我有这样的代码:连接到MySQL
package FirstServlet;
import java.beans.Statement;
import java.sql.DriverManager;
import java.sql.ResultSet;
import com.mysql.jdbc.ResultSetMetaData;
public class Codb{
public static void connect() {
try{
Class.forName("com.mysql.jdbc.Driver");
String url = "jdbc:mysql://" + "localhost:3306/bd1";
String user = "root";
String passwd = "root";
Connection conn = (Connection) DriverManager.getConnection(url, user, passwd);
java.sql.Statement state =((java.sql.Connection) conn).createStatement();
ResultSet result = ((java.sql.Statement) state).executeQuery("SELECT * FROM consomateur");
ResultSetMetaData resultMeta = (ResultSetMetaData) result.getMetaData();
System.out.println("\n**********************************");
for(int i = 1; i <= resultMeta.getColumnCount(); i++)
System.out.print("\t" + resultMeta.getColumnName(i).toUpperCase() + "\t *");
System.out.println("\n**********************************");
while(result.next()) {
for(int i = 1; i <= resultMeta.getColumnCount(); i++)
System.out.print("\t" + result.getObject(i).toString() + "\t |");
System.out.println("\n---------------------------------");
}
result.close();
} catch (Exception e) {
e.printStackTrace();
}
return false;
}
}
当我把它写在main方法中它工作得很好,但是当我把它写在一个新的类,然后再初始化它的主要方法,它不起作用。 我有这些错误。
java.lang.ClassCastException: com.mysql.jdbc.Connection cannot be cast to FirstServlet.Connection
at FirstServlet.Connect.connect(Connect.java:23)
at FirstServlet.Main.main(Main.java:16)
这是主类:
package FirstServlet;
public class Main {
public static void main(String[] args) {
Connect c = new Connect();
c.connect();
}
}
感谢您的probleme确实是类的名字,我也有另外一个问题。 我有这个我创建的servlet的方法,我想要做的是让用户输入一个登录名和一个密码来连接。检查用户名和密码的方法是这样的:
protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
Codb c = new Codb();
c.connect();
Statement state =conn.createStatement();
ResultSet result = (ResultSet) state.executeQuery("SELECT * FROM consomateur");
ResultSetMetaData resultMeta = (ResultSetMetaData) result.getMetaData();
String us= resultMeta.getColumnName(1);
String pass= resultMeta.getColumnName(2);
String username=us;
String password=pass;
String un=request.getParameter("username");
String pw=request.getParameter("password");
String msg=" ";
if(un.equals(username) && pw.equals(password)){
msg="Hello "+ un + " your login is sucess";
}
else{
msg="Hello "+un + " your login is unsucess";
}
response.setContentType("text/html");
PrintWriter out = response.getWriter();
out.println("<font siez='6' color=red>"+ msg+ "</font>");
}
}
但是行“Statement state = conn.createStatement();”以红色下划线并且错误是conn无法解决。
这是一个明显的例子,为什么你不应该命名类与JDK类相似。 –