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	Java Programming Language Basics: Java Logging API Basics
	Java Bits: Chapters from Murach's Java Servlets and JSP
	Making Sense of Java Classes: Format Class
	Program Challenge
	Sun's Online Courses: Programming With the Java 3D API: A Technical Overview
	Sun's Instructor Led Courses: Java Programming Language for Visual Basic Programmers
	2004 JavaOne Conference and Article: Moscone Center, San Francisco, California
	For More Information: Read articles, Tech Tips, trails, and tutorials that provide more information on the topics discussed here.

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Java Programming Language Basics

Java Logging API Basics

New to the Java 2 Platform, Standard Edition, verison 1.4, the java.util.logging package offers the Java Logging API. This logging facility allows you to embed messages inside your code, and configure at runtime whether or not the mesages should be displayed or logged. If you don't need the information all the time, turn it off, and enable it when the user needs it (or you need it to get debug output from the user). Want to control the level of messages logged such that you only want serious logging messages from a particular package? This too is configurable.

In the simplest case, you get the logger and log the message:

• Get the Logger for the currrent package Logger logger = Logger.getLogger(packageName);



• Log your message logger.log(level, text, exception)

To demonstrate, the following program logs a severe message:

package com.sun.java;
    import java.util.logging.*;

    public class LogSample {
        private static Logger logger =
                         Logger.getLogger("com.sun.java");
        public static void main(String args[]) {
            logger.log(Level.SEVERE, "Testing - Level = SEVERE");
        }
    }

First, compile the program. Since the program is in a package, be sure to use the -d option to send the .class file to the appropriate subdirectory:

javac -d . LogSample.java

Then, run the program:

java com.sun.java.LogSample

By default, logging output goes to the console. Depending upon when you run the program, you'll get an appropriate time stamp.

May 15, 2004 9:08:33 AM com.sun.java.LogSample main
SEVERE: Testing - Level = SEVERE

The reason you get the Logger for a particular package is so that you can enable or disable logging for a particular package. Before we look at that though, let us explain the logging levels, of which there are seven.

• SEVERE
• WARNING
• INFO
• CONFIG
• FINE
• FINER
• FINEST

By having different logging levels, you can control when a message is logged and the level of detail. So, for a SEVERE-level message, you might dump a stack trace at a location where the program shouldn't get to under normal circumstances. For INFO-level, you might have entry / exit from methods. And, FINEST-level might be as each line is executed. There is no hard definition of what each level must print out. It is completely up to you during your development. There is a small amount of overhead to test if the current logging level is enabled for the given package, but having the logging information available during testing allows a better level of debug information to come back to the development team from say a quality assurance (QA) or user testing group.

There's much more to the logging facility than just saying, here's a message, log it. For instance, to send out to a file, use a FileHandler:

package com.sun.java;
import java.util.logging.*;
import java.io.*;

public class LogSample2 {
  private static Logger logger =
                   Logger.getLogger("com.sun.java");
  public static void main(String args[]) throws IOException {
      FileHandler fh = new FileHandler("log.out");
      // Send logger output to FileHandler.
      logger.addHandler(fh);
// Log all
logger.setLevel(Level.ALL);
      logger.log(Level.FINE, "Testing - Level = FINE");
  }
}

This sends the log message to the file log.out, as XML.

<?xml version="1.0" encoding="windows-1252" standalone="no"?>
<!DOCTYPE log SYSTEM "logger.dtd">
<log>
<record>
<date>2004-05-26T09:41:20</date>
<millis>1085578880859</millis>
<sequence>0</sequence>
<logger>com.sun.java</logger>
<level>FINE</level>
<class>com.sun.java.LogSample2</class>
<method>main</method>
<thread>10</thread>
<message>Testing - Level = FINE</message>
</record>
</log>

The system also provides other handlers, like the MemoryHandler for storing the last 'n' records, without worrying about formatting until you wish to display / save. Through constructive use of the logging facility, you can better maintain and service all your software. For additional information on the available APIs, see the Java Logging Overview document.

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Java Bits

Chapters from Murach's Java Servlets and JSP
by Andrea Steelman and Joel Murach

Last month you had an introduction to JavaServer Pages (JSP) technologies, and you learned to create an online quiz. If you want to learn more about using JSP pages and want a book to get you going, consider Murach's Java Servlets and JSP by Andrea Steelman and Joel Murach.

