我有一段非常基础的代码,执行一个select查询并根据结果集是否为空返回一个布尔值。
public boolean checkIfUserHasPreferences(String username){
ResultSet rs = null;
boolean checkBoolean = false;
try {
DriverManager.registerDriver(new oracle.jdbc.driver.OracleDriver());
con = DriverManager.getConnection(Messages.getString("OracleUserManagement.0"), Messages.getString("OracleUserManagement.1"), Messages.getString("OracleUserManagement.2")); //$NON-NLS-1$ //$NON-NLS-2$ //$NON-NLS-3$
PreparedStatement statement = con.prepareStatement("SELECT USERNAME FROM USER_PREFERENCES WHERE USERNAME = ?");
statement.setString(1, username);
rs = statement.executeQuery();
if (rs == null){
System.out.println("I checked it was true!");
checkBoolean = true;
} else {
System.out.println("I checked it was false!");
checkBoolean = false;
}
con.commit();
con.close();
} catch (SQLException e) {
e.printStackTrace();
}
return checkBoolean;
}
我感到困惑的是,即使表/数据库为空,它总是打印出"I checked it was false!"。这是因为结果集返回0行,也不等于null吗?我应该使用while(rs.next())来进行检查吗?