Implementing Streaming Reads with MyBatis for Large-Scale Java Report Export

When the company's legacy reporting module failed to export datasets larger than ten thousand rows, analysis revealed that the default JDBC fetch retrieved all rows at once, causing excessive memory usage and GC pressure. The solution was to adopt a forward‑only streaming read, which fetches rows incrementally.

JDBC three read modes:

1. Full fetch (default) – retrieves the entire result set in one go.

2. Streaming – fetches one row at a time.

3. Cursor – fetches multiple rows per round.

MyBatis uses the first mode by default.

Development environment: JDK 1.8, IntelliJ IDEA 2018, MyBatis 3, Spring MVC, Spring 4.

Implementation steps: The project adopts a layered architecture (controller → service → DAO) and modifies the service method to accept a ResultHandler callback, while the DAO method returns void. The mapper XML is configured with resultSetType="FORWARD_ONLY" and fetchSize="-2147483648" to enable streaming.

Controller layer:

@RequestMapping("/export")
public void export(Vo vo, String props, HttpServletResponse response) {
    // ...
    list = ossVipCustomService.selectForwardOnly(vo, Order.build());
    // ...
}

Service layer (core logic):

public List<Bo> selectForwardOnly(Vo vo, Order order) {
    final List<Bo> list = new ArrayList<>();
    mapper.selectForwardOnly(vo, order, new ResultHandler<Bo>() {
        @Override
        public void handleResult(ResultContext<? extends Bo> resultContext) {
            // callback processing
            list.add(resultContext.getResultObject());
        }
    });
    return list;
}

DAO interface:

/**
 * Streaming read of data
 */
void selectForwardOnly(@Param("record") Vo vo,
                       @Param("order") Order order,
                       ResultHandler<Bo> handler);

Mapper XML configuration:

<select id="selectForwardOnly"
        parameterType="com.*.Vo" resultMap="GetListBo"
        resultSetType="FORWARD_ONLY" fetchSize="-2147483648">
    SELECT * FROM customer
</select>

The author notes that returning void from the DAO is intentional because the result is processed in the callback, not passed back to the service layer.

Personal reflections mention extensive Googling, adjustments to MySQL connection parameters and MyBatis settings, and the realization that the DAO should not expose a return value.

Additional resources and promotional links are included but are not part of the technical solution.