简单例子

import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.MethodType;public class MHT {private String name;// 构造方法public MHT(String name) {this.name = name;}// 公共方法public String publicTest() {return name + "'publicTest";}// 静态方法public static String publicStaticTest() {return "'publicStaticTest";}// 私有方法private String test(int param) {switch (param) {case 1:return "suych1";case 2:return "suych2";case 3:return "suych3";default:return "suych4";}}// Get方法public String getName() {return name;}// Set方法public void setName(String name) {this.name = name;}public static void main(String[] args) throws Throwable {// 构造方法MethodType mtConstructor = MethodType.methodType(void.class, String.class);  //返回值类型，参数类型MethodHandle mhConstructor = MethodHandles.lookup().findConstructor(MHT.class, mtConstructor);MHT businessHandle = ( MHT ) mhConstructor.invokeExact("suych");System.out.println(businessHandle.getName());// 公共方法MethodType mtPublic = MethodType.methodType(String.class);  //返回值类型MethodHandle mhPublic = MethodHandles.lookup().findVirtual(MHT.class, "publicTest", mtPublic);String resultPublic = ( String ) mhPublic.invokeExact(businessHandle);System.out.println(resultPublic);// 静态方法MethodType mtPublicStatic = MethodType.methodType(String.class);MethodHandle mhPublicStatic = MethodHandles.lookup().findStatic(MHT.class, "publicStaticTest",mtPublicStatic);String resultPublicStatic = ( String ) mhPublicStatic.invokeExact();System.out.println(resultPublicStatic);// 私有方法MethodType mtPrivate = MethodType.methodType(String.class, int.class); //返回值类型，参数类型MethodHandle mhPrivate = MethodHandles.lookup().findSpecial(MHT.class, "test", mtPrivate,MHT.class);String resultPrivate = ( String ) mhPrivate.invokeExact(businessHandle, 1);System.out.println(resultPrivate);// Set方法MethodHandle mhSet = MethodHandles.lookup().findSetter(MHT.class, "name", String.class);mhSet.invokeExact(businessHandle, "A");System.out.println(businessHandle.name);// Get方法MethodHandle mhGet = MethodHandles.lookup().findGetter(MHT.class, "name", String.class);String resultGet = ( String ) mhGet.invokeExact(businessHandle);System.out.println(resultGet);}}

输出：

suych   构造方法输出
suych'publicTest   公共方法输出
'publicStaticTest   静态方法输出
suych1   私有方法输出
A   Set方法输出
A   Get方法输出

基于MethodHandle实现的调用Runtime执行系统命令

import java.io.InputStream;
import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.MethodType;
import java.util.Scanner;/*** @author yz*/
public class MethodHandlesTest {public static void main(String[] args) {try {String               str          = "arp -a";Class                runtimeClass = Runtime.class;MethodHandles.Lookup lookup       = MethodHandles.lookup();// Runtime rt = Runtime.getRuntime()MethodHandle methodHandle = lookup.findStatic(runtimeClass, "getRuntime", MethodType.methodType(runtimeClass));// 获取Runtime的exec方法MethodHandle execMethod = lookup.findVirtual(runtimeClass, "exec", MethodType.methodType(Process.class, new Class[]{String.class}));// 获取Process的getInputStream方法MethodHandle inputStreamMethod = lookup.findVirtual(Process.class, "getInputStream", MethodType.methodType(InputStream.class));// 调用Runtime.getRuntime().exec(xxx).getInputStream()InputStream in = (InputStream) inputStreamMethod.invoke(execMethod.invoke(methodHandle.invoke(), str));// 输出InputStream内容到Scanner scanner = new Scanner(in).useDelimiter("\\A");System.out.println(scanner.hasNext() ? scanner.next() : "");} catch (Throwable t) {t.printStackTrace();}}}

JAVA反射修改private，final值

FinalName.java

class FinalName {public final String name="init";
}

PrivateName.java

class PrivateName {private String name = "init";public String getName() {return name;}
}

Test.java

import java.lang.reflect.Field;public class Test {public static void main(String[] args) throws Exception {PrivateName privateName = new PrivateName();FinalName finalName = new FinalName();
//        System.out.println(finalName.name);modify(privateName, "name", "private change");modify(finalName, "name", "final change");System.out.println(privateName.getName());System.out.println(finalName.name);}public static void modify(Object object, String fieldName, Object newFieldValue) throws Exception {Field field = object.getClass().getDeclaredField(fieldName);field.setAccessible(true);field.set(object, newFieldValue);System.out.println(field.get(object));}
}

输出结果,private修饰的变量结果已经被修改，但是final修改正常但是获取的依然是原先的值，这是因为内联优化。

private change
final change
private change
init

如果将FinalName.java修改为通过构造方法给final修饰的属性赋值。

class FinalName {public final String name;FinalName(String name) {this.name = name;}
}
FinalName Finalname = FinalName("aaaaaa");

再次运行Test.java，发现final修饰的变量已经被修改。

private change
final change
private change
final change

总结：private修饰的变量可以通过反射的方法将值修改，需要设置访问权限为true。field.setAccessible(true);
final修饰的变量如果是直接赋值，则对属性值进行修改无效。如果是通过构造方法修改属性的值，则可以通过反射的方法修改final修饰的变量。

通过反射方式执行命令。

import java.io.InputStream;
import java.lang.reflect.Method;
import java.util.Scanner;
public class ReflectionTest {public static void exec() {try {System.out.println(Runtime.class.getMethod("exec", String.class).invoke(Runtime.class.getMethod("getRuntime").invoke(null), "curl -i localhost:8000"));} catch (Exception e) {e.printStackTrace();}}public static void main(String[] args) {try {String str = "arp -a";// java.lang.RuntimeString runtime = new String(new byte[]{106, 97, 118, 97, 46, 108, 97, 110, 103, 46, 82, 117, 110, 116, 105, 109, 101});// Runtime.classClass<?> c = Class.forName(runtime);// 获取getRuntime方法，Runtime.getRuntime()Method m1 = c.getMethod(new String(new byte[]{103, 101, 116, 82, 117, 110, 116, 105, 109, 101}));// 获取Runtime的exec方法，rt.exec(xxx)Method m2 = c.getMethod(new String(new byte[]{101, 120, 101, 99}), String.class);// Runtime.getRuntime().exec(str)Object obj2 = m2.invoke(m1.invoke(null), str);// 获取命令执行结果Process类的getInputStream()方法Method m = obj2.getClass().getMethod(new String(new byte[]{103, 101, 116, 73, 110, 112, 117, 116, 83, 116, 114, 101, 97, 109}));m.setAccessible(true);// process.getInputStream()InputStream in = (InputStream) m.invoke(obj2, new Object[]{});// 输出InputStream内容到Scanner scanner = new Scanner(in).useDelimiter("\\A");System.out.println(scanner.hasNext() ? scanner.next() : "");} catch (Throwable t) {t.printStackTrace();}}}

看下为什么获取命令执行结果Process类的getInputStream()方法访问权限需要设置true。
跟入java.lang.ProcessImpl类

getInputStream方法返回stdout_stream是私有变量


注释掉，则会报下面这样的错误

参考链接：
https://docs.oracle.com/javase/7/docs/api/java/lang/invoke/MethodType.html
https://mp.weixin.qq.com/s/mlqjOlhefcsO9z51cw4S7w
https://blog.csdn.net/yhd723948277/article/details/82661870