JDK：如何以编程方式启用 PlatformLogger

Question

我需要以编程方式为某些 JDK7 内部类启用日志记录。

这是我在应用程序初始化时所做的：

httpLogger = Logger.getLogger("sun.net.www.protocol.http.HttpURLConnection");
httpLogger.setLevel(Level.FINEST);

httpLogger 是一个强引用（为了避免记录器被垃圾收集）。我还将 ConsoleHandler 的级别设置为 ALL。但是我无法得到任何输出。

如果我通过日志记录配置文件执行此操作，它会按预期工作。

我可能错了，但我认为这与我不理解 Java 7 中引入的 PlatformLogger 以及 - afaik - 现在用于所有 JDK 内部日志记录有关。或者也许我只是不明白 J.U.L.很好。

如果我这样做，我猜它会起作用：

httpLogger = PlatformLogger.getLogger("sun.net.www.protocol.http.HttpURLConnection");
httpLogger.setLevel(Level.FINEST);

但PlatformLogger 类位于我无法引用的包中。

PlatformLogger 是什么？

这是 JavaDoc：

Platform logger provides an API for the JRE components to log
messages.  This enables the runtime components to eliminate the
static dependency of the logging facility and also defers the
java.util.logging initialization until it is enabled.
In addition, the PlatformLogger API can be used if the logging
module does not exist.

If the logging facility is not enabled, the platform loggers
will output log messages per the default logging configuration
(see below). In this implementation, it does not log the
the stack frame information issuing the log message.

When the logging facility is enabled (at startup or runtime),
the java.util.logging.Logger will be created for each platform
logger and all log messages will be forwarded to the Logger
to handle.

Logging facility is "enabled" when one of the following
conditions is met:
1) a system property "java.util.logging.config.class" or
    "java.util.logging.config.file" is set
2) java.util.logging.LogManager or java.util.logging.Logger
    is referenced that will trigger the logging initialization.

Default logging configuration:
  global logging level = INFO
  handlers = java.util.logging.ConsoleHandler
  java.util.logging.ConsoleHandler.level = INFO
  java.util.logging.ConsoleHandler.formatter = java.util.logging.SimpleFormatter

Limitation:
<JAVA_HOME>/lib/logging.properties is the system-wide logging
configuration defined in the specification and read in the
default case to configure any java.util.logging.Logger instances.
Platform loggers will not detect if <JAVA_HOME>/lib/logging.properties
is modified. In other words, unless the java.util.logging API
is used at runtime or the logging system properties is set,
the platform loggers will use the default setting described above.
The platform loggers are designed for JDK developers use and
this limitation can be workaround with setting
-Djava.util.logging.config.file system property.

@since 1.7

Answer 1

我在一个小的自定义小部件演示程序开头出现的解决方案：

// Log all focus messages.
final Logger rootLogger = Logger.getLogger("");
rootLogger.setLevel(Level.ALL);
final ConsoleHandler consoleHandler = new ConsoleHandler();
consoleHandler.setLevel(Level.ALL);
// Because there are a lot of focus messages, make them
// a little easier to read by logging only the message.
consoleHandler.setFormatter(new Formatter() {
    @Override
    public String format(LogRecord record) {
        return "FOCUS: " + record.getMessage() + '\n';
    }
});
final Logger logger = Logger.getLogger("java.awt.focus.Component");
logger.setLevel(Level.ALL);
logger.setUseParentHandlers(false);
logger.addHandler(consoleHandler);

我不清楚为什么我需要获取然后将 rootLogger 级别设置为 ALL，但这正是我所需要的。

Answer 2

你必须先阅读它在说什么。

 the PlatformLogger API can be used if the logging module does not exist

好吧，如果您想使用该 API，那么您可以使用以下 import 语句。

import sun.util.logging.PlatformLogger;

以上是对您目的地的完整参考。

更多参考请访问BUG Tracking of Java