Ajax的JSP示例以及相关知识

package project1;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class DBMS_Conn {
    Connection conn;
    Statement st;
    public DBMS_Conn() {
        conn_init();
    }
    void conn_init() {
        setConnection();
        setStatement();
    }
    public void setConnection() {
        try {
            //Class.forName("org.gjt.mm.mysql.Driver").newInstance();
            Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
            //db.mdb有一个名为user表，至少有一个名为username的字段
            String strurl =
            "jdbc:odbc:driver={Microsoft Access Driver (*.mdb)};DBQ=E:\\db.mdb";
            //conn=DriverManager.getConnection("jdbc:mysql://localhost/palfinger?
            //user=root&password=admin&useUnicode=true&characterEncoding=8859_1");
            conn = DriverManager.getConnection(strurl);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    /**
     * 设置Statement
     */
    public void setStatement() {
        try {
            st = conn.createStatement(
ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_READ_ONLY);
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
    /**
     * 根据用户名确定用户是否存在
     */
    public boolean checkUser(String username) {
        String sql="select * from user where username='"+username+"'";
        ResultSet rs;
        try {
            rs = st.executeQuery(sql);
            if(rs.next())
            {
                conn.close();
                return true;
            }           
        } catch (SQLException e) {
            e.printStackTrace();
        }
        try {
            conn.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return false;
    }  
}