content: package com.alibaba.fastjson2.issues_1900;
  
  import com.alibaba.fastjson2.JSON;
  import com.alibaba.fastjson2.JSONWriter;
  import com.alibaba.fastjson2.annotation.JSONField;
  import com.alibaba.fastjson2.writer.ObjectWriter;
  import com.google.common.collect.Lists;
  import org.junit.jupiter.api.Test;
  
  import java.lang.reflect.Type;
  import java.util.List;
  
  import static org.junit.jupiter.api.Assertions.*;
  
  public class Issue1948 {
      @Test
      public void test() {
          A a = new A();
          a.list = Lists.newLinkedList();
          a.list.add("test 1");
          a.list.add("test 2");
  
          assertEquals("{\"list\":\"TEST 1\"\"TEST 2\"}", JSON.toJSONString(a));
      }
  
      public static class A {
          @JSONField(serializeUsing = FieldWriteTest.class)
          public List<String> list;
      }
  
      public static class FieldWriteTest
              implements ObjectWriter<List<String>> {
          @Override
          public void write(JSONWriter jsonWriter, Object object, Object fieldName, Type fieldType, long features) {
              for (String s : (List<String>) object) {
                  jsonWriter.writeString(s.toUpperCase());
              }
          }
      }
  }
  