fix: preserve property order in auto-generated examples

The openapi-yaml generator was using HashMap when building object-level
examples from property examples, which caused unstable field ordering
that didn't match the source spec declaration order.

Switch to LinkedHashMap to preserve the order as defined in the
OpenAPI spec. This improves readability in Swagger UI and other
downstream tools that render the auto-generated examples.

Add test to verify property order preservation.

Author: Swapneswar Sundar Ray

modules/openapi-generator/src/main/java/org/openapitools/codegen/examples/ExampleGenerator.java

@@ -351,7 +351,7 @@ private Object resolveModelToExample(String name, String mediaType, Schema schem
         }
 
         processedModels.add(name);
-        Map<String, Object> values = new HashMap<>();
+        Map<String, Object> values = new LinkedHashMap<>();
         LOGGER.debug("Resolving model '{}' to example", name);
         if (schema.getExample() != null) {
             LOGGER.debug("Using example from spec: {}", schema.getExample());

modules/openapi-generator/src/test/java/org/openapitools/codegen/ExampleGeneratorTest.java

@@ -1,6 +1,8 @@
 package org.openapitools.codegen;
 
 import io.swagger.v3.oas.models.OpenAPI;
+import io.swagger.v3.oas.models.media.Schema;
+import io.swagger.v3.oas.models.media.IntegerSchema;
 import org.openapitools.codegen.examples.ExampleGenerator;
 import org.testng.annotations.Test;
 
@@ -11,6 +13,7 @@
 
 import static org.testng.AssertJUnit.assertEquals;
 import static org.testng.AssertJUnit.assertNull;
+import static org.testng.AssertJUnit.assertTrue;
 
 public class ExampleGeneratorTest {
     @Test
@@ -334,4 +337,73 @@ public void generateFromResponseSchemaWithAnyOfComposedModel() {
         assertEquals(String.format(Locale.ROOT, "{%n  \"example_schema_property\" : \"example schema property value\"%n}"), examples.get(0).get("example"));
         assertEquals("200", examples.get(0).get("statusCode"));
     }
+
+    @Test
+    public void testExamplePropertyOrderPreservation() {
+        OpenAPI openAPI = new OpenAPI();
+        
+        // Create a schema with properties in a specific order
+        Schema<?> testSchema = new Schema<>();
+        testSchema.setType("object");
+        
+        // Use LinkedHashMap to preserve property order as defined in spec
+        Map<String, Schema> properties = new LinkedHashMap<>();
+        
+        // Add properties in the specific order: zebra, apple, mango, cherry, banana
+        IntegerSchema zebraSchema = new IntegerSchema();
+        zebraSchema.setExample(1);
+        properties.put("zebra", zebraSchema);
+        
+        IntegerSchema appleSchema = new IntegerSchema();
+        appleSchema.setExample(2);
+        properties.put("apple", appleSchema);
+        
+        IntegerSchema mangoSchema = new IntegerSchema();
+        mangoSchema.setExample(3);
+        properties.put("mango", mangoSchema);
+        
+        IntegerSchema cherrySchema = new IntegerSchema();
+        cherrySchema.setExample(4);
+        properties.put("cherry", cherrySchema);
+        
+        IntegerSchema bananaSchema = new IntegerSchema();
+        bananaSchema.setExample(5);
+        properties.put("banana", bananaSchema);
+        
+        testSchema.setProperties(properties);
+        
+        // Create examples map
+        Map<String, Schema> examples = new HashMap<>();
+        examples.put("TestModel", testSchema);
+        
+        // Generate the example using the model name approach
+        ExampleGenerator generator = new ExampleGenerator(examples, openAPI);
+        Set<String> mediaTypeKeys = new TreeSet<>();
+        mediaTypeKeys.add("application/json");
+        
+        List<Map<String, String>> generatedExamples = generator.generate(null, new ArrayList<>(mediaTypeKeys), "TestModel");
+        
+        assertEquals(1, generatedExamples.size());
+        String exampleOutput = generatedExamples.get(0).get("example");
+        
+        // Verify the example contains properties in the correct order
+        // The order should be: zebra, apple, mango, cherry, banana
+        assertTrue(exampleOutput.contains("\"zebra\" : 1"));
+        assertTrue(exampleOutput.contains("\"apple\" : 2"));
+        assertTrue(exampleOutput.contains("\"mango\" : 3"));
+        assertTrue(exampleOutput.contains("\"cherry\" : 4"));
+        assertTrue(exampleOutput.contains("\"banana\" : 5"));
+        
+        // Verify the order by checking the position of each field in the string
+        int zebraPos = exampleOutput.indexOf("\"zebra\"");
+        int applePos = exampleOutput.indexOf("\"apple\"");
+        int mangoPos = exampleOutput.indexOf("\"mango\"");
+        int cherryPos = exampleOutput.indexOf("\"cherry\"");
+        int bananaPos = exampleOutput.indexOf("\"banana\"");
+        
+        assertTrue("zebra should come before apple", zebraPos < applePos);
+        assertTrue("apple should come before mango", applePos < mangoPos);
+        assertTrue("mango should come before cherry", mangoPos < cherryPos);
+        assertTrue("cherry should come before banana", cherryPos < bananaPos);
+    }
 }