1. Overview
In this tutorial, we’re going to create an example of a simple CRUD application using AngularJS for the front-end and Spring Data REST for the back-end.
2. Creating the REST Data Service
In order to create the support for persistence, we’ll make use of the Spring Data REST specification that will enable us to perform CRUD operations on a data model.
You can find all the necessary information on how to setup the REST endpoints in the introduction to Spring Data REST. In this article, we will reuse the existing project we have setup for the introduction tutorial.
For persistence, we will use the H2 in memory database.
As a data model, the previous article defines a WebsiteUser class, with id, name and email properties and a repository interface called UserRepository.
Defining this interface instructs Spring to create the support for exposing REST collection resources and item resources. Let’s take a closer look at the endpoints available to us now that we will later call from AngularJS.
2.1. The Collection Resources
A list of all the users will be available to us at the endpoint /users. This URL can be called using the GET method and will return JSON objects of the form:
{
"_embedded" : {
"users" : [ {
"name" : "Bryan",
"age" : 20,
"_links" : {
"self" : {
"href" : "http://localhost:8080/users/1"
},
"User" : {
"href" : "http://localhost:8080/users/1"
}
}
},
...
]
}
}
2.2. The Item Resources
A single WebsiteUser object can be manipulated by accessing URLs of the form /users/{userID} with different HTTP methods and request payloads.
For retrieving a WebsiteUser object, we can access /users/{userID} with the GET method. This returns a JSON object of the form:
{
"name" : "Bryan",
"email" : "[email protected]",
"_links" : {
"self" : {
"href" : "http://localhost:8080/users/1"
},
"User" : {
"href" : "http://localhost:8080/users/1"
}
}
}
To add a new WebsiteUser, we will need to call /users with POST method. The attributes of the new WebsiteUser record will be added in the request body as a JSON object:
{name: "Bryan", email: "[email protected]"}
If there are no errors, this URL returns a status code 201 CREATED.
If we want to update the attributes of the WebsiteUser record, we need to call the URL /users/{UserID} with the PATCH method and a request body containing the new values:
{name: "Bryan", email: "[email protected]"}
To delete a WebsiteUser record, we can call the URL /users/{UserID} with the DELETE method. If there are no errors, this returns status code 204 NO CONTENT.
2.3. MVC Configuration
We’ll also add a basic MVC configuration to display html files in our application:
@Configuration
@EnableWebMvc
public class MvcConfig implements WebMvcConfigurer {
public MvcConfig(){
super();
}
@Override
public void configureDefaultServletHandling(
DefaultServletHandlerConfigurer configurer) {
configurer.enable();
}
@Bean
WebServerFactoryCustomizer<ConfigurableServletWebServerFactory> enableDefaultServlet() {
return (factory) -> factory.setRegisterDefaultServlet(true);
}
}
2.4. Allowing Cross Origin Requests
If we want to deploy the AngularJS front-end application separately than the REST API – then we need to enable cross-origin requests.
Spring Data REST has added support for this starting with version 1.5.0.RELEASE. To allow requests from a different domain, all you have to do is add the @CrossOrigin annotation to the repository:
@CrossOrigin
@RepositoryRestResource(collectionResourceRel = "users", path = "users")
public interface UserRepository extends CrudRepository<WebsiteUser, Long> {}
As a result, on every response from the REST endpoints, a header of Access-Control-Allow-Origin will be added.
3. Creating the AngularJS Client
For creating the front end of our CRUD application, we’ll use AngularJS – a well-know JavaScript framework that eases the creation of front-end applications.
In order to use AngularJS, we first need to include the angular.min.js file in our html page that will be called users.html:
<script
src="https://ajax.googleapis.com/ajax/libs/angularjs/1.5.6/angular.min.js">
</script>
Next, we need to create an Angular module, controller, and service that will call the REST endpoints and display the returned data.
These will be placed in a JavaScript file called app.js that also needs to be included in the users.html page:
<script src="view/app.js"></script>
3.1. Angular Service
First, let’s create an Angular service called UserCRUDService that will make use of the injected AngularJS $http service to make calls to the server. Each call will be placed in a separate method.
Let’s take a look at defining the method for retrieving a user by id using the /users/{userID} endpoint:
app.service('UserCRUDService', [ '$http', function($http) {
this.getUser = function getUser(userId) {
return $http({
method : 'GET',
url : 'users/' + userId
});
}
} ]);
Next, let’s define the addUser method which makes a POST request to the /users URL and sends the user values in the data attribute:
this.addUser = function addUser(name, email) {
return $http({
method : 'POST',
url : 'users',
data : {
name : name,
email: email
}
});
}
The updateUser method is similar to the one above, except it will have an id parameter and makes a PATCH request:
this.updateUser = function updateUser(id, name, email) {
return $http({
method : 'PATCH',
url : 'users/' + id,
data : {
name : name,
email: email
}
});
}
The method for deleting a WebsiteUser record will make a DELETE request:
this.deleteUser = function deleteUser(id) {
return $http({
method : 'DELETE',
url : 'users/' + id
})
}
And finally, let’s take a look at the methods for retrieving the entire list of users:
this.getAllUsers = function getAllUsers() {
return $http({
method : 'GET',
url : 'users'
});
}
All of these service methods will be called by an AngularJS controller.
