Java: Logging API - Revision history

Onnowpurbo at 04:20, 6 September 2011

2011-09-06T04:20:07Z

Onnowpurbo at 02:28, 5 September 2011

2011-09-05T02:28:36Z

Onnowpurbo at 01:56, 5 September 2011

2011-09-05T01:56:22Z

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Onnowpurbo: New page: Java Logging This article describes how to use the Logging API in Java programs. It includes an example for creating a HTML logger. Table of Contents 1. Overview 1.1. Logging in Ja...

2011-08-06T02:45:02Z

New page: Java Logging This article describes how to use the Logging API in Java programs. It includes an example for creating a HTML logger. Table of Contents 1. Overview 1.1. Logging in Ja...

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Java Logging

This article describes how to use the Logging API in Java programs. It includes an example for creating a HTML logger.

Table of Contents

1. Overview

1.1. Logging in Java
1.2. Create a logger
1.3. Level
1.4. Handler
1.5. Formatter
1.6. Log Manager
1.7. Best Practices

2. Example
3. Thank you
4. Questions and Discussion
5. Links and Literature

1. Overview
1.1. Logging in Java

The JDK contains the "Java Logging API". Via a logger you can save text to a central place to report on errors, provide additional information about your program, etc. This logging API allows to configure how messages are written by which class with which priority.
1.2. Create a logger

The package java.util.logging provides the logging capabilities via the class Logger.

To create a logger in your Java coding.

import java.util.logging.Logger;

private final static Logger LOGGER = Logger.getLogger(MyClass.class .getName());

1.3. Level

The log levels define the severity of a message. The class Level is used to define which messages should be written to the log.

Die Log Levels in descending order are:

SEVERE (highest)

WARNING

INFO

CONFIG

FINE

FINER

FINEST

In addition to that you have also the levels OFF and ALL to turn the logging of or to log everything.

For example the following will set the logger to level info which means all messages with severe, warning and info will be logged.

LOGGER.setLevel(Level.INFO);

1.4. Handler

Each logger can have access to several handler.

The handler receives the log message from the logger and exports it to a certain target

A handler can be turn off with setLevel(Level.OFF) and turned on with setLevel(...)

You have several standard handler, e.g.

ConsoleHandler: Write the log message to console

FileHandler: Writes the log message to file

Log Levels INFO and higher will be automatically written to the console.
1.5. Formatter

Each handlers output can be configured with a formatter

Available formatter

SimpleFormatter Generate all messages as text

XMLFormatter Generates XML output for the log messages

You can also build your own formatter. The following is an example of a formatter which will use create HTML output.

package logging;

import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.logging.Formatter;
import java.util.logging.Handler;
import java.util.logging.Level;
import java.util.logging.LogRecord;

//This custom formatter formats parts of a log record to a single line
class MyHtmlFormatter extends Formatter
{
// This method is called for every log records
public String format(LogRecord rec)
{
StringBuffer buf = new StringBuffer(1000);
// Bold any levels >= WARNING
buf.append("<tr>");
buf.append("<td>");

if (rec.getLevel().intValue() >= Level.WARNING.intValue())
{
buf.append("<b>");
buf.append(rec.getLevel());
buf.append("</b>");
} else
{
buf.append(rec.getLevel());
}
buf.append("</td>");
buf.append("<td>");
buf.append(calcDate(rec.getMillis()));
buf.append(' ');
buf.append(formatMessage(rec));
buf.append('\n');
buf.append("<td>");
buf.append("</tr>\n");
return buf.toString();
}

private String calcDate(long millisecs)
{
SimpleDateFormat date_format = new SimpleDateFormat("MMM dd,yyyy HH:mm");
Date resultdate = new Date(millisecs);
return date_format.format(resultdate);
}

// This method is called just after the handler using this
// formatter is created
public String getHead(Handler h)
{
return "<HTML>\n<HEAD>\n" + (new Date()) + "\n</HEAD>\n<BODY>\n<PRE>\n"
+ "<table border>\n "
+ "<tr><th>Time</th><th>Log Message</th></tr>\n";
}

// This method is called just after the handler using this
// formatter is closed
public String getTail(Handler h)
{
return "</table>\n </PRE></BODY>\n</HTML>\n";
}
}

1.6. Log Manager

The log manager is responsible for creating and managing the logger and the maintenance of the configuration.

