Use Log4j ObjectRenderer To Log Java Object

The log is an essential feature for each java application, and log4j is one of many uses. Generally, we use the java code logger.info(“Hello World”); to log a String value. it will output “Hello World” in the appender destination.

But how about logging a java object like this logger.info(new LogJavaObjectInfo());. Generally, it will output data like INFO [main] (LogJavaObjectInfo.java:18) – [email protected].
This is not human-readable and friendly. To resolve this issue, we have the below solutions.

1. Create a Java Class To Implements The org.apache.log4j.or.ObjectRenderer Interface.

The custom class name is com.dev2qa.java.basic.log4jexample.LogJavaObjectInfoRenderer.

You should override the method doRender(Object obj) to return customize String value when logging obj ( This renderer decorated java object ).

public class LogJavaObjectInfoRenderer implements ObjectRenderer {

	@Override
	public String doRender(Object obj) {
		// Convert the obj parameter to LogJavaObjectInfo class object.
		LogJavaObjectInfo logJavaObjectInfo = (LogJavaObjectInfo)obj;
		
		// Invoke the converted object's method.
		String ret = logJavaObjectInfo.getUserName() + " : " + logJavaObjectInfo.getMessage();
		
		return ret;
	}

}

Set The Renderer Class in Eclipse Java Project resources / log4j.properties file. Please see the first line configuration of the below content.

# This means when log LogJavaObjectInfo object, use LogJavaObjectInfoRenderer to output String data.
log4j.renderer.com.dev2qa.java.basic.log4jexample.LogJavaObjectInfo=com.dev2qa.java.basic.log4jexample.LogJavaObjectInfoRenderer

# Define root logger, logger level is INFO, appender name is appender1
log4j.rootLogger = INFO, appender1

# Set appender1 to be a Console appender that will print log data to console.
log4j.appender.appender1=org.apache.log4j.ConsoleAppender

# Define appender1's layout
log4j.appender.appender1.layout=org.apache.log4j.PatternLayout
log4j.appender.appender1.layout.ConversionPattern=%5p [%t] (%F:%L) - %m%n

Log the LogJavaObjectInfo Object ( instance of the class com.dev2qa.java.basic.log4jexample.LogJavaObjectInfo ) in the below java source code.

public class LogJavaObjectInfo{
	
	private String userName;
	
	private String message;
	

	public static void main(String[] args) {
		
		// Get root logger.
		Logger logger = Logger.getRootLogger();
		
		// Create a new object.
		LogJavaObjectInfo logJavaObjectInfo = new LogJavaObjectInfo();
		
		// Set object's properties.
		logJavaObjectInfo.setUserName("Jerry");
		logJavaObjectInfo.setMessage("Welcome to dev2qa.com");
		
		// Log the object use root logger.
		logger.info(logJavaObjectInfo);
	}


	public String getUserName() {
		return userName;
	}


	public void setUserName(String userName) {
		this.userName = userName;
	}


	public String getMessage() {
		return message;
	}


	public void setMessage(String message) {
		this.message = message;
	}

}

Run the above source code will get the below output. This is user-friendly enough and human-readable.
```
INFO [main] (LogJavaObjectInfo.java:25) - Jerry : Welcome to dev2qa.com
```

2. Override The LogJavaObjectInfo Class toString() Method.

LogJavaObjectInfo.toString().

@Override
public String toString() {
	StringBuffer retBuf = new StringBuffer();
	retBuf.append("This message is generated from toString() method. ");
	retBuf.append(this.getUserName());
	retBuf.append(" : ");
	retBuf.append(this.getMessage());
	return retBuf.toString();
}

Now you can remove the object renderer configuration in log4j.properties file and run LogJavaObjectInfo main method again, you can get below output.
```
INFO [main] (LogJavaObjectInfo.java:25) - This message is generated from toString() method. Jerry : Welcome to dev2qa.com
```

3. Example Project Full Source Code.

Below is the example project source files list.

