正如马克Rotteveel到问题的评论中提到，MysqL的高速缓存默认的ResultSet数据（也由Ben J. Christensen的一篇博客文章中讨论这里）。这种缓存的明显副作用是MysqL Connector / J将“升级” TYPE_FORWARD_ONLY ResultSet使其实际上是可滚动的：
Statement s = dbConnection.createStatement(
ResultSet.TYPE_FORWARD_ONLY,
ResultSet.CONCUR_READ_ONLY);
ResultSet rs = s.executeQuery("SELECT * FROM testdata");
rs.last();
System.out.println(String.format("Current row number: %d", rs.getRow()));
rs.prevIoUs();
System.out.println(String.format("Current row number: %d", rs.getRow()));
Current row number: 3
Current row number: 2
根据上面引用的博客文章，防止缓存和“流式处理” ResultSet数据的方法是使用Statement.setFetchSize：
Statement s = dbConnection.createStatement(
ResultSet.TYPE_FORWARD_ONLY,
ResultSet.CONCUR_READ_ONLY);
s.setFetchSize(Integer.MIN_VALUE);
ResultSet rs = s.executeQuery("SELECT * FROM testdata");
rs.next();
System.out.println("Data from first row: " + rs.getString(2));
System.out.println("Now let's try rs.last() ...");
try {
rs.last();
System.out.println("... Okay, done.");
} catch (Exception e) {
System.out.println("... Exception: " + e.getMessage());
}
导致
Data from first row: Gord
Now let's try rs.last() ...
... Exception: Operation not supported for streaming result sets
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