We could set the logging level for a package, or even a set of packages, by calling the LogManager.setLevel(String name, Level level) method. So, for example, we could set the logging level of all loggers "logging" to Level.FINE by making this call:

LogManager.getLogManager().setLevel("logging", Level.FINE)

1.7. Best Practices

It is common practice to use the fully qualified name of each class whose activity is being logged as a message category because this allows developers to fine-tune log settings for each class.

Using the fully qualified class name of your class as the name of your Logger is the approach recommended by the Logging API documentation.
2. Example

This example is stored in the project "de.vogella.logger".

Create your own formatter.

package logging;

import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.logging.Formatter;
import java.util.logging.Handler;
import java.util.logging.Level;
import java.util.logging.LogRecord;

//This custom formatter formats parts of a log record to a single line
class MyHtmlFormatter extends Formatter
{
// This method is called for every log records
public String format(LogRecord rec)
{
StringBuffer buf = new StringBuffer(1000);
// Bold any levels >= WARNING
buf.append("<tr>");
buf.append("<td>");

if (rec.getLevel().intValue() >= Level.WARNING.intValue())
{
buf.append("<b>");
buf.append(rec.getLevel());
buf.append("</b>");
} else
{
buf.append(rec.getLevel());
}
buf.append("</td>");
buf.append("<td>");
buf.append(calcDate(rec.getMillis()));
buf.append(' ');
buf.append(formatMessage(rec));
buf.append('\n');
buf.append("<td>");
buf.append("</tr>\n");
return buf.toString();
}

private String calcDate(long millisecs)
{
SimpleDateFormat date_format = new SimpleDateFormat("MMM dd,yyyy HH:mm");
Date resultdate = new Date(millisecs);
return date_format.format(resultdate);
}

// This method is called just after the handler using this
// formatter is created
public String getHead(Handler h)
{
return "<HTML>\n<HEAD>\n" + (new Date()) + "\n</HEAD>\n<BODY>\n<PRE>\n"
+ "<table border>\n "
+ "<tr><th>Time</th><th>Log Message</th></tr>\n";
}

// This method is called just after the handler using this
// formatter is closed
public String getTail(Handler h)
{
return "</table>\n </PRE></BODY>\n</HTML>\n";
}
}

Initialize the logger.

package logging;

import java.io.IOException;
import java.util.logging.FileHandler;
import java.util.logging.Formatter;
import java.util.logging.Level;
import java.util.logging.Logger;
import java.util.logging.SimpleFormatter;

public class MyLogger {
static private FileHandler fileTxt;
static private SimpleFormatter formatterTxt;

static private FileHandler fileHTML;
static private Formatter formatterHTML;

static public void setup() throws IOException {
// Create Logger
Logger logger = Logger.getLogger("");
logger.setLevel(Level.INFO);
fileTxt = new FileHandler("Logging.txt");
fileHTML = new FileHandler("Logging.html");

// Create txt Formatter
formatterTxt = new SimpleFormatter();
fileTxt.setFormatter(formatterTxt);
logger.addHandler(fileTxt);

// Create HTML Formatter
formatterHTML = new MyHtmlFormatter();
fileHTML.setFormatter(formatterHTML);
logger.addHandler(fileHTML);
}
}

Use the logger.

