Expose enums with Spring Data REST - spring

Question

I'm using Spring Boot 1.5.3, Spring Data REST, HATEOAS.
I've a simple entity model:
#Entity
public class User extends AbstractEntity implements UserDetails {
private static final long serialVersionUID = 5745401123028683585L;
public static final PasswordEncoder PASSWORD_ENCODER = new BCryptPasswordEncoder();
#NotNull(message = "The name of the user cannot be blank")
#Column(nullable = false)
private String name;
/** CONTACT INFORMATION **/
private String landlinePhone;
private String mobilePhone;
#NotNull(message = "The username cannot be blank")
#Column(nullable = false, unique = true)
private String username;
#Email(message = "The email address is not valid")
private String email;
#JsonIgnore
private String password;
#Column(nullable = false)
private String timeZone = "Europe/Rome";
#JsonIgnore
private LocalDateTime lastPasswordResetDate;
#Column(nullable = false, columnDefinition = "BOOLEAN default true")
private boolean enabled = true;
#Type(type = "json")
#Column(columnDefinition = "json")
private Roles[] roles = new Roles[] {};
and my enum Roles is:
public enum Roles {
ROLE_ADMIN, ROLE_USER, ROLE_MANAGER, ROLE_TECH;
#JsonCreator
public static Roles create(String value) {
if (value == null) {
throw new IllegalArgumentException();
}
for (Roles v : values()) {
if (value.equals(v.toString())) {
return v;
}
}
throw new IllegalArgumentException();
}
}
I'm creating a client in Angular 4. Spring Data REST is great and expose repository easily return my model HATEOAS compliant:
{
"_embedded": {
"users": [
{
"name": "Administrator",
"username": "admin",
"roles": [
"Amministratore"
],
"activeWorkSession": "",
"_links": {
"self": {
"href": "http://localhost:8080/api/v1/users/1"
},
"user": {
"href": "http://localhost:8080/api/v1/users/1{?projection}",
"templated": true
}
}
},
Like you can see I'm also translating via rest-messages.properties the value of my enums. Great!
My Angular page now needs the complete lists of roles (enums). I've some question:
understand the better way for the server to return the list of roles
how to return this list
My first attemp was to create a RepositoryRestController in order to take advantage of what Spring Data REST offers.
#RepositoryRestController
#RequestMapping(path = "/api/v1")
public class UserController {
#Autowired
private EntityLinks entityLinks;
#RequestMapping(method = RequestMethod.GET, path = "/users/roles", produces = "application/json")
public Resource<Roles> findRoles() {
Resource<Roles> resource = new Resource<>(Roles.ROLE_ADMIN);
return resource;
}
Unfortunately, for some reason, the call to this methods return a 404 error. I debugged and the resource is created correctly, so I guess the problem is somewhere in the JSON conversion.

Answer 1

how to return this list?
#RepositoryRestController
#RequestMapping("/roles")
public class RoleController {
#GetMapping
public ResponseEntity<?> getAllRoles() {
List<Resource<Roles>> content = new ArrayList<>();
content.addAll(Arrays.asList(
new Resource<>(Roles.ROLE1 /*, Optional Links */),
new Resource<>(Roles.ROLE2 /*, Optional Links */)));
return ResponseEntity.ok(new Resources<>(content /*, Optional Links */));
}
}

Answer 2

I was playing around with this and have found a couple of ways to do it.
Assume you have a front end form that wants to display a combo box containing priorities for a single Todo such as High, Medium, Low. The form needs to know the primary key or id which is the enum value in this instance and the value should be the readable formatted value the combo box should display.
If you wish to customize the json response in 1 place only such as a single endpoint then I found this useful. The secret sauce is using the value object PriorityValue to allow you to rename the json field through #Relation.
public enum Priority {
HIGH("High"),
NORMAL("Normal"),
LOW("Low");
private final String description;
Priority(String description) {
this.description = description;
}
public String getDescription() {
return description;
}
public static List<Priority> orderedValues = new ArrayList<>();
static {
orderedValues.addAll(Arrays.asList(Priority.values()));
}
}
#RepositoryRestController
#RequestMapping(value="/")
public class PriorityController {
#Relation(collectionRelation = "priorities")
#JsonAutoDetect(fieldVisibility = JsonAutoDetect.Visibility.ANY)
private class PriorityValue {
private String id;
private String value;
public PriorityValue(String id,
String value) {
this.id = id;
this.value = value;
}
}
#GetMapping(value = "/api/priorities", produces = MediaTypes.HAL_JSON_VALUE)
public ResponseEntity<Resources<PriorityValue>> getPriorities() {
List<PriorityValue> priorities = Priority.orderedValues.stream()
.map(p -> new PriorityValue(p.name(), p.getDescription()))
.collect(Collectors.toList());
Resources<PriorityValue> resources = new Resources<>(priorities);
resources.add(linkTo(methodOn(PriorityController.class).getPriorities()).withSelfRel());
return ResponseEntity.ok(resources);
}
}
Another approach is to use a custom JsonSerializer. The only issue using this is everywhere a Priority enum is serialized you will end up using this format which may not be what you want.
#JsonSerialize(using = PrioritySerializer.class)
#Relation(collectionRelation = "priorities")
public enum Priority {
HIGH("High"),
NORMAL("Normal"),
LOW("Low");
private final String description;
Priority(String description) {
this.description = description;
}
public String getDescription() {
return description;
}
public static List<Priority> orderedValues = new ArrayList<>();
static {
orderedValues.addAll(Arrays.asList(Priority.values()));
}
}
#RepositoryRestController
#RequestMapping(value="/api")
public class PriorityController {
#GetMapping(value = "/priorities", produces = MediaTypes.HAL_JSON_VALUE)
public ResponseEntity<Resources<Priority>> getPriorities() {
Resources<Priority> resources = new Resources<>(Priority.orderedValues);
resources.add(linkTo(methodOn(PriorityController.class).getPriorities()).withSelfRel());
return ResponseEntity.ok(resources);
}
}
public class PrioritySerializer extends JsonSerializer<Priority> {
#Override
public void serialize(Priority priority,
JsonGenerator generator,
SerializerProvider serializerProvider)
throws IOException, JsonProcessingException {
generator.writeStartObject();
generator.writeFieldName("id");
generator.writeString(priority.name());
generator.writeFieldName("value");
generator.writeString(priority.getDescription());
generator.writeEndObject();
}
}
The final json response from http://localhost:8080/api/priorities
{
"_embedded": {
"priorities": [
{
"id": "HIGH",
"value": "High"
},
{
"id": "NORMAL",
"value": "Normal"
},
{
"id": "LOW",
"value": "Low"
}
]
},
"_links": {
"self": {
"href": "http://localhost:8080/api/priorities"
}
}
}