如何通过MethodHandles.lookup()获取所有声明的方法？如何获取所有声明的字段？

MethodHandle.invoke()、MethodHandle.invokeExact() 和 MethodHandle.invokeWithArguments()

另外，我将不胜感激为 Java 开发人员 使用 MethodHandle API 的教程。我强调，我是在静态类型语言纯旧 Java 上编程，我不是 JVM 开发人员，特别是我对整个字节码废话(invokedynamic)不感兴趣。我想弄清楚如何使用这个新 API 而不是 Java Core API。

EDITED-2:

@Glen Best 下面提供了一些引用我只想提供一个 http://www.oraclejavamagazine-digital.com/javamagazine/20130102?pg=52&search_term=methodhandle&doc_id=-1#pg50这正是我一直在寻找的。我发现实际上有一些新词汇。例如，target 实际上是指 MethodHandle(而不是要进行调度的对象)，而 call site 实际上是代码“调用”“函数指针”又名 MethodHandle。此外，必须了解 MethodHandle API 不是核心反射 API 的替代品，而不是补充它。例如，您无法使用 MethodHandle “发现”所有方法，而您需要 Core Reflection API。但是当你“找到”你想要的方法时，你可以切换到 MethodHandle，例如，绑定(bind)它的一些参数或“改变”(适应)它的签名，例如可变参数。

已编辑:

我仍在试图找出答案。我写了一些测试，想和大家分享。

package alexander.berkovich;

import static org.junit.Assert.assertSame;

import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.MethodType;
import java.lang.reflect.Field;
import java.lang.reflect.Method;

import org.junit.BeforeClass;
import org.junit.Test;

public class MethodHandlerCleanTest {

    public static MethodHandles.Lookup lookup;

    @BeforeClass
    public static void asetUp(){
        lookup = MethodHandles.lookup();
    }

    public static class Check {
        public void primitive(final int i){
        }
        public void wrapper(final Integer i){
        }
    }

    @Test
    public void testPrimitive() throws Throwable {
        Check check = new Check();

        MethodType type = MethodType.methodType(void.class, int.class);

        MethodHandle mh = lookup.findVirtual(Check.class, "primitive", type);
        mh.invokeWithArguments(check, 1);
        mh.invoke(check, (short)2);
        mh.invoke(check, Integer.valueOf(3));

        Method method = Check.class.getMethod("primitive", int.class);
        method.invoke(check, (short)20);
        method.invoke(check, Integer.valueOf(21));

    }

    @Test
    public void testWrapper() throws Throwable {
        Check check = new Check();

        MethodType type = MethodType.methodType(void.class, Integer.class);

        MethodHandle mh = lookup.findVirtual(Check.class, "wrapper", type);
        mh.invoke(check, 2);

        Method method = Check.class.getMethod("wrapper", Integer.class);
        method.invoke(check, 20);

    }

    @SuppressWarnings("unused")
    public static class StaticInnerClass {

        public static String staticName;
        public String name;


        public void foo(){}

        public static void staticFoo(){}

    }

    @Test
    public void testStaticInnerClassStaticField() throws Throwable {
        MethodHandle mhSet = lookup.findStaticSetter(StaticInnerClass.class, "staticName", String.class);
        String expected = "mama";
        mhSet.invoke(expected);

        MethodHandle mhGet = lookup.findStaticGetter(StaticInnerClass.class, "staticName", String.class);
        Object obj = mhGet.invoke();
        String value = (String)obj;
        assertSame(expected, value);

    }

    @Test
    public void testStaticInnerClassField() throws Throwable {
        StaticInnerClass sut = new StaticInnerClass();
        Field f = StaticInnerClass.class.getDeclaredField("name");
        MethodHandle mhSetUnreflect = lookup.unreflectSetter(f); 
        String expectedUnreflect = "unreflect";
        mhSetUnreflect.invoke(sut, expectedUnreflect);


        MethodHandle mhSet = lookup.findSetter(StaticInnerClass.class, "name", String.class);
        String expected = "mama";
        mhSet.invoke(sut, expected);

