关于Class的invokeDynamic指令
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（2）invokedynamic指令 https://www.cnblogs.com/wade-luffy/p/6058087.html
public class InDyTest {
public static void main(String[] args) {
Runnable x = () -> {
//System.out.println("Hello, World!");
};
}
}
生成的Class结构如下：
Classfile /C:/Users/mazhi/Desktop/InDyTest.class
Last modified 2018-7-5; size 986 bytes
MD5 checksum 03d0c485e603b294e8de271d879c7b8f
Compiled from "InDyTest.java"
public class com.test01.InDyTest
SourceFile: "InDyTest.java"
BootstrapMethods:
0: #34 invokestatic java/lang/invoke/LambdaMetafactory.metafactory:(Ljava/la ng/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Lj ava/lang/invoke/MethodType;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/Meth odType;)Ljava/lang/invoke/CallSite;
Method arguments:
#35 ()V
#38 invokestatic com/test01/InDyTest.lambda$0:()V
#39 ()V
InnerClasses:
public static final #45= #41 of #43; //Lookup=class java/lang/invoke/Meth odHandles$Lookup of class java/lang/invoke/MethodHandles
minor version: 0
major version: 52
flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
#1 = Class #2 // com/test01/InDyTest
#2 = Utf8 com/test01/InDyTest
#3 = Class #4 // java/lang/Object
#4 = Utf8 java/lang/Object
#5 = Utf8 <init>
#6 = Utf8 ()V
#7 = Utf8 Code
#8 = Methodref #3.#9 // java/lang/Object."<init>":()V
#9 = NameAndType #5:#6 // "<init>":()V
#10 = Utf8 LineNumberTable
#11 = Utf8 LocalVariableTable
#12 = Utf8 this
#13 = Utf8 Lcom/test01/InDyTest;
#14 = Utf8 main
#15 = Utf8 ([Ljava/lang/String;)V
#16 = NameAndType #17:#18 // run:()Ljava/lang/Runnable;
#17 = Utf8 run
#18 = Utf8 ()Ljava/lang/Runnable;
#19 = InvokeDynamic #0:#16 // #0:run:()Ljava/lang/Runnable;
#20 = Utf8 args
#21 = Utf8 [Ljava/lang/String;
#22 = Utf8 x
#23 = Utf8 Ljava/lang/Runnable;
#24 = Utf8 lambda$0
#25 = Utf8 SourceFile
#26 = Utf8 InDyTest.java
#27 = Utf8 BootstrapMethods
#28 = Methodref #29.#31 // java/lang/invoke/LambdaMetafactory .metafactory:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lan g/invoke/MethodType;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodHandle; Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite;
#29 = Class #30 // java/lang/invoke/LambdaMetafactory
#30 = Utf8 java/lang/invoke/LambdaMetafactory
#31 = NameAndType #32:#33 // metafactory:(Ljava/lang/invoke/Met hodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/invo ke/MethodType;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodType;)Ljava /lang/invoke/CallSite;
#32 = Utf8 metafactory
#33 = Utf8 (Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/St ring;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodType;Ljava/lang/invoke /MethodHandle;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite;
#34 = MethodHandle #6:#28 // invokestatic java/lang/invoke/Lamb daMetafactory.metafactory:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/Str ing;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/ MethodHandle;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite;
#35 = MethodType #6 // ()V
#36 = Methodref #1.#37 // com/test01/InDyTest.lambda$0:()V
#37 = NameAndType #24:#6 // lambda$0:()V
#38 = MethodHandle #6:#36 // invokestatic com/test01/InDyTest.l ambda$0:()V
#39 = MethodType #6 // ()V
#40 = Utf8 InnerClasses
#41 = Class #42 // java/lang/invoke/MethodHandles$Loo kup
#42 = Utf8 java/lang/invoke/MethodHandles$Lookup
#43 = Class #44 // java/lang/invoke/MethodHandles
#44 = Utf8 java/lang/invoke/MethodHandles
#45 = Utf8 Lookup
{
public com.test01.InDyTest();
flags: ACC_PUBLIC
