通过log4j发送JNI C stderr / stdout [英] Send JNI C stderr/stdout through log4j

问题描述

我的java应用程序使用JNI来调用用C编写的库。这个本机库将错误记录到stderr，但我想以某种方式通过我的log4j记录器重定向错误流。这可能吗？

My java app uses JNI to invoke a library written in C. This native library logs errors to stderr but I would like to redirect the error stream through my log4j logger somehow. Is this possible?

C库是外部的 - 我没有源代码，因此无法更改它。

The C library is external - I don't have the source, so cannot change it.

谢谢

推荐答案

注意：我没有尝试过这个答案; YMMV。

Note: I have not tried this answer; YMMV.

POSIX方法 freopen 将更改与流关联的基础文件。正如联机帮助页所述：freopen（）函数的主要用途是更改与标准文本流（stderr，stdin或stdout）关联的文件。

The POSIX method freopen will change the underlying file associated with a stream. As the manpage states: "The primary use of the freopen() function is to change the file associated with a standard text stream (stderr, stdin, or stdout)".

因此，您可以创建自己的JNI库，只需将流重定向到文件中。 然而，使这项工作有几个严重的障碍：

So, you could create your own JNI library that simply redirects the stream into a file. However, there are several serious roadblocks to making this work:

1. 你需要确保你的Java
   程序本身不使用标准的
   流，因为它们也将被重定向
   。
   的解决方法是在程序启动时将 System.out 等
   更改为其他内容。


2. 第二方库的
   可能会绕过标准的
   文本流，并直接写入底层文件描述符
   。不太可能，但可能是
   。我不能
   记住freopen（）只是
   更改缓冲流
   使用的文件描述符，或者实际
   重新打开底层fd。


3. 您还需要
   将
   更改连接到文件到记录器。

1. You'll need to ensure that your Java program doesn't itself use standard streams, because they'll be redirected too. A workaround for this is to change System.out et al to something else when your program starts up.
2. It's possible that the third-party library bypasses the standard text streams, and writes directly to the underlying file descriptor. It's unlikely but possible. I can't remember whether freopen() just changes the file descriptor used by the buffered stream, or actually re-opens the underlying fd.
3. You'll still have the problem of connecting changes to the "file" to a logger.

最后一点是迄今为止最大的：stdio写入操作系统级文件描述符。您必须创建一些Java级代码来读取该描述符并写入日志。我的第一个想法是你必须使用命名管道，然后启动一个新的Java线程来读取该管道。但是这不能移植到不同的操作系统，并且你将在程序的配置中管理管道名称。

That last point is by far the biggest: stdio writes to an OS-level file descriptor. You would have to create some Java-level code to read that descriptor and write to a log. My first thought is that you'd have to use a named pipe, and then spin up a new Java thread to read that pipe. But that won't be portable to different operating systems, and will that you manage the pipe name in your program's configuration.

假设这是一个服务器程序，并且不是自己处理标准IO流，我认为你最好的解决方案是用控制台记录器配置Log4J，并简单地将所有控制台输出重定向到一个文件。

Assuming that this is a server program, and does not itself process the standard IO streams, I think your best solution will be to configure Log4J with a console logger, and simply redirect all console output to a file.

或者谈谈对编写库的人来说，让他们添加可配置的日志记录。

Or talk to the people who wrote the library, to get them to add configurable logging.

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