        MethodHandle mhGet = lookup.findGetter(StaticInnerClass.class, "name", String.class);
        Object obj = mhGet.invoke(sut);
        String value = (String)obj;
        assertSame(expected, value);

    }

    @Test
    public void testStaticInnerClassConstructor() throws Throwable {
        StaticInnerClass sut = new StaticInnerClass();
        MethodType type = MethodType.methodType(void.class);
        MethodHandle mh = lookup.findConstructor(StaticInnerClass.class, type);
        mh.invoke();
    }

    @Test
    public void testStaticInnerClassMethod() throws Throwable {
        StaticInnerClass sut = new StaticInnerClass();
        MethodType type = MethodType.methodType(void.class);
        MethodHandle mh = lookup.findVirtual(StaticInnerClass.class, "foo", type);
        mh.invoke(sut);
    }

    @Test
    public void testStaticInnerClassStaticMethod() throws Throwable {
        MethodType type = MethodType.methodType(void.class);
        MethodHandle mh = lookup.findStatic(StaticInnerClass.class, "staticFoo", type);
        mh.invoke();
    }

    @SuppressWarnings("unused")
    private class InnerClass {
        public String name;

        public void foo(){}

    }
    @Test
    public void testInnerClassField() throws Throwable {
        InnerClass sut = new InnerClass();
        MethodHandle mhSet = lookup.findSetter(InnerClass.class, "name", String.class);
        String expected = "mama";
        mhSet.invoke(sut, expected);

        MethodHandle mhGet = lookup.findGetter(InnerClass.class, "name", String.class);
        Object obj = mhGet.invoke(sut);
        String value = (String)obj;
        assertSame(expected, value);

    }


    @Test
    public void testInnerClassConstructor() throws Throwable {
        MethodType type = MethodType.methodType(void.class, MethodHandlerCleanTest.class);

        //default constructor is private
        Field field = MethodHandles.Lookup.class.getDeclaredField("IMPL_LOOKUP");
        field.setAccessible(true);
        MethodHandles.Lookup trustedLookup = (MethodHandles.Lookup) 
                field
                .get(null);

        MethodHandle mh = trustedLookup.findConstructor(InnerClass.class, type);
        mh.invoke(this);
    }


    @Test
    public void testInnerClassMethod() throws Throwable {
        InnerClass sut = new InnerClass();
        MethodType type = MethodType.methodType(void.class);
        MethodHandle mh = lookup.findVirtual(InnerClass.class, "foo", type);
        mh.invoke(sut);
    }

}

最佳答案

How can I obtain all declared method through MethodHandles.lookup()? How can I obtain all declared fields?

将 java.lang.invoke 视为反射 (java.lang.reflect) 的(快速执行)扩展 - 即“调用”类依赖于“反射”类。

• 您通过反射(java.lang.Class 和 java.lang.reflect)获得对所有方法/构造函数/字段的引用:

  java.lang.Class<?> someClass = ...;  // obtain a Class somehow
  
  // Returns all constructors/methods/fields declared in class, 
  // whether public/protected/package/private, 
  // but does NOT include definitions from any ancestors:
  
  java.lang.reflect.Constructor<?>[] declaredConstructors = someClass.getDeclaredConstructors();
  java.lang.reflect.Method[] declaredMethods = someClass.getDeclaredMethods();
  java.lang.reflect.Field[] declaredFields   = someClass.getDeclaredFields();
  
  // Returns all constructors/methods/fields declared as public members 
  // in the class AND all ancestors: 
  
  java.lang.reflect.Constructor<?>[] publicInheritedConstructors = someClass.getConstructors();
  java.lang.reflect.Method[] publicInheritedMethods = someClass.getMethods();
  java.lang.reflect.Field[] publicInheritedFields   = someClass.getFields();
  

• 您可以通过 java.lang.invoke.MethodHandles.Lookup 将它们转换为 MethodHandles:

  java.lang.invoke.MethodType mt; 
  java.lang.invoke.MethodHandle mh;
  java.lang.invoke.MethodHandles.Lookup lookup = MethodHandles.lookup();
  
  // process methods
  for (java.lang.reflect.Method method: declaredMethods) {
      mh = lookup.unreflect(method);
  
