在Java中删除对System.out的访问 [英] Removing access to System.out in java

问题描述

我维护着一个应用程序，该应用程序充当多个单独程序的容器.这些程序具有自己专用的日志记录功能，即它们记录的所有内容都记录到一个特殊的日志文件中.

I maintain an application which acts as a container for multiple individual programs. These programs have their own dedicated logging facility, i.e. everything they log does to a special log file.

尽管如此，应用程序开发人员似乎爱全程抛出System.out.println和e.printStackTrace调用，这使得在运行容器时无法维护一个干净的控制台.

Nevertheless, application developers seem to love to throw System.out.println and e.printStackTrace calls all over, making it impossible to maintain a clean console when running the container.

如何防止这些应用程序污染System.out和System.err?

How can I prevent these applications from polluting System.out and System.err?

实施说明:

• 应用程序使用Log4j进行记录；
• 该容器还使用控制台进行日志记录，但是它严格保留用于生命周期事件和问题，因此我仍然需要该控制台；
• 使用自定义类加载器加载应用程序，但不应用安全检查.

更新:

仅重定向System.out无效，因为它会重定向所有输出，因此类似的操作会失败:

Simply redirecting System.out would not work since it redirects all output, so something like this fails:

    System.setOut(new PrintStream(new OutputStream() {

        @Override
        public void write(int b) {

            throw new Error("Not on my watch you don't");

        }
    }));

    Logger logger = Logger.getLogger(Runner.class);
    logger.info("My log message");

这应该成功.

更新2:

使用类似于以下代码的代码加载和配置应用程序

The applications are loaded and configured using code similar to

App app = new UrlClassLoader(...).loadClass(className)).newInstance();
app.setLogger(loggerForClass(app));

Log4j是从系统类加载器加载的.

Log4j is loaded from the system class loader.

推荐答案

此处的关键是在重定向输出流(例如

The key here is to configure log4j before redirecting the output streams, e.g.

BasicConfigurator.configure();
System.setOut(...);
System.setErr(...);

System.out.println("I fail");
Logger.getLogger(...).info("I work");

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