[8.6] Cache the result of JsonProvider.provider() (#485)

java-client/src/main/java/co/elastic/clients/json/JsonpUtils.java

@@ -42,12 +42,24 @@
 
 public class JsonpUtils {
 
+    private static JsonProvider systemJsonProvider = null;
+
     /**
      * Get a <code>JsonProvider</code> instance. This method first calls the standard `JsonProvider.provider()` that is based on
-     * the current thread's context classloader, and in case of failure tries to find a provider in other classloaders.
+     * the current thread's context classloader, and in case of failure tries to find a provider in other classloaders. The
+     * value is cached for subsequent calls.
      */
-    @AllowForbiddenApis("Implementation of the JsonProvider lookup")
     public static JsonProvider provider() {
+        JsonProvider result = systemJsonProvider;
+        if (result == null) {
+            result = findProvider();
+            systemJsonProvider = result;
+        }
+        return result;
+    }
+
+    @AllowForbiddenApis("Implementation of the JsonProvider lookup")
+    static JsonProvider findProvider() {
         RuntimeException exception;
         try {
             return JsonProvider.provider();

java-client/src/test/java/co/elastic/clients/json/JsonpUtilsTest.java

@@ -69,6 +69,16 @@ public Enumeration<URL> getResources(String name) {
         }
     }
 
+    @Test
+    @AllowForbiddenApis("Testing JsonpUtil.provider()")
+    public void testProviderCache() {
+        // A new provider at each call
+        assertNotSame(JsonpUtils.findProvider(), JsonpUtils.findProvider());
+
+        // Result is cached
+        assertSame(JsonpUtils.provider(), JsonpUtils.provider());
+    }
+
     @Test
     public void testObjectToString() {
         // Test that we call toString() on application classes.