Ricardo Jara Miñano

lambda-code

Problem

We are working with data structures, we want to process an array which have complex objects
this will ended up in a lot of lines of code and plenty of loops to perform for example a simple data filter.

Solution

I use lambdas to save code lines and to make more readable code.
Also I would keep in mind do not overuse lambdas making confuse code.

                        
//LAMBDA
//read each object and for each object read and array of object and their "piece" int value and sum them all.
var totalDepartingPieces = departingFlights.stream()
        .flatMap(flight -> flight.getCargo().getBaggageList().stream())
        .mapToInt(Load::getPieces).sum();
//VS

//NO LAMBDA
int totalDepartingPiecesNoLambda = 0;
for (var flight : departingFlights) {
    for(var baggage : flight.getCargo().getBaggageList()) {
        totalDepartingPiecesNoLambda += baggage.getPieces();
    }
}
                        
                      

Java Reflaction and generic

Problem

We are working with a library or a requisite,
which we have to transform list of complex object into a select like object with only label and value
We will do this with a lot of different object which will map to label and value differents fields
for example User will use as label "name" property and "id" as value property
But another object can use another fields. like Country will use "countryCode" as value for example

Solution

Using Java generic and reflaction we can create a method which recives:
the list of X type object, a String which defines the property which will act as a label,
another String which tell us which property is the value.
This way we can reduce lot of repeating code.
I used to use this with selectItem of JSF but it might has more applications.

                        
public static  List> listToSelectItem(
  List list, String label, String value, Class selectItemKeyClass )
  throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {
  List> itemList = new ArrayList<>();
  for (T item : list) {
      R fieldValue = null;
      Method methodValue = item.getClass().getMethod("get" + getSetterGetterName(value));
      fieldValue = (R) methodValue.invoke(item);
      Method methodLabel = item.getClass().getMethod("get" + getSetterGetterName(label));
      Object campoLabelValor = methodLabel.invoke(item);
      itemList.add(new SelectItem(fieldValue,String.valueOf(campoLabelValor)));
  }
  return itemList;
}
public static void main(String[] arg) throws InvocationTargetException, NoSuchMethodException, IllegalAccessException {
  List countries = List.of(new Country(1, "ES", "Spain"),
          new Country(2, "US", "USA"));
  System.out.println(countries);
  List> selectItems = listToSelectItem(countries, "id", "name", Integer.class);
  System.out.println(selectItems);
}
                        
                      

                        
[Country(id=1, name=ES, description=Spain), Country(id=2, name=US, description=USA)]
[SelectItem{id=ES, value='1'}, SelectItem{id=US, value='2'}]
                        
                      

Building self-container java app

Problem

We have build a desktop java application
But we have used java 17 and java fx, so the final user's system will have to have a correct jre 17 compatible with java FX
we are lossing users who do not have the last jdk and java FX also force to have prebuilt jre with fx.

Solution

We will package a final source directory which will include all necessary files to run the app
the drawback of this is we will have a final program bigger however nowadays that is not a problem
we can also distribute two version the little without integrate sdk and the self-container only with the jar.
Keep in mind that before the media player "VLC" we all had problem with the video codecs until they decided to included all in the final app.

pom.xml

zip.xml

result

OPEN API VALIDATION

Problem

We have a back-end service which recives input data which have to be validated
if we recive in an endpoint 10 fields and each one have restrinctions like:
not null field, maxlength field, minlength field, pattern format field
We will have to manually (even using methods) make minimum 10 ifs and if each field has 3 validations 30 ifs.

