JDK：如何以编程方式启用 PlatformLogger

我需要以编程方式启用某些 JDK7 内部类的日志记录。

这就是我在应用程序初始化时所做的事情：

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

where httpLogger是一个强引用（以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。

如果我通过记录配置文件来执行此操作，它将按预期工作。

我可能是错的，但我认为这与我不理解有关PlatformLogger它是在 Java 7 中引入的，据我所知，它现在用于所有 JDK 内部日志记录。或者也许我只是不明白 J.U.L.足够好。

我猜如果我这样做的话它会起作用：

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

but PlatformLogger类位于我无法引用的包中。

What is PlatformLogger ?

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

我的解决方案出现在一个小型自定义小部件演示程序的开头：

// 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将 rootLogger 级别设置为 ALL，但这正是我所需要的。