Java Notes-12(Preferences API, The Logging API)

浏览数：26 / 时间：2015年06月08日

Summary:Preferences API, The Logging API

- The Preferences API is like a portable version of the Windows registry, a mini-database in which you can keep small amounts of information, accessible to all applications

-Preferences are stored logically in a tree.

Preferences prefs = Preferences.userRoot().node("oreilly/learningjava");
prefs.put("author", "Niemeyer");
prefs.putInt("edition", 4);
String author = prefs.get("author", "unknown");
int edition = prefs.getInt("edition", -1);

-Preferences are stored in two separate trees: system preferences and user preferences.System preferences are shared by all users of the Java installation. But user preferences
are maintained separately for each user;

-The node() method accepts either a relative or an absolute path.

Preferences prefs =
Preferences.userRoot().node("oreilly").node("learningjava");

-Often your application should be notified if changes are made to the preferences while it’s running. You can get updates on preference changes using the PreferenceChange
Listener and NodeChangeListener interfaces.

Preferences prefs =
Preferences.userRoot().node("/oreilly/learningjava");
prefs.addPreferenceChangeListener( new PreferenceChangeListener() {
public void preferenceChange(PreferenceChangeEvent e) {
System.out.println("Value: " + e.getKey()
+ " changed to "+ e.getNewValue() );
}
} );

-The java.util.logging package provides a highly flexible and easy-to-use logging framework for system information, error messages, and fine-grained tracing (debugging) output.

-The heart of the logging framework is the logger, an instance of java.util.logging.Logger .

package com.oreilly.learnjava;
public class Book {
static Logger log = Logger.getLogger("com.oreilly.learnjava.Book");

-The logger provides a wide range of methods to log messages; some take very detailed information, and some convenience methods take only a string for ease of use

log.warning("Disk 90% full.");
log.info("New user joined chat room.");

-a logger for the name “global” is provided in the static field Logger.global . You can use it as an alternative to the old standby System.out.println()

Logger.global.info("Doing foo...")

-Before a logger hands off a message to its handlers or its parent’s handlers, it first checks whether the logging level is sufficient to proceed. If the message doesn’t meet the required level, it is discarded at the source.

Level	Meaning
SEVERE	Application failure
WARNIN	Notification of potential problem
INFO	Messages of general interest to end users
CONFIG	Detailed system configuration information for administrators
FINE	Successively more detailed application tracing information for developers
FINER
FINEST