Solution

We can use javax.validation using hibernate validator,
But instead of using annotations like "@Size()"" we will use open api definition
This way our open api definition api will document the field restrinctions and at the same time hibernate will validate these fields automatically

open api definition with restrinctions

Server validation fails response

Efective use of strategy pattern

Problem

We have a translator app, this app can translate from differents sources (google api, microsoft api, cambrigde dictionary)
We want to do the same thing regardless the translator provider isolating our app logic

Solution

We will use an Interface and implementations of this per each translator source
In our "controller" class we will use this Interface which will take the implementation depending on the translator we choose
We also will use the factory pattern to generate differents implementation depending on the parameter we give.

strategy pattern example

Integration with FTP service and Files

Problem

We have to integrate with a low level system, which it has a primitive interface to receive data.
So primitive that instead of using REST, SOAP or gRPC, the system uses an FTP with files to receive the data each line of the file would be a registry.
Working with files in some program language like java do not give us any data consistency, also modifyng some column and line might be very tricky.

Solution

We have to work with java Class models. which will map each file column into a property
We will also add a javax.validation yo get a Strong model.

                          
@Data
public class RegistrationLPR {
  /**
    * (start character)
    */
  @CsvBindByPosition(position = 0)
  @Size(min = 1, max = 1, message = "initial character should contain 1 character")
  private String n = "N";
  /**
    * (must be unique) (Up to 10 characters)
    */
  @CsvBindByPosition(position = 1)
  @Size(min = 1, max = 10, message = "voucher number must be between 1 and 10 characters")
  private String voucherNumber;
  /**
    * (Up to 10 characters)
    */
  @CsvBindByPosition(position = 2)
  @Size(min = 1, max = 10, message = "voucher product code must be between 1 and 10 characters")
  private String voucherProductCode;
  /**
    * (Up to 20 characters)
    */
  @CsvBindByPosition(position = 3)
  @Size(max = 20, message = "patronSurname code overpass 20 characters")
  private String patronSurname;
}
                          
                        

                          
String createFileContentToSent(List registrationLPRSToBeSent) throws CsvRequiredFieldEmptyException, CsvDataTypeMismatchException {
  Writer writer = new StringWriter();
  StatefulBeanToCsv sbc = new StatefulBeanToCsvBuilder(writer)
          .withQuotechar(CSVWriter.NO_QUOTE_CHARACTER)
          .withSeparator(CSVWriter.DEFAULT_SEPARATOR)
          .withLineEnd("\r\n")
          .build();

  sbc.write(registrationLPRSToBeSent);
  return writer.toString();
}
                          
                        

                          
@Override
public void addRegister(RegisterCreation registerCreation) {
  RegistrationLPR registrationLPR = mapper.fromRegisterCreation(registerCreation);
  //validation using javax.validation
  objectValidator.validate(registrationLPR);
  service.addRegistryReadyToBeSent(registrationLPR)
}
                          
                        

                        
public void sendToSftp(String fileContent) throws JSchException, SftpException {
  ChannelSftp channelSftp = SftpConfiguration.createChannelSftp();
  try {
      InputStream fileContentInputStream = IOUtils.toInputStream(fileContent);
      channelSftp.connect();
      //send register file
      channelSftp.put(fileContentInputStream, remoteDir + REGISTRATION_FILE_NAME);
  } finally {
      SftpUtil.closeSftpConnection(channelSftp);
  }
}
                        
                      

Testing email service

Problem

We have a back-end application which will send emails in some processes.
We want to perform integration tests our app to do that we use memory databases and we mock using wiremock to the rest calls
But when we try to call the smpt service will fail or we will have to mock the response therefore we will not doing a real integration test.

Solution

Using the java library: "greenmail junit extension" we can up smpt service

                        
@SpringBootTest
@ActiveProfiles("test")
@AutoConfigureWebTestClient
class AdministratorControllerTest {
    @Autowired
    private MongoAdministratorClient mongoAdministratorClient;
    @Autowired
    private WebTestClient webClient;
    @RegisterExtension
    static GreenMailExtension greenMail = new GreenMailExtension(ServerSetupTest.SMTP)
            .withConfiguration(GreenMailConfiguration.aConfig().withUser("test", "password"))
            .withPerMethodLifecycle(false);
    @Test
    @DisplayName("should send forgotPassword")
    void should_send_forgotPassword() throws Exception {
        // GIVEN
        SendForgotPasswordDto sendForgot = mockSendForgotPasswordDto();
        AdministratorDocument adminDocument = mockAdministratorDocument();
        mongoAdministratorClient.save(adminDocument).block();
        String url = String.format("%s/%s", ADMINISTRATOR_API, SEND_FORGOT_PASSWORD_API);
        // WHEN
        webClient.post()
                .uri(url)
                .body(Mono.just(sendForgot), SendForgotPasswordDto.class)
                .exchange()
                // THEN response
                .expectStatus().is2xxSuccessful();
        // THEN database
        AdministratorDocument adminDoc = mongoAdministratorClient.findById(adminDocument.getId().toString()).block();
        assertThat(adminDoc).isNotNull();
        assertThat(adminDoc.getForgetPasswordToken()).isNotNull();
    }
}
                        
