DEV Community: Mustapha Belmokhtar

FQN in Java

Mustapha Belmokhtar — Mon, 06 Feb 2023 02:55:35 +0000

Hi, I have made some cards about the #java FQN.
I truly prefer cards over lots of text.

any kind of feedback is welcome.
follow the @java_snippet for more java content.

Writing better code

Mustapha Belmokhtar — Sun, 10 Apr 2022 23:01:50 +0000

Hi, in this article we will shed the light on an important topic.
Every programmer knows how to sort an array, how to balance a tree, how to create and use complex data structures, or event how to convert business specifications to a working code.
BUT.
Are all programmers aware of the importance of writing a good readable code? I bet the answer is a big NO.
Let's take an example of a code I came across while ago, when I was reviewing a merge request submitted by a colleague :

 public static int get(Person p) {
        return Period.between(p.getBirthDate(), LocalDate.now()).getYears();
    }

The above code computes the age of a given person, it is flawless and gets the results correctly, but to understand that, it requires more effort and maybe you will have to dig into more details, or maybe ask your friend about the intention of a such code snippet.
Below a suggestion to re-write the same code, but in a more understandable way :

public static int calculateAgeOfAPerson(Person person) {
        LocalDate now = LocalDate.now();
        Period difference = Period.between(person.getBirthDate(), now);
        return difference.getYears();
    }

It is obvious now, that the intention of this snippet is clear as it is described by the code itself, no documentation is required, and the idea becomes clear without the need of going further into the details.

An easy way to group objects in java

Mustapha Belmokhtar — Mon, 04 Apr 2022 03:06:51 +0000

In this example, we will be making grouping easy to use on Maps objects that contain collections as values.
For instance, we hava a Map of Integers, that has its values as an ArrayList of Strings :

Grouper<Integer, String> grouper = new ArrayListGrouper<>();
        grouper.put(1, "a");
        grouper.put(1, "b");
        grouper.put(1, "c");
        grouper.put(1, "c");
        grouper.put(2, "c");

The output will be :

{1=[a, b, c, c], 2=[c]}

All we have to do, is to define a grouping strategy, for example the already defined ArrayListGrouper class uses an ArrayList as its strategy.
We can always define a new Grouper that will use another
GroupingStrateg.

Let's change the ArrayList to a HashSet, so that the elements become unique :

public class HashSetGrouper<K, V> extends Grouper<K, V> {

    public HashSetGrouper() {
        super(HashSet::new);
    }
}

Testing it like :

@Test
    public void testHashSetGrouper() {
        Grouper<Integer, String> grouper = new HashSetGrouper<>();
        grouper.put(1, "a");
        grouper.put(1, "b");
        grouper.put(1, "c");
        grouper.put(1, "c");
        grouper.put(2, "c");
        System.out.println(grouper);

    }

The output will become :

{1=[a, b, c], 2=[c]}

The 1 key has now a set in which the "c" value is not repeated.

the code is hosted on Github : https://github.com/BelmoMusta/java-Grouper
Your feedback is welcomed.

Java REGEX based scanner

Mustapha Belmokhtar — Sat, 04 Jul 2020 16:17:27 +0000

I often use the java built-in java.util.Scanner in order to retrieve information from string streams, but what I wasn't able to do, is to extract some tokens that match a predefined regex, and then consume the character sequence till the end.
For the java built-in scanner example, the regex is used only to define the delimiters, for example the tokens are separated by blank spaces, say , \t, or \n.
I could not tell it to retrieve well defined information, for example 123a4567-e89b-12d3-a456-123442445670, especially when it is inside a text mixed with some other tokens.
All I have to do now is to provide the regex example, and I get all the matching tokens from the given text.

