improved compatible for 1.x, for issue #2450

core/src/main/java/com/alibaba/fastjson2/JSONWriter.java

@@ -2466,4 +2466,43 @@ public String toString() {
     protected static IllegalArgumentException illegalYear(int year) {
         return new IllegalArgumentException("Only 4 digits numbers are supported. Provided: " + year);
     }
+
+    /**
+     * @deprecated
+     */
+    public final void incrementIndent() {
+        indent++;
+    }
+
+    /**
+     * @deprecated
+     */
+    public final void decrementIdent() {
+        indent--;
+    }
+
+    /**
+     * @deprecated
+     */
+    public void println() {
+        writeChar('\n');
+        for (int i = 0; i < indent; ++i) {
+            writeChar('\t');
+        }
+    }
+
+    /**
+     * @deprecated
+     * @param object
+     */
+    public final void writeReference(Object object) {
+        if (refs == null) {
+            return;
+        }
+
+        Path path = refs.get(object);
+        if (path != null) {
+            writeReference(path.toString());
+        }
+    }
 }

core/src/main/java/com/alibaba/fastjson2/JSONWriterJSONB.java

@@ -2507,4 +2507,8 @@ public String toString() {
             return JSONB.typeName(bytes[0]) + ", bytes length " + off;
         }
     }
+
+    @Override
+    public void println() {
+    }
 }

fastjson1-compatible/src/main/java/com/alibaba/fastjson/serializer/JSONSerializer.java

@@ -171,4 +171,23 @@ public SerialContext getContext() {
     public void setContext(SerialContext context) {
         this.context = context;
     }
+
+    public final boolean containsReference(Object value) {
+        return out.raw.containsReference(value);
+    }
+
+    public final void writeReference(Object object) {
+        out.raw.writeReference(object);
+    }
+
+    public final void incrementIndent() {
+        out.raw.incrementIndent();
+    }
+
+    public final void decrementIdent() {
+        out.raw.decrementIdent();
+    }
+
+    public void println() {
+    }
 }

fastjson1-compatible/src/main/java/com/alibaba/fastjson/serializer/SerializeWriter.java

@@ -247,4 +247,8 @@ public SerializeWriter append(char c) {
         raw.writeRaw(c);
         return this;
     }
+
+    public JSONWriter getJSONWriter() {
+        return raw;
+    }
 }

fastjson1-compatible/src/test/java/com/alibaba/fastjson/v2issues/Issue2450.java

@@ -0,0 +1,46 @@
+package com.alibaba.fastjson.v2issues;
+
+import com.alibaba.fastjson.serializer.JSONSerializer;
+import com.alibaba.fastjson.serializer.SerializeConfig;
+import com.alibaba.fastjson2.JSONWriter;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+public class Issue2450 {
+    @Test
+    public void test() {
+        Bean bean = new Bean();
+        bean.self = bean;
+
+        JSONSerializer serializer = new JSONSerializer(SerializeConfig.global);
+        assertFalse(serializer.containsReference(bean));
+
+        serializer.incrementIndent();
+        serializer.decrementIdent();
+
+        serializer.write(bean);
+
+        assertEquals("{\"name\":\"\",\"self\":{\"$ref\":\"..\"}}", serializer.toString());
+        serializer.println();
+        serializer.writeReference(bean);
+    }
+
+    @Test
+    public void test1() {
+        Bean bean = new Bean();
+        bean.self = bean;
+
+        JSONSerializer serializer = new JSONSerializer(SerializeConfig.global);
+        JSONWriter jsonWriter = serializer.out.getJSONWriter();
+        jsonWriter.setPath("$", bean);
+        jsonWriter.writeReference(bean);
+        assertEquals("{\"$ref\":\"$\"}", serializer.toString());
+    }
+
+    public class Bean {
+        public String name;
+
+        public Bean self;
+    }
+}