Usage of ClassifierCompositeItemWriter in Spring Batch

I have a legacy database which has data stored as JSON in clob columns. The JSON in clob needs to be normalized and put into respective tables to support a new solution.

The clob data will produce 1 Company record, multiple department records and each department will have any number of employees. All this data is to be persisted into 3 tables i.e. Company, Department & Employee. I want to read the source data only once and perform the "data split" operation in one item-writer class using Spring Batch

Which item-writer will be more appropriate for this use case ClassifierCompositeItemWriter or CompositeItemWriter?

The processor seems to be simple:

public class ClientProfileEVProcessor implements ItemProcessor<ClientProfile, ClientCompositeVO> {

    /**
     * 
     */
    @Override
    public ClientCompositeVO process(ClientProfile item) throws Exception {
        ClientEntity client = populateClientProfile(item);
        List<DeptEntity> deptEntities = populateDept(item);
        List<Employee> evEntities = populateEmployee(item);
        return new ClientCompositeVO(client, deptEntities, evEntities);
    }
}

Here is my attempt of the Classifier. I am getting compilation error clazz instanceof List. How should I check if the clazz instance of list.get(0).class in the below code?

    public class ClientClassifier<T> implements Classifier<T, ItemWriter<? super T>> {
    
    private final Map<Class<T>, ItemWriter<T>> itemWriterMap;
    
    public EVProfileClassifier(Map<Class<T>, ItemWriter<T>> itemWriterMap) {
        super();
        this.itemWriterMap = itemWriterMap;
    }

    @Override
    public ItemWriter<? super T> classify(T classifiable) {
        Class<?> clazz = classifiable.getClass();
        if (this.itemWriterMap.containsKey(clazz)) {
            return this.itemWriterMap.get(clazz);
        } else if(clazz instanceof List) {
            List<?> list = (List<?>) classifiable;
            return this.itemWriterMap.get(list.get(0).getClass());
        } else {
            throw new IllegalArgumentException("No writer found for domainn class: " + clazz.getTypeName());
        }
    }

    public Map<Class<T>, ItemWriter<T>> getItemWriterMap() {
        return itemWriterMap;
    }
    
}

Any suggestions for a simpler solution approach are also welcome.

Solution

the following solution works. My domain classes extend from a common BaseEntity. I wrote writers for the 3 entities i.e., Company, Department & Employee

I wrote a Delegate Writer as follows:

public class DelegateItemWriter implements ItemWriter<List<CCTBaseEntity>> {

    private final LinkedHashMap<Class<? extends BaseEntity>, ItemWriter<? extends BaseEntity>> itemWriterMap;

    public DelegateItemWriter(
            LinkedHashMap<Class<? extends BaseEntity>, ItemWriter<? extends BaseEntity>> itemWriterMap) {
        this.itemWriterMap = itemWriterMap;
    }

    @Override
    public void write(Chunk<? extends List<BaseEntity>> chunk) throws Exception {
        List<BaseEntity> listEntities = chunk.getItems().get(0);
        for (BaseEntity b : listEntities) {
            this.itemWriterMap.get(b.getClass()).write(new Chunk(Arrays.asList(b)));
        }
    }
}

Bean definitions for itemWriterMap & DelegateItemWriter:

@Bean
public LinkedHashMap<Class<? extends BaseEntity>, ItemWriter<? extends BaseEntity>> itemWriterMap(MongoTemplate mongoTemplate) {
    LinkedHashMap<Class<? extends BaseEntity>, ItemWriter<? extends BaseEntity>> itemWriterMap = new LinkedHashMap<>();
    itemWriterMap.put(CompanyEntity.class, companyItemWriter(mongoTemplate));
    itemWriterMap.put(DepartmentEntity.class, deptEntityWriter(mongoTemplate));
    itemWriterMap.put(Employee.class, employeeItemWriter(mongoTemplate));
    return itemWriterMap;
}

@Bean
public DelegateItemWriter delegateItemWriter(LinkedHashMap<Class<? extends BaseEntity>, ItemWriter<? extends BaseEntity>> itemWriterMap) {
    return new DelegateItemWriter(itemWriterMap);
}

Step Definition:

@Bean
    public Step step1(@Qualifier(value = "dataSource") final DataSource dataSource,
            final JobRepository jobRepository, 
            final PlatformTransactionManager transactionManager,
            final DelegateItemWriter delegateItemWriter) {
        return new StepBuilder("step1", jobRepository).<ClientProfile, List<BaseEntity>>chunk(10, transactionManager)
                .reader(reader(dataSource)).processor(profileProcessor()).writer(delegateItemWriter)
                .build();
    }