使用FrontPage可以很方便的预览vm文件，见梁夏峰的《Velocity之Web实践》一文：http://www.javayou.com/showlog.jspe?log_id=528，其中这样说道：“

       打开FrontPage（或其他类似工具）网页编辑器，点击"工具－选项－配置编辑器"，上面列出了FrontPage能打开的文件，点击添加，填入文件类型：vm，编辑器名称：FrontPage，命令：C:\Program Files\Microsoft Office\Office\frontpg.exe（FrontPage运行的完整路径，可从已有的文件类型中Copy出完整路径），点击打开界面的确定后，我们从FrontPage的文件菜单中选择打开文件，选择上面新建的sample.vm，怎么样，编辑、预览和修改都一目了然吧（如下图），即使不清楚VTL的，也可以通过简单的手册查询知道（一般都不会用到吧），这样对于网页设计师、开发人员和维护人员来说，都是很容易的事。而如果你使用了一些开发工具，如Jbuilder则在tools－proference的编辑类型里，在Html档增加.vm的支持，则就可以进行编辑和用html预览器预览了，其他的开发工具自己摸索吧。 ”

       然而在DreamWeaver中我怎么样改配置也不行。于是用google大神上网求助，终于发现了这个好东西：DreamWeaver的Velocity插件：http://velocity.gilluminate.com/，作者比我强多了，自己动手，丰衣足食啊，呵呵。下载后用用DreamWeaver的插件管理器安装，对，就是那个VelocitySuite.mxp文件。

       这样一来，DreamWeaver在编辑vm时能提供的功能就大大超过其他html编辑器了。爽啊。

       不过作者还说了几个注意点，如果你在使用过程中觉得有问题，可以去他的主页http://velocity.gilluminate.com/看看。这里就不再多言了。
 

 原文作者：天才    Kylin项目小组

import org.apache.log4j.*;
 
public class LogTest {
 
 
    static Logger logger = Logger.getLogger(LogTest.class.getName());
 
    public static void main(String[] args) {
 
        PropertyConfigurator.configure ( “.\\src\log4j.properties”)；
logger.debug("Debug ...");
 
        logger.info("Info ...");
 
        logger.warn("Warn ...");
 
        logger.error("Error ...");
 
    }
}
程序说明：
① static Logger logger = Logger.getLogger(LogTest.class.getName());就是创建一个属于LogTest类的Logger对象，创建时要告知Logger你当前的Class是什么。
② PropertyConfigurator.configure ( “log4j.properties”)就是说使用当前工程目录下的src文件夹中的log4j.properties文件作为配置文件。若将log4j.properties放在工程根目录下也可不写此句，程序会自动找到配置文件。
③ logger.debug就是输出debug的信息，logger.info就是输出提示信息，logger.warn就是显示警告信息，logger.error就是显示错误信息。
下面是配置文件log4j.properties的内容：
log4j.rootCategory=DEBUG, stdout，R
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%5p (%F:%L) - %m%n
log4j.appender.R=org.apache.log4j.RollingFileAppender
log4j.appender.R.File=log.txt
log4j.appender.R.MaxFileSize=100KB
log4j.appender.R.MaxBackupIndex=1
log4j.appender.R.layout=org.apache.log4j.PatternLayout
log4j.appender.R.layout.ConversionPattern=%d{yyyy MMM dd HH:mm:ss} %-5p %c - %m%n
程序说明：
① log4j.rootCategory=DEBUG, stdout，R
就是说我要显示所有优先权等於和高于Debug的信息。
"stdout"，”R”表示我定义了两个输出端(随便什么名字都好)。
②下面的三行说stdout输出端其实是标准输出Console，也就是屏幕。输出的格式是PatternLayout。转换方式是%5p (%F:%L) - %m%n，即前五格用来显示优先权，再显示当前的文件名，加当前的行数。最后是logger.debug()或logger.info()或logger.warn()或logger.error()里的信息。%n表示回车空行。
③再加上下面六行则log信息不光显示在屏幕上，而且将被保存在一个叫"log.txt"的文件里，文件最大为100KB。如果文件大小超过100KB，文件会被备份成"log.txt.1"，新的"log.txt"继续记录log信息。
接下来我们可以改变log4j.properties，而不需重新编译就可以控制log信息是否显示、log信息的输出端类型、输出方式、输出格式，等等。举例如下：
①在log4j.properties文件里把"log4j.rootCategory=DEBUG,stdout,R"改写成"log4j.rootCategory=OFF, stdout,R"，这样所有的log信息都不会显示了；解决了本文开始提出的问题。
②在log4j.properties文件里把"log4j.rootCategory=DEBUG,stdout,R"改写成"log4j.rootCategory=INFO, stdout,R"，这样只显示INFO, WARN, ERROR的log信息，而DEBUG信息不会被显示；

