java 使用 PreparedStatement 执行 sql 查询
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sql query execute with PreparedStatement
提问by URL87
I have the follow code in a servlet -
我在 servlet 中有以下代码 -
String loginID = request.getParameter("loginId").toString();
String loginPassword = request.getParameter("loginPassword").toString();
String strSQLcount = "SELECT COUNT(*) as 'Number Of Match' "
+ "FROM persons " + "WHERE (password =? AND id =?);";
PreparedStatement prepareSQL = connection
.prepareStatement(strSQLcount);
prepareSQL.setString(1, loginPassword);
prepareSQL.setString(2, loginID);
ResultSet numOfMatchResult = prepareSQL.executeQuery();
// now we know number of matchs ...
int numOfMatch = numOfMatchResult.getInt(1);
When on running and reach to the line int numOfMatch = numOfMatchResult.getInt(1);it throws the exception - java.sql.SQLException. I checked it and seen that it because the executeQuery()retrieved no one . it occur although I have in personstable ,created with MySQL, the 2 fields -
id (text)with value "300" and password (text)with value "500" . and of course I check it when loginIDand loginPasswordwith same 2 values . I checked all the other things about the connection to the DB and it was OK .. so I think the problem is in the SQL syntax in strSQLcount.
在运行并到达该行时，int numOfMatch = numOfMatchResult.getInt(1);它会引发异常 - java.sql.SQLException。我检查了一下，看到它是因为executeQuery()没有检索到任何人。尽管我在persons用 MySQL 创建的表中有 2 个字段 -id (text)值“300”和password (text)值“500” ，
但它还是会发生。当然我检查时loginID，并loginPassword用同样的2倍的值。我检查了有关与数据库连接的所有其他内容，一切正常.. 所以我认为问题出在strSQLcount.
采纳答案by JB Nizet
You forgot to call next()on the result set:
你忘了调用next()结果集：
ResultSet numOfMatchResult = prepareSQL.executeQuery();
int numOfMatch = 0;
if (rs.next() {
numOfMatch = numOfMatchResult.getInt(1);
}
If that is not sufficient to solve the problem, paste the whole stack trace of the exception: it contains meaningful information.
如果这不足以解决问题，请粘贴异常的整个堆栈跟踪：它包含有意义的信息。