                      

Using Threads and executor to increment performance

Problem

We have an application which have a periodic job such as:
Sending processed data to another application.
We have a cron which will have to send to several applications some data or requests
the process will take too much time if we only use one thread since we have to connect with several apps.

Solution

We will use multithread process. Using java executors.

Cron Job

                        
@Component
@RequiredArgsConstructor
@Slf4j
public class ProccesorDataScheduler {
    private final Processor processor;

    /**
      * Process data and send them to different systems
      */
    @Scheduled(cron = "${processor.cron.cronToSendSftpFile}")
    public void gatherDataAndSend() {
      processor.sendDataToSystems();
    }
}
                        
                      

Proccessor using Threads and Executors

                        
@RequiredArgsConstructor
@Service
@Slf4j
public class ProcessorImpl implements Processor {
    private static final int MAX_THREADS_NUMBER = 4;

    @Override
    void sendDataToSystems() {
        ExecutorService executor = Executors.newFixedThreadPool(MAX_THREADS_NUMBER);

        //job work
        Callable jobWork = this::executeJob;
        executor.submit(jobWork);

        //shutdown
        executor.shutdown();
        try {
            if (!executor.awaitTermination(1, TimeUnit.MINUTES)) {
                executor.shutdownNow();
            }
        } catch (InterruptedException e) {
            log.error("Error while waiting for executor termination", e);
            executor.shutdownNow();
        }
    }

    String executeJob() {
        //code here
        return "codeResult";
    }
}
                        
                      

Implementing cache system

Problem

We have an application which have a filter which will be used by many people.
We are reciving a lot of requests and the database system we contracted required to increment its budget.
We should have to pay more money to our provider to manage this number of requests.

Solution

We will implement a simple cache system using "ehcache" library with Spring.
This way the database response will be cached by some parameters like eviction time etc...

                        
@Service
@Transactional(readOnly = true)
public class ProductPriceServiceImpl implements ProductPriceService {
    //this will connect with database which is very expensive.
    @Autowired
    private PriceRepository priceRepository;
    
    //we will cache by the filter (complex object)
    @Cacheable(cacheNames="productPriceCache", key="#filterProductPrice")
    @Override
    public ProductPrice findByFilterProductPrice(FilterProductPrice filterProductPrice) {
        return priceRepository.findByFilter(filterProductPrice);
    }
}
                        
                      

EhCache Configuration

Creating a library with Logging system

Problem

We are performing a library to be used by 3 applications or more
We need a logging system to inform of errors or information.
But one application uses Log4j2, another uses LogBack and the final uses Log4j v1
So we library can not use neither of them because of the compatibility.

Solution

We will use "facade" pattern through the library "slf4j" in our library
This way our library logging system will not care about what logging system the final app uses
The final apps will be able to use their own logging systems and using a slf4j binding

Library maven configuration

Application maven configuration

Using SCSS loop to create classes without code duplication

Problem

We are working in a webpage, we do not want to fill our html tags with style attributes
Because if you wanted to change some parameters you will have to modify all styles manually
We will work with classes, but sometimes you need to create too many classes for example
if you want several margins and padding or width and so on. ej: .little-margin, big-margin, .width-20-percent ...

Solution

We will use SCSS using loop to create massive util classes in the resulting CSS.

Scss

Css result