Skip to main content

Make Our Code More Testable with Proxy Design Pattern


If you heard about the term separation of concerns, you could agree this concept is very important for making a system "clean". One of the most important characteristics of a clean system is testable.

Let me tell you my story about how I've just come acrosss the design pattern Proxy.

Note: to get started, you can find a very simple example of the pattern Proxy here

Let's start!

I have an interface as below:
public interface DocumentGenerator {
    File generate(Document document) throws BusinessException;
}

The following is my first implementation for a concrete class of DocumentGenerator.
public class DocumentGeneratorImpl implements DocumentGenerator {
 private Dossier dossier;
 private Locale locale;
 
 public DocumentGeneratorImpl(Dossier dossier, Locale locale) {
  validateNotNullParams(dossier, locale);
  this.dossier = dossier;
  this.locale = locale;
 }
 
 private void validateNotNullParams(LibertyDossier dossier, Locale locale) {
  if(Objects.isNull(dossier)) {
   throw new IllegalArgumentException("Dossier must not be null!");
  }
  
  if(Objects.isNull(dossier.getDossierType())){
   throw new IllegalArgumentException("Dossier type must not be null!");
  }
  
  if(Objects.isNull(locale)) {
   throw new IllegalArgumentException("Locale must be defined!");
  }
 }
 
 @Override
 public File generate(Document document, boolean temporary) 
  throws BusinessException {
  setCobIdForDossierIfNotExist();
  switch (dossier.getDossierType()) {
  case TYPE_A:
   // Do some logic here in case TYPE_A
  case TYPE_BA:
   // Do some logic here in case TYPE_B
  default:
   throw new BusinessException("Not supported dossier type");
  }
 }
 
 private void setCobIdForDossierIfNotExist() {
  if(StringUtils.isEmpty(dossier.getCobId())) {
   String generatedCobId = DossierService.getInstance().generateCobId();
   dossier.setCobId(generatedCobId);
  }
 }
}

The client code constructs the concrete class DocumentGeneratorImpl.
DocumentGenerator  generator = new DocumentGeneratorImpl(dossier, locale);

I saw that some private methods "validateNotNullParams(dossier, locale)" and "setCobIdForDossierIfNotExist()" are just a second responsibility of class DocumentGeneratorImpl.

Follow "S" of SOLID  - Single Responsibility

Firstly, I was thinking about how to separate these methods into another class. Then, I create a class called DocumentGeneratorHelper which contains to these methods. It was just improved a bit.

public class DocumentGeneratorImpl implements DocumentGenerator {
 private Dossier dossier;
 private Locale locale;
 
 public DocumentGeneratorImpl(Dossier dossier, Locale locale) {
  DocumentGeneratorHelper.validateNotNullParams(dossier, locale);
  this.dossier = dossier;
  this.locale = locale;
 }
 
 @Override
 public File generate(Document document, boolean temporary) 
   throws BusinessException {
  DocumentGeneratorHelper.setCobIdForDossierIfNotExist();
  switch (dossier.getDossierType()) {
  case TYPE_A:
   // Do some logic here in case TYPE_A
  case TYPE_BA:
   // Do some logic here in case TYPE_B
  default:
   throw new BusinessException("Not supported dossier type");
  }
 }
 
}

However, if I create tests for DocumentGeneratorImpl, I need to mock DocumentGeneratorHelper. Huh....! Any better approach?

I was thinking about that it is somehow I need to apply an Aspect-Oriented Programming (AOP) approach. As my google searching result, there are some approaches but they are quite complicated and heavy. They use Java Proxy or AOP Frameworks such as AspectJ.

A Simple AOP Approach

Fortunately, the keyword "proxy" leads me to the pattern Proxy. The idea of Proxy is really simple and cool!



Okay, now I create a Proxy instead of a Helper as before.

public class DocumentGeneratorProxy implements DocumentGenerator{
 private DocumentGenerator generator;
 private Dossier dossier;
 
 public DocumentGeneratorProxy(Dossier dossier, Locale locale) {
  validateNotNullParams(dossier, locale);
  this.dossier = dossier;
  this.generator = new DocumentGenerator(this.dossier, locale);
 }

 private void validateNotNullParams(Dossier dossier, Locale locale) {
  if(Objects.isNull(dossier)) {
   throw new IllegalArgumentException("Dossier must not be null!");
  }
  
  if(Objects.isNull(dossier.getDossierType())){
   throw new IllegalArgumentException("Dossier type must not be null!");
  }
  
  if(Objects.isNull(locale)) {
   throw new IllegalArgumentException("Locale must be defined!");
  }
 }

 @Override
 public File generate(Document document, boolean temporary)
   throws BusinessException {
  setCobIdForDossierIfNotExist();
  return generator.generate(document, temporary);
 }

 private void setCobIdForDossierIfNotExist() {
  if(StringUtils.isEmpty(dossier.getCobId())) {
   String generatedCobId = DossierService.getInstance().generateCobId();
   dossier.setCobId(generatedCobId);
  }
 }