3.2. Angular Controller
We will create an UserCRUDCtrl AngularJS controller that will have an UserCRUDService injected and will use the service methods to obtain the response from the server, handle the success and error cases, and set $scope variables containing the response data for displaying it in the HTML page.
Let’s take a look at the getUser() function that calls the getUser(userId) service function and defines two callback methods in case of success and error. If the server request succeeds, then the response is saved in a user variable; otherwise, error messages are handled:
app.controller('UserCRUDCtrl', ['$scope','UserCRUDService',
function ($scope,UserCRUDService) {
$scope.getUser = function () {
var id = $scope.user.id;
UserCRUDService.getUser($scope.user.id)
.then(function success(response) {
$scope.user = response.data;
$scope.user.id = id;
$scope.message='';
$scope.errorMessage = '';
},
function error (response) {
$scope.message = '';
if (response.status === 404){
$scope.errorMessage = 'User not found!';
}
else {
$scope.errorMessage = "Error getting user!";
}
});
};
}]);
The addUser() function will call the corresponding service function and handle the response:
$scope.addUser = function () {
if ($scope.user != null && $scope.user.name) {
UserCRUDService.addUser($scope.user.name, $scope.user.email)
.then (function success(response){
$scope.message = 'User added!';
$scope.errorMessage = '';
},
function error(response){
$scope.errorMessage = 'Error adding user!';
$scope.message = '';
});
}
else {
$scope.errorMessage = 'Please enter a name!';
$scope.message = '';
}
}
The updateUser() and deleteUser() functions are similar to the one above:
$scope.updateUser = function () {
UserCRUDService.updateUser($scope.user.id,
$scope.user.name, $scope.user.email)
.then(function success(response) {
$scope.message = 'User data updated!';
$scope.errorMessage = '';
},
function error(response) {
$scope.errorMessage = 'Error updating user!';
$scope.message = '';
});
}
$scope.deleteUser = function () {
UserCRUDService.deleteUser($scope.user.id)
.then (function success(response) {
$scope.message = 'User deleted!';
$scope.User = null;
$scope.errorMessage='';
},
function error(response) {
$scope.errorMessage = 'Error deleting user!';
$scope.message='';
});
}
And finally, let’s define the function that retrieves a list of users, and stores it in the users variable:
$scope.getAllUsers = function () {
UserCRUDService.getAllUsers()
.then(function success(response) {
$scope.users = response.data._embedded.users;
$scope.message='';
$scope.errorMessage = '';
},
function error (response) {
$scope.message='';
$scope.errorMessage = 'Error getting users!';
});
}
3.3. HTML Page
The users.html page will make use of the controller functions defined in the previous section and the stored variables.
First, in order to use the Angular module, we need to set the ng-app property:
<html ng-app="app">
Then, to avoid typing UserCRUDCtrl.getUser() every time we use a function of the controller, we can wrap our HTML elements in a div with a ng-controller property set:
<div ng-controller="UserCRUDCtrl">
Let’s create the form that will input and display the values for the WebiteUser object we want to manipulate. Each of these will have a ng-model attribute set, which binds it to the value of the attribute:
<table>
<tr>
<td width="100">ID:</td>
<td><input type="text" id="id" ng-model="user.id" /></td>
</tr>
<tr>
<td width="100">Name:</td>
<td><input type="text" id="name" ng-model="user.name" /></td>
</tr>
<tr>
<td width="100">Age:</td>
<td><input type="text" id="age" ng-model="user.email" /></td>
</tr>
</table>
Binding the id input to the user.id variable, for example, means that whenever the value of the input is changed, this value is set in the user.id variable and vice versa.
Next, let’s use the ng-click attribute to define the links that will trigger the invoking of each CRUD controller function defined:
<a ng-click="getUser(user.id)">Get User</a>
<a ng-click="updateUser(user.id,user.name,user.email)">Update User</a>
<a ng-click="addUser(user.name,user.email)">Add User</a>
<a ng-click="deleteUser(user.id)">Delete User</a>
Finally, let’s display the list of users entirely and by name:
<a ng-click="getAllUsers()">Get all Users</a><br/><br/>
<div ng-repeat="usr in users">
{{usr.name}} {{usr.email}}
4. Conclusion
In this tutorial, we have shown how you can create a CRUD application using AngularJS and the Spring Data REST specification.
The complete code for the above example can be found in the GitHub project.
To run the application, you can use the command mvn spring-boot:run and access the URL /users.html.