Exemple

@Test
    public void testUUID() {
        final String regex = "[0-9abcdef]{8}(-[0-9abcdef]{4}){3}-[0-9abcdef]{12}";
        final String text = "uuid : 6d0a3538-9760-41ae-965d-7aad70021f81\n" +
                "uuid : d7d97fb3-3676-4109-9a94-7acc5f593ace\n" +
                "uuid : 02e87dd3-10ff-43cf-9572-bd9d151bb439\n" +
                "uuid : 632a4c31-8dfe-43a3-8f8d-15b472292cc9";

        final List<String> expectedUUIDs = Arrays.asList("6d0a3538-9760-41ae-965d-7aad70021f81",
                "d7d97fb3-3676-4109-9a94-7acc5f593ace",
                "02e87dd3-10ff-43cf-9572-bd9d151bb439",
                "632a4c31-8dfe-43a3-8f8d-15b472292cc9");

        final List<String> foundUUIDs = new ArrayList<>();
        final RegexScanner regexScanner = new RegexScanner(text, regex);
        while (regexScanner.hasNext()) {
            foundUUIDs.add(regexScanner.next());
        }
        Assert.assertArrayEquals(expectedUUIDs.toArray(), foundUUIDs.toArray());
    }

This way, the scanner is consumed by the while loop until the end is reached, which means all the token are read and processed.

It is possible also to provide a function that maps the found token to another object using the next(Function<String ,R> mapper) method.

The code is available on github via this link.

Devoxx: a learner journey

Mustapha Belmokhtar — Fri, 15 Nov 2019 00:21:39 +0000

I have attended the #devoxxma event which has been hosted in Agadir, a beautiful city of Morocco in the Atlantic Ocean.
The main event consists of conferences handed by people working on big IT companies such as IBM, RedHat, Twitter, Facebook, Oracle and so on.
To be honest, I couldn't be present in all the conferences because most of them occur at the same time. But, I tried to attend the maximum of shows I could, prioritizing them by the relationship with the field of work I'm in.
Among the things I have loved is the choice of the city which is amazing, with a good weather, about 20°C, and also the organization team who provided us with all the information and the tools we needed to accomplish this journey.
As a learner, I will summarize the keynotes of the topics I have attended :

Optimize your compiler may decrease the electricity consumption, and then you will win on both sides: you will preserve energy and the benefits of your company will increase. This was the main idea of the conference handed by Chris Thalinger who works for Twitter.
A snapshot of 10 ways by which you can secure your web application : presented by Matt Raible, a java champion and a developer advocate at Okta, going through the layers of an http application that has to use https whenever it comes possible, enable the CORS and CSRF to prevent attacks, and also hash passwords after inserting them into a database.
Work with CI/CD just by using .yml configuration files of the Jenkins pipeline : it was a presentation of Anas Moutaki and Ayoub Ed-dafali who are both devOps engineers at SQLI. It was essentially about how to configure and automate the Jenkins builds as a code in order to have our applications up and running within few minutes.
Using quarkus by RedHat to ensure the start of web applications within milliseconds! : Edson Yanaga was rockibg with his special topic about the quarkus pluging and how it can enable java web app developers to let go off all the frameworks they may use and focus on the one who is promising the sustainability of java as programming language in the upcoming years, not just because it is robust, but all the inconveniences of slowness will disappear. Quarkus supports spring annotations, it supports also orms JPA and hibernates.
Now, one can code and see his changes withing no time (about 200 milliseconds in a bad day, says Edson 😁).
Create a modern web applications with java using eclipse microprofile and liberty plugin with Sebastian Daschner, a java advocate at IBM who handed a good session about how the world of web apps will look like in the future.

Java Object Validation

Mustapha Belmokhtar — Tue, 29 Oct 2019 20:30:51 +0000

Validation is a wide known process in programming.
Say for example that you want to check whether the provided objects meet some specified rules before using them or persisting them into a database.
In spring for example, validation included and may be used at any stage of the flow of the application.
I tried to think out of the box, and imagine a customized object-validation using java, using annotation over fields of a class, or using specified list of criteria without annotating the class to validate.

To do so, I kind of created a repository on github to validate objects.
You can check it over here, any suggestions are welcome.
Start the repo if you like it, and if you want to contribute create a pull/merge request.

