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7.3.1 GETting resources

Suppose that you want to fetch an ingredient from the Taco Cloud API. For that, you can use RestTemplate’s getForObject() to fetch the ingredient. For example, the following code uses RestTemplate to fetch an Ingredient object by its ID:

java

public Ingredient getIngredientById(String ingredientId) {
  return rest.getForObject("http://localhost:8080/ingredients/{id}",
                    Ingredient.class, ingredientId);
}

Here you’re using the getForObject() variant that accepts a String URL and uses a variable list for URL variables. The ingredientId parameter passed into getForObject() is used to fill in the {id} placeholder in the given URL. Although there’s only one URL variable in this example, it’s important to know that the variable parameters are assigned to the placeholders in the order that they’re given.

The second parameter to getForObject() is the type that the response should be bound to. In this case, the response data (that’s likely in JSON format) should be deserialized into an Ingredient object that will be returned.

Alternatively, you can use a Map to specify the URL variables, as shown next:

java

public Ingredient getIngredientById(String ingredientId) {
  Map<String, String> urlVariables = new HashMap<>();
  urlVariables.put("id", ingredientId);
  return rest.getForObject("http://localhost:8080/ingredients/{id}",
                  Ingredient.class, urlVariables);
}

In this case, the value of ingredientId is mapped to a key of id. When the request is made, the {id} placeholder is replaced by the map entry whose key is id.

Using a URI parameter is a bit more involved, requiring that you construct a URI object before calling getForObject(). Otherwise, it’s similar to both of the other variants, as shown here:

java

public Ingredient getIngredientById(String ingredientId) {
  Map<String, String> urlVariables = new HashMap<>();
  urlVariables.put("id", ingredientId);
  URI url = UriComponentsBuilder
          .fromHttpUrl("http://localhost:8080/ingredients/{id}")
          .build(urlVariables);
  return rest.getForObject(url, Ingredient.class);
}

Here the URI object is defined from a String specification, and its placeholders filled in from entries in a Map, much like the previous variant of getForObject(). The getForObject() method is a no-nonsense way of fetching a resource. But if the client needs more than the payload body, you may want to consider using getForEntity().

getForEntity() works in much the same way as getForObject(), but instead of returning a domain object that represents the response’s payload, it returns a ResponseEntity object that wraps that domain object. The ResponseEntity gives access to additional response details,

For example, suppose that in addition to the ingredient data, you want to inspect the Date header from the response. With getForEntity() that becomes straightforward, as shown in the following code:

java

public Ingredient getIngredientById(String ingredientId) {
  ResponseEntity<Ingredient> responseEntity =
    rest.getForEntity("http://localhost:8080/ingredients/{id}",
              Ingredient.class, ingredientId);
  log.info("Fetched time: " +
              responseEntity.getHeaders().getDate());
  return responseEntity.getBody();
}

The getForEntity() method is overloaded with the same parameters as getForObject(), so you can provide the URL variables as a variable list parameter or call getForEntity() with a URI object.

7.3.1 GETting resources ​

7.3.1 GETting resources