Lab 6: Return JSON of DTO via GET

Goals

• Return a Data Transfer Object (DTO) as a JSON string
• Understand the difference between Domain Objects and DTOs
• Learn more about the Jackson ObjectMapper class

a. Create DTO

1. Create a new Class, CoffeeItemResponse, that has four instance variables: a long for the id, and four Strings: size, kind, creamer, and price.
2. Generate getters and setters for all 5 variables.
3. Write a static factory method, from that takes a CoffeeItem and returns a converted CoffeeItemResponse containing the information from the coffee item.

b. JSON Web Test

1. Add the following autowired dependency to the CoffeeOrderWebTest:

   // in tests, it's OK to do "field" Autowiring (injection)
   @Autowired
   ObjectMapper objectMapper;
   

2. Add this new test method:

   @Test
   public void getCoffeeOrderReturnsCompleteJson() throws Exception {
     MvcResult mvcResult = mockMvc.perform(get("/api/coffee/order")
                                               .accept(MediaType.APPLICATION_JSON))
                                  .andExpect(content().contentType(MediaType.APPLICATION_JSON))
                                  .andReturn();
   
     CoffeeItem coffeeItem = new CoffeeItem("small", "latte", "milk");
     coffeeItem.setId(1L);
     CoffeeItemResponse expectedResponse = CoffeeItemResponse.from(coffeeItem);
     String expectedJson = objectMapper.writeValueAsString(expectedResponse);
   
     assertThat(mvcResult.getResponse().getContentAsString())
         .isEqualTo(expectedJson);
   }
   

Test Fails

Run the above test, and it should compile, but fail.

c. Convert Item to Response

In the CoffeeOrderController change the GET-mapped method to return a CoffeeItemResponse DTO instead of the domain object.

Note

Use the from method to convert the CoffeeItem object to a DTO, don't just create the DTO directly.

If you do this correctly, the above test should pass.

Browser

Now that the test passes, run the application and try it in the browser: http://localhost:8080/api/coffee/order

Is that what you expected to see?

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Glossary

JavaBean

A class that exposes instance variables as properties via getters and setters.

Data Transfer Object

A DTO is a data-only class following the JavaBean getter/setter naming pattern, used for incoming and outgoing data to be transformed to JSON, XML, and other Media Types.

Response Object

A response object is a DTO that's meant to be returned to the caller of an HTTP-based Web API.

ObjectMapper

Part of the Jackson library. Converts JavaBean-style objects to and from JSON, XML, and other formats.