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It’s hard to overestimate the importance of having a good logging facility when you develop distributed  applications. Did the client’s request reached the server-side component? What did the server send back?  Add to this the inability to use debuggers while processing GUI events like focus change, and you may   need to spend hours if not days trying to spot some sophisticated errors. That’s why a commercial-grade  logger is a must if you work with an application that is spread over the network and written in  different languages such as Adobe Flex and Java.

Log4Fx is an advanced, yet very simple to use, logger component for Adobe Flex applications that use Java application servers. You can set up the logging on the client or server sides, and you can redirect the output of the log messages to local log windows or make the log output easily available to the production support teams located remotely.  Think of a production situation when a particular client complains that the application runs slow. Log4Fx allows you to turn on the logging just for this client and you can do it remotely with Web-browser access to the log output.

Log4Fx comes with several convenient and easy-to-use display panels with log messages. This manual also covers techniques of logging mixed Flex/Java projects with or without Flex Builder.

USING LOG4FX
If you’ve been using other loggers like log4j, you’ll be pleasantly surprised at how Log4Fx automatically inserts required logging code in your existing Flex project. It comes down to memorizing a couple of keystroke combinations as explained below. But first, you need to install Log4Fx, and then add it to your Flex project. Just right-click on your Flex Project, select Log4Fx > Add Dependency Files from the popup menu.This action will add several new artifacts to your project:

• A new Flex component Log4FxLoggingTarget.mxml, will be automatically added to your project directory
• An extra tag <Log4FxLoggingTarget xmlns=”*”> will be added at the end of the source code of your default Flex application
• A new application RemoteLogReceiver.mxml is added to the project to provide remote access to the log messages
• The Log4Fx.swc is added to your project’s build path
• A small file log4flex.jar is added to the your Java server’s lib folder

Now you can use the hot keys to add required log lines to your application code. You can see the list of available hot keys by pressing CTRL + R. 

For example, let’s say you are considering adding a line to the application called MyStockProtflio:

trace(“Entered  the method getPriceQuotes”);

Just press the cursor in the script section of your application and press Ctrl+R followed by M, which will insert the  following lines in your program:

  import mx.logging.Log;
  import mx.logging.ILogger;
  private var logger:ILogger = Log.getLogger("MyStockPortfolio");

Now place the cursor, say in the function getPriceQuotes(), and press Ctrl+R followed by D and the following line will be added at your cursor location:

if (Log.isDebug()) logger.debug("");

Enter the text between the double quotes, and if you’ll set the level of logging to Debug, this message will be sent to the specified destination selected with the Logging Manager as explained below.

If you need to write a log message that will deliver fatal errors, press Ctrl+R, F , and you’ll see a new line in your code:

if (Log.isFatal()) logger.fatal("");

Just enter appropriate error information inside the quotes, and Log4Fx will send the information of this error to the selected log target.  

Here’s the code for the HelloWorld application with highlighted inserts from Log4Fx:

<?xml version="1.0" encoding="UTF-8"?><mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute">
    <mx:Grid>
        <mx:GridRow>
            <mx:GridItem>
                <mx:LinkButton label="Hello world!"           
                           click="logger.warn('Warning');"/>
            </mx:GridItem>
        </mx:GridRow>
        <mx:GridRow>
            <mx:GridItem>
                <mx:LinkButton label="Hello world again!"
                             click="logger.info('Info');"/>
            </mx:GridItem>
        </mx:GridRow>
    </mx:Grid>
    <mx:Script>
        <![CDATA[
            import mx.logging.Log;
            import mx.logging.ILogger;
            private var logger:ILogger = Log.getLogger("com.farata.samples");
        ]]>
    </mx:Script>

<Log4FlexLoggingTarget xmlns="*"/>
</mx:Application>

You still need to take care of two more items:

1. Define the destination of log messages by specifying the logging target.
2. Using Logging Manager, define the properties for various logging categories, set the default logging level et al.

Using Logging Manager
The logging manager is a part of Log4Fx, and it allows you to change the logging settings on the fly while debugging the application is in progress. During the lifespan of the application, you may need to be able to redirect the log messages to a different target(s). This functionality is implemented in the Logging Manager, which is a UI component that supports interactive control levels, categories, and targets. This is what you can do with the Logging Manager on the client side:

• Automatically discover and list logging categories, and allow changing of the logging level for each logical category or a package.
• List registered targets/destinations, and set default logging level and other common parameters.
• Store the logging settings on the client's computer.

