Resource Access Exception

When trying to resolve the test described in Where exactly is the NullPointer Exception?, I used a seemingly simpler approach, being the resource test the next:

public class CustomerResourceFunctionalTesting {

private static final String SERVER_URL = "http://localhost:8080/api/v0/";

@Rule
 public ExpectedException thrown = ExpectedException.none();

private int createCustomer(String name) {
    CustomerDto customerDto = new CustomerDto(name, name + " address");
    return new RestBuilder2<Integer>(SERVER_URL).path(CustomerResource.CUSTOMERS)
    .body(customerDto).clazz(Integer.class).post().build();
}

private int createCustomer() {
    return this.createCustomer("customer1");
}

@Test
public void testReadCustomers() {
     List<CustomerDto> customerDtoList = Arrays.asList(new RestBuilder2<CustomerDto[]>
     (SERVER_URL).path(CustomerResource.CUSTOMERS).clazz(CustomerDto[].class).get().build());
     assertEquals(0, customerDtoList.size());
     int id = this.createCustomer();
     customerDtoList = Arrays.asList(new RestBuilder2<CustomerDto[]>
     (SERVER_URL).path(CustomerResource.CUSTOMERS).clazz(CustomerDto[].class)
     .get().build());
     assertEquals(1, customerDtoList.size());
     this.deleteCustomer(id);
}

private void deleteCustomer(int id) {
     new RestBuilder<Object>
     (SERVER_URL).path(CustomerResource.CUSTOMERS).path(CustomerResource.CUSTOMER_ID)
     .expand(id).delete().build();
}
}

And the RestBuilder a bit different:

public class RestBuilder<T> {

private RestTemplate restTemplate = new RestTemplate();

private String uri;

private List<Object> expandList;

private Map<String, String> headerValues;

private String authorization = null;

private Object body = null;

private MultiValueMap<String, String> params;

private Class<T> clazz;

private HttpMethod method;

public RestBuilder(String serverUri) {
    restTemplate.setRequestFactory(new HttpComponentsClientHttpRequestFactory());
    this.uri = serverUri;
    this.expandList = new ArrayList<>();
    headerValues = new HashMap<>();
    params = new HttpHeaders();
}

public RestBuilder<T> path(String path) {
    this.uri = this.uri + path;
    return this;
}

public RestBuilder<T> expand(Object... values) {
   for (Object value : values) {
        this.expandList.add(value);
    }
    return this;
}

public RestBuilder<T> pathId(int path) {
    this.uri = this.uri + "/" + path;
    return this;
}

public RestBuilder<T> pathId(String path) {
    this.uri = this.uri + "/" + path;
    return this;
}

public RestBuilder<T> authorization(String authorizationValue) {
    this.authorization = authorizationValue;
    return this;
}

public RestBuilder<T> basicAuth(String nick, String pass) {
    String auth = nick + ":" + pass;
    String encodedAuth = Base64.getEncoder().encodeToString(auth.getBytes(StandardCharsets.UTF_8));
    String authHeader = "Basic " + encodedAuth;
    this.authorization = authHeader;
    return this;
}

public RestBuilder<T> param(String key, String value) {
    this.params.add(key, value);
    return this;
}

public RestBuilder<T> header(String key, String value) {
    this.headerValues.put(key, value);
    return this;
}

public RestBuilder<T> body(Object body) {
    this.body = body;
    return this;
}

public RestBuilder<T> notError() {
    restTemplate.setErrorHandler(new DefaultResponseErrorHandler() {
        protected boolean hasError(HttpStatus statusCode) {
            return false;
        }
    });
    return this;
}

public RestBuilder<T> clazz(Class<T> clazz) {
    this.clazz = clazz;
    return this;
}

private HttpHeaders headers() {
    HttpHeaders headers = new HttpHeaders();
    for (String key : headerValues.keySet()) {
        headers.set(key, headerValues.get(key));
    }
    if (authorization != null) {
        headers.set("Authorization", authorization);
    }
    return headers;
}

private URI uri() {
    UriComponents uriComponents;
    if (params.isEmpty()) {
        uriComponents = UriComponentsBuilder.fromHttpUrl(uri).build();
    } else {
        uriComponents = UriComponentsBuilder.fromHttpUrl(uri).queryParams(params).build();
    }
    if (!expandList.isEmpty()) {
        uriComponents = uriComponents.expand(expandList.toArray());
    }
    return uriComponents.encode().toUri();

