Calling a micro service

Question

I looked for the similar question but could not find any . I have a micro service created with drop-wizard which is running in localhost:9000.

I am working in another project(with spring mvc) running in 8080. I wan to call the above service which gives me string back from any of my controllers in main project .lets say the path is "localhost:9000/giveMeString" .

Answer 1

You can use Apache's HTTP Client. See this example borrowed from their documentation:

  // Create an instance of HttpClient.
  HttpClient client = new HttpClient();

  // Create a method instance.
  GetMethod method = new GetMethod("http://localhost:9000/giveMeString");

  // Execute the method.
  int statusCode = client.executeMethod(method);

  // Read the response body.
  byte[] responseBody = method.getResponseBody();

  //Print the response
  System.out.println(new String(responseBody));

Answer 2

If you're really going down the microservice path, note that creating an HTTP client for every request and making synchronous, blocking requests won't really scale.

Here are a few ideas, if you're using Spring:

Create a single RestTemplate instance

You can create a single RestTemplate instance and inject it in multiple places in your application.

@Configuration
public class MyConfiguration {
  @Bean
  public RestTemplate restTemplate() {
    return new RestTemplate(new HttpComponentsClientHttpRequestFactory());
  }
}

Better, wrap that REST client with a Cache

Check out Sagan's take on this .

Even better, go asynchronous

You can use an AsyncRestTemplate ; very useful, especially if your Controllers need to make multiple requests and if you don't want to block your webapp thread. Your Controller can even return a DeferredResult or a ListenableFuture , which will make your webapp more scalable.

And Spring Cloud + Netflix

You can also check Spring Cloud and Spring Cloud Netflix . You'll see there interesting features: load-balancing, recovery, circuit breakers, etc.