public T registerWriteHandler(WriteHandler writeHandler) {
        if (parameter().getCustomWriteHandlerList() == null) {
            parameter().setCustomWriteHandlerList(new ArrayList<WriteHandler>());
        }
        parameter().getCustomWriteHandlerList().add(writeHandler);
        return self();
    }
Custom write handler

@param writeHandler
@return
fastexcel-core/src/main/java/cn/idev/excel/write/builder/AbstractExcelWriterParameterBuilder.java