}

public T build() {
    if (body != null && !method.equals(HttpMethod.GET)) {
        return restTemplate.exchange(this.uri(), method, new HttpEntity<Object>(body, this.headers()), clazz).getBody();
    } else {
        return restTemplate.exchange(this.uri(), method, new HttpEntity<Object>(this.headers()), clazz).getBody();
    }
}

public RestBuilder<T> post() {
    this.method = HttpMethod.POST;
    return this;
}

public RestBuilder<T> get() {
    this.method = HttpMethod.GET;
    return this;
}

public RestBuilder<T> put() {
    this.method = HttpMethod.PUT;
    return this;
}

public RestBuilder<T> patch() {
    this.method = HttpMethod.PATCH;
    return this;
}

public RestBuilder<T> delete() {
    this.method = HttpMethod.DELETE;
    return this;
}

}

But then I take an error whose trace is:

org.springframework.web.client.ResourceAccessException: I/O error on GET request for "http://localhost:8080/api/v0/customers": Connect to localhost:8080 [localhost/127.0.0.1, localhost/0:0:0:0:0:0:0:1] failed: Connection refused: connect; nested exception is org.apache.http.conn.HttpHostConnectException: Connect to localhost:8080 [localhost/127.0.0.1, localhost/0:0:0:0:0:0:0:1] failed: Connection refused: connect
at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:674)
at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:636)
at org.springframework.web.client.RestTemplate.exchange(RestTemplate.java:557)
at account.persistence.resources.RestBuilder2.build(RestBuilder2.java:143)
at account.persistence.resources.CustomerResource2FunctionalTesting.testReadCustomers(CustomerResource2FunctionalTesting.java:34)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.junit.rules.ExpectedException$ExpectedExceptionStatement.evaluate(ExpectedException.java:239)
at org.junit.rules.RunRules.evaluate(RunRules.java:20)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:538)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:760)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:460)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:206)
Caused by: org.apache.http.conn.HttpHostConnectException: Connect to localhost:8080 [localhost/127.0.0.1, localhost/0:0:0:0:0:0:0:1] failed: Connection refused: connect
at org.apache.http.impl.conn.DefaultHttpClientConnectionOperator.connect(DefaultHttpClientConnectionOperator.java:159)
at org.apache.http.impl.conn.PoolingHttpClientConnectionManager.connect(PoolingHttpClientConnectionManager.java:373)
at org.apache.http.impl.execchain.MainClientExec.establishRoute(MainClientExec.java:381)
at org.apache.http.impl.execchain.MainClientExec.execute(MainClientExec.java:237)
at org.apache.http.impl.execchain.ProtocolExec.execute(ProtocolExec.java:185)
at org.apache.http.impl.execchain.RetryExec.execute(RetryExec.java:89)
at org.apache.http.impl.execchain.RedirectExec.execute(RedirectExec.java:111)
at org.apache.http.impl.client.InternalHttpClient.doExecute(InternalHttpClient.java:185)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:83)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:56)
at org.springframework.http.client.HttpComponentsClientHttpRequest.executeInternal(HttpComponentsClientHttpRequest.java:89)
at org.springframework.http.client.AbstractBufferingClientHttpRequest.executeInternal(AbstractBufferingClientHttpRequest.java:48)
at org.springframework.http.client.AbstractClientHttpRequest.execute(AbstractClientHttpRequest.java:53)
at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:660)
... 29 more
Caused by: java.net.ConnectException: Connection refused: connect
at java.net.DualStackPlainSocketImpl.connect0(Native Method)
at java.net.DualStackPlainSocketImpl.socketConnect(Unknown Source)
at java.net.AbstractPlainSocketImpl.doConnect(Unknown Source)
at java.net.AbstractPlainSocketImpl.connectToAddress(Unknown Source)
at java.net.AbstractPlainSocketImpl.connect(Unknown Source)
at java.net.PlainSocketImpl.connect(Unknown Source)
at java.net.SocksSocketImpl.connect(Unknown Source)

The rest of implied parts of the application is the same as the indicated in the link post, except for not using any RestService.

I think that, in this case, I could not get the NullPointerException, but before I need to resolve the ResourceAccess Exception.