如何使用MethodDelegation或Forwarding创建Buddy代理？

Question

当我尝试执行以下操作时，在加载调用中会出现异常：

  Field datasourceExtensionField = Grid.class.getDeclaredField("datasourceExtension");
  datasourceExtensionField.setAccessible(true);
  RpcDataProviderExtension rpcDataProviderExtension = (RpcDataProviderExtension) datasourceExtensionField.get(grid);

  Field activeItemHandlerField = RpcDataProviderExtension.class.getDeclaredField("activeItemHandler");
  activeItemHandlerField.setAccessible(true);
  Object activeItemHandler = activeItemHandlerField.get(rpcDataProviderExtension);

  Field keyMapperField = activeItemHandler.getClass().getDeclaredField("keyMapper");
  keyMapperField.setAccessible(true);
  KeyMapper original = (KeyMapper) keyMapperField.get(activeItemHandler);

  KeyMapper wrapper = new ByteBuddy() //
      .subclass(KeyMapper.class) //
      .defineField("original", KeyMapper.class, Visibility.PUBLIC) //
      .method(ElementMatchers.any()) //
      .intercept(Forwarding.toField("original")) //
      .method(ElementMatchers.named("get")) //
      .intercept(MethodDelegation.to(new KeyMapperWrapper(grid, original))) //
      .make() //
      .load(KeyMapperWrapper.class.getClassLoader()) //
      .getLoaded() //
      .newInstance();

  // give wrapper the reference to the original
  wrapper.getClass().getDeclaredField("original").set(wrapper, original);

  // replace original with wrapper
  keyMapperField.set(activeItemHandler, wrapper);

例外情况：

java.lang.VerifyError: Bad access to protected data in invokevirtual
Exception Details:
  Location:
    com/vaadin/server/KeyMapper$ByteBuddy$WlWljaQa.clone()Ljava/lang/Object; @4: invokevirtual
  Reason:
    Type 'com/vaadin/server/KeyMapper' (current frame, stack[0]) is not assignable to 'com/vaadin/server/KeyMapper$ByteBuddy$WlWljaQa'
  Current Frame:
    bci: @4
    flags: { }
    locals: { 'com/vaadin/server/KeyMapper$ByteBuddy$WlWljaQa' }
    stack: { 'com/vaadin/server/KeyMapper' }
  Bytecode:
    0x0000000: 2ab4 000c b600 1cb0                    

    at java.lang.Class.getDeclaredFields0(Native Method)
    at java.lang.Class.privateGetDeclaredFields(Class.java:2583)
    at java.lang.Class.getDeclaredField(Class.java:2068)
    at net.bytebuddy.implementation.LoadedTypeInitializer$ForStaticField.onLoad(LoadedTypeInitializer.java:101)
    at net.bytebuddy.implementation.LoadedTypeInitializer$Compound.onLoad(LoadedTypeInitializer.java:180)
    at net.bytebuddy.dynamic.TypeResolutionStrategy$Passive.initialize(TypeResolutionStrategy.java:75)
    at net.bytebuddy.dynamic.DynamicType$Default$Unloaded.load(DynamicType.java:4525)
    at net.bytebuddy.dynamic.DynamicType$Default$Unloaded.load(DynamicType.java:4514)
    at test.KeyMapperWrapper.patch(KeyMapperWrapper.java:62)

我显然不明白Forwarding应该如何工作，我做错了什么？

我的意图是用一个代理替换现有的KeyMapper，其中我覆盖一个方法，并将其余的方法委托给原始方法。

编辑:我现在也尝试使用MethodDelegation，它会引发相同的异常：

 .method(ElementMatchers.any()) //
 .intercept(MethodDelegation.to(original)) //
 .method(ElementMatchers.named("get")) //
 .intercept(MethodDelegation.to(new KeyMapperWrapper(grid, original))) //

Answer 1

这是拜德·巴迪的一个窃听器。但是，您要创建的类型是不合法的，Buddy无法提供正确的错误消息。子类化时，重写protected方法是合法的。但是，由于可见性约束，在另一种类型上调用这些方法并不总是合法的。因此，在转发调用时，只能重写public方法。你想要做的是匹配：

.method(ElementMatchers.isPublic())

错误不再发生的地方。我已经添加了一个补丁，在Buddy的下一个版本(1.5.8)中提供了这个错误消息。

Answer 2

用InvocationHandlerAdapter找到了一个解决方案。不过，我还是不明白为什么我最初的尝试没有奏效。

public class KeyMapperProxyHandler implements InvocationHandler
{
  @SuppressWarnings("unused")
  private static final Logger LOGGER              = Logger.getLogger(KeyMapperProxyHandler.class.getName());

  private Grid                m_grid              = null;
  private KeyMapper           m_originalKeyMapper = null;

  public KeyMapperProxyHandler(Grid grid, KeyMapper originalKeyMapper)
  {
    m_grid = grid;
    m_originalKeyMapper = originalKeyMapper;
  }

  /**
   * call after container data source has been set
   */
  public static void patch(Grid grid)
  {
    try
    {
      Field datasourceExtensionField = Grid.class.getDeclaredField("datasourceExtension");
      datasourceExtensionField.setAccessible(true);
      RpcDataProviderExtension rpcDataProviderExtension = (RpcDataProviderExtension) datasourceExtensionField.get(grid);

      Field activeItemHandlerField = RpcDataProviderExtension.class.getDeclaredField("activeItemHandler");
      activeItemHandlerField.setAccessible(true);
      Object activeItemHandler = activeItemHandlerField.get(rpcDataProviderExtension);

