Verifica dei tipi di dato

Pulizia dei dati in Java

Dennis Lee

Software Engineer

Perché controllare i tipi di dato?

Devi eseguire il parsing di testo da sorgenti esterne
Tipi non validi causano errori a runtime
Una valida verifica evita crash

String priceText = "$30.61";
double price = Double.parseDouble(priceText);  // Fails: $ not valid in number

Exception in thread "main" java.lang.NumberFormatException

Validare testo numerico

// Utility for number validation
import org.apache.commons.lang3.math.NumberUtils;

String reviewCountText = "165";
System.out.println(NumberUtils.isParsable(reviewCountText));

true

String priceText = "$30.61"; // Invalid number
System.out.println(NumberUtils.isParsable(priceText)); // false: has $ symbol

false

DNT_CURLLY_TAG_1

Eseguire il parsing di testo numerico

private static String validateNumeric(String value) {
    if (NumberUtils.isParsable(value)) return value;  // Return if valid number
    throw new IllegalArgumentException("Invalid: " + value);  // Else throw error
}

int reviews = Integer.parseInt(validateNumeric("165"));  // Validate then parse

// Remove $ first
double price = Double.parseDouble(validateNumeric("$30.61".replace("$", "")));
System.out.println("reviews: " + reviews + "\nprice in $: " + price);

reviews: 165
price in $: 30.61

Validare formati data

import java.time.format.DateTimeFormatter; // For date pattern formatting

private static LocalDate parseDate(String dateStr) {
    DateTimeFormatter format = DateTimeFormatter.ofPattern("M/d/yy");

    return LocalDate.parse(dateStr, format); // Convert string to LocalDate
}


LocalDate date = parseDate("1/10/23"); // "1/10/23" converts to 2023-01-10 
System.out.println("Date: " + date);

Date: 2023-01-10

Combinare validazioni numeriche e date

private static double parsePrice(String price) {
    return Double.parseDouble(validateNumeric(price.replace("$", "")); // Remove $
}


// Convert CSV fields to BookSales
public static BookSales parseSalesData(String[] fields) {
    String title = fields[0];
    LocalDate publishDate = parseDate(fields[1]); // Custom date parsing
    int reviews = Integer.parseInt(validateNumeric(fields[2]));
    double rating = Double.parseDouble(validateNumeric(fields[3]));
    double price = parsePrice(fields[4]); // Handle currency format
    return new BookSales(title, publishDate, reviews, rating, price);
}

Lettura sicura di file CSV

List<BookSales> sales = new ArrayList<>(); // Store BookSales objects


try (BufferedReader reader = new BufferedReader(new FileReader("book_sales.csv"))) {

    String line = reader.readLine(); // Skip header row

    while ((line = reader.readLine()) != null) {  // Read until end of file
      String[] fields = line.split(",");  // Split CSV line into array
      sales.add(parseSalesData(fields));  // Convert fields to BookSales object
    }
}

sales.forEach(System.out::println);  // Print each sale

BookSales[title=Python Crash Course, publishDate=2023-01-10, 
reviewCount=165, rating=4.8, price=30.61]

Riepilogo: verifica dei tipi di dato

Valida il testo prima del parsing per evitare errori a runtime
Import principali
- org.apache.commons.lang3.math.NumberUtils
- java.time.format.DateTimeFormatter
Usa NumberUtils.isParsable() per verificare stringhe numeriche
Gestisci più formati data con DateTimeFormatter
Catturare i problemi di tipo garantisce l’integrità dei dati

Passons à la pratique !

Pulizia dei dati in Java