33. Calling REST services
If you need to call remote REST services from your application, you can use Spring Framework’s RestTemplate
class. Since RestTemplate
instances often need to be customized before being used, Spring Boot does not provide any single auto-configured RestTemplate
bean. It does, however, auto-configure a RestTemplateBuilder
which can be used to create RestTemplate
instances when needed. The auto-configured RestTemplateBuilder
will ensure that sensible HttpMessageConverters
are applied to RestTemplate
instances.
Here’s a typical example:
@Service public class MyBean { private final RestTemplate restTemplate; public MyBean(RestTemplateBuilder restTemplateBuilder) { this.restTemplate = restTemplateBuilder.build(); } public Details someRestCall(String name) { return this.restTemplate.getForObject("/{name}/details", Details.class, name); } }
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There are three main approaches to RestTemplate
customization, depending on how broadly you want the customizations to apply.
To make the scope of any customizations as narrow as possible, inject the auto-configured RestTemplateBuilder
and then call its methods as required. Each method call returns a new RestTemplateBuilder
instance so the customizations will only affect this use of the builder.
To make an application-wide, additive customization a RestTemplateCustomizer
bean can be used. All such beans are automatically registered with the auto-configured RestTemplateBuilder
and will be applied to any templates that are built with it.
Here’s an example of a customizer that configures the use of a proxy for all hosts except 192.168.0.5
:
static class ProxyCustomizer implements RestTemplateCustomizer { @Override public void customize(RestTemplate restTemplate) { HttpHost proxy = new HttpHost("proxy.example.com"); HttpClient httpClient = HttpClientBuilder.create() .setRoutePlanner(new DefaultProxyRoutePlanner(proxy) { @Override public HttpHost determineProxy(HttpHost target, HttpRequest request, HttpContext context) throws HttpException { if (target.getHostName().equals("192.168.0.5")) { return null; } return super.determineProxy(target, request, context); } }).build(); restTemplate.setRequestFactory( new HttpComponentsClientHttpRequestFactory(httpClient)); } }
Lastly, the most extreme (and rarely used) option is to create your own RestTemplateBuilder
bean. This will switch off the auto-configuration of a RestTemplateBuilder
and will prevent any RestTemplateCustomizer
beans from being used.