclaredMethod(reinitialize);
assertTrue(isPackageAccess(m.getModifiers()));
assertFalse(Modifier.isFinal(m.getModifiers()));
assertFalse("would override, except they are in different packages",
overrides(SubHashMap.class, HashMap.class, reinitialize));
}
@Test
public void compareAccessTest() {
assertEquals( 0, compareAccess(Modifier.PUBLIC, Modifier.PUBLIC));
assertEquals(+1, compareAccess(Modifier.PUBLIC, Modifier.PROTECTED));
assertEquals(+1, compareAccess(Modifier.PUBLIC, 0));
assertEquals(+1, compareAccess(Modifier.PUBLIC, Modifier.PRIVATE));
assertEquals(-1, compareAccess(Modifier.PROTECTED, Modifier.PUBLIC));
assertEquals( 0, compareAccess(Modifier.PROTECTED, Modifier.PROTECTED));
assertEquals(+1, compareAccess(Modifier.PROTECTED, 0));
assertEquals(+1, compareAccess(Modifier.PROTECTED, Modifier.PRIVATE));
assertEquals(-1, compareAccess(0, Modifier.PUBLIC));
assertEquals(-1, compareAccess(0, Modifier.PROTECTED));
assertEquals( 0, compareAccess(0, 0));
assertEquals(+1, compareAccess(0, Modifier.PRIVATE));
assertEquals(-1, compareAccess(Modifier.PRIVATE, Modifier.PUBLIC));
assertEquals(-1, compareAccess(Modifier.PRIVATE, Modifier.PROTECTED));
assertEquals(-1, compareAccess(Modifier.PRIVATE, 0));
assertEquals( 0, compareAccess(Modifier.PRIVATE, Modifier.PRIVATE));
int notModsL = Modifier.PRIVATE | Modifier.PUBLIC;
int notModsR = Modifier.PRIVATE | Modifier.PROTECTED;
assertEquals("this might as well be undefined, but it's here for posterity",
0, compareAccess(notModsL, notModsR));
}
}
答案 1 :(得分：2)
我认为你已经获得了超类方法和测试注释。除了java不支持获取超级方法注释。
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.FIELD, ElementType.METHOD, ElementType.TYPE})
@Inherited
public @interface SomeAnnotation {
}
@SomeAnnotation
public class Parent {
@SomeAnnotation
public void someMethod() {
System.out.println("Parent");
}
}
public class Child extends Parent {
@Override
public void someMethod() {
super.someMethod();
}
public static void main(String[] args) throws NoSuchMethodException {
Class clazz = Child.class;
System.out.println("Child Method");
Method method = clazz.getMethod("someMethod");
Arrays.stream(method.getDeclaredAnnotations()).forEach(annotation -> System.out.println(annotation));
System.out.println("Parent Method");
Method superMethod = clazz.getSuperclass().getMethod("someMethod");
Arrays.stream(superMethod.getDeclaredAnnotations()).forEach(annotation -> System.out.println(annotation));
System.out.println("Class Level support inherited annotations. ");
Arrays.stream(clazz.getAnnotations()).forEach(annotation -> System.out.println(annotation));
}
}
另外你可以做一些通用的方法是动态访问supper类。如
public void printAnnotationInMethod(String methodName, Class clazz) {
try {
Method method = clazz.getDeclaredMethod(methodName);
Arrays.stream(method.getDeclaredAnnotations()).forEach(annotation -> System.out.println(annotation));
if (null != clazz.getSuperclass()) {
printAnnotationInMethod(methodName, clazz.getSuperclass());
}
} catch (NoSuchMethodException e) {
//e.printStackTrace();
} catch (SecurityException e) {
//e.printStackTrace();
}
}
@Inhertied仅用于使用TYPE的注释的注释支持。 （仅限课程级别）
答案 2 :(得分：0)
您需要将SELECT CAST(GETDATE() as datetime2(6)) 'Date';
声明为@SomeAnnotation：
@Inherited答案 3 :(得分：0)
这是你想要的，还是我错过了什么？
@Retention(RetentionPolicy.RUNTIME)
@interface SomeAnnotation{
}
class Parent {
@SomeAnnotation()
public void someMethod(){
}
}
class Child extends Parent {
@Override
public void someMethod(){
}
}
class Test{
public static void main(String[] args) throws NoSuchMethodException {
Child child = new Child();
Method someMethodChild = child.getClass().getMethod("someMethod");
Class<?> superclass = someMethodChild.getDeclaringClass().getSuperclass();
System.out.println(superclass.getMethod("someMethod").getAnnotations().length); //prints 1
}
}