To see this panel, start the application that uses Log4Fx and press CTRL+SHIFT+BACKSPACE  –  the  logging manager will pop up on top of your application window. The following screenshot shows the logging manager panel on top of the HelloWorld application after the user pressed CTRL+SHIFT+BACKSPACE.



You can change the logging level at any time while your application is running. This feature is crucial for mission-critical production applications, where you can’t ask the user to stop the application (i.e., financial trading systems), but need to obtain the logging information to help the customer on the live system.

Even if the user is not an IT professional, s/he can do this by following directions of the production support engineer.
You can also change the default log level by selecting the required log level from the dropdown box. The destination (target) of your log messages can be selected from another dropdown as described in the section Working with Log targets.

WORKING WITH LOG TARGETS
Trace
If you set the target Trace on the Logging Manager panel, all program messages will be output using the class from Flex framework called TraceTarget as if you've been using the function trace().

Socket
Setting the target to Socket will engage SocketTarget class for logging your program messages via HTTP connection.

 
If your Flex project was configured to work with the Java Servlet container, i.e., Apache Tomcat, adding Log4Fx dependency files creates a small file on the server side log4flex.jar, which contains two Java classes – FlexLoggerServlet and ServerFlexLogger.  The file web.xml will be automatically modified to add a section that maps the requests that contain the url-pattern “logging” to FlexLoggerServlet.

You can also use this reference implementation if you decide to customize the logger to utilize non-Java Web servers, i.e., PHP or .Net.

Server
This option can be used by applications that utilize Flex remoting via LiveCycle Data Services ES (LCDS), OpenAMF, or any other remoting transport. If you want to send the log output to the server, create a Java class that will support logging on the server side. Here's the sample version of a class that uses popular Log4J component:

package com.theriabook.logging;
import org.apache.log4j.Logger;
import org.apache.log4j.Level;

public class ServerFlexLogger {
    
    static public void log(String levelStr, String message)
    {
        logger.log(Level.toLevel(levelStr), message);
    }
    static Logger logger;  
    static
    {
          logger = Logger.getLogger("MyFlexLogger");
        logger.setLevel(Level.ALL);
    }
}

In Logging Manager, as soon as you select Server as a target, a text field will be shown where you need to enter the name of the server-side destination that is mapped to the class com.theriabook.logging.ServerFlexLogger.

Now the log messages from your Flex programs will be sent to the server destination ServerFlexLogger and logged there. The section 5.4 shows an example of how such communication could have been programmed manually, but Log4Fx spares you from this. Just configure the Flex remoting destination and enter its name in the Destination field as shown above.
 
Local Panel
Flex developers who spend most of the time “inside” the Eclipse IDE, send the log output to the local panel, which is nothing else but yet another Eclipse View.
 
Right-click on your Flex Project, select Log4Fx > Show Workbench Viewer from the popup menu. You'll see a new view panel in your Eclipse workbench:


 

Select Local Panel as a target, and now you can your log messages will be sent to a new Farata Logger View:

 
The push buttons on the toolbar allow you to turn on/off the output of debug, info, warning, fatal and error messages. You can also sort the messages by level, time, category, and message text.

XPanel
The XPanel target allows to trace Flex/Flash applications interactively in a separate window. It also gives you native platform features like the ability to save a log to a file, keep the log window always on top and redirect the output to platform-specific debugging API. XPanel runs on Windows 95/98/Me, NT/2000/XP/Vista.  To configure output to the external XPanel, just right-click on your Flex Project, and select Log4Fx > Show External Viewer from the popup menu. You’ll see an empty XPanel window will be displayed. Ensure that the target on the Logging Monitor is set to XPanel. Now your log messages will be streamed to an external XPanel window:


 
XPanel's toolbar provides quick access to Exit, Save Log, Start/Stop Logging, Clear Log, independent logging levels, Text/DataGrid Mode and “About” menu options.