在web程序中使用log4j注意问题
1、    由于jsp或servlet在执行状态时没有当前路径概念，所有使用PropertyConfigurator.configure（String）语句找log4j.properties文件时要给出相对于当前jsp或servlet的路径转化成为一个绝对的文件系统路径。方法是使用servletcontext.getrealpath(string)语句。例：
//得到当前jsp路径
String prefix =  getServletContext().getRealPath("/");
//读取log4j.properties
PropertyConfigurator.configure(prefix+"\\WEB-INF\\log4j.properties");
2、相应的log4j.properties设置某个属性时也要在程序中设置绝对路径。例：
log4j.appender.R.File属性设置日志文件存放位置。我们可以用读写.properties配置文件的方法进行灵活设置。

log4e使用说明
在了解了log4j的功能后，我们肯定会我们的程序中编写一些Log4j日志记录。对于使用Eclipse的程序员Log4e将是我们最得力的log4j日志编写助手，现在开始Log4e之旅。
Log4e是一个免费的Eclipse Plugin，它可帮助你在你的Java工程中快速加入Log； 我们可以在http://log4e.jayefem.de/index.php/Download网站上下载Log4e最新版本。下载后将相应文件夹拷贝到Eclipse的插件目录下，重新Eclipse，在首选项中会多出一个Log4e选项。
Log4e可以有多个插入Log为一个方法、类，当然也可以在当前位置插入Log，同时其也可以把Sysout.out.println()的转换为log；所有的这一切只需要你点点鼠标或者按一次快捷键。

Log4e的实例参照http://log4e.jayefem.de

How to do the initial setup of my logging framework

如何设置我的日志框架？

原文来自于http://log4e.jayefem.de/index.php/Log4E:FAQ

If you are already familiar with your logging framework you might want to skip this section.

This chapter gives you a slight idea of how to make the initial setup of your logger. This is NOT supported by Log4E at the moment and was not the intended use at the beginning of this project.

Log4E does not ship any logging framework which means that you have to download and install it for yourself!

Examples are available for Log4j, Commons Logging, JDK 1.4 Logging (again: you have to do this for yourself).

Log4j

1. Download Log4j at http://logging.apache.org/ and copy the log4j.jar to your lib directory.

2. Create a new file 'log4j.properties' or 'log4j.xml' (case sensitive) and put it in your classpath. To be more concrete: Put in your source directory, the file will be copied by Eclipse automatically to your build directory.

For example:

	.../MyEclipseProject/
    .../MyEclipseProject/src/log4j.properties
    .../MyEclipseProject/src/com/mycompany/myapp/...
    


2a. Alternatively, you can use the method org.apache.log4j.PropertyConfigurator.configure("..../log4j.properties");



3. Edit the 'log4j.properties' to declare your own categories, log levels and appenders (which means the output like standard out or a log file).

log4j.properties example:

	#######################################################################
    # Categories and levels
    #######################################################################
    log4j.rootCategory=ERROR, FileApp, ConApp
    log4j.category.de.jayefem=DEBUG
    #######################################################################
    # Appenders
    #######################################################################
    # ConApp is set to be a ConsoleAppender.
    log4j.appender.ConApp=org.apache.log4j.ConsoleAppender
    # ConApp uses PatternLayout.
    log4j.appender.ConApp.layout=org.apache.log4j.PatternLayout
    # Define Pattern
    log4j.appender.ConApp.layout.ConversionPattern=%d [%t] %-5p %c - %m%n
    # FileApp
    log4j.appender.FileApp=org.apache.log4j.RollingFileAppender
    log4j.appender.FileApp.File=D:/proj/Devel/Java/de.jayefem.log4e/log/log4e.log
    log4j.appender.FileApp.MaxFileSize=500KB
    # Keep one backup file
    log4j.appender.FileApp.MaxBackupIndex=1
    log4j.appender.FileApp.layout=org.apache.log4j.PatternLayout
    log4j.appender.FileApp.layout.ConversionPattern=%d [%t] %-5p %c - %m%n
    

"de.jayefem", "ConApp", "FileApp" and the path to the logfile are selfdefined. All other words are keywords of Log4j.

4. That's all. Have fun.


Note that there are much more possibilities to configure Log4j. Check http://logging.apache.org/ for more.

