JDBC-2 package tool class, prepareStaement

preparedstatment: more readable, safe, prevent sql injection, more efficient

PreparedStatment syntax:

Connection conn = null;
        PreparedStatement ps = null;
        ResultSet res = null;

        try {
            conn = DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:orcl", "scott", "tiger");
            // sql 语句
            String sql = "select * from userinfos where user_id = ? and user_password = ?";
            ps = conn.prepareStatement(sql);
             // Set the value of the question mark placeholder of sql 
            ps.setString(1 , id);
            ps.setString(2, password);
            res = ps.executeQuery();

Package tool class: *

package tool;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.List;

public class DBTool {
    static Connection conn = null;
    static{
        try {
            Class.forName("oracle.jdbc.driver.OracleDriver");
        } catch (ClassNotFoundException e) {
            e.printStackTrace ();
        }
        try {
            conn = DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:orcl","scott","tiger");
        } catch (SQLException e) {
            e.printStackTrace ();
        }
    }
    // Add, delete and modify methods, no need to pass in the operation value 
    public  int executeOper(String sql){
         int ret = 0 ;
         try {
            PreparedStatement ps = DBTool.conn.prepareStatement(sql);
             ret = ps.executeUpdate();
             close(null, ps, conn);
        } catch (SQLException e) {
            e.printStackTrace ();
        }
        return ret;
    }
    // Add, delete and modify methods, sql statement with question mark 
    public  int executeOper(String sql,List<Object> list){
         int ret = 0 ;
         try {
            PreparedStatement ps = DBTool.conn.prepareStatement(sql);
            for(int i = 0; i < list.size(); i++){
                Object obj = list.get(i);
                if(obj instanceof String){
                    ps.setString(i+1, obj.toString());
                }
                if(obj instanceof Integer){
                    ps.setInt(i+1, (int)obj);
                }
                if(obj instanceof Float){
                    ps.setFloat(i+1, (float)obj);
                }
                ret = ps.executeUpdate();
            }
            close(null, ps, conn);
        } catch (SQLException e) {
            e.printStackTrace ();
        }
        return ret;
    }
    
    // Query method without parameters 
    public ResultSet Query(String sql){
        ResultSet res = null;
        try {
            PreparedStatement ps = DBTool.conn.prepareStatement(sql);
            res = ps.executeQuery();
            //close(null, ps, conn);
        } catch (SQLException e) {
            e.printStackTrace ();
        }
        return res;
    }
    // Query method with question mark 
    public ResultSet Query(String sql,List<Object> list){
        ResultSet res = null;
        try {
            PreparedStatement ps = DBTool.conn.prepareStatement(sql);
            for (int i = 0; i < list.size(); i++) {
                Object obj = list.get(i);
                if(obj instanceof String){
                    ps.setString(i+1, obj.toString());
                }
                if(obj instanceof Integer){
                    ps.setInt(i+1, (int)obj);
                }
                if(obj instanceof Float){
                    ps.setFloat(i+1, (float)obj);
                }
            }
            res = ps.executeQuery();
            //close(null, ps, conn);
        } catch (SQLException e) {
            e.printStackTrace ();
        }
        return res;
    }
    public void close(ResultSet res,Statement ps,Connection conn){
        try {
            if(res != null){
                res.close();
            }
            if(ps != null){
                ps.close();
            }
            if(conn != null){
                conn.close();
            }
        } catch (SQLException e) {
            e.printStackTrace ();
        }
    }
}