使用java 8 lambda表达式打印错误的调试信息 [英] Printing debug info on errors with java 8 lambda expressions

问题描述

我想使用静态方法作为setter helper来捕获异常并打印有关失败的操作的调试信息。我不想只有异常细节。我想显示正在设置的属性，以便细节帮助快速调试问题。我正在使用Java 8。

I want to use a static method as setter helper that catch exceptions and print debug info about the operation that failed. I don't want the exception details only. I want to show what property was being set so that detail help to debug the problem quickly. I am working with Java 8.

如何提供或检测要设置的属性？

我希望删除示例中的名称字符串并获得相同的结果。

我知道我不能对所提供的提供的转换为lambda表达式的setter方法使用反射，然后转换为BiConsumer。

I know I can't use reflection over the supplied setter method supplied that is transformed to lambda expression and then to BiConsumer.

我得到这个，但需要提供属性名称。 / p>

I got this but the property name needs to be provided.

/** setter helper method **/
private static <E, V> void set(E o, BiConsumer<E, V> setter,
        Supplier<V> valueSupplier, String propertyName) {
    try {
        setter.accept(o, valueSupplier.get());
    } catch (RuntimeException e) {
        throw new RuntimeException("Failed to set the value of " + propertyName, e);
    }
}

示例：

    Person p = new Person();
    Supplier<String> nameSupplier1 = () ->  "MyName";
    Supplier<String> nameSupplier2 = () -> { throw new RuntimeException(); };
    set(p, Person::setName, nameSupplier1, "name");
    System.out.println(p.getName()); // prints MyName
    set(p, Person::setName, nameSupplier2, "name"); // throws exception with message  Failed to set the value of name
    System.out.println(p.getName()); // Does not execute

编辑：我知道反思没有帮助羔羊我知道AOP，我知道这可以用纯粹的反思来做，但是我想知道如果有更好的方法来完成这个使用Java 7不兼容的Java 8，那么它似乎应该对我来说。现在可以做一些事情，比如把传统方法传递给另一个。

I know reflection does not help with the lambdas. I know AOP and I know this can be made with pure reflection too but I want to know if there a better way to get this done with Java 8 that didn't exist with Java 7. It seems it should to me. Now it is possible to do things like to pass a setter method to another one.

推荐答案

case你希望方法引用作为唯一的输入，你可以调试它们到可打印的名称与以下的技巧：

In case you expect method references as the only input, you can debug them to printable names with the following trick:

public static void main(String[] args) {
  Person p = new Person();
  Supplier<String> nameSupplier1 = () -> "MyName";
  Supplier<String> nameSupplier2 = () -> { throw new RuntimeException(); };
  set(p, Person::setName, nameSupplier1);
  System.out.println(p.getName()); // prints MyName
  set(p, Person::setName, nameSupplier2); // throws exception with message
  System.out.println(p.getName()); // Does not execute
}

interface DebuggableBiConsumer<A, B> extends BiConsumer<A, B>, Serializable {}

private static <E, V> void set(
    E o, DebuggableBiConsumer<E, V> setter, Supplier<V> valueSupplier) {
  try {
    setter.accept(o, valueSupplier.get());
  } catch (RuntimeException e) {
    throw new RuntimeException("Failed to set the value of "+name(setter), e);
  }
}

private static String name(DebuggableBiConsumer<?, ?> setter) {
  for (Class<?> cl = setter.getClass(); cl != null; cl = cl.getSuperclass()) {
    try {
      Method m = cl.getDeclaredMethod("writeReplace");
      m.setAccessible(true);
      Object replacement = m.invoke(setter);
      if(!(replacement instanceof SerializedLambda))
        break;// custom interface implementation
      SerializedLambda l = (SerializedLambda) replacement;
      return l.getImplClass() + "::" + l.getImplMethodName();
    }
    catch (NoSuchMethodException e) {}
    catch (IllegalAccessException | InvocationTargetException e) {
      break;
    }
  }
  return "unknown property";
}

限制是打印不是很有用的lambda表达式的方法引用（引用包含lambda代码的合成方法）和未知属性用于界面的自定义实现。

The limitations are that it will print not very useful method references for lambda expressions (references to the synthetic method containing the lambda code) and "unknown property" for custom implementations of the interface.

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