fix: prevent StackOverflowError in ObjectView JSON mode for circular references

When watch command uses JSON format (options json true), fastjson2
serialization can enter infinite recursion on objects with circular
references or deeply nested object graphs, causing StackOverflowError.

Fix by adding JSONWriter.Feature.ReferenceDetection to detect and break
circular references using JSON $ref syntax, and catch StackOverflowError
as a safety net with a user-friendly error message.

Fixes #3095

Author: daguimu

core/src/main/java/com/taobao/arthas/core/view/ObjectView.java

@@ -38,13 +38,20 @@ protected void setDefaultValue(List<FieldWriter> fieldWriters, Class objectClass
             });
 
     public static String toJsonString(Object object) {
-        JSONWriter.Context context = new JSONWriter.Context(JSON_OBJECT_WRITER_PROVIDER);
-        context.setMaxLevel(4097);
-        context.config(JSONWriter.Feature.IgnoreErrorGetter,
-                JSONWriter.Feature.ReferenceDetection,
-                JSONWriter.Feature.IgnoreNonFieldGetter,
-                JSONWriter.Feature.WriteNonStringKeyAsString);
-        return JSON.toJSONString(object, context);
+        try {
+            JSONWriter.Context context = new JSONWriter.Context(JSON_OBJECT_WRITER_PROVIDER);
+            context.setMaxLevel(4097);
+            context.config(JSONWriter.Feature.IgnoreErrorGetter,
+                    JSONWriter.Feature.ReferenceDetection,
+                    JSONWriter.Feature.IgnoreNonFieldGetter,
+                    JSONWriter.Feature.WriteNonStringKeyAsString);
+            return JSON.toJSONString(object, context);
+        } catch (StackOverflowError e) {
+            logger.error("ObjectView JSON serialization stackoverflow, object class: {}", object == null ? "null" : object.getClass(), e);
+            return "ERROR DATA!!! object class: " + (object == null ? "null" : object.getClass())
+                    + ", StackOverflowError: circular reference or object graph too deep. "
+                    + "Try disabling json mode: options json false";
+        }
     }
 
     private final Object object;

core/src/test/java/com/taobao/arthas/core/view/ObjectViewTest.java

@@ -393,4 +393,27 @@ public static JsonFormatSingleton getInstance() {
             return INSTANCE;
         }
     }
+
+    @Test
+    public void testJsonModeCircularReference() {
+        GlobalOptions.isUsingJson = true;
+        try {
+            CircularRef a = new CircularRef("a");
+            CircularRef b = new CircularRef("b");
+            a.ref = b;
+            b.ref = a;
+            ObjectView objectView = new ObjectView(a, 3);
+            String result = objectView.draw();
+            // Should not throw StackOverflowError
+            Assert.assertNotNull(result);
+        } finally {
+            GlobalOptions.isUsingJson = false;
+        }
+    }
+
+    private static class CircularRef {
+        String name;
+        CircularRef ref;
+        CircularRef(String name) { this.name = name; }
+    }
 }