Enhancements to Spring RestTemplate

Recently I had to choose a client to make REST requests from a Grails application. I decided to give the Spring RestTemplate a try. It has worked very well, but was missing some functionality that most other clients provide. First off, most clients allow you to set a base URL. This is nice since usually you have a service that builds and configures the client for you. The second was the ability to use Basic Auth. The final piece was to allow for URL parameters to be automatically added to a get request. Thankfully the additional pieces of functionality were easy to add. I have shown what was needed below along with some examples.


The custom rest template that extends RestTemplate and allows for a base path and the automatic addition of url parameters.

import org.springframework.web.client.RequestCallback
import org.springframework.web.client.ResponseExtractor
import org.springframework.web.client.RestClientException
import org.springframework.web.client.RestTemplate
import org.springframework.web.util.UriComponentsBuilder
import org.springframework.web.util.UriTemplate
class CustomRestTemplate extends RestTemplate {
    String baseUrl
    //allow for the use of a base url
    protected  T doExecute(URI url, HttpMethod method, RequestCallback requestCallback, ResponseExtractor responseExtractor) throws RestClientException {
        return super.doExecute(new URI(baseUrl + url.toString()), method, requestCallback, responseExtractor)
    //handle the url expansion our self and if any of the url variables are not in the url add them as a query parameter
    public  T execute(String url, HttpMethod method, RequestCallback requestCallback, ResponseExtractor responseExtractor, Map urlVariables) throws RestClientException {
        URI expanded = new UriTemplate(url).expand(urlVariables)
        UriComponentsBuilder uriComponentsBuilder = UriComponentsBuilder.fromUri(expanded)
        urlVariables.each { key, value ->
            if(!url.contains("{$key}")) {
                if(value instanceof List) {
                    value.each {
                        uriComponentsBuilder.queryParam(key, it)
                } else {
                    uriComponentsBuilder.queryParam(key, value)
        return super.execute(uriComponentsBuilder.toUriString(), method, requestCallback, responseExtractor)

The interceptor that allows for basic auth.

import org.apache.commons.codec.binary.Base64
import org.springframework.http.HttpHeaders
import org.springframework.http.HttpRequest
import org.springframework.http.client.ClientHttpRequestExecution
import org.springframework.http.client.ClientHttpRequestInterceptor
import org.springframework.http.client.ClientHttpResponse
public class BasicAuthInterceptor implements ClientHttpRequestInterceptor {
    private final String username
    private final String password
    public BasicAuthInterceptor(String username, String password) {
        this.username = username
        this.password = password
    //If the basic auth credentials are missing add them to the request header
    public ClientHttpResponse intercept(HttpRequest request, byte[] body, ClientHttpRequestExecution execution ) throws IOException {
        HttpHeaders httpHeaders = request.getHeaders()
        if(!httpHeaders.containsKey(HttpHeaders.AUTHORIZATION)) {
            byte[] userPasswordBytes = (username + ":" + password).bytes
            String basicAuth = "Basic " + new String(Base64.encodeBase64(userPasswordBytes))
            httpHeaders.set(HttpHeaders.AUTHORIZATION, basicAuth)
        return execution.execute(request, body)


An example service that builds our rest template and adds the basic auth interceptor.

import org.springframework.web.client.RestTemplate
class ExampleService {
	static transactional = false
	def grailsApplication
	//returns a rest template that has its base url and basic auth credentials configured
	RestTemplate getRestTemplate() {
		//Create a rest template with the base url set from a grails config property
		def baseUrl = grailsApplication.config.client.api.baseUrl
		def template = new CustomRestTemplate(baseUrl: baseUrl)
		//add basic auth credentials to the template with an interceptor
		def username = grailsApplication.config.client.api.username
		def password = grailsApplication.config.client.api.password
		def basicAuthInterceptor = new BasicAuthInterceptor(username, password)
		template.interceptors = [basicAuthInterceptor]
		return template

The following example now makes a request to http://base-url/object?sort=attribute&order=desc&offset=10&max=10 with the basic auth header included. Notice has the params are just added to the URL.

def restTemplate = exampleService.getRestTemplate()
def params = [sort: "attribute", order: "desc", offset: 10, max: 100]
def jsonObject = restTemplate.getForObject("/object", JSONObject, params)

While this example makes a request to http://base-url/object/1?detail=full with the basic auth header included. This shows we can combine the two methods and use the Spring parameter replacement method, {id}, also.

params = [id: 1, detail: "full"]
jsonObject = restTemplate.getForObject("/object/{id}", JSONObject, params)

One thought on “Enhancements to Spring RestTemplate

  1. Søren Berg Glasius says:

    Great example. You could even do your configuration in resources.groovy:

    beans = {
    restInterceptor(BasicAuthInterceptor) {
    username = application.config.client.api.username
    password = application.config.client.api.password

    restTemplate(CustomRestTemplate) {
    baseUrl = application.config.client.api.baseUrl
    interceptors= [ref(‘restInterceptor’)]

    restBuilder(RestBuilder) {
    restTemplate = ref(‘restTemplate’)

    then you can inject the restBuilder bean where you need to do rest-calls.

    1. Thank You. While you certainly could I personally only like to have injected beans only come from services in Grails. I feel it adds extra complexity if you add them in resources.grooy or by another method, because then you have to hunt down how the bean was created.

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