Play Store Application link – Java to AngularJS in 16 Steps – App on Google Play
Step 0 – AngularJS Definition and Code Setup
Definition:
AngularJS is a JavaScript framework based on the MVC (Model-View-Controller) architectural pattern, designed to build dynamic web applications.
Comparing with Java (Servlets):
In Java, especially with Servlets, we follow a similar pattern:
- Model: The data you manage, typically in Java Beans or plain Java objects.
- View: The JSP or HTML that renders the data.
- Controller: The Servlet that processes requests, interacts with the Model, and sends the data to the View.
Similarly, in AngularJS:
- Model is the data object.
- View is the HTML using AngularJS directives.
- Controller is the JavaScript function that manages the interaction between the Model and the View.
What is MVC in Simple Terms?
Think of MVC as a way to structure your code:
- Model: Like a Java object holding data, it represents the state of the application.
- View: Like JSP in Java, this shows the data to the user.
- Controller: Like a Java Servlet, it handles user input, updates the Model, and determines which View to display.
Basic AngularJS Code Setup
In Java, you would create an HTML form and a Servlet like this:
Java Servlet Code:
@WebServlet("/greet")
public class GreetServlet extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
out.println("<html><body>");
out.println("<h1>Hello, " + request.getParameter("name") + "!</h1>");
out.println("</body></html>");
}
}
In AngularJS, the code is simpler and more dynamic, as shown below:
AngularJS Example:
<pre class="wp-block-syntaxhighlighter-code"><html ng-app>
<head>
<a href="https://ajax.googleapis.com/ajax/libs/angularjs/1.8.2/angular.min.js">https://ajax.googleapis.com/ajax/libs/angularjs/1.8.2/angular.min.js</a>
</head>
<body>
<div ng-init="name='World'">
<p>Hello, {{name}}!</p>
</div>
</body>
</html></pre>
Breaking it Down:
- ng-app: Just like in Java, we need to initialize the application (like starting a Servlet or a web app).
- ng-init: Similar to initializing variables in a Java method or constructor, this sets a value.
- {{name}}: In AngularJS, we use this expression to bind the data from the model (just like how we use Java objects to store data and output them in JSP).
Controller in AngularJS (Similar to a Servlet Controller)
In Java Servlets, the controller handles the requests. In AngularJS, we have a controller function written in JavaScript that manages how the data flows.
Java Servlet Controller Code:
@WebServlet("/controller")
public class MyControllerServlet extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
// business logic
request.setAttribute("message", "Hello World from Servlet!");
request.getRequestDispatcher("view.jsp").forward(request, response);
}
}
AngularJS Controller Code:
<pre class="wp-block-syntaxhighlighter-code"><html>
<head>
<a href="https://ajax.googleapis.com/ajax/libs/angularjs/1.8.2/angular.min.js">https://ajax.googleapis.com/ajax/libs/angularjs/1.8.2/angular.min.js</a>
</head>
<body>
<div ng-controller="MyController">
<p>{{message}}</p>
</div>
<script>
var app = angular.module('myApp', []);
app.controller('MyController', function($scope) {
$scope.message = 'Hello World from AngularJS!';
});
</script>
</body>
</html></pre>
Key Points:
- The Controller in AngularJS, like a Java Servlet, controls what happens between the data (Model) and the user interface (View).
- $scope: In AngularJS,
$scopeis a JavaScript object that binds the data from the controller to the view. It’s similar to setting request attributes in Servlets and accessing them in JSP.
Quick Comparison Table:
| Concept | Java (Servlets + JSP) | AngularJS |
|---|---|---|
| Model | Java objects, Request parameters | Data inside $scope |
| View | JSP, HTML | HTML with AngularJS expressions |
| Controller | Servlet | AngularJS Controller function |
| Initialization | @WebServlet annotation, JSP files | ng-app, ng-controller in HTML |
Conclusion:
In Java, we handle data flow using Servlets, JSP, and request-response mechanisms. AngularJS simplifies this process by providing a direct link between the HTML (View), the data (Model), and the controlling logic (Controller), allowing for a more dynamic and seamless user experience.