JDBC1

Posted 2020-09-19 司机刹一脚

1.jdbc的概述

　　是sun公司统一提供的一套接口规范,各个数据库生产商提供实现

　　注册驱动,获得连接,获得执行的SQL语句对象,释放资源

package com.learn.jdbc;

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

import org.junit.Test;

public class Demo1 {
    Connection conn = null;
    @Test
    public void test() {
        try {
            //注册驱动
            Class.forName("com.mysql.jdbc.Driver");
            //获得连接
            String url = "jdbc:mysql///mydatebase";
            String user = "root";
            String password = "root";
            conn = DriverManager.getConnection(url, user, password);
        } catch (Exception e) {
            e.printStackTrace();
            //释放资源
            if( conn != null) {
                try {
                    conn.close();
                } catch (SQLException e1) {
                    e1.printStackTrace();
                }
                //垃圾回收尽快回收对象
                conn = null;
            }
        }
    }
}

2.JDBC的API

　　connection

 

 

　　statement

3.JDBC的元数据MataDate(提高通用性较高的代码)

• DatabaseMetaData：获得数据库连接的信息,获得数据库的表的信息.

* 获得数据库元数据:Connection中getMetaData();

 

• ParameterMetaData：获得SQL中的参数的个数及类型.

* 获得参数元数据：PreparedStatement中getParameterMetaData()

 

• ResultSetMetaData：获得结果集中的列名及列的类型.

* 获得结果集元数据：ResultSet中getMeta()

4.元数据的使用

public void demo2(){
        Connection conn = null;
        conn = JDBCUtils2.getConnection();
        // 获得数据库元数据:
        try {
            DatabaseMetaData metaData = conn.getMetaData();
            System.out.println("获得驱动名称:"+metaData.getDriverName());
            System.out.println("获得驱动URL:"+metaData.getURL());
            System.out.println("获得用户名:"+metaData.getUserName());
            
            // 获得表中的主键：
            ResultSet rs = metaData.getPrimaryKeys(null, null, "category");
            if(rs.next()){
                String name = rs.getString("COLUMN_NAME");
                System.out.println(name);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

参数元数据

　　

public void demo3(){
        Connection conn = null;
        PreparedStatement stmt = null;
        try{
            conn = JDBCUtils2.getConnection();
            String sql = "update category set cname = ? where cid = ?";
            stmt = conn.prepareStatement(sql);
            ParameterMetaData metaData = stmt.getParameterMetaData();
            int count = metaData.getParameterCount();
            System.out.println(count);
        }catch(Exception e){
            
        }
    }

结果集元数据

public void demo4(){
        Connection conn = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;
        try{
            conn = JDBCUtils2.getConnection();
            String sql = "select * from category";
            stmt = conn.prepareStatement(sql);
            rs = stmt.executeQuery();
            
            ResultSetMetaData metaData = rs.getMetaData();
            int count = metaData.getColumnCount();
            for(int i = 1;i<=count ;i++){
                String name = metaData.getColumnName(i);
                
                String type = metaData.getColumnTypeName(i);
                System.out.println(name+type);
            }
        }catch(Exception e){
            
        }
    }