Play Store Application link – Java to Angular in 19 Steps – App on Google Play

Github project link – https://github.com/kuldeep101990/angular-step7

In this step, we’ll dive into Angular’s structural directives like *ngIf, *ngFor, and ngSwitch, and explore how ng-template can be used for dynamic content rendering. For Java developers, this is akin to using conditional logic in JSP or JSTL tags to control what gets displayed in a web application.

Concept

Structural directives in Angular allow you to dynamically modify the DOM by adding, removing, or altering elements based on conditions. This is comparable to conditional rendering in Java web applications, where logic determines what content is presented.

ng-template provides a clean way to define reusable templates, making it a powerful tool for dynamic content rendering.

Step 1: Using *ngIf for Conditional Rendering

Example:

<div>
  <ng-template [ngIf]="counter > 4" [ngIfElse]="none">
    <p>The click counter <strong>IS GREATER</strong> than 4.</p>
  </ng-template>
  <ng-template #none>
    <p>The click counter is <strong>not greater</strong> than 4.</p>
  </ng-template>
</div>

Explanation:

1. [ngIf]: Displays the template if the condition evaluates to true.
2. [ngIfElse]: Defines an alternative template to display when the condition is false.
3. #none: A reference to the alternative template for the ngIfElse directive.

Java Comparison

In a Java web application, you might use JSTL tags to achieve similar functionality:

<c:choose>
  <c:when test="${counter > 4}">
    <p>The click counter <strong>IS GREATER</strong> than 4.</p>
  </c:when>
  <c:otherwise>
    <p>The click counter is <strong>not greater</strong> than 4.</p>
  </c:otherwise>
</c:choose>

Here, JSTL’s <c:choose> acts as the conditional logic, similar to *ngIf in Angular.

Step 2: Using *ngFor for Iteration

Angular’s *ngFor directive allows you to iterate over a list and render dynamic content.

Example:

<ul>
  <li *ngFor="let item of items; let i = index">
    {{ i + 1 }}. {{ item }}
  </li>
</ul>

Explanation:

• *ngFor: Iterates over the items array and creates an <li> element for each item.
• let i = index: Provides the index of the current item in the loop.

Java Comparison

In JSP, you might use JSTL’s <c:forEach> tag:

<ul>
  <c:forEach var="item" items="${items}" varStatus="status">
    <li>${status.index + 1}. ${item}</li>
  </c:forEach>
</ul>

Both approaches dynamically render a list of items based on data from the backend or component logic.

Step 3: Using ng-template for Dynamic Content

ng-template allows you to define reusable templates and conditionally display them.

Example:

<div>
  <ng-template [ngIf]="isLoggedIn">
    <p>Welcome back, user!</p>
  </ng-template>
  <ng-template [ngIf]="!isLoggedIn">
    <p>Please log in to continue.</p>
  </ng-template>
</div>

Java Comparison:

In JSP, this could be achieved with conditional JSTL tags:

<c:choose>
  <c:when test="${isLoggedIn}">
    <p>Welcome back, user!</p>
  </c:when>
  <c:otherwise>
    <p>Please log in to continue.</p>
  </c:otherwise>
</c:choose>

Step 4: Using ngSwitch for Multiple Conditions

ngSwitch provides a way to render content based on multiple conditions.

Example:

<div [ngSwitch]="userRole">
  <p *ngSwitchCase="'admin'">Welcome, Admin!</p>
  <p *ngSwitchCase="'user'">Hello, User!</p>
  <p *ngSwitchDefault>Access denied.</p>
</div>

Java Comparison:

In JSP, this could be implemented using nested <c:choose> tags:

<c:choose>
  <c:when test="${userRole == 'admin'}">
    <p>Welcome, Admin!</p>
  </c:when>
  <c:when test="${userRole == 'user'}">
    <p>Hello, User!</p>
  </c:when>
  <c:otherwise>
    <p>Access denied.</p>
  </c:otherwise>
</c:choose>

Major Version Differences

1. Angular 5:
   • Limited support for advanced dynamic templating. For instance, ng-template usage was less optimized and required more boilerplate code.
   • Java Comparison: Similar to older Java frameworks where complex JSTL logic or custom tag libraries were less efficient.
2. Angular 9+:
   • Improved performance for structural directives, with faster rendering and better handling of dynamic content.
   • Java Comparison: Comparable to newer versions of Java EE or Spring MVC, which introduced optimized handling for JSP or Thymeleaf templates.

Conclusion

Angular’s structural directives like *ngIf, *ngFor, and ngSwitch offer powerful tools for dynamic content rendering, akin to JSTL tags in Java web applications. The ng-template directive adds a structured way to manage reusable and conditional templates, enhancing code readability and maintainability.

For Java developers, these concepts mirror familiar practices, making the transition to Angular smoother and more intuitive. With these tools, you can build highly dynamic and interactive user interfaces while drawing on your Java expertise.