Hotswap code with lambda 失败，说明方法无法删除

Question

问题

热交换 lambda 失败。

进程

我尝试热交换包含 lambda 的方法体。

1。热插拔代码

public class Example {
    private int x;
    public void print (int y) {
       Consumer<Integer> consumer = (key) -> System.out.println(key);
    }
}

2。一个例子

 //Methods after sugar removal
First use code 1 to compile a class and put it in the directory, then run code 2 hot change
        //from static to instance method failed
        1、Consumer<Integer> consumer = (key) -> System.out.println(key);     
        2、Consumer<Integer> hot = (key) -> System.out.println(key + "" + this);
        //After desugar method
       private static synthetic lambda$print[=11=](Ljava/lang/Integer;)V
       private synthetic lambda$print(Ljava/lang/Integer;)V

        //change static method params count successful
        String str = "args";
        Consumer<Integer> methodCount1 = (key) -> System.out.println(key);
        Consumer<Integer> methodCount2 = (key) -> System.out.println(key + str);
        private static synthetic lambda$print(Ljava/lang/Integer;)V
        private static synthetic lambda$print(Ljava/lang/String;Ljava/lang/Integer;)V

        //change instance method params count failed
        Consumer<Integer> instanceCount2 = (key) -> System.out.println(key + "" + this);
        Consumer<Integer> instanceCount3 = (key) -> System.out.println(key + str + this);
        private synthetic lambda$print(Ljava/lang/Integer;)V
        private synthetic lambda$print(Ljava/lang/String;Ljava/lang/Integer;)V


        //from nothing add or delete lambd  successful (compile static method)

        //from nothing add or delete lambd  fail (compile instance method)
        Consumer<Integer> instaceMethod = (key) -> System.out.println(this);
        private synthetic lambda$print(Ljava/lang/Integer;)V
        hot.accept(1);
        consumer.accept(1);

3。热插拔类型代码

代理代码

   public class JavaAgent {

        public static void agentmain(String agentArgs, Instrumentation inst) throws Exception {
            System.out.println("开始热更新");
            // 获得所有已被装载的class文件
            Class[] classes = inst.getAllLoadedClasses();
            for (Class clazz : classes) {
                if (clazz.getName().equalsIgnoreCase(agentArgs) || clazz.getName().equalsIgnoreCase("com.jason.Normal")) {
                    System.out.println(clazz.getName());
                    inst.addTransformer(new ClassFileTransformer() {

                        @Override
                        public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {

                                //System.out.println("hotswap class name :" + className);
                                String str = "";
                                if (className.contains("Example")){
                                    str = "Example.class";
                                }else if (className.contains("Norm")){
                                    str = "Normal.class";
                                }else {
                                    return null;
                                }
                                byte[] bytes = fileToBytes(new File("C:\hot\"+str));
                                return bytes;
                        }
                    }, true);
                    // 重转换
                    inst.retransformClasses(clazz);
                }
            }
            System.out.println("热更新结束");
        }

        public static byte[] fileToBytes(File file) {
            try {
                FileInputStream in = new FileInputStream(file);
                byte[] bytes = new byte[in.available()];
                in.read(bytes);
                in.close();
                return bytes;
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return null;
        }
     }

热插拔代码

     public class HotSwap {
         public static void hot(){
                try {
                    List<VirtualMachineDescriptor> list = VirtualMachine.list();
                    for (VirtualMachineDescriptor vmd : list) {
                            VirtualMachine virtualMachine = null;
                            virtualMachine = VirtualMachine.attach(vmd.id());
                            // 获得代理类位置 + 传递参数
                            virtualMachine.loadAgent("C:\Users\DELL\Downloads\JavaHotSwap-master\JavaAgent\target\agentmain.jar", "com.jason.Example");
                            virtualMachine.detach();
                    }
                } catch (AttachNotSupportedException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                } catch (AgentLoadException e) {
                    e.printStackTrace();
                } catch (AgentInitializationException e) {
                    e.printStackTrace();
                }
            }  
}

主要代码

int i = new Random().nextInt();
        new Example().print(i);
       // Normal.show();
       // System.out.println("hot");
        HotSwap.hot();
        new Example().print(i);
       // Normal.show();
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

例外

java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at sun.instrument.InstrumentationImpl.loadClassAndStartAgent(InstrumentationImpl.java:386)
    at sun.instrument.InstrumentationImpl.loadClassAndCallAgentmain(InstrumentationImpl.java:411)
Caused by: java.lang.UnsupportedOperationException: class redefinition failed: attempted to add a method
    at sun.instrument.InstrumentationImpl.retransformClasses0(Native Method)
    at sun.instrument.InstrumentationImpl.retransformClasses(InstrumentationImpl.java:144)
    at com.jason.JavaAgent.agentmain(JavaAgent.java:60)
    ... 6 more
com.sun.tools.attach.AgentInitializationException: Agent JAR loaded but agent failed to initialize
    at sun.tools.attach.HotSpotVirtualMachine.loadAgent(HotSpotVirtualMachine.java:121)
    at com.jason.HotSwap.hot(HotSwap.java:23)
    at com.jason.Main.main(Main.java:33)
Agent failed to start!
Exception in thread "Attach Listener"

3。想法

我知道编译字节码的时候，仪器是不能改变（增删改查）方法的。为什么我可以随意修改静态方法，却不能修改实例方法？

Answer 1

你无意中遇到了 JDK-8192936。根据错误报告，围绕 Java 6 所做的更改使实现接受有关添加或删除 private static 和 private final 方法的更改，尽管规范继续声明这不是支持。

因此，当将 lambda 表达式脱糖为 private static 方法时，它适用于所有未捕获 this 的 lambda 表达式，更改它们恰好有效。

对于捕获 this 的 lambda 表达式，行为取决于编译器。将它们脱糖到没有 final 修饰符的 private 实例方法中已经变得很普遍，因此，它们不受报告行为的影响。但原则上，编译器可以添加冗余 final 修饰符。也可以将这种 lambda 表达式的主体转换为 static 方法，接受 this 引用作为参数。旧编译器会发生这种情况。

根据报告的修复不是考虑规范中“这些限制可能会在未来版本”的声明，而是删除功能以匹配字面上的规范。将有一个选项 -XX:{+|-}AllowRedefinitionToAddOrDeleteMethods 来切换以 JDK 13 开头的行为一段时间。

Hotswap code with lambda 失败，说明方法无法删除

Hotswap code with lambda fails, indicating that the method cannot be deleted

java

lambda

bytecode

hotswap

问题

进程

1。热插拔代码

2。一个例子

3。热插拔类型代码

3。想法