Adapter Design Pattern With Scala

In our last blog, we discussed the decorator design pattern with Scala. Today, we will explore the Adapter design pattern. We will also implement this pattern in Scala.

Earlier, in many applications, all the user-specific details, like username, IP addresses, phone number, etc., were logged directly without scrambling it. But, after new data protection law, i.e. EUGDPR, it is now mandatory to scramble any user-specific data.

So, we need to change the logging logic for all such applications. In order to do this, we will add some extra methods to our logging framework. But, wait! We all know that most of our applications are generally flooded with logging statements and replacing all the statements with new method names is not logically and practically possible.

So, what can we do now? We can use the Adapter design pattern!

What Is the Adapter Design Pattern?

Convert the interface of a class into another interface clients expect. Adapter lets classes work together that could not otherwise because of incompatible interfaces. Adapter is also known as wraper.

Solution to our Problem

We will change our existing logger framework to a framework that supports methods like scrambledInfo(), scambledError(), scrambledDebug() , etc.

We will create a LoggerAdapter class, which will adapt or wrap the ScrambledLogger . And, whenever the client calls the info method, it will call thescrambledInfo method and will do the same for the methods debug ,error , etc.

The Client class is the class that will actually call the logging methods.

The LoggerHelper trait is an existing trait on which all the required logging methods are declared.

Now,ScrambledLogger is the new class that will scramble all logs before logging. It is basically an Adaptee.

LoggerAdapter is the class that will act as an interface between our Clientand our adaptee class ScrambledLogger.

package com.knoldus

import org.apache.log4j.BasicConfigurator

object Client extends App {
BasicConfigurator.configure()
val logger : LoggerHelper = LoggerAdapter.getLogger(this.getClass.getName)
logger.info("Log Contains IP address: 127.0.0.1")
logger.debug("UserName: jainnancy trying to sign in")
logger.error("Password: abxyz is wrong ")
}

package com.knoldus

object LoggerAdapter extends LoggerHelper {
var scrambledLogger : ScrambledLogger = _

override def info(msg : String) = scrambledLogger.scrambledInfo(msg)

override def debug(msg : String) = scrambledLogger.scrambledDebug(msg)

override def error(msg : String) = scrambledLogger.scrambledError(msg)

def getLogger(s : String) : LoggerHelper =
{
scrambledLogger = new ScrambledLogger(s)
LoggerAdapter
}
}

package com.knoldus

import org.apache.log4j.BasicConfigurator

trait LoggerHelper {
def info(msg : String)

def debug(msg : String)

def error(msg : String)
}

package com.knoldus

import org.apache.log4j.Logger

class ScrambledLogger(name : String)
{
    private val regex = "\\b\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}\\b"
    private val password = "Password: "
    private val userName = "UserName: "
    private val logger = Logger.getLogger(name)

    def scrambledInfo(message : String) =  logger.info(scramble(message))

    def scrambledDebug(message : String) = logger.debug(scramble(message))

    def scrambledError(message : String) = logger.error(scramble(message))

    private def scramble(message : String) = scrambleUsername(scrambleIp((scramblePassword(message))))

    private def scrambleUsername(message : String) = {
        if(message.contains(userName)) {
            val index = message.indexOf(userName) + userName.length()
            val textStartedPassword = message.substring(index)
            message.substring(0, index) + "X" + textStartedPassword.substring(textStartedPassword.indexOf(" "))
        }
        else {
            message
        }
    }

    private def scrambleIp(message : String) = message.replaceAll(regex, "XXX.XXX.XXX.XXX")

    private def scramblePassword(message : String) = {
        if(message.contains(password)) {
            val index = message.indexOf(password) + password.length()
            val textStartedPassword = message.substring(index)
            message.substring(0, index) + "X" + textStartedPassword.substring(textStartedPassword.indexOf(" "))
        }
        else {
            message
        }
    }
}

Note:

1. We are using the following dependency for Logger: libraryDependencies += "log4j" % "log4j" % "1.2.17"
2. ScrambledLoggeris also somehow using the Proxy design pattern, which we will discuss in the upcoming blog post.

Hope you enjoyed!

References

• https://www.scala-lang.org/old/sites/default/files/FrederikThesis.pdf
• https://sourcemaking.com/design_patterns/adapter