JDBC 笔记2 封装

1 封装

         新建类 DBConnUtil  ，新建database.properties 文件储存链接信息如下所示

       

jdbcDriver=com.mysql.jdbc.Driver
jdbcUrl=jdbc\:mysql\://localhost\:3306/homework
jdbcUser=root
jdbcPasswd=123

public class DBConnUtil {
    
    private static String jdbcDriver = "";      //定义连接信息
    private static String jdbcUrl = "";

    private static String jdbcUser = "";

    private static String jdbcPasswd = "";
    
    static{
        InputStream is = null;
        try {
            is = DBConnUtil.class.getClassLoader().getResourceAsStream("database.properties");   //加载database.properties文件
            Properties p = new Properties();
            p.load(is);
            jdbcDriver = p.getProperty("jdbcDriver");    //赋值
            jdbcUrl = p.getProperty("jdbcUrl");
            jdbcUser = p.getProperty("jdbcUser");
            jdbcPasswd = p.getProperty("jdbcPasswd");

        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if(is != null){
                try {
                    is.close();   //  关闭is
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
    
    public static Connection getConn(){   // 建立连接方法
        Connection conn = null;
        try {
            Class.forName(jdbcDriver);
            conn = DriverManager.getConnection(jdbcUrl, jdbcUser, jdbcPasswd);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return conn;
    }
    
    public static void closeAll(ResultSet rs ,Statement st,Connection conn){  //关闭连接（用于增删改）
        if(rs != null){
            try {
                rs.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if(st != null){
            try {
                st.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if(conn != null){
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
    
    public static void closeAll(ResultSet rs ,PreparedStatement ps,Connection conn){  // 关闭连接（用于查）
        if(rs != null){
            try {
                rs.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if(ps != null){
            try {
                ps.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if(conn != null){
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
    
}

2 测试增删改差

　　2.1 插入数据

public boolean ChaRu1(User user){
        boolean flag=true;
        Connection conn=null;
        Statement st=null;
        String sql="insert into user (name,pwd) values('"+user.getName()+"','"+user.getPwd()+"')";
        conn=DBConnUtil.getConn();   // getConn()方法是静态的，直接用类调用建立连接。
        try {
            st=conn.createStatement();
            int i=st.executeUpdate(sql);
            if(i==0){
                flag=false;
            }
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally{
            DBConnUtil.closeAll(null, st, conn);   //关闭连接，由于插入操作不涉及ResultSet类，故其对象rs无需关闭，用null代替。
        }
        return flag;
    }

　　2.2 修改数据

    public boolean XiuGai2(User user){
        boolean flag=true;
        Connection conn =null;
        Statement st=null;
        String sql="update user set pwd='"+user.getPwd()+"' where name='"+user.getName()+"'";
        conn=DBConnUtil.getConn();
        try {
            st=conn.createStatement();
            st.executeUpdate(sql);
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally{
            DBConnUtil.closeAll(null, st, conn);
        }
        return flag;
    }

　　2.3 删除数据

public boolean ShanChu2(int id){
        boolean flag=true;
        Connection conn=null;
        Statement st=null;
        String sql="delete from user where id="+id;
        conn=DBConnUtil.getConn();
        try {
            st=conn.createStatement();
            int i=st.executeUpdate(sql);
            if(i==0){
                flag=false;
            }
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally{
            DBConnUtil.closeAll(null, st, conn);
        }
        
        return flag;
    }

　　2.4删除数据

    public List<User> ChanKan2(){
        List<User> list= new ArrayList<User>();
        Connection conn=null;
        Statement st= null;
        ResultSet rs=null;
        String sql="select * from user";
        conn=DBConnUtil.getConn();
        try {
            st=conn.createStatement();
            rs=st.executeQuery(sql);
            while(rs.next()){
                User user=new User();
                user.setName(rs.getString("name"));
                list.add(user);
            }
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally{
            DBConnUtil.closeAll(rs, st, conn);
        }
        return list;
    }