java 如何从 MySQL 中检测空的 ResultSet？
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时间：2020-10-30 19:01:55 来源:igfitidea点击:
How to detect empty ResultSet from MySQL?
提问by Jayanga Kaushalya
How can I detect the empty result set sending from MySQL if there is no possible result.
如果没有可能的结果，如何检测从 MySQL 发送的空结果集。
回答by BalusC
Just check if ResultSet#next()returns true. E.g.
只需检查是否ResultSet#next()返回true。例如
public boolean exist(String username, String password) throws SQLException {
Connection connection = null;
PreparedStatement statement = null;
ResultSet resultSet = null;
boolean exist = false;
try {
connection = database.getConnection();
statement = connection.prepareStatement("SELECT id FROM user WHERE username = ? AND password = MD5(?)");
statement.setString(1, username);
statement.setString(2, password);
resultSet = statement.executeQuery();
exist = resultSet.next();
} finally {
close(resultSet, statement, connection);
}
return exist;
}
which you can use like follows
您可以使用如下
if (userDAO.exist(username, password)) {
// Proceed with login?
} else {
// Show error?
}
Alternatively, you could also let it return a fullworhy Useror nullif there's none. E.g.
或者，您也可以让它返回 fullworhyUser或者null如果没有。例如
public User find(String username, String password) throws SQLException {
Connection connection = null;
PreparedStatement statement = null;
ResultSet resultSet = null;
User user = null;
try {
connection = database.getConnection();
statement = connection.prepareStatement("SELECT id, username, email, dateOfBirth FROM user WHERE username = ? AND password = MD5(?)");
statement.setString(1, username);
statement.setString(2, password);
resultSet = statement.executeQuery();
if (resultSet.next()) {
user = new User(
resultSet.getLong("id"),
resultSet.getString("username"),
resultSet.getString("email"),
resultSet.getDate("dateOfBirth"));
}
} finally {
close(resultSet, statement, connection);
}
return user;
}
with
和
User user = userDAO.find(username, password);
if (user != null) {
// Proceed with login?
} else {
// Show error?
}
