Mybatis实现百万级数据导出(重点代码摘要)

MyBatis 实现逐条获取数据，必须要自定义 ResultHandler，然后在 mapper.xml 文件中，对应的 select 语句中添加 fetchSize=“-2147483648”。

最后将自定义的 ResultHandler 传给 SqlSession 来执行查询，并将返回的结果进行处理。

public class DownloadProcessor {
    private final HttpServletResponse response;
     
    public DownloadProcessor(HttpServletResponse response) {
        this.response = response;
        String fileName = System.currentTimeMillis() + ".csv";
        this.response.addHeader("Content-Type", "application/csv");
        this.response.addHeader("Content-Disposition", "attachment; filename="+fileName);
        this.response.setCharacterEncoding("UTF-8");
    }
     
    public  void processData(E record) {
        try {
            response.getWriter().write(record.toString()); //如果是要写入csv,需要重写toString,属性通过","分割
            response.getWriter().write("\n");
        }catch (IOException e){
            e.printStackTrace();
        }
    }
}

然后通过实现 org.apache.ibatis.session.ResultHandler，自定义我们的 ResultHandler，它用于获取 java 对象，然后传递给上面的 DownloadProcessor 处理类进行写文件操作：

public class CustomResultHandler implements ResultHandler {

    private final DownloadProcessor downloadProcessor;
     
    public CustomResultHandler(
            DownloadProcessor downloadProcessor) {
        super();
        this.downloadProcessor = downloadProcessor;
    }
     
    @Override
    public void handleResult(ResultContext resultContext) {
        Authors authors = (Authors)resultContext.getResultObject();
        downloadProcessor.processData(authors);
    }
}

private final SqlSessionTemplate sqlSessionTemplate;
/**
     * stream读数据写文件方式
     * @param httpServletResponse
     * @throws IOException
     */
    public void streamDownload(HttpServletResponse httpServletResponse)
            throws IOException {
        AuthorsExample authorsExample = new AuthorsExample();
        authorsExample.createCriteria();
        HashMap param = new HashMap<>();
        param.put("oredCriteria", authorsExample.getOredCriteria());
        param.put("orderByClause", authorsExample.getOrderByClause());
        CustomResultHandler customResultHandler = new CustomResultHandler(new DownloadProcessor (httpServletResponse));
        sqlSessionTemplate.select(
                "com.alphathur.mysqlstreamingexport.mapper.AuthorsMapper.streamByExample", param, customResultHandler);
        httpServletResponse.getWriter().flush();
        httpServletResponse.getWriter().close();
    }