javac -parameters标志的缺点 [英] Drawbacks of javac -parameters flag

问题描述

我想尝试一些在运行时需要参数名称的框架功能，所以我需要用 -parameters 编译我的应用程序，它将存储参数的名称JVM字节码。

I want to try some frameworks features that required names of parameter in runtime, so I need to compile my app with -parameters and it will store the names of parameter in JVM byte code.

除了这个参数用法的jar / war大小外还有哪些缺点？

Which drawbacks except the size of jar/war exist of this parameter usage?

推荐答案

JEP 118 <涵盖了为类文件格式添加参数名称的方法/ a>，它是用Java 8提供的。有一些关于为什么在OpenJDK电子邮件线程中包含参数名称是可选的讨论此处和这里。简而言之，声明参数名称可选的原因是关于类文件大小，兼容性表面和敏感信息暴露的担忧。

The addition of parameter names to the class file format is covered by JEP 118, which was delivered in Java 8. There was a little bit of discussion about why inclusion of parameter names was made optional in OpenJDK email threads here and here. Briefly, the stated reasons to make parameter names optional are concerns about class file size, compatibility surface, and exposure of sensitive information.

兼容性表面的问题值得进一步讨论。上面链接的一个线程表示更改参数名称是二进制兼容的更改。这是事实，但仅限于JVM二进制兼容性概念的严格上下文。也就是说，更改方法的参数名称永远不会改变JVM是否可以链接该方法。但该声明一般不符合兼容性。

The issue of compatibility surface deserves some additional discussion. One of the threads linked above says that changing a parameter name is a binary compatible change. This is true, but only in the strict context of the JVM's notion of binary compatibility. That is, changing a parameter name of a method will never change whether or not that method can be linked by the JVM. But the statement doesn't hold for compatibility in general.

历史上，参数名称被视为局部变量名称。 （毕竟，它们是本地的。）您可以随意更改它们，方法之外的任何内容都不会受到影响。但是，如果启用对参数名称的反射访问，则突然您无法在不考虑程序的其他部分可能正在使用它的情况下更改名称。更糟糕的是，除非您对参数名称的所有使用都有严格的测试用例，否则没有任何东西可以告诉您，或者您有一个非常好的静态分析器可以找到这些情况（我不知道）。

Historically, parameter names have been treated like local variable names. (They are, after all, local in scope.) You could change them at will and nothing outside the method will be affected. But if you enable reflective access to parameter names, suddenly you can't change a name without thinking about what other parts of the program might be using it. Worse, there's nothing that can tell you unless you have strict test cases for all uses of parameter names, or you have a really good static analyzer that can find these cases (I'm not aware of one).

与使用Jackson（一个JSON处理库）的问题相关的注释，该函数具有将方法参数名称映射到JSON属性名称的功能。这可能非常方便，但这也意味着如果更改参数名称，JSON绑定可能会中断。更糟糕的是，如果程序基于Java方法参数名称生成JSON结构，则更改方法参数名称可能会静默更改数据格式或有线协议。显然，在这样的环境中，可靠地使用此功能意味着您必须进行非常好的测试，并在代码周围添加注释，指示不得更改哪些参数名称。

The comments linked to a question about using Jackson (a JSON processing library) which has a feature that maps method parameter names to JSON property names. This may be quite convenient, but it also means that if you change a parameter name, JSON binding might break. Worse, if the program is generating JSON structures based on Java method parameter names, then changing a method parameter name might silently change a data format or wire protocol. Clearly, in such an environment, using this feature reliably means that you have to have very good tests, plus comments sprinkled around the code indicating what parameter names mustn't be changed.

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