[Java][apache-httpclient][feign][okhttp-gson] Enable access token refresh (#17086)

* add setter of bearer token supplier

* run generate-samples.sh

* add test of bearer auth

samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/ApiClient.java

@@ -2,6 +2,7 @@ package org.openapitools.client;
 
 import java.util.LinkedHashMap;
 import java.util.Map;
+import java.util.function.Supplier;
 import java.util.logging.Level;
 import java.util.logging.Logger;
 
@@ -206,6 +207,15 @@ public class ApiClient {
     apiAuthorization.setBearerToken(bearerToken);
   }
 
+  /**
+   * Helper method to configure the supplier of bearer tokens.
+   * @param tokenSupplier the supplier of bearer tokens.
+   */
+  public void setBearerToken(Supplier<String> tokenSupplier) {
+    HttpBearerAuth apiAuthorization =  getAuthorization(HttpBearerAuth.class);
+    apiAuthorization.setBearerToken(tokenSupplier);
+  }
+
   /**
    * Helper method to configure the first api key found
    * @param apiKey API key

samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/auth/HttpBearerAuth.java

@@ -2,13 +2,15 @@ package org.openapitools.client.auth;
 
 import feign.RequestInterceptor;
 import feign.RequestTemplate;
+import java.util.Optional;
+import java.util.function.Supplier;
 
 /**
  * An interceptor that adds the request header needed to use HTTP bearer authentication.
  */
 public class HttpBearerAuth implements RequestInterceptor {
   private final String scheme;
-  private String bearerToken;
+  private Supplier<String> tokenSupplier;
 
   public HttpBearerAuth(String scheme) {
     this.scheme = scheme;
@@ -16,21 +18,35 @@ public class HttpBearerAuth implements RequestInterceptor {
 
   /**
    * Gets the token, which together with the scheme, will be sent as the value of the Authorization header.
+   *
+   * @return The bearer token
    */
   public String getBearerToken() {
-    return bearerToken;
+    return tokenSupplier.get();
   }
 
   /**
    * Sets the token, which together with the scheme, will be sent as the value of the Authorization header.
+   *
+   * @param bearerToken The bearer token to send in the Authorization header
    */
   public void setBearerToken(String bearerToken) {
-    this.bearerToken = bearerToken;
+    this.tokenSupplier = () -> bearerToken;
+  }
+
+  /**
+   * Sets the supplier of tokens, which together with the scheme, will be sent as the value of the Authorization header.
+   *
+   * @param tokenSupplier The supplier of bearer tokens to send in the Authorization header
+   */
+  public void setBearerToken(Supplier<String> tokenSupplier) {
+    this.tokenSupplier = tokenSupplier;
   }
 
   @Override
   public void apply(RequestTemplate template) {
-    if(bearerToken == null) {
+    String bearerToken = Optional.ofNullable(tokenSupplier).map(Supplier::get).orElse(null);
+    if (bearerToken == null) {
       return;
     }