Conversion and Validation

Jakarta EE: Conversion & Validation 🎭

The Magical Translator & Gatekeeper Story

Imagine you’re at a magical post office. People come in speaking different languages and writing letters in strange formats. Before any letter can be delivered, two important helpers work together:

1. The Translator (Converter) - Changes words from one language to another
2. The Gatekeeper (Validator) - Checks if the letter follows the rules

That’s exactly what Faces Converters and Faces Validators do in Jakarta EE!

🔄 What Are Faces Converters?

Think of a converter like a language translator at an airport.

The Problem:

• Humans type text: "January 15, 2024"
• Computers need objects: LocalDate(2024, 1, 15)

The Solution: Converters translate between human text and computer objects!

graph TD
    A["User Types Text"] --> B["Converter"]
    B --> C["Java Object"]
    C --> B
    B --> D["Display Text"]

How It Works

When you submit a form:

1. String → Object (User input becomes Java object)
2. Server processes the object
3. Object → String (Java object becomes display text)

📦 Standard Converters

Jakarta Faces gives you FREE translators for common types. No coding needed!

The Built-In Helpers

Example: Number Converter

<h:inputText value="#{bean.price}">
  <f:convertNumber
    type="currency"
    currencySymbol="quot;/>
</h:inputText>

User types: 1234.50 User sees: $1,234.50

Example: Date Converter

<h:inputText value="#{bean.birthday}">
  <f:convertDateTime
    pattern="MM/dd/yyyy"/>
</h:inputText>

User types: 01/15/2024 Java gets: LocalDate object!

🛠️ Custom Converters

What if you have a special language nobody speaks?

Build your own translator!

When You Need One

• Converting user IDs to User objects
• Phone numbers with special formats
• Custom codes like product SKUs

Building a Custom Converter

Step 1: Create the class

@FacesConverter("phoneConverter")
public class PhoneConverter
    implements Converter<Phone> {

  @Override
  public Phone getAsObject(
      FacesContext ctx,
      UIComponent comp,
      String value) {
    // String → Phone object
    return new Phone(value);
  }

  @Override
  public String getAsString(
      FacesContext ctx,
      UIComponent comp,
      Phone phone) {
    // Phone object → String
    return phone.format();
  }
}

Step 2: Use it in your page

<h:inputText value="#{bean.phone}"
  converter="phoneConverter"/>

The Magic Ingredients

graph TD
    A["Implement Converter"] --> B["getAsObject"]
    A --> C["getAsString"]
    B --> D["String to Object"]
    C --> E["Object to String"]
    A --> F["@FacesConverter"]

✅ What Are Faces Validators?

If converters are translators, validators are gatekeepers.

The gatekeeper checks:

• Is this letter addressed correctly?
• Does it have a stamp?
• Is the message appropriate?

Validators check if user input follows your rules!

When Validation Happens

graph TD
    A["User Submits Form"] --> B["Convert Input"]
    B --> C["Validate Input"]
    C -->|Pass| D["Process Data"]
    C -->|Fail| E["Show Error"]

📏 Standard Validators

Free rule-checkers included with Jakarta Faces!

The Built-In Gatekeepers

Example: Length Check

<h:inputText value="#{bean.username}">
  <f:validateLength
    minimum="3"
    maximum="20"/>
</h:inputText>

Rules: Username must be 3-20 characters!

Example: Number Range

<h:inputText value="#{bean.age}">
  <f:validateLongRange
    minimum="1"
    maximum="120"/>
</h:inputText>

Rules: Age must be between 1 and 120!

Example: Pattern Match

<h:inputText value="#{bean.email}">
  <f:validateRegex
    pattern="[^@]+@[^@]+\.[^@]+"/>
</h:inputText>

Rules: Must look like an email!

Combining Validators

You can stack multiple gatekeepers:

<h:inputText value="#{bean.code}"
  required="true">
  <f:validateLength
    minimum="5" maximum="10"/>
  <f:validateRegex
    pattern="[A-Z0-9]+"/>
</h:inputText>

All rules must pass!

🎨 Custom Validators

Sometimes you need special rules nobody thought of.

When You Need One

• Check if username already exists
• Validate credit card numbers
• Business-specific rules

Building a Custom Validator

Step 1: Create the class

@FacesValidator("ageValidator")
public class AgeValidator
    implements Validator<Integer> {

  @Override
  public void validate(
      FacesContext ctx,
      UIComponent comp,
      Integer value)
      throws ValidatorException {

    if (value < 18) {
      throw new ValidatorException(
        new FacesMessage(
          "Must be 18 or older!"));
    }
  }
}

Step 2: Use it in your page

<h:inputText value="#{bean.age}">
  <f:validator validatorId="ageValidator"/>
</h:inputText>

The Validation Blueprint

graph TD
    A["Implement Validator"] --> B["validate method"]
    B --> C{Value OK?}
    C -->|Yes| D["Continue"]
    C -->|No| E["Throw ValidatorException"]
    E --> F["Show Error Message"]

Bean Validation Integration

Even easier! Use annotations:

public class User {
  @NotNull
  @Size(min=3, max=20)
  private String username;

  @Min(18)
  private Integer age;

  @Email
  private String email;
}

The annotations validate automatically!

🔗 How They Work Together

Converters and Validators are best friends:

graph TD
    A["User Input"] --> B["CONVERT"]
    B --> C["VALIDATE"]
    C -->|Pass| D["Bean Property"]
    C -->|Fail| E["Error Message"]
    B -->|Fail| E

The Complete Flow

1. User types "25" in age field
2. Converter turns "25" into Integer(25)
3. Validator checks: Is 25 ≥ 18? ✅
4. Value goes to your bean!

Real Example

<h:inputText value="#{user.birthday}">
  <!-- Convert string to date -->
  <f:convertDateTime
    pattern="yyyy-MM-dd"/>
  <!-- Check date is in past -->
  <f:validator
    validatorId="pastDateValidator"/>
</h:inputText>
<h:message for="birthday"/>

🎯 Quick Summary

💡 Key Takeaways

1. Converters change text ↔ objects
2. Validators enforce your rules
3. Standard ones are free and ready
4. Custom ones handle special cases
5. They work together in every form!

Remember: Every time a user fills out a form, your translators and gatekeepers spring into action, making sure the right data gets through in the right format!

🚀 Now you understand the magic behind web form processing!