[JAVA] Prepare for log output using log4j in Eclipse.

This article describes the preparations for enabling log output using the org.apache.log4j package in Eclipse.

First, download the log4j package (here log4j-1.2.17.zip) from the following site. http://www.apache.org/dyn/closer.cgi/logging/log4j/1.2.17/log4j-1.2.17.zip
Unzip the log4j-1.2.17.zip file and add the log4j-1.2.17.jar file to your project's external library. From the Eclipse screen

Right-click on the relevant project-> Click Properties
Click Java build path-> Library- (L) tab-> Add external JAR
Open log4j-1.2.17.jar from the file selection screen
Click Apply and Close Now you have an environment where you can output logs using log4j in your project.

Let's test if the log is output in a simple project.

In the above, if the external JAR is not added, the class of org.apache.log4j. * Cannot be imported, so that part seems to be okay.

package test.project; import org.apache.log4j.Logger;

public class TestClass { public static void main(String[] args) { Logger logger = Logger.getLogger(TestClass.class.getName()); // Log output logger.info("This is info."); } }

When I execute it, the log is not output. The following error is output. log4j:WARN No appenders could be found for logger (test.project.TestClass). log4j:WARN Please initialize the log4j system properly. log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info. Upon examination, this error seems to be an error asking me to set the log output setting because I can't find it in test.project.TestClass. As a setting method, there is a method to set in the property file (log4j.properties) and the XML file (log4j.xml), so this time, we will use the XML file.

Create a log4j.xml file. (Created in the same location as the source file) By default, the ~ </ appender> part is on the net, so it will be plagiarized as it is. The ~ </ category> part is the newly created definition. *** is the package name, not the class name (in this case, "test.project")

< ?xml version="1.0" encoding="UTF-8" ?> < !DOCTYPE log4j:configuration SYSTEM "log4j.dtd"> < log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/"> < appender name="stdout" class="org.apache.log4j.ConsoleAppender"> < param name="Target" value="System.out" /> < layout class="org.apache.log4j.PatternLayout"> < param name="ConversionPattern" value="%d{yyyy/MM/dd HH: mm:ss SSS} %5p %5t %c{1} - %m%n" /> < /layout> < /appender>

< category name="test.project" > < appender-ref ref="stdout" /> < /category>

< /log4j:configuration >

I will try it again. That will come out again. log4j:WARN No appenders could be found for logger (test.project.TestClass). log4j:WARN Please initialize the log4j system properly. log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info. Why is it still an error? After investigating various things, it seems that I can not see it because log4j.xml is in the place where the classpath does not pass.

public class TestClass { public static void main(String[] args) { Logger logger = Logger.getLogger(TestClass.class.getName()); // Add and confirm URL fileXmlUrl = Loader.getResource("log4j.xml"); DOMConfigurator.configure (fileXmlUrl); // <-fileXmlUrl is null // Add and confirm // Log output logger.info("This is info."); } }

Set the classpath in the location of the log4j.xml file.

Right-click on the relevant project-> Click Properties
Click Java build path-> Library- (L) tab-> Add external class folder
Select external class folder-> Select the folder containing log4j.xml (this time src folder)-> Click OK
Click Apply and Close Now you have an environment where you can output logs using log4j in your project.

Now if you run the source you ran above, you'll get a value instead of null. Next, if you delete the added part and move it, it will work properly this time.

2017/XX/XX 14:56:09 781 INFO main TestClass - This is info.