Murach's Java Servlets and JSP is designed for the programmer who has experience with the Java programming language, but is new to developing web applications. It provides hands-on experience while you learn the skills necessary to develop server-side applications at a professional level. In addition, the bound-in CD contains the software and source code presented in the book.

Read two sample chapters on java.sun.com

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Making Sense of the Java Class

Format Class

Format is an abstract class for formatting locale-sensitive information such as dates, messages, and numbers.

Format defines the programming interface for formatting locale-sensitive objects into Strings (the format method), and for parsing Strings back into objects (the parseObject method).

A parseObject method parses any string formatted by its format method. However, there may be exceptional cases where this is not possible. For example, a format method might create two adjacent integer numbers with no separator in between, and in this case the parseObject could not tell which digits belong to which number.

Subclassing

The Java 2 platform provides three specialized subclasses of Format: DateFormat, MessageFormat, and NumberFormat.

Concrete subclasses must implement three methods:

1. format(Object obj, StringBuffer toAppendTo, FieldPosition pos)
2. formatToCharacterIterator(Object obj)
3. parseObject(String source, ParsePosition pos)

These general methods allow polymorphic parsing and formatting of objects and are used, for example, by MessageFormat. Subclasses often also provide additional format methods for specific input types as well as parse methods for specific result types. Any parse method that does not take a ParsePosition argument should throw ParseException when no text in the required format is at the beginning of the input text.

Most subclasses will also implement the following factory methods:

1. getInstance for getting a useful format object appropriate for the current locale
2. getInstance(Locale) for getting a useful format object appropriate for the specified locale

In addition, some subclasses may also implement other getXxxxInstance methods for more specialized control. For example, the NumberFormat class provides getPercentInstance and getCurrencyInstance methods for getting specialized number formatters.

Subclasses of Format that allow programmers to create objects for locales (with getInstance(Locale) for example) must also implement the following class method:

public static Locale[] getAvailableLocales()

And finally, subclasses may define a set of constants to identify the various fields in the formatted output. These constants are used to create a FieldPosition object which identifies what information is contained in the field and its position in the formatted result. These constants should be named item_FIELD where item identifies the field. For examples of these constants, see ERA_FIELD and its friends in DateFormat.

From the Java API Documentation

Test what you learned in this article about logging

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Program Challenge

Using the Logging API, create a logging Handler that sends logged messages to a separate window. Demonstrate the handler in a simple test program.

See a possible solution

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Sun's Web Courses

Programming With the Java 3D API: A Technical Overview

This course presents basic concepts and key features of the Java 3D API. It also discusses a graphics programming paradigm, providing an overview of creating visual three-dimensional (3D) objects and features to be applied, such as lighting, shading, animation, user navigation and interaction within a 3D scene. As a powerful component of Java Media Technologies, the Java 3D API extends the Java Programming language to the 3D graphics world.

Find out more

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Sun's Instructor Led Courses

Java Programming Language for Visual Basic Programmers

The Java Programming Language for Visual Basic Programmers course provides students with an in-depth introduction to object-oriented programming concepts and the fundamentals of the Java programming language. Students learn to construct basic Java technology applications using a variety of object-oriented techniques.

Find out more

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2004 JavaOne Conference and Article

Moscone Center, San Francisco, California

JavaOne, Sun's 2004 Worldwide Java Developer Conference
June 28 - July 1, 2004
Moscone Center, San Francisco, California

The JavaOne conference is less than a month away. Hundreds of in-depth technical and Birds-of-a-Feather sessions, interactive Hands-on Labs, visionary General Session presentations, and the Java University program equip you with the skills, solutions, and knowledge you need to be efficient and successful in your role as a Java technology professional.

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For More Information

• Using the J2SE 1.4 Logging API in Systems Management
  
  
• Java Logging APIs
  
  
• Tracing and Logging
  
  
• Class Format
  
  
• 2004 JavaOne Conference
  
  

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Downloading the Java 2 Platform

For most Java development, you need the class libraries, compiler, tools, and runtime environment provided with the J2SE development kit.

• Download J2SE
• Bookmark the specifications
• New to Java Programming Center

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