批量时使用Lists.partition(list,num)

场景：当我们通过一堆ID,批量查数据库，并写入文件时，oracle数据库的 in(xx,xx,xx,xx..)里面的个数不能超过1000，超过1000则会报错,我们就可以批量去做这件事；

public static void main(String[] args) {
        List<String> list = Lists.newArrayList();
        for (int i = 0; i < 21; i++) {
            list.add("data"+i);
        }
        List<List<String>> result = Lists.partition(list,5);
        System.out.println(result.get(0));
        System.out.println(result.get(1));
        System.out.println(result.get(2));
        System.out.println(result.get(3));
        System.out.println(result.get(4));
    }

结果：
[data5, data6, data7, data8, data9]
[data10, data11, data12, data13, data14]
[data15, data16, data17, data18, data19]
[data20]

工作中代码：

@SuppressWarnings("unchecked")
    private void write2TempFile(String sql, String tFile, DiyDataExportTask task) {
        DiyDataExportTask.Query batchQuery = task.getBatchQuery();
        // 打开一个写文件器，构造函数中的第二个参数true表示以追加形式写文件
        File tempFile = new File(tFile);
        try (OutputStreamWriter writerOut = new OutputStreamWriter(new FileOutputStream(tempFile, true), "GBK"); CSVWriter writer = new CSVWriter(writerOut, CSVWriter.DEFAULT_SEPARATOR, CSVWriter.DEFAULT_QUOTE_CHARACTER, CSVWriter.DEFAULT_ESCAPE_CHARACTER, CSVWriter.DEFAULT_LINE_END)) {
            final Map<String, Long> counts = Maps.newHashMap();
            counts.put("index", 0L);
            if (batchQuery != null && task.getQueryInfo().size() == 0) {// 有查询条件先
                List<String> batchValue = (List<String>) batchQuery.getValue();
                List<List<String>> list = Lists.partition(batchValue, BATCH_NUM);// 500个数据分组执行
                for (int i = 0; i < list.size(); i++) {
                    StringBuilder batchSql = new StringBuilder(sql);
                    appendFilterIn(batchSql, "T." + batchQuery.getName(), list.get(i));
                    queryData(batchSql.toString(), writer, counts);
                }
            } else {
                queryData(sql, writer, counts);
            }
        } catch (DataAccessException | IOException e) {
            logger.error(e.getMessage(), e);
            throw new ServiceException("please check template!",e);
        }
    }