      // can call mh.invokeExact (requiring first parameter to be the class' 
      // object instance upon which the method will be invoked, followed by 
      // the methodparameter types, with an exact match parameter and return 
      // types) or
      // mh.invoke/invokeWithArguments (requiring first parameter to be the 
      // class' object instance upon which the method will be invoked, 
      // followed by the method parameter types, with compatible conversions 
      // performed on input/output types)
  }
  
  // process constructors
  for (java.lang.reflect.Constructor<?> constructor: declaredConstructors) {
      mh = lookup.unreflectConstructor(constructor);
  
      // can call mh.invokeExact or
      // mh.invoke/invokeWithArguments 
  }
  
  // process field setters
  for (java.lang.reflect.Field field: declaredFields) {
      mh = lookup.unreflectSetter(field);
  
      // can call mh.invokeExact or
      // mh.invoke/invokeWithArguments 
  }
  
  // process field getters
  for (java.lang.reflect.Field field: declaredFields) {
      mh = lookup.unreflectGetter(field);
  
      // can call mh.invokeExact or
      // mh.invoke/invokeWithArguments 
  }
  

• 你可以通过java.lang.reflect判断方法/构造函数/字段的签名:

  // If generics involved in method signature:
  Type[] paramTypes = method.getGenericParameterTypes(); 
  Type returnType = method.getGenericReturnType(); 
  // Note: if Class is non-static inner class, first parameter of 
  // getGenericParameterTypes() is the enclosing class
  
  // If no generics involved in method signature:
  Class<?>[] paramTypes = declaredMethod.getParameterTypes(); 
  Class<?> returnType = declaredMethod.getReturnType(); 
  // Note: if Class is non-static inner class, first parameter of 
  // getParameterTypes() is the enclosing class
  
  // Same method calls for declaredConstructor
  

• 您可以通过 java.lang.reflect 确定方法/构造函数/字段是否为静态:

  int modifiers = method.getModifiers();  // same method for constructor/field
  boolean isStatic = java.lang.Modifier.isStatic(modifiers);
  

What is difference betweeen MethodHandle.invoke(), MethodHandle.invokeExact() and MethodHandle.invokeWithArguments()?

• 见 http://docs.oracle.com/javase/7/docs/api/java/lang/invoke/MethodHandle.html#invoke%28java.lang.Object...%29
• 如果 MethodHandle对于非静态方法，提供给这些方法的第一个参数是 Class 的实例它声明了方法。该方法在该类的实例上调用(或在静态方法的类本身上)。如果 Class是非静态内部类，第二个参数是封闭/声明类的实例。后面的参数依次为方法签名参数。
• invokeExact 不对输入参数进行自动兼容类型转换。它要求参数值(或参数表达式)与方法签名的类型完全匹配，每个参数作为单独的参数提供，或者所有参数作为数组一起提供(签名:Object invokeExact(Object... args))。
• invoke 要求参数值(或参数表达式)与方法签名的类型兼容 - 执行自动类型转换，每个参数作为单独的参数提供或所有参数作为数组一起提供(签名:对象调用(对象...参数))
• invokeWithArguments 要求参数值(或参数表达式)与方法签名的类型兼容 - 执行自动类型转换，每个参数都在 List 中提供(签名:Object invokeWithArguments(List<?> arguments))

I will be appreciate for tutorial about using MethodHandle API for Java devloper

不幸的是，那里没有太多东西。您可以尝试以下方法。希望我在上面提供了足够的信息:^)

http://docs.oracle.com/javase/7/docs/api/java/lang/invoke/MethodHandle.html
http://docs.oracle.com/javase/7/docs/api/java/lang/invoke/MethodHandles.Lookup.html
http://www.java7developer.com/blog/?p=191
http://www.oraclejavamagazine-digital.com/javamagazine/20130102?pg=52&search_term=methodhandle&doc_id=-1#pg50
http://www.amazon.com/Well-Grounded-Java-Developer-techniques-programming/dp/1617290068

关于java - 关于 MethodHandle API 的一些基本问题，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/16005824/