Jakarta Commons Logging

Jakarta Commons Logging Framework is a wrapper for all common logging frameworks. If you want to use it, you have to install it AND the underlying logging framework. To install the Commons Logging download it from http://jakarta.apache.org/commons/logging/ and put the commons-logging.jar in your lib directory.
The Commons Logging Frameworks uses Log4j by default. When Log4j isn't found in classpath and JDK 1.4 or higher is being used, the JDK 1.4 logger will be used. If none of the above applies, Commons Logging will fall back to the internal SimpleLog.

It is also possible to specify the logging framework directly:

1. Create a new file 'commons-logging.properties' and put it in your classpath. To be more concrete: Put it in your source directory, the file will be copied by Eclipse automatically to your build directory.

For example:

	.../MyEclipseProject/
    .../MyEclipseProject/src/commons-logging.properties
    .../MyEclipseProject/src/com/mycompany/myapp/...
    

2. Edit the 'commons-logging.properties'.

commons-logging.properties example:

	#
    #org.apache.commons.logging.LogFactory=org.apache.commons.logging.impl.LogFactoryImpl
    # SimpleLog
    #org.apache.commons.logging.Log = org.apache.commons.logging.impl.SimpleLog
    # JDK 1.4 logger
    #org.apache.commons.logging.Log=org.apache.commons.logging.impl.Jdk14Logger
    # Avalon Toolkit
    #org.apache.commons.logging.Log=org.apache.commons.logging.impl.LogKitLogger
    # Log4j
    org.apache.commons.logging.Log=org.apache.commons.logging.impl.Log4JLogger
    

 


As though it is not recommended to use Simplelog because it is not threadsafe, here's an example how to set it up:

 

1. Create a new file 'simplelog.properties' and put it in your classpath. To be more concrete: Put it in your source directory, the file will be copied by Eclipse automatically to your build directory.

For example:

	.../MyEclipseProject/
    .../MyEclipseProject/src/simplelog.properties
    .../MyEclipseProject/src/com/mycompany/myapp/...
    

2. Edit the 'simplelog.properties' to declare your own categories and log levels.

simplelog.properties example:

	# Default logging detail level for all instances of SimpleLog. Must be one of
    # ("trace", "debug", "info", "warn", "error", or "fatal"). If not specified,
    # defaults to "info".
    org.apache.commons.logging.simplelog.defaultlog=warn
    # Logging detail level for a SimpleLog instance named "xxxxx". Must be one of
    # ("trace", "debug", "info", "warn", "error", or "fatal"). If not specified, the
    # default logging detail level is used.
    org.apache.commons.logging.simplelog.log.de.jayefem.log4e=debug
    # Set to true if you want the Log instance name to be included in output
    # messages. Defaults to false.
    org.apache.commons.logging.simplelog.showlogname=false
    # Set to true if you want the last componet of the name to be included in
    # output messages. Defaults to true.
    org.apache.commons.logging.simplelog.showShortLogname=true
    # Set to true if you want the current date and time to be included in output
    # messages. Default is false.
    org.apache.commons.logging.simplelog.showdatetime=true
    

 

See http://jakarta.apache.org/commons/logging/ for more.

JDK 1.4 Logging

1. Use JDK 1.4 or higher :-)

2. Create a new file 'logging.properties'.

3. Invoke your application with:
java -Djava.util.logging.config.file=D:\your\path\to\logging.properties com.mycompany.myproject.MyClass



logging.properties example:

	# handlers
    handlers=java.util.logging.FileHandler, java.util.logging.ConsoleHandler
    # general level
    .level=INFO
    # file handler
    java.util.logging.FileHandler.pattern = %h/java%u.log
    java.util.logging.FileHandler.limit = 50000
    java.util.logging.FileHandler.count = 1
    java.util.logging.FileHandler.formatter = java.util.logging.XMLFormatter
    # console handler
    java.util.logging.ConsoleHandler.level = FINEST
    java.util.logging.ConsoleHandler.formatter = java.util.logging.SimpleFormatter
    test.de.jayefem.log4e.logkits.JDK1_4_Logging.level = FINEST
    

Since I am not an expert of JDK 1.4 logging there might be better ways to configure the logging framework. Suggestions are welcome.
See http://java.sun.com/j2se/1.4.2/docs/api/java/util/logging/package-summary.html for more information.

 

据说apache Jakarta小组曾经强烈建议sun把log4j作为jdk1.4的日志工具，但这条建议没有被采纳。于是他们就开发了common logging 来兼容log4j和jdk的logging，呵呵。简单一点，还是使用log4j吧。

note：在eclipse中运行程序时似乎并不会搜索本机的classpath，因此即使把log4j.properties文件放到classpath中也没用。

最近发现Weblogic也是用的log4j，呵呵。