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!
Labels:

Comments

Post a Comment

Popular posts from this blog

Junit - Test fails on French or German string assertion

In my previous post about building a regex to check a text without special characters but allow German and French . I met a problem that the unit test works fine on my machine using Eclipse, but it was fail when running on Jenkins' build job. Here is my test: @Test public void shouldAllowFrenchAndGermanCharacters(){ String source = "ÄäÖöÜüß áÁàÀâÂéÉèÈêÊîÎçÇ"; assertFalse(SpecialCharactersUtils.isExistSpecialCharater(source)); } Production code: public static boolean isExistNotAllowedCharacters(String source){ Pattern regex = Pattern.compile("^[a-zA-Z_0-9_ÄäÖöÜüß áÁàÀâÂéÉèÈêÊîÎçÇ]*$"); Matcher matcher = regex.matcher(source); return !matcher.matches(); } The result likes the following: Failed tests: SpecialCharactersUtilsTest.shouldAllowFrenchAndGermanCharacters:32 null A guy from stackoverflow.com says: "This is probably due to the default encoding used for your Java source files. The ö in the string literal in the J...
5 comments
Read more

Math fundamentals and Katex

It was really tough for me to understand many articles about data science due to the requirements of understanding mathematics (especially linear algebra). I’ve started to gain some basic knowledges about Math by reading a book first. The great tool Typora and stackedit with supporting Katex syntax simply helps me to display Math-related symbols. Let’s start! The fundamental ideas of mathematics: “doing math” with numbers and functions. Linear algebra: “doing math” with vectors and linear transformations. 1. Solving equations Solving equations means finding the value of the unknown in the equation. To find the solution, we must break the problem down into simpler steps. E.g: x 2 − 4 = 4 5 x 2 − 4 + 4 = 4 5 + 4 x 2 = 4 9 x = 4 9 ∣ x ∣ = 7 x = 7  or  x = − 7 \begin{aligned} x^2 - 4 &= 45\\ x^2 - 4 + 4 &= 45 + 4\\ x^2 &= 49\\ \sqrt{x}&=\sqrt{49}\\ |x| &= 7\\ x=7 &\text{ or } x=-7 \end{aligned} x 2 − 4 x 2 − 4 + 4 x 2 x ​ ∣ x ∣ x = 7 ​ = 4 5 = 4 ...
Post a Comment
Read more

Styling Sort Icons Using Font Awesome for Primefaces' Data Table

So far, Primefaces has used image sprites for displaying the sort icons. This leads to 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 the table loading because I want to highlight the icon "arrow down". I found a way that I can replace these icons with Font Awesome icons. We will use "CSS Pseudo-classes" to achieve 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: ...
Post a Comment
Read more

The HelloWorld example of JSF 2.2 with Myfaces

I just did by myself create a very simple app "HelloWorld" of JSF 2.2 with a concrete implementation Myfaces that we can use it later on for our further JSF trying out. I attached the source code link at the end part. Just follow these steps below: 1. Create a Maven project in Eclipse (Kepler) with a simple Java web application archetype "maven-archetype-webapp". Maven should be the best choice for managing the dependencies , so far. JSF is a web framework that is the reason why I chose the mentioned archetype for my example. 2. Import dependencies for JSF implementation - Myfaces (v2.2.10) into file pom.xml . The following code that is easy to find from  http://mvnrepository.com/  with key words "myfaces". <dependency> <groupId>org.apache.myfaces.core</groupId> <artifactId>myfaces-api</artifactId> <version>2.2.10</version> </dependency> <dependency> <groupId>org.apache.myfaces.core<...
Post a Comment
Read more

JSF, Primefaces - Invoking Application Code Even When Validation Failed

A use case I have a form which has requirements as follow: - There are some mandatory fields. - Validation is triggered when changing value on each field. - A button "Next" is enable only when all fields are entered. It turns to disabled if any field is empty. My first approach I defined a variable "isDisableNext" at a backend bean "Controller" for dynamically disabling/enabling the "Next" button by performing event "onValueChange", but, it had a problem: <h:form id="personForm"> <p:outputLabel value="First Name" for="firstName"/> <p:inputText id="firstName" value="#{person.firstName}" required="true"> <p:ajax event="change" listener="#{controller.onValueChange}" update="nextButton"/> </p:inputText> <p:outputLabel value="Last Name" for="lastName"/> <p:i...
Post a Comment
Read more