How can I output the return value of a Method like totalAmount in an Spring Rest Entity - spring

Question

is it possible to output a return Value totalAmount of an Entity ShoppingCart that is not a Value in the Class but a Method? So for example I have a Class Shoppingcart with a List of Items. and a Method totalAmount. Now when I make a request to the API with the URL http://localhost:8082/carts/1 I want to get a response like the following:
{
"creationDate": "2016-12-07T09:45:38.000+0000",
"items": [
{
"itemName": "Nintendo 2DS",
"description": "Konsole from Nintendo",
"price": 300.5,
"quantity": 3
},
{
"itemName": "Nintendo Classic",
"description": "Classic nintendo Console from the 80th...",
"price": 75,
"quantity": 2
}
],
"totalAmount": "1051,50",
"_links": {
"self": {
"href": "http://localhost:8082/carts/2"
},
"cart": {
"href": "http://localhost:8082/carts/2"
},
"checkout": {
"href": "http://localhost:8083/order"
}
}
}
Currently the response of an API request looks like the following:
{
"creationDate": "2016-12-07T09:45:38.000+0000",
"items": [
{
"itemName": "Nintendo 2DS",
"description": "Konsole from Nintendo",
"price": 300.5,
"quantity": 3
},
{
"itemName": "Nintendo Classic",
"description": "Classic nintendo Console from the 80th...",
"price": 75,
"quantity": 2
}
],
"_links": {
"self": {
"href": "http://localhost:8082/carts/2"
},
"cart": {
"href": "http://localhost:8082/carts/2"
},
"checkout": {
"href": "http://localhost:8083/order"
}
}
}
Is there an Annotation that do this job or something other. I tried to add it in the CartResourceProcessor (org.springframework.hateoas.ResourceProcessor) but there is only the possibility to add additional links. Or do I need to add a Class value totalAmount?

Answer 1

Yes you can achieve that by annotating your method with Jackson #JsonProperty annotation
Code sample
#JsonProperty("totalAmount")
public double computeTotalAmount()
{
// compute totalAmout and return it
}

Answer 2

And to answer the possible next question you get after reading this. How the totalAmount is calculated. Here the snippet
public Class Cart{
// some Class values
#JsonProperty("totalAmount")
public BigDecimal total(){
return items.stream()
.map(Item::total)
.reduce(BigDecimal.ZERO, BigDecimal::add);
}
}
public class Item{
// some Item values
#JsonProperty("totalAmount")
public BigDecimal total(){
return price.multiply(new BigDecimal(this.quantity));
}
}
Outputs something similar to this:
{
"creationDate": "2016-12-07T09:45:38.000+0000",
"items": [
{
"itemName": "Nintendo 2DS",
"description": "Konsole from Nintendo",
"price": 300.5,
"quantity": 3,
"totalAmount": 901.5
},
{
"itemName": "Nintendo Classic",
"description": "Classic nintendo Console from the 80th...",
"price": 75,
"quantity": 2,
"totalAmount": 150
}
],
"totalAmount": 1051.5,
"_links": {
"self": {
"href": "http://localhost:8082/carts/2"
},
"cart": {
"href": "http://localhost:8082/carts/2"
},
"checkout": {
"href": "http://localhost:8083/order"
}
}
}
Hope it helps you :)