Code:
stack=1, locals=1, args_size=1
0: aload_0
1: invokespecial #8 // Method java/lang/Object."<init> ":()V
4: return
LineNumberTable:
line 4: 0
LocalVariableTable:
Start Length Slot Name Signature
0 5 0 this Lcom/test01/InDyTest;
public static void main(java.lang.String[]);
flags: ACC_PUBLIC, ACC_STATIC
Code:
stack=1, locals=2, args_size=1
0: invokedynamic #19, 0 // InvokeDynamic #0:run:()Ljava/la ng/Runnable;
5: astore_1
6: return
LineNumberTable:
line 7: 0
line 10: 6
LocalVariableTable:
Start Length Slot Name Signature
0 7 0 args [Ljava/lang/String;
6 1 1 x Ljava/lang/Runnable;
}
import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodType;
import static java.lang.invoke.MethodHandles.lookup;
public class TestMethod {
static class ClassA {
public void println(String s) {
System.out.println(s);
}
}
public static void main(String[] args) throws Throwable {
Object obj = System.currentTimeMillis() % 2 == 0 ? System.out : new ClassA();
/*
* 无论obj最终是哪个实现类，下面这句都能正确调用到println方法
**/
getPrintlnMH(obj).invokeExact("icyfenix");
}
private static MethodHandle getPrintlnMH(Object reveiver) throws Throwable {
/*
* MethodType：代表“方法类型”，包含了方法的返回值（methodType（）的第一个参数）
* 和具体参数（methodType（） 第二个及以后的参数）
*/
MethodType mt = MethodType.methodType(void.class, String.class);
/*
* lookup（）方法来自于MethodHandles.lookup，这句的作用是在指定类中查找符合给定的方法名称、方法类型，
* 并且符合调用权限的方法句柄
* 因为这里调用的是一个虚方法，按照Java语言的规则，方法第一个参数是隐式的，代表该方法的接收者，也即是this指向的对象，
* 这个参数以前是放在参数列表中进行传递的，而现在提供了bindTo（）方法来完成这件事情
*/
return lookup().findVirtual(reveiver.getClass(), "println", mt).bindTo(reveiver);
}
}
import static java.lang.invoke.MethodHandles.lookup;
import java.lang.invoke.CallSite;
import java.lang.invoke.ConstantCallSite;
import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.MethodType;
public class InvokeDynamicTest {
public static void main(String[] args) throws Throwable {
INDY_BootstrapMethod().invokeExact("icyfenix");
}
public static void testMethod(String s) {
System.out.println("hello String：" + s);
}
public static CallSite BootstrapMethod(
MethodHandles.Lookup lookup,
String name,
MethodType mt) throws Throwable {
return new ConstantCallSite(
lookup.findStatic(InvokeDynamicTest.class, name, mt));
}
private static MethodType MT_BootstrapMethod() {
return MethodType.fromMethodDescriptorString(
"(Ljava/lang/invoke/MethodHandles $Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite;",
null);
}
private static MethodHandle MH_BootstrapMethod() throws Throwable {
return lookup().findStatic(
InvokeDynamicTest.class,
"BootstrapMethod",
MT_BootstrapMethod());
}
private static MethodHandle INDY_BootstrapMethod() throws Throwable {
CallSite cs = (CallSite) MH_BootstrapMethod().invokeWithArguments(
lookup(),
"testMethod",
MethodType.fromMethodDescriptorString("(Ljava/lang/String;)V", null));
return cs.dynamicInvoker();
}
}
import static java.lang.invoke.MethodHandles.lookup;
import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodType;
public class Test02 {
class GrandFather {
void thinking() {
System.out.println("i am grandfather");
}
}
class Father extends GrandFather {
void thinking() {
System.out.println("i am father");
}
}
class Son extends Father {
void thinking() {
try {
MethodType mt = MethodType.methodType(void.class);
MethodHandle mh = lookup().findVirtual(
GrandFather.class,
"thinking",
mt)
.bindTo(new Test02().new GrandFather());
mh.invokeExact();
} catch (Throwable e) {
}
}
}
public static void main(String[] args) {
(new Test02().new Son()).thinking();
}
}
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