The Master Class of "Learn Spring Security" is out:
1. Overview
In this article we will mainly focus on implementing server side pagination in a Spring REST API and a simple AngularJS frontend.
We’ll also explore a commonly used table grid in Angular named UI Grid.
2. Dependencies
Here we detail various dependencies that are required for this article.
2.1. JavaScript
In order for Angular UI Grid to work we will need the below scripts imported in our HTML.
2.2. Maven
For our backend we will be using Spring Boot, so we’ll need the below dependencies:
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-tomcat</artifactId>
<scope>provided</scope>
</dependency>
Note: Other dependencies were not specified here, for the full list, check the complete pom.xml in the github project.
3. About the Application
The application is a simple student’s directory app which allows users to see the student details in a paginated table grid.
The application uses Spring Boot and runs in an embedded Tomcat server with an embedded database.
Finally, on the API side of things, there are a few ways to do pagination, described in the REST Pagination in Spring article here – which is highly recommended reading in conjunction with this article.
Our solution here is simple – having the paging information in a URI query as follows: /student/get?page=1&size=2.
4. The Client Side
First we need to create the client-side logic.
4.1. The UI-Grid
Our index.html will have the imports we need and a simple implementation of the table grid:
<!DOCTYPE html>
<html lang="en" ng-app="app">
<head>
<link rel="stylesheet" href="https://cdn.rawgit.com/angular-ui/
bower-ui-grid/master/ui-grid.min.css">
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/
1.5.6/angular.min.js"></script>
<script src="https://cdn.rawgit.com/angular-ui/bower-ui-grid/
master/ui-grid.min.js"></script>
<script src="view/app.js"></script>
</head>
<body>
<div ng-controller="StudentCtrl as vm">
<div ui-grid="gridOptions" class="grid" ui-grid-pagination>
</div>
</div>
</body>
</html>
Let’s have a closer look at the code:
- ng-app – is the Angular directive that loads the module app. All elements under these will be part of the app module
- ng-controller – is the Angular directive that loads the controller StudentCtrl with an alias of vm. All elements under these will be part of the StudentCtrl controller
- ui-grid – is the Angular directive that belongs to Angular ui-grid and uses gridOptions as its default settings, gridOptions is declared under $scope in app.js
4.2. The AngularJS Module
Let’s first define the module in app.js:
var app = angular.module('app', ['ui.grid','ui.grid.pagination']);
We declared the app module and we injected ui.grid to enable UI-Grid functionality; we also injected ui.grid.pagination to enable pagination support.
Next we’ll define the controller:
app.controller('StudentCtrl', ['$scope','StudentService',
function ($scope, StudentService) {
var paginationOptions = {
pageNumber: 1,
pageSize: 5,
sort: null
};
StudentService.getStudents(
paginationOptions.pageNumber,
paginationOptions.pageSize).success(function(data){
$scope.gridOptions.data = data.content;
$scope.gridOptions.totalItems = data.totalElements;
});
$scope.gridOptions = {
paginationPageSizes: [5, 10, 20],
paginationPageSize: paginationOptions.pageSize,
enableColumnMenus:false,
useExternalPagination: true,
columnDefs: [
{ name: 'id' },
{ name: 'name' },
{ name: 'gender' },
{ name: 'age' }
],
onRegisterApi: function(gridApi) {
$scope.gridApi = gridApi;
gridApi.pagination.on.paginationChanged(
$scope,
function (newPage, pageSize) {
paginationOptions.pageNumber = newPage;
paginationOptions.pageSize = pageSize;
StudentService.getStudents(newPage,pageSize)
.success(function(data){
$scope.gridOptions.data = data.content;
$scope.gridOptions.totalItems = data.totalElements;
});
});
}
};
}]);
Let’s now have a look at the custom pagination settings in $scope.gridOptions:
- paginationPageSizes – defines the available page size options
- paginationPageSize – defines the default page size
- enableColumnMenus – is used to enable/disable the menu on columns
- useExternalPagination – is required if you are paginating on the server side
- columnDefs – the column names that will be automatically mapped to the JSON object returned from the server. The field names in the JSON Object returned from the server and the column name defined should match.
- onRegisterApi – the ability to register public methods events inside the grid. Here we registered the gridApi.pagination.on.paginationChanged to tell UI-Grid to trigger this function whenever the page was changed.
And to send the request to the API:
app.service('StudentService',['$http', function ($http) {
function getStudents(pageNumber,size) {
pageNumber = pageNumber > 0?pageNumber - 1:0;
return $http({
method: 'GET',
url: 'student/get?page='+pageNumber+'&size='+size
});
}
return {
getStudents: getStudents
};
}]);
5. The Backend and the API
5.1. The RESTful Service
Here’s the simple RESTful API implementation with pagination support:
@RestController
public class StudentDirectoryRestController {
@Autowired
private StudentService service;
@RequestMapping(
value = "/student/get",
params = { "page", "size" },
method = RequestMethod.GET
)
public Page<Student> findPaginated(
@RequestParam("page") int page, @RequestParam("size") int size) {
Page<Student> resultPage = service.findPaginated(page, size);
if (page > resultPage.getTotalPages()) {
throw new MyResourceNotFoundException();
}
return resultPage;
}
}
The @RestController was introduced in Spring 4.0 as a convenience annotation which implicitly declares @Controller and @ResponseBody.
For our API, we declared it to accept two parameters which are page and size that would also determine the number of records to return to the client.
We also added a simple validation that will throw a MyResourceNotFoundException if the page number is higher than the total pages.
Finally, we’ll return Page as the Response – this is a super helpful component of Spring Data which has holds pagination data.
