Implementing Streaming Reads with MyBatis and JDBC for Large Report Exports

When a company's legacy system failed to export reports larger than ten thousand rows, the root cause was identified as the default JDBC fetch mode that loads the entire result set into memory, causing excessive GC pressure.

The solution is to switch to a streaming read mode, which retrieves rows incrementally, reducing memory consumption. MyBatis supports three read modes:

Full fetch (default): loads all rows at once.

Streaming: fetches one row at a time.

Cursor: fetches multiple rows per round.

Implementation uses a layered architecture (controller → service → DAO) and introduces a ResultHandler callback in the service layer. The DAO method returns void, while the mapper is configured with resultSetType="FORWARD_ONLY" and fetchSize="-2147483648" to enable forward‑only streaming.

Controller example:

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

Service example (key part):

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 logic
            list.add(resultContext.getResultObject());
        }
    });
    return list;
}

DAO interface (key part):

void selectForwardOnly(@Param("record") Vo vo,
                       @Param("order") Order order,
                       ResultHandler<Bo> handler);

Mapper XML configuration (key part):

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

With these changes, the application can export large datasets without running out of memory, demonstrating a practical use of JDBC streaming reads in a Spring‑MyBatis backend.