}

Done! DocumentGeneratorImpl  doesn't contain its second responsibilities anymore. These methods are tested by the Proxy and we don't need to mock in DocumentGeneratorImpl.
the public class DocumentGeneratorImpl implements DocumentGenerator {
 private Dossier dossier;
 private Locale locale;
 
 public LibertyDocumentGenerator(Dossier dossier, Locale locale) {
  this.dossier = dossier;
  this.locale = locale;
 }
 
 @Override
 public File generate(Document document, boolean temporary) 
   throws BusinessException {
  switch (dossier.getDossierType()) {
  case TYPE_A:
   // Do some logic here in case TYPE_A
  case TYPE_BA:
   // Do some logic here in case TYPE_B
  default:
   throw new BusinessException("Not supported dossier type");
  }
 }
 
}

So, instead of calling directly DocumentGeneratorImpl, we call DocumentGeneratorProxy in the client code as below:

DocumentGenerator  generator = new DocumentGeneratorProxy(dossier, locale);

Happy codings!

Comments

Popular posts from this blog

My 2017 Review

Passion for System Design After finishing a one year project, my longest stable team (3 years) was separated into two smaller teams. Sadly, but that was a good chance for me to become a key member in my new team. My preferred skills is about system architectures; therefore most of the tasks of building the application structures are handled by me. In order to enhance my design system skills, I have spent much my time for reading books closely after work. These following books helps me a lot.
- Object-Oriented Thought Process | Matt Weisfeld
- Head First Design Pattern | Elisabeth Freeman and Kathy Sierra
- Java 8 in Action: Lambdas, Streams, and Functional-style Programming | Alan Mycroft and Mario Fusco
Junior Technical Architect I was requested to join a technical architect team (aka Team. Alpha) where I actually has gained experiences almost on interviewing candidates for my company (lol). Besides, I noticed myself must improve the skills of convincing people because I have had a …

AngularJS - Build a custom validation directive for using multiple emails in textarea

AngularJS already supports the built-in validation with text input with type email. Something simple likes the following:
<input name="input" ng-model="email.text" required="" type="email" /> <span class="error" ng-show="myForm.input.$error.email"> Not valid email!</span>
However, I used a text area and I wanted to enter some email addresses that's saparated by a comma (,). I had a short research and it looked like AngualarJS has not supported this functionality so far. Therefore, I needed to build a custom directive that I could add my own validation functions. My validation was done only on client side, so I used the $validators object.

Note that, there is the $asyncValidators object which handles asynchronous validation, such as making an $http request to the backend.

This is just my implementation on my project. In order to understand that, I supposed you already had experiences with Angular…

Strategy Design Pattern

For example, I have an program with an Animal abstract class and two sub-classes Dog and Bird. I want to add a new behavior for the class Animal, this is "fly".  Now, I face to two approaches to solve this issue:

1. Adding an abstract method "fly" into the class Animal. Then, I force the sub-classes should be implemented this method, something like:

public abstract class Animal{ //bla bla public abstract void fly(); } public class Bird extends Animal{ //bla bla public void fly(){ System.out.println("Fly high"); } } public class Dog extends Animal{ //bla bla public void fly(){ System.out.println("Cant fly"); } }
2. Creating an interfaces with method "fly" inside. The same issue to abstract class, I force the classes these implement this interface should have a method "fly" inside:

public interface Flyable{ public void fly(); } public class Bird implements Flyable{ //bla bla public void fly(){ System.out.println…

How did I start practising BDD?

At the beginning days I have practised TDD (Test Driven Development) with using JUnit, I approached that I should test methods belong to a class. For example:

I have a class with some methods:

public class A{ public void method1(){ } public void method2(){ } }
And then, I wrote some test methods to check the corresponding ones, for example:

public class ATest{ @Test public void testMethod1(){ .... assertTrue(...); ..... assertEquals(...); } @Test public void testMethod2(){ } }
After that, I know that a test method (ex: testMethod1) should just only tests one thing, so I decided to write more methods for each cases. It looks like the following:

@Test public void testMethod1_When_Case1(){ .... assertTrue(...); } @Test public void testMethod1_When_Case2(){ .... assertEquals(...); }
However, it was not a really good approach because it seems that I just focused on test the functionality of the method of the class. With TDD approach, I knew that I should test the…

Styling Sort Icons Using Font Awesome for Primefaces' Data Table

So far, Primefaces has used image sprites for displaying the sort icons. This leads a problem if we want to make a different style for these icons; for example, I would make the icon "arrow up" more blurry at the first time table loading because I want to highlight the icon "arrow down". I found a way that I can replace these icons to Font Awesome icons.


We will use "CSS Pseudo-classes" to archive it. The hardest thing here is that we should handle displaying icons in different cases. There is a case both "arrow up" and "arrow down" showing and other case is only one of these icons is shown.

.ui-sortable-column-icon.ui-icon.ui-icon-carat-2-n-s { background-image: none; margin-left: 5px; font-size: 1.1666em; position: relative; } .ui-sortable-column-icon.ui-icon.ui-icon-carat-2-n-s:not(.ui-icon-triangle-1-s)::before { content: "\f106"; font-family: "FontAwesome"; position: absolute; t…