Examples of use :

1. Using annotations

Suppose we have a Person class, and for all the instances, we want that the first name and the last name be assigned and not left null :

class Person {
    @Validation
    private String name;

    @Validation
    private String lastName;
    // .... other fields...
    // .... getters and setters..
    }

And we will create an instance, then we check if it is valid or not:

     AnnotationValidator annotationValidator = new AnnotationValidator();
     Person person = new Person();
            person.setName("Mustapha");
            person.setLastName("Belmokhtar");

     boolean isValid = annotationValidator.checkValidation(person);
     ValidationReport validationReportItem = annotationValidator.getValidationReport(person); // gives the details of each field

Result :

   true
  {lastName=|found=String:Belmokhtar, expected={!=null}:[], valid=true|, name=|found=String:Mustapha, expected={!=null}:[], valid=true|}

Validation by Operators:

   class Person{
   // ... others fields 
   @Validation(operator = Operator.GREATER_THAN, value = "18")
    private int age;
    // ... getters and setters ...
    }

     Person person = new Person(); 
     person.setAge(20);

     AnnotationValidator annotationValidator = AnnotationValidator.getInstance();
     boolean isValid = annotationValidator.check(person);
     ValidationReport validationReportItem = annotationValidator.getValidationReport(person);

Result :

   true
   {age=|found=Integer:20, expected={>}:[18], valid=true|}

2.Using criteria :

You can also perform validation over objects using Criteria:

        Student student = new Student();
        CriteriaValidator criteriaValidator = CriteriaValidator.getInstance();
        Criteria criteria = new Criteria();
        criteria.setObject(student);
        criteria.add(Criterion.of("name").is("mustapha"));
        criteria.add(Criterion.of("address").notNull());
        criteria.add(Criterion.of("age").greaterOrEquals(4));
        criteria.add(Criterion.of("phoneNumber").matches("\\d{10}"));

        student.setName("mustapha");
        student.setAddress("wall street");
        student.setAge(4);
        student.setPhoneNumber("1234567890");
        System.out.println(criteriaValidator.getValidationReport(criteria));
        assertTrue(criteriaValidator.check(criteria));

Output :

 address=|found=String:wall street, expected={!=null}:[null], valid=true|, phoneNumber=|found=String:1234567890, expected={REGEX}:[\d{10}], valid=true|, name=|found=String:mustapha, expected={==}:[mustapha], valid=true|, age=|found=Integer:4, expected={>=}:[4], valid=true|}

Criteria over complex Objects:

To perform validation by criteria over complex objects, you only have to specify the filed path of the wanted field, for example:

  class Student {
   // omittd fields for brievety 
    private Matters matters
    //... getters and setters
    }

    //....
      class Matters {
    private double science;
    private double maths;
    private double languages;
    //...
    }
    //...

Validation process:

  CriteriaValidator criteriaValidator = CriteriaValidator.getInstance();
        Criteria criteria = Criteria.of(student);
        criteria.add(Criterion.of("matters.maths").lessThan(20.0));
        Matters matters = new Matters();
        matters.setMaths(19.99);
        student.setMatters(matters);
        System.out.println(criteriaValidator.getValidationReport(criteria));
        assertTrue(criteriaValidator.check(criteria));

###### Output

 {matters.maths=|found=Double:19.99, expected={<}:[20.0], valid=true|}

Validation overs arrays and collections:

class Book {
private int[] isbn; 
private TreeSet<String> keywords;

// .. other fields 
//.. getters and setters
 }

Validation process:

        Book book = new Book();
        CriteriaValidator criteriaValidator = CriteriaValidator.getInstance();
        Criteria criteria = Criteria.of(book);
        criteria.add(Criterion.of("keywords").length(3));
        criteria.add(Criterion.of("isbn").length(11));
        int[] isbn = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11};
        Set<String> keywords = new TreeSet<>();
        keywords.add("science");
        keywords.add("earth");
        keywords.add("universe");

        book.setKeywords(keywords);
        book.setIsbn(isbn);
System.out.println(criteriaValidator.getValidationReport(criteria));
        assertTrue(criteriaValidator.check(criteria));

Output

 {keywords=|found=TreeSet:[earth, science, universe], expected={length}:[3], valid=true|, isbn=|found=int[]:[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11], expected={length}:[11], valid=true|}