5.2. The Service Implementation
Our service will simply return the records based on page and size provided by the controller:
@Service
public class StudentServiceImpl implements StudentService {
@Autowired
private StudentRepository dao;
@Override
public Page<Student> findPaginated(int page, int size) {
return dao.findAll(new PageRequest(page, size));
}
}
5.3. The Repository Implementation
For our persistence layer, we’re using an embedded database and Spring Data JPA.
First we need to setup our persistence config:
@EnableJpaRepositories("org.baeldung.web.dao")
@ComponentScan(basePackages = { "org.baeldung.web" })
@EntityScan("org.baeldung.web.entity")
@Configuration
public class PersistenceConfig {
@Bean
public JdbcTemplate getJdbcTemplate() {
return new JdbcTemplate(dataSource());
}
@Bean
public DataSource dataSource() {
EmbeddedDatabaseBuilder builder = new EmbeddedDatabaseBuilder();
EmbeddedDatabase db = builder
.setType(EmbeddedDatabaseType.HSQL)
.addScript("db/sql/data.sql")
.build();
return db;
}
}
The persistence config is simple – we have @EnableJpaRepositories to scan the specified package and find our Spring Data JPA repository interfaces.
We have the @ComponentScan here to automatically scan for all beans and we have @EntityScan (from Spring Boot) to scan for entity classes.
We also declared our simple datasource – using an embedded database that will run the SQL script provided on startup.
Now it’s time we create our data repository:
public interface StudentRepository extends JpaRepository<Student, Long> {}
This is basically all that we need to do here; if you want to go deeper into how to set up and use the highly powerful Spring Data JPA, definitely read the guide to it here.
6. Pagination Request and Response
When calling the API – http://localhost:8080/student/get?page=1&size=5, the JSON response will look something like this:
{
"content":[
{"studentId":"1","name":"Bryan","gender":"Male","age":20},
{"studentId":"2","name":"Ben","gender":"Male","age":22},
{"studentId":"3","name":"Lisa","gender":"Female","age":24},
{"studentId":"4","name":"Sarah","gender":"Female","age":26},
{"studentId":"5","name":"Jay","gender":"Male","age":20}
],
"last":false,
"totalElements":20,
"totalPages":4,
"size":5,
"number":0,
"sort":null,
"first":true,
"numberOfElements":5
}
One thing to notice here is that server returns a org.springframework.data.domain.Page DTO, wrapping our Student Resources.
The Page object will have the following fields:
- last – set to true if its the last page otherwise false
- first – set to true if it’s the first page otherwise false
- totalElements – the total number of rows/records. In our example we passed this to the ui-grid options $scope.gridOptions.totalItems to determine how many pages will be available
- totalPages – the total number of pages which was derived from (totalElements / size)
- size – the number of records per page, this was passed from the client via param size
- number – the page number sent by the client, in our response the number is 0 because in our backend we are using an array of Students which is a zero based index, so in our backend we decrement the page number by 1
- sort – the sorting parameter for the page
- numberOfElements – the number of rows/records return for the page
7. Testing Pagination
Let’s now set up a a test for our pagination logic, using RestAssured; to learn more about RestAssured you can have a look at this tutorial.
7.1. Preparing the Test
For ease of development of our test class we will be adding the static imports:
io.restassured.RestAssured.* io.restassured.matcher.RestAssuredMatchers.* org.hamcrest.Matchers.*
Next, we’ll set up the Spring enabled test:
@RunWith(SpringJUnit4ClassRunner.class)
@SpringApplicationConfiguration(classes = Application.class)
@WebAppConfiguration
@IntegrationTest("server.port:8888")
The @SpringApplicationConfiguration helps Spring know how to load the ApplicationContext, in this case we used the Application.java to configure our ApplicationContext.
The @WebAppConfiguration was defined to tell Spring that the ApplicationContext to be loaded should be a WebApplicationContext.
And the @IntegrationTest was defined to trigger the application startup when running the test, this makes our REST services available for testing.
7.2. The Tests
Here is our first test case:
@Test
public void givenRequestForStudents_whenPageIsOne_expectContainsNames() {
given().params("page", "0", "size", "2").get(ENDPOINT)
.then()
.assertThat().body("content.name", hasItems("Bryan", "Ben"));
}
This test case above is to test that when page 1 and size 2 is passed to the REST service the JSON content returned from the server should have the names Bryan and Ben.
Let’s dissect the test case:
- given – the part of RestAssured and is used to start building the request, you can also use with()
- get – the part of RestAssured and if used triggers a get request, use post() for post request
- hasItems – the part of hamcrest that checks if the values have any match
We add a few more test cases:
@Test
public void givenRequestForStudents_whenResourcesAreRetrievedPaged_thenExpect200() {
given().params("page", "0", "size", "2").get(ENDPOINT)
.then()
.statusCode(200);
}
This test asserts that when the point is actually called an OK response is received:
@Test
public void givenRequestForStudents_whenSizeIsTwo_expectNumberOfElementsTwo() {
given().params("page", "0", "size", "2").get(ENDPOINT)
.then()
.assertThat().body("numberOfElements", equalTo(2));
}
This test asserts that when page size of two is requested the pages size that is returned is actually two:
@Test
public void givenResourcesExist_whenFirstPageIsRetrieved_thenPageContainsResources() {
given().params("page", "0", "size", "2").get(ENDPOINT)
.then()
.assertThat().body("first", equalTo(true));
}
This test asserts that when the resources is called the first time the first page name value is true.
There are many more tests in the repository, so definitely have a look at the github project.
8. Conclusion
This article illustrated how to implement a data table grid using UI-Grid in AngularJS and how to implement the required server side pagination.
The implementation of these examples and tests can be found in the github project. This is a Maven project, so it should be easy to import and run as it is.
To run the Spring boot project, you can simply do mvn spring-boot:run and access it locally on http://localhost:8080/.