(6)Method的invoke方法解析

网上有一遍文章讲解得比较深入也比较详细，地址如下：https://www.cnblogs.com/onlywujun/p/3519037.html

我这边就简单演示一下，invoke的调用链过程 ,先准备演示类：

public class A {
    public void foo(String name) {
        System.out.println("Hello, " + name);
    }
}

public class TestClassLoad {
    public static void main(String[] args) throws Exception {
        Class<?> clz = Class.forName(A.class.getName());
        Object o = clz.newInstance();
        Method m = clz.getMethod("foo", String.class);
        for (int i = 0; i < 16; i++) {
            if(i==15){
                m.invoke(o, Integer.toString(i));
            }else{
                m.invoke(o, Integer.toString(i));
            }
        }
    }
}

在控制台加上-XX:+TraceClassLoading的参数 ，运行

image.png

[Loaded java.lang.Void from C:\Program Files\Java\jdk1.8.0_92\jre\lib\rt.jar]
[Loaded com.java.reflect.invoke.A from file:/D:/Eclipse2018Data/personProject/jdk/java-lang-reflect/target/classes/]
Hello, 0
Hello, 1
Hello, 2
Hello, 3
Hello, 4
Hello, 5
Hello, 6
Hello, 7
Hello, 8
Hello, 9
Hello, 10
Hello, 11
Hello, 12
Hello, 13
Hello, 14
[Loaded sun.reflect.ClassFileConstants from C:\Program Files\Java\jdk1.8.0_92\jre\lib\rt.jar]
[Loaded sun.reflect.AccessorGenerator from C:\Program Files\Java\jdk1.8.0_92\jre\lib\rt.jar]
[Loaded sun.reflect.MethodAccessorGenerator from C:\Program Files\Java\jdk1.8.0_92\jre\lib\rt.jar]
[Loaded sun.reflect.ByteVectorFactory from C:\Program Files\Java\jdk1.8.0_92\jre\lib\rt.jar]
[Loaded sun.reflect.ByteVector from C:\Program Files\Java\jdk1.8.0_92\jre\lib\rt.jar]
[Loaded sun.reflect.ByteVectorImpl from C:\Program Files\Java\jdk1.8.0_92\jre\lib\rt.jar]
[Loaded sun.reflect.ClassFileAssembler from C:\Program Files\Java\jdk1.8.0_92\jre\lib\rt.jar]
[Loaded sun.reflect.UTF8 from C:\Program Files\Java\jdk1.8.0_92\jre\lib\rt.jar]
[Loaded sun.reflect.Label from C:\Program Files\Java\jdk1.8.0_92\jre\lib\rt.jar]
[Loaded sun.reflect.Label$PatchInfo from C:\Program Files\Java\jdk1.8.0_92\jre\lib\rt.jar]
[Loaded sun.reflect.MethodAccessorGenerator$1 from C:\Program Files\Java\jdk1.8.0_92\jre\lib\rt.jar]
[Loaded sun.reflect.ClassDefiner from C:\Program Files\Java\jdk1.8.0_92\jre\lib\rt.jar]
[Loaded sun.reflect.ClassDefiner$1 from C:\Program Files\Java\jdk1.8.0_92\jre\lib\rt.jar]
[Loaded sun.reflect.GeneratedMethodAccessor1 from __JVM_DefineClass__]
Hello, 15
[Loaded java.lang.Shutdown from C:\Program Files\Java\jdk1.8.0_92\jre\lib\rt.jar]
[Loaded java.lang.Shutdown$Lock from C:\Program Files\Java\jdk1.8.0_92\jre\lib\rt.jar]

主要看Loaded sun.reflect.GeneratedMethodAccessor1 这一句，表示在invoke调用15次之后用了jdk自带的方法生成器来进行调用

invoke 调用是由MethodAccessor来进行调用的，而具体的NativeMethodAccessorImpl和DelegatingMethodAccessorImpl是由ReflectionFactory创建而来的，DelegatingMethodAccessorImpl这里是一个委托，会把调用链关系转换为NativeMethodAccessorImpl的invoke方法进行调用

    public MethodAccessor newMethodAccessor(Method var1) {
        checkInitted();
        if (noInflation && !ReflectUtil.isVMAnonymousClass(var1.getDeclaringClass())) {
            return (new MethodAccessorGenerator()).generateMethod(var1.getDeclaringClass(), var1.getName(), var1.getParameterTypes(), var1.getReturnType(), var1.getExceptionTypes(), var1.getModifiers());
        } else {
            NativeMethodAccessorImpl var2 = new NativeMethodAccessorImpl(var1);
            DelegatingMethodAccessorImpl var3 = new DelegatingMethodAccessorImpl(var2);
            var2.setParent(var3);
            return var3;
        }
    }

而NativeMethodAccessorImpl的invoke方法如下，默认调用的是本地的invoke0方法，但是会有一个调用次数的判断，如果调用次数大于15，则由MethodAccessorGenerator生成方法的MethodAccessorImpl的实现，然后改变DelegatingMethodAccessorImpl的委托类设置为jdk生成方法访问器，则调用次数大于15的时候是由jdk的生成方法访问器进行方法调用的

    public Object invoke(Object var1, Object[] var2) throws IllegalArgumentException, InvocationTargetException {
        if (++this.numInvocations > ReflectionFactory.inflationThreshold() && !ReflectUtil.isVMAnonymousClass(this.method.getDeclaringClass())) {
            MethodAccessorImpl var3 = (MethodAccessorImpl)(new MethodAccessorGenerator()).generateMethod(this.method.getDeclaringClass(), this.method.getName(), this.method.getParameterTypes(), this.method.getReturnType(), this.method.getExceptionTypes(), this.method.getModifiers());
            this.parent.setDelegate(var3);
        }

        return invoke0(this.method, var1, var2);
    }
  private static native Object invoke0(Method var0, Object var1, Object[] var2);