      Field keyMapperField = activeItemHandler.getClass().getDeclaredField("keyMapper");
      keyMapperField.setAccessible(true);
      KeyMapper original = (KeyMapper) keyMapperField.get(activeItemHandler);

      KeyMapperProxyHandler proxyHandler = new KeyMapperProxyHandler(grid, original);

      KeyMapper proxy = new ByteBuddy() //
          .subclass(KeyMapper.class) //
          .method(ElementMatchers.any()) //
          .intercept(InvocationHandlerAdapter.of(proxyHandler)) //
          .method(ElementMatchers.named("get")) //
          .intercept(MethodDelegation.to(proxyHandler)) //
          .make() //
          .load(KeyMapperProxyHandler.class.getClassLoader()) //
          .getLoaded() //
          .newInstance();

      keyMapperField.set(activeItemHandler, proxy);
    }
    catch(Throwable t)
    {
      throw new RuntimeException(t);
    }
  }

  /**
   * override for get method
   */
  public Object get(String key)
  {
    Object staleItemId = m_originalKeyMapper.get(key);
    Optional freshItemId = m_grid.getContainerDataSource().getItemIds().stream().filter(i -> i.equals(staleItemId)).findAny();
    //    LOGGER.log(Level.INFO, "intercept: stale=" + staleItemId + ", fresh=" + freshItemId);
    return freshItemId.isPresent() ? freshItemId.get() : null;
  }

  /**
   * proxy all other methods
   */
  @Override
  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable
  {
    return method.invoke(m_originalKeyMapper, args);
  }
}

Answer 3

这并不是对我提出的问题的回答，而是对我的问题的另外两种解决方案：

我说服自己，我可以在尚未使用的时候替换所需的对象引用。因此，我决定不委托/代理任何东西，并丢弃原始对象实例，完全用字节巴迪动态类型替换它：

public class GridKeyMapperPatch
{
  @SuppressWarnings("unused")
  private static final Logger LOGGER = Logger.getLogger(GridKeyMapperPatch.class.getName());

  private Grid                m_grid = null;

  public GridKeyMapperPatch(Grid grid)
  {
    m_grid = grid;
  }

  /**
   * call immediately after setting container data source
   */
  public static void patch(Grid grid)
  {
    try
    {
      GridKeyMapperPatch gridKeyMapperPatch = new GridKeyMapperPatch(grid);

      KeyMapper patchedKeyMapper = new ByteBuddy() //
          .subclass(KeyMapper.class) //
          .method(ElementMatchers.named("get")) //
          .intercept(MethodDelegation.to(gridKeyMapperPatch)) //
          .make() //
          .load(GridKeyMapperPatch.class.getClassLoader()) //
          .getLoaded() //
          .newInstance();

      Field datasourceExtensionField = Grid.class.getDeclaredField("datasourceExtension");
      datasourceExtensionField.setAccessible(true);
      RpcDataProviderExtension rpcDataProviderExtension = (RpcDataProviderExtension) datasourceExtensionField.get(grid);

      Field activeItemHandlerField = RpcDataProviderExtension.class.getDeclaredField("activeItemHandler");
      activeItemHandlerField.setAccessible(true);
      Object activeItemHandler = activeItemHandlerField.get(rpcDataProviderExtension);

      Field keyMapperField = activeItemHandler.getClass().getDeclaredField("keyMapper");
      keyMapperField.setAccessible(true);
      keyMapperField.set(activeItemHandler, patchedKeyMapper);
    }
    catch(Throwable t)
    {
      throw new RuntimeException(t);
    }
  }

  public Object get(@SuperCall Callable superCall, String key) throws Exception
  {
    Object staleItemId = superCall.call();
    Optional freshItemId = m_grid.getContainerDataSource().getItemIds().stream().filter(i -> i.equals(staleItemId)).findAny();
    LOGGER.log(Level.INFO, "intercept: stale=" + staleItemId + ", fresh=" + freshItemId);
    return freshItemId.isPresent() ? freshItemId.get() : null;
  }
}

退一步，我发现，由于所讨论的类和方法是公开的，所以我通常只需将其子类：

public class GridTools
{
  @SuppressWarnings("unused")
  private static final Logger LOGGER = Logger.getLogger(GridTools.class.getName());

  /**
   * call immediately after setting container data source
   */
  public static void replaceKeyMapper(Grid grid) throws Exception
  {
    Field datasourceExtensionField = Grid.class.getDeclaredField("datasourceExtension");
    datasourceExtensionField.setAccessible(true);
    RpcDataProviderExtension rpcDataProviderExtension = (RpcDataProviderExtension) datasourceExtensionField.get(grid);

    Field activeItemHandlerField = RpcDataProviderExtension.class.getDeclaredField("activeItemHandler");
    activeItemHandlerField.setAccessible(true);
    Object activeItemHandler = activeItemHandlerField.get(rpcDataProviderExtension);

    Field keyMapperField = activeItemHandler.getClass().getDeclaredField("keyMapper");
    keyMapperField.setAccessible(true);
    keyMapperField.set(activeItemHandler, new NonCachingKeyMapper(grid));
  }

  private static class NonCachingKeyMapper extends KeyMapper
  {
    private Grid m_grid = null;

    public NonCachingKeyMapper(Grid grid)
    {
      m_grid = grid;
    }

    @Override
    public Object get(String key)
    {
      Object staleItemId = super.get(key);
      Optional freshItemId = m_grid.getContainerDataSource().getItemIds().stream().filter(i -> i.equals(staleItemId)).findAny();
      LOGGER.log(Level.INFO, "intercept: stale=" + staleItemId + ", fresh=" + freshItemId);
      return freshItemId.isPresent() ? freshItemId.get() : null;
    }
  }
}