在Java(或任何其他带有受控异常的语言)中,当创建您自己的异常类时,您如何决定它应该被检查还是未检查?
我的直觉是,在调用者可能能够以某种有效的方式恢复的情况下,将调用checked异常,而作为未检查的异常则更多地用于不可恢复的情况,但我对其他人的想法感兴趣。
在Java(或任何其他带有受控异常的语言)中,当创建您自己的异常类时,您如何决定它应该被检查还是未检查?
我的直觉是,在调用者可能能够以某种有效的方式恢复的情况下,将调用checked异常,而作为未检查的异常则更多地用于不可恢复的情况,但我对其他人的想法感兴趣。
当前回答
这不仅仅是从异常中恢复的能力问题。在我看来,最重要的是调用者是否对捕获异常感兴趣。
如果您编写的库用于其他地方,或应用程序中的较低级别层,请询问自己调用者是否有兴趣捕获(了解)您的异常。如果他不是,那么使用一个未检查的异常,这样就不会给他带来不必要的负担。
这是许多框架使用的哲学。尤其是Spring和hibernate——它们精确地将已知的受控异常转换为未检查异常,因为Java中过度使用了受控异常。我能想到的一个例子是来自json.org的JSONException,这是一个受检查的异常,最烦人的是——它应该是不受检查的,但开发人员根本没有考虑到这一点。
顺便说一下,大多数情况下,调用者对异常的兴趣与从异常中恢复的能力直接相关,但情况并非总是如此。
其他回答
在任何一个足够大的系统上,有很多层,检查异常是无用的,因为无论如何,您需要一个架构级策略来处理异常将如何处理(使用故障屏障)。
使用受控异常,您的错误处理策略是微管理的,在任何大型系统上都无法承受。
大多数情况下,您不知道错误是否“可恢复”,因为您不知道API的调用者位于哪一层。
假设我创建了一个StringToInt API,用于将整数的字符串表示形式转换为Int。如果API是用“foo”字符串调用的,我必须抛出检查异常吗?它可以恢复吗?我不知道,因为在他的层中,我的StringToInt API的调用者可能已经验证了输入,如果抛出这个异常,它要么是一个错误,要么是一个数据损坏,它是不可恢复的这一层。
在这种情况下,API的调用者不想捕获异常。他只想让异常“冒出来”。如果我选择了一个受控异常,这个调用者将有大量无用的catch块,只能人为地重新抛出异常。
大多数时候,什么是可恢复的取决于API的调用者,而不是API的编写者。API不应该使用受控异常,因为只有未受控异常才允许选择捕获或忽略异常。
You can call it a checked or unchecked exception; however, both types of exception can be caught by the programmer, so the best answer is: write all of your exceptions as unchecked and document them. That way the developer who uses your API can choose whether he or she wants to catch that exception and do something. Checked exceptions are a complete waste of everyone's time and it makes your code a shocking nightmare to look at. Proper unit testing will then bring up any exceptions that you may have to catch and do something with.
来自Java学习者:
When an exception occurs, you have to either catch and handle the exception, or tell compiler that you can't handle it by declaring that your method throws that exception, then the code that uses your method will have to handle that exception (even it also may choose to declare that it throws the exception if it can't handle it). Compiler will check that we have done one of the two things (catch, or declare). So these are called Checked exceptions. But Errors, and Runtime Exceptions are not checked for by compiler (even though you can choose to catch, or declare, it is not required). So, these two are called Unchecked exceptions. Errors are used to represent those conditions which occur outside the application, such as crash of the system. Runtime exceptions are usually occur by fault in the application logic. You can't do anything in these situations. When runtime exception occur, you have to re-write your program code. So, these are not checked by compiler. These runtime exceptions will uncover in development, and testing period. Then we have to refactor our code to remove these errors.
我使用的规则是:永远不要使用未经检查的异常!(或者当你看不到任何方法的时候)
有一种情况正好相反:永远不要使用受控异常。我不愿意在辩论中偏袒任何一方(双方都有很好的论据!),但相当多的专家认为,事后看来,受控例外是一个错误的决定。
对于一些讨论,请查看维基百科网站的“已检查异常的价值可疑”。另一个早期广泛争论的例子是Rod Waldhoff的博客文章。
以下是我的“最终经验法则”。 我使用:
方法代码中由于调用者导致的失败而出现的未检查的异常(这涉及一个显式和完整的文档) 检查异常失败由于被调用,我需要明确的任何人想要使用我的代码
与前面的答案相比,这是使用一种或另一种(或两种)例外的明确理由(人们可以同意或不同意)。
对于这两个异常,我将为我的应用程序创建自己的未检查和已检查的异常(这里提到过,这是一个很好的实践),除了非常常见的未检查异常(如NullPointerException)
例如,下面这个特定函数的目标是创建(如果已经存在,则获取)一个对象, 意义:
the container of the object to make/get MUST exist (responsibility of the CALLER => unchecked exception, AND clear javadoc comment for this called function) the other parameters can not be null (choice of the coder to put that on the CALLER: the coder will not check for null parameter but the coder DOES DOCUMENT IT) the result CAN NOT BE NULL (responsibility and choice of the code of the callee, choice which will be of great interest for the caller => checked exception because every callers MUST take a decision if the object can not be created/found, and that decision must be enforced at the compilation time: they can not use this function without having to deal with this possibility, meaning with this checked exception).
例子:
/**
* Build a folder. <br />
* Folder located under a Parent Folder (either RootFolder or an existing Folder)
* @param aFolderName name of folder
* @param aPVob project vob containing folder (MUST NOT BE NULL)
* @param aParent parent folder containing folder
* (MUST NOT BE NULL, MUST BE IN THE SAME PVOB than aPvob)
* @param aComment comment for folder (MUST NOT BE NULL)
* @return a new folder or an existing one
* @throws CCException if any problems occurs during folder creation
* @throws AssertionFailedException if aParent is not in the same PVob
* @throws NullPointerException if aPVob or aParent or aComment is null
*/
static public Folder makeOrGetFolder(final String aFoldername, final Folder aParent,
final IPVob aPVob, final Comment aComment) throws CCException {
Folder aFolderRes = null;
if (aPVob.equals(aParent.getPVob() == false) {
// UNCHECKED EXCEPTION because the caller failed to live up
// to the documented entry criteria for this function
Assert.isLegal(false, "parent Folder must be in the same PVob than " + aPVob); }
final String ctcmd = "mkfolder " + aComment.getCommentOption() +
" -in " + getPNameFromRepoObject(aParent) + " " + aPVob.getFullName(aFolderName);
final Status st = getCleartool().executeCmd(ctcmd);
if (st.status || StringUtils.strictContains(st.message,"already exists.")) {
aFolderRes = Folder.getFolder(aFolderName, aPVob);
}
else {
// CHECKED EXCEPTION because the callee failed to respect his contract
throw new CCException.Error("Unable to make/get folder '" + aFolderName + "'");
}
return aFolderRes;
}