D:\WORK\DEV2QA.COM-EXAMPLE-CODE\JAVACOREEXAMPLEPROJECT\SRC\COM\DEV2QA\JAVA\BASIC\LOG4JEXAMPLE
    log4j.properties
    Log4jBasicExample.java
    LogJavaObjectInfo.java
    LogJavaObjectInfoRenderer.java

log4j.properties

# Define com.dev2qa.java.basic.log4jexample class logger
log4j.logger.com.dev2qa.java.basic.log4jexample = warn, appender1
# Set appender1 to be a Console appender which will print log data to console.
log4j.appender.appender1=org.apache.log4j.ConsoleAppender
# Define appender1's layout
log4j.appender.appender1.layout=org.apache.log4j.PatternLayout
log4j.appender.appender1.layout.ConversionPattern=%5p [%t] (%F:%L) - %m%n
 
 # Define root logger, logger level is INFO, appender name is appender2
 log4j.rootLogger = info, appender2
 # Appender2 will save log data to file.
 log4j.appender.appender2=org.apache.log4j.FileAppender
 log4j.appender.appender2.File=C:/WorkSpace/logData.log
 log4j.appender.appender2.layout=org.apache.log4j.PatternLayout
 log4j.appender.appender2.layout.ConversionPattern=%5p [%t] (%F:%L) - %m%n

Log4jBasicExample.java

package com.dev2qa.java.basic.log4jexample;

import org.apache.log4j.Logger;
import org.apache.log4j.PropertyConfigurator;

public class Log4jBasicExample {

    public static void main(String[] args) {
        
        //You can specify log4j.properties location if you do not save it in CLASSPATH directory.
        PropertyConfigurator.configure("C:/WorkSpace/dev2qa.com/Code/src/com/dev2qa/java/basic/log4jexample/log4j.properties");
         
        Logger rootLogger = Logger.getRootLogger();
        
        // Get this class related logger object.
        Logger logger = Logger.getLogger(Log4jBasicExample.class);
        
        logger.debug("This is debug message.");
        logger.info("This is info message.");
        logger.warn("This is warn message.");
        logger.error("This is error message.");
        logger.fatal("This is fatal message.");
        
        
        rootLogger.debug("This is rootLogger debug message.");
        rootLogger.info("This is rootLogger info message.");
        rootLogger.warn("This is rootLogger warn message.");
        rootLogger.error("This is rootLogger error message.");
        rootLogger.fatal("This is rootLogger fatal message.");
        
    }

}

LogJavaObjectInfo.java

package com.dev2qa.java.basic.log4jexample;

import org.apache.log4j.Logger;

public class LogJavaObjectInfo{
    
    private String userName;
    
    private String message;
    

    public static void main(String[] args) {
        
        // Get root logger.
        Logger logger = Logger.getRootLogger();
        
        // Create a new object.
        LogJavaObjectInfo logJavaObjectInfo = new LogJavaObjectInfo();
        
        // Set object's properties.
        logJavaObjectInfo.setUserName("Jerry");
        logJavaObjectInfo.setMessage("Welcome to dev2qa.com");
        
        // Log the object use log4j root logger.
        logger.info(logJavaObjectInfo);
    }


    public String getUserName() {
        return userName;
    }


    public void setUserName(String userName) {
        this.userName = userName;
    }


    public String getMessage() {
        return message;
    }


    public void setMessage(String message) {
        this.message = message;
    }


    @Override
    public String toString() {
        StringBuffer retBuf = new StringBuffer();
        retBuf.append("This message is generated from toString() method. ");
        retBuf.append(this.getUserName());
        retBuf.append(" : ");
        retBuf.append(this.getMessage());
        return retBuf.toString();
    }
    
    

}

LogJavaObjectInfoRenderer.java

package com.dev2qa.java.basic.log4jexample;

import org.apache.log4j.or.ObjectRenderer;

public class LogJavaObjectInfoRenderer implements ObjectRenderer {

    @Override
    public String doRender(Object obj) {
        // Convert the obj parameter to LogJavaObjectInfo class object.
        LogJavaObjectInfo logJavaObjectInfo = (LogJavaObjectInfo)obj;
        
        // Invoke the converted object's method.
        String ret = logJavaObjectInfo.getUserName() + " : " + logJavaObjectInfo.getMessage();
        
        return ret;
    }

}