package logging;

import java.io.IOException;
import java.util.logging.Level;
import java.util.logging.Logger;

public class UseLogger {
// Always use the classname, this way you can refactor
private final static Logger LOGGER = Logger.getLogger(UseLogger.class
.getName());

public void writeLog() {
// Set the LogLevel to Severe, only severe Messages will be written
LOGGER.setLevel(Level.SEVERE);
LOGGER.severe("Info Log");
LOGGER.warning("Info Log");
LOGGER.info("Info Log");
LOGGER.finest("Really not important");

// Set the LogLevel to Info, severe, warning and info will be written
// Finest is still not written
LOGGER.setLevel(Level.INFO);
LOGGER.severe("Info Log");
LOGGER.warning("Info Log");
LOGGER.info("Info Log");
LOGGER.finest("Really not important");
}

public static void main(String[] args) {
UseLogger logger = new UseLogger();
try {
MyLogger.setup();
} catch (IOException e) {
e.printStackTrace();
throw new RuntimeException("Problems with creating the log files");
}
logger.writeLog();
}
}

==Referensi==

* http://www.vogella.de/articles/Logging/article.html

==Pranala Menarik==

* [[Pemrograman Java]]
* [[Java Menggunakan Eclipse]]
* [[Java Menggunakan NetBeans]]
* [[Pemrogramman Menggunakan Aptana IDE]]
* [[Programman Android | Pemrogramman Android]]

[[Category: Programming]]
[[Category: Java]]

@@ Line 6: / Line 6: @@
 ==Logging di Java==
-The JDK contains the "Java Logging API". Via a logger you can save text to a central place to report on errors, provide additional information about your program, etc. This logging API allows to configure how messages are written by which class with which priority.
+Dalam JDK terdapat "Java Logging API". Melalui sebuah logger kita dapat menyimpan text ke lokasi yang terpusat untuk menulis laporan saat terjadi error, memberikan informasi tambahan tentang program kita, dll. Melalui logging API memungkinkan konfigurasi bagaimana message di tulis dengan class yang mana dengan prioritas yang mana.
 ==Membuat sebuah Logger==
-The package java.util.logging provides the logging capabilities via the class Logger.
+Paket java.util.logging memberikan kemampuan logging melalui class Logger.
-To create a logger in your Java coding.
+Untuk membuat sebuah logger di source code java yang kita buat
   import java.util.logging.Logger;

@@ Line 4: / Line 4: @@
-. Overview
+==Logging di Java==
 The JDK contains the "Java Logging API". Via a logger you can save text to a central place to report on errors, provide additional information about your program, etc. This logging API allows to configure how messages are written by which class with which priority.
-.2. Create a logger
 The package java.util.logging provides the logging capabilities via the class Logger.
@@ Line 20: / Line 20: @@
-.3. Level
+==Level==
 The log levels define the severity of a message. The class Level is used to define which messages should be written to the log.
@@ Line 26: / Line 26: @@
 Die Log Levels in descending order are:
-    SEVERE (highest)
+ SEVERE (highest)
+ WARNING
-    WARNING
+ INFO
+ CONFIG
-    INFO
+ FINE
+ FINER
-    CONFIG
+ FINEST
 In addition to that you have also the levels OFF and ALL to turn the logging of or to log everything.
@@ Line 48: / Line 42: @@
-.4. Handler
+==Handler==
 Each logger can have access to several handler.
@@ Line 64: / Line 58: @@
 Log Levels INFO and higher will be automatically written to the console.
-.5. Formatter
+==Formatter==
 Each handlers output can be configured with a formatter
@@ Line 142: / Line 136: @@
-.6. Log Manager
+==Log Manager==
 The log manager is responsible for creating and managing the logger and the maintenance of the configuration.
@@ Line 152: / Line 146: @@
-.7. Best Practices
+==Best Practices==
 It is common practice to use the fully qualified name of each class whose activity is being logged as a message category because this allows developers to fine-tune log settings for each class.
@@ Line 158: / Line 152: @@
 Using the fully qualified class name of your class as the name of your Logger is the approach recommended by the Logging API documentation.
-. Example
+==Example==
 This example is stored in the project "de.vogella.logger".