Log4FlexLoggingTarget Explained
When you first added the Log4Fx dependency files, the file Log4FlexLoggingTarget.mxml was automatically added to your application project. It allows setting default targets for Log4Fx. In this section we'll discuss the code for the Log4FlexLoggingTarget.mxml:

<fx:LoggingTarget
xmlns:fx="http://www.faratasystems.com/2006/components"
xmlns:mx="http://www.adobe.com/2006/mxml"
defaultLoggerLevel="{LogEventLevel.INFO}">

<mx:Script>
    import mx.logging.LogEventLevel;
</mx:Script>

 <!-- Setting default output to XPanel -->
<fx:XPanelLogOutput
  fieldSeparator=" -> " />
     <!-- Setting special popup window for filtering -->
     <fx:adjustmentManager>
      <fx:LoggingAdjustmentManager
       keyCode="{Keyboard.BACKSPACE}"
       shiftKey="true"
       ctrlKey="true">
       <mx:Array>
        <!-- List of available outputs (with their own settings) -->
        <fx:XPanelOutputDescription />
        <fx:TraceOutputDescription
         fieldSeparator=" -> "
         includeCategory="true"
         includeDate="true"
         includeLevel="true"
         includeTime="true" />
        <fx:SocketOutputDescription />
        <fx:ServerOutputDescription/>
        <fx:LocalConnectionOutputDescription/>
        <fx:RemoteOutputDescription/>
       </mx:Array>
      </fx:LoggingAdjustmentManager>
     </fx:adjustmentManager>
</fx:LoggingTarget>

This code performs the following actions:
1. Set the default logger level. You can change it by modifying the value of the property defaultLoggerLevel, which has a default value of LogEventLevel.INFO, and we’ve included this code for illustration purposes.
2. Set the destination of the default output of the logger. By default, the log info goes to XPanel. You can change the default value either by assigning appropriate value to XPanelLogOutput, (for example, LocalConnectionOutput) or by using Logging Manager. You can also specify additional parameters for targets, for example, fieldSeparator, which denotes the field delimiter to be used in log files. All available parameters are listed in Eclipse Help (see, com.theriabook.util.XPanelTarget or other targets). The next section of this document describes how to set such parameters.
3. You can redefine the hot keys that bring up the Logging Settings panel by changing the values of the properties keyCode, shiftKey and/or ctrlKey. For example, if you use the combination keyCode=“{Keyboard.ESCAPE}”, ctrlKey="false" and shiftKey="true" in the code, pressing SHIFT + ESC will open the Logging Monitor window. If none of these properties are set, you can open the Logging Monitor by pressing F12.
4. In the code section “List of available outputs” you can change the list of available logging targets in the Logging Manager panel. By default, it shows XPanelOutput, TraceOutput, SocketOutput, ServerOutput, LocalConnectionOutput ? RemoteOutput, which were described above. If you do not need all targets, remove some of the available outputs from Log4FlexLoggingTarget.mxml.

You can set the default logging level is defined in the file Log4FlexLoggingTarget.mxml and in the Logging Manager panel. The latter has higher priority over the settings specified in Log4FlexLoggingTarget.mxml. For example, after adding Log4Fx to your project, you can specify LogEventLevel.WARN as the default logger level that will take effect on the application startup. But if you change this level to ERROR using the Logging Manager panel, it’ll remember the ERROR level till the next start of your application despite the fact that the file Log4FlexLoggingTarget.mxml still has the WARN level. To remove all logger settings made from the panel, press the button Clear Local Storage on the Logging Manager panel. After that, the settings from the file Log4FlexLoggingTarget.mxml will be in effect again.

Remote Logging
Adding dependency file described above created a new application in your project – RemoteLogReceiver.mxml, which can be used by a remote production support crew. Let’s say the user’s application is deployed at the following URL:
http://230.123.12.10:8080/myapplication.html. By pressing the CTRL-SHIFT-BACKSPACE, the user brings the Logging Manager and selects the target Remote Logging.


 
The destination RemoteLogging is selected automatically, and the user needs to input a password, which he will share with the production support engineer.

Since the RemoteLogReceiver.mxml is also an application that is sitting right next to your main application in Flex Builder’s project, it’ll also will get compiled into an SWF file, the html wrapper will be generated too, and it will be deployed in the Web server of your choice too. The end users will never use it, and they won’t even know that it exists. But production engineer can enter its URL in his browser when needed:

http://230.123.12.10:8080/RemoteLogReceiver.html

Think of an undercover informant who just lives in the neighborhood, but when engaged, it immediately starts sending the information out.

After entering the password provided by the user and pressing the button Connect, he’ll start receiving Log messages sent by the user’s application.
 


The pushbuttons on the toolbar allow selective output of log messages – it works the same way as with XPanel.

Summary
Given the huge productivity boost, the cost of $99 for Log4Fx component seems to be nominal. Even if you are not planning to purchase the logger, give it a try and download its manual at myflex.org, which also has good coverage of Adobe  Flex logging aspects.