Remove vulnerable transitive dependency. Fix checkstyle.

spring-cloud-openfeign-core/src/main/java/org/springframework/cloud/openfeign/FeignAutoConfiguration.java

@@ -346,6 +346,7 @@ public class FeignAutoConfiguration {
 	@Configuration(proxyBeanMethods = false)
 	@ConditionalOnClass(OAuth2ClientContext.class)
 	@ConditionalOnProperty("spring.cloud.openfeign.oauth2.enabled")
+	@Deprecated // spring-security-oauth2 reached EOL
 	protected static class Oauth2FeignConfiguration {
 
 		@ConditionalOnBean({ RetryLoadBalancerInterceptor.class, OAuth2ClientContext.class,

spring-cloud-openfeign-core/src/main/java/org/springframework/cloud/openfeign/security/OAuth2FeignRequestInterceptor.java

@@ -43,6 +43,7 @@ import org.springframework.security.oauth2.common.OAuth2AccessToken;
  * @author Tim Ysewyn
  * @since 3.0.0
  */
+@Deprecated // spring-security-oauth2 reached EOL
 public class OAuth2FeignRequestInterceptor implements RequestInterceptor {
 
 	/**

spring-cloud-openfeign-core/src/test/java/org/springframework/cloud/openfeign/encoding/Invoices.java

@@ -27,9 +27,14 @@ import org.springframework.cloud.openfeign.encoding.app.domain.Invoice;
  * Utility class used for testing.
  *
  * @author Jakub Narloch
+ * @author Olga Maciaszek-Sharma
  */
 final class Invoices {
 
+	private Invoices() {
+		throw new IllegalStateException("Can't instantiate a utility class");
+	}
+
 	public static List<Invoice> createInvoiceList(int count) {
 		final List<Invoice> invoices = new ArrayList<>();
 		for (int ind = 0; ind < count; ind++) {

spring-cloud-openfeign-core/src/test/java/org/springframework/cloud/openfeign/test/EqualsAndHashCodeAssert.java

@@ -24,8 +24,13 @@ import static org.assertj.core.api.Assertions.assertThat;
  * {@link Object#equals(Object)} and {@link Object#hashCode()}.
  *
  * @author Jonatan Ivanov
+ * @author Olga Maciaszek-Sharma
  */
-public class EqualsAndHashCodeAssert {
+public final class EqualsAndHashCodeAssert {
+
+	private EqualsAndHashCodeAssert() {
+		throw new IllegalStateException("Can't instantiate a utility class");
+	}
 
 	/**
 	 * Checks if equals is reflexive: for any non-null reference value x, x.equals(x)