首先，我不建议为此使用servlet。有关正确的方法，请参见aioobe和mdma的答案。但是，如果真的没有其他选择，请继续阅读：
只需在数据输入时 将数据写入响应即可。不要将所有内容都存储在Java的内存中。所以基本上：writer.write(resultSet.getString("col"))。此外，默认情况下，MysqL JDBC驱动程序将所有内容缓存在Java内存中，然后再提供给ResultSet#next()。您希望通过Statement#setFetchSize()按照MySQL JDBC驱动程序文档设置来逐行立即为数据提供数据。
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setContentType("text/csv");
Connection connection = null;
Statement statement = null;
ResultSet resultSet = null;
PrintWriter writer = response.getWriter();
try {
connection = database.getConnection();
statement = connection.createStatement(ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY);
statement.setFetchSize(Integer.MIN_VALUE);
resultSet = statement.executeQuery("SELECT col1, col2, col3 FROM tbl");
while (resultSet.next()) {
writer.append(resultSet.getString("col1")).append(',');
writer.append(resultSet.getString("col2")).append(',');
writer.append(resultSet.getString("col3")).println();
// PS: don't forget to sanitize quotes/commas as per RFC4130.
}
} catch (sqlException e) {
throw new ServletException("Query Failed!", e);
} finally {
if (resultSet != null) try { resultSet.close; } catch (sqlException logorIgnore) {}
if (statement != null) try { statement.close; } catch (sqlException logorIgnore) {}
if (connection != null) try { connection.close; } catch (sqlException logorIgnore) {}
}
}
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