JDBC 增删改查代码 过滤查询语句

package test;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

public class CRUD {

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        try {
            create();
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    static void create() throws SQLException {
        Connection conn = null;
        Statement st = null;

        PreparedStatement ps =null;//这种statement可以用来过滤数据库查询语句，防止SQL注入
        ResultSet rs = null;
        try {
            conn = JdbcUtils.getConnection();
            //3，Statement用于“运送”sql语句和sql语句执行结果
            String paraSql = “select * from user hwere name=?”;

            //对于上面这种带？的sql可以用下面这个办法来获取statement     

            ps=conn.prepareStatement(sql)；//这种创建连接的办法虽然安全但是创建的时候比较耗时

            String paraName = “’’ or 1 or ‘”;

            ps.setString(1,paraName);

            rs=ps.executeQuery();//这样是查询不到结果的，因为没有一个用户名叫做’’ or 1 or ‘

            st = conn.createStatement();
        
            String sql = "insert into user(name,birthday,money) values ('name1','1987-01-01','400')";
           
            String sql1 = "update user set money=money+10";
           
            String sql2 = "delete from user where id>5";
            //4,执行sql
            int count = st.executeUpdate(sql1);//增删改全用这个，返回值是受影响的行数
            rs = st.executeQuery("select * from user");
            
            while(rs.next()) {
                //也可以使用列名，使用列号要从1开始
                //for(int i = 1)
                int i = rs.getMetaData().getColumnCount(); //获取列数
                for(int j=1;j<=i;j++)
                System.out.print(rs.getObject(j)+" ");
                System.out.println();
            }
            System.out.println(count);
        } finally {
            JdbcUtils.free(rs, st, conn);
        }
    }
}

package test;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

/* 简陋工具类  */
public final class JdbcUtils {
    private static String url="jdbc:mysql://localhost:3306/world";
    private static String user = "root";
    private static String password="mysql";

    static {
        try {
            Class.forName("com.mysql.jdbc.Driver");
        } catch (ClassNotFoundException e) {
            throw new ExceptionInInitializerError(e);
        }

    }
   
    private JdbcUtils() {}
   
    public static Connection getConnection() throws SQLException {
        return DriverManager.getConnection(url,user,password);
    }
   
    public static void free(ResultSet rs,Statement st,Connection conn) {
        try {
            if (rs != null) {
                rs.close();
            }
        }catch(SQLException e) {
            e.printStackTrace();
        }
        finally {
            try {
                if (st != null) {
                    st.close();
                }
            } catch(SQLException e){
                e.printStackTrace();
            } finally {
                if (conn != null)
                    try {
                        conn.close();
                    } catch (SQLException e) {
                        e.printStackTrace();
                    }
            }
        }
    }
}