用于包装方法的 Java 注释 [英] Java annotation for wrapping a method

问题描述

我有很多基本遵循这种模式的样板代码:

I have a lot of boilerplate code that basically follows this pattern:

function doSomething() {
  try {
    [implementation]
    [implementation]
    [implementation]
    [implementation]
  } catch (Exception e) {
    MyEnv.getLogger().log(e);
  } finally {
    genericCleanUpMethod();
  }
}

我很想创建我自己的注释来清理我的代码:

I'd love to create my own annotation to clean my code up a bit:

@TryCatchWithLoggingAndCleanUp
function doSomething() {
  [implementation]
  [implementation]
  [implementation]
  [implementation]
}

方法签名变化很大(取决于方法的实际实现)，但样板文件 try/catch/finally 部分始终相同.

The method signatures vary wildly (depending on the actual implementation of the method), but the boilerplate try/catch/finally part is always the same.

我想到的注释会自动用整个try...catch...finally hoopla 包装带注释方法的内容.

The annotation I have in mind would automatically wrap the contents of the annotated method with the whole try...catch...finally hoopla.

我已经四处寻找一种简单的方法来做到这一点，但一无所获.我不知道，也许我只是看不到所有带注释的树木的树林.

I've searched high and low for a straightforward way to do this, but have found nothing. I don't know, maybe I just can't see the woods for all the annotated trees.

任何有关我如何实现此类注释的指示将不胜感激.

Any pointers on how I might implement such an annotation would be greatly appreciated.

推荐答案

要做到这一点，您需要一些 AOP 框架来在您的方法周围使用代理.该代理将捕获异常并执行 finally 块.坦率地说，如果你还没有使用支持 AOP 的框架，我不确定我是否会使用一个来保存这几行代码.

To do this, you would need some AOP framework that would use a proxy around your method. This proxy would catch the exception and execute the finally block. Quite frankly, if you don't use a framework supporting AOP already, I'm not sure I would use one just to save these few lines od code.

不过，您可以使用以下模式以更优雅的方式执行此操作:

You could use the following pattern to do this in a more elegant way, though:

public void doSomething() {
    logAndCleanup(new Callable<Void>() {
        public Void call() throws Exception {
            implementationOfDoSomething();
            return null;
        }
    });
}

private void logAndCleanup(Callable<Void> callable) {
    try {
        callable.call();
    } 
    catch (Exception e) {
        MyEnv.getLogger().log(e);
    } 
    finally {
        genericCleanUpMethod();
    }
}

我只是使用 Callable 作为接口，但你可以定义自己的 Command 接口:

I just used Callable<Void> as an interface, but you could define your own Command interface:

public interface Command {
    public void execute() throws Exception;
}

从而避免使用通用 Callable 并从 Callable 返回 null 的需要.

and thus avoid the need to use a generic Callable<Void> and return null from the Callable.

如果你想从你的方法中返回一些东西，那么让 logAndCleanup() 方法通用.这是一个完整的示例:

in case you want to return something from your methods, then make the logAndCleanup() method generic. Here's a complete example:

public class ExceptionHandling {
    public String doSomething(final boolean throwException) {
        return logAndCleanup(new Callable<String>() {
            public String call() throws Exception {
                if (throwException) {
                    throw new Exception("you asked for it");
                }
                return "hello";
            }
        });
    }

    public Integer doSomethingElse() {
        return logAndCleanup(new Callable<Integer>() {
            public Integer call() throws Exception {
                return 42;
            }
        });
    }

    private <T> T logAndCleanup(Callable<T> callable) {
        try {
            return callable.call();
        }
        catch (Exception e) {
            System.out.println("An exception has been thrown: " + e);
            throw new RuntimeException(e); // or return null, or whatever you want
        }
        finally {
            System.out.println("doing some cleanup...");
        }
    }

    public static void main(String[] args) {
        ExceptionHandling eh = new ExceptionHandling();

        System.out.println(eh.doSomething(false));
        System.out.println(eh.doSomethingElse());
        System.out.println(eh.doSomething(true));
    }
}

使用 Java 8，包装的代码可以更漂亮一些:

EDIT : And with Java 8, the wrapped code can be a bit prettier :

public String doSomething(final boolean throwException) {
    return logAndCleanup(() -> {                
        if (throwException) {
            throw new Exception("you asked for it");
        }
        return "hello";                
    });
}

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