Day03--JDBC

Posted 2020-10-01

怎么说呢，本来挺有激情的，突然炸掉了，不知道今天的效率会咋样A

使用Java代码发送sql语句的技术

1、JDBC接口核心的API：java.sql 和 javax.sql

1.1、Driver接口：Java驱动类接口

1.2、DriverManager类：驱动管理器类

1.3、Connection接口：表示Java程序和数据库连接对象

1.4、statement接口：用于执行静态的sql语句

1.5、preparedstatement接口：用于执行预编译sql语句

1.6、resultset接口：用于封装查询出来的数据

1.7、CallableStatement：程序中调用存储过程

/**
 * Jdbc工具类
 * */
public class JdbcUtil
{
    private static String url = null;
    private static String user = null;
    private static String password = null;
    private static String driverClass = null;
    
    /**
     * 静态代码块（只加载一次）
     * */
    static{
        //读取db.properties文件
        Properties properties = new Properties();
        //.java命令运行的目录
        //FileInputStream in = new FileInputStream("./src/db.properties");
        //使用类路径的读取方式,在Java项目中，classpath的根目录从bin目录开始；web中，从WEB-INF/classes目录开始
        InputStream in = JdbcUtil.class.getResourceAsStream("/db.properties");
        try
        {
            //加载文件
            properties.load(in);
            //读取信息
            url = properties.getProperty("url");
            user = properties.getProperty("user");
            password = properties.getProperty("password");
            driverClass = properties.getProperty("driverClass");
            //注册驱动程序
            Class.forName(driverClass);
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
        
    }
    
    public static Connection getConnection(){
        try
        {
            Connection connection = DriverManager.getConnection(url,user,password);
            return connection;
        }
        catch (SQLException e)
        {
            e.printStackTrace();
            throw new RuntimeException();
        }
    }
    
    public static void close(Connection conn,Statement stmt,ResultSet rs){
        if(rs!=null)
            try {
                rs.close();
            } catch (SQLException e1) {
                e1.printStackTrace();
                throw new RuntimeException(e1);
            }
        if(stmt!=null){
            try {
                stmt.close();
            } catch (SQLException e) {
                e.printStackTrace();
                throw new RuntimeException(e);
            }
        }
        if(conn!=null){
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
                throw new RuntimeException(e);
            }
        }
    }
}

public void test1(){
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        try
        {
            connection = JdbcUtil.getConnection();
            String sql = "update manager set account = ?  where id = ?";
            preparedStatement = (PreparedStatement) connection.prepareStatement(sql);
            preparedStatement.setString(1, "Rose黄");
            preparedStatement.setInt(2, 2);
            int count = preparedStatement.executeUpdate();
            System.out.println("受影响的行数"+count);
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }finally {
            JdbcUtil.close(connection, preparedStatement, null);
        }
    }

public void test2(){
        Connection connection = null;
        Statement statement = null;
        ResultSet rs = null;
        try
        {
            connection = JdbcUtil.getConnection();
            statement = connection.createStatement();
            String sql = "select * from manager";
            rs = statement.executeQuery(sql);
            while(rs.next()){
                int id = rs.getInt("id");
                String name = rs.getString("account");
                System.out.println(id+";"+name);
            }
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }finally {
            JdbcUtil.close(connection, statement, rs);
        }
        
    }

 

2、批处理：一次批量执行大量的命令

void  addBatch(String sql)：添加批处理

void  clearBatch()：清空批处理

int[] executeBatch()：执行批处理

　　 private Connection conn;
    private PreparedStatement ps;
    private ResultSet rs;
    
    public void save(List<Admin> list){
        String sql = "insert into admin (username,pwd) values (?,?)";
        try
        {
            conn = JdbcUtil.getConnection();
            ps = conn.prepareStatement(sql);

            for (int i = 0; i < list.size(); i++)
            {
                Admin admin = list.get(i);
                ps.setString(1, admin.getUsername());
                ps.setString(2, admin.getPwd());
                //添加批处理
                ps.addBatch();
            }
　　　　　　　ps.executeBatch(); //执行批处理
            ps.clearBatch();    //清除批处理
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }finally{
            JdbcUtil.close(conn, ps, rs);
        }
    }
    
    public static void main(String[] args) throws Exception
    {
        List<Admin> list = new ArrayList<Admin>();
        for (int i = 0; i < 5; i++)
        {
            Admin admin = new Admin();
            admin.setUsername("xiao");
            admin.setPwd("12");
            list.add(admin);
        }
        AdminDao dao = new AdminDao();
        dao.save(list);
    }

3、插入数据，获取自增长值

参照员工、部门表

　　private Connection conn;
    private java.sql.PreparedStatement ps;
    private ResultSet rs;
    
    public void save(Employee emp){
        String sql_dept = "insert into dept (name) values (?)";
        String sql_emp = "insert into employee (name,deptid) values (?,?)";
        int deptid = 0;
        try
        {
            conn = JdbcUtil.getConnection();
            //保存部门，获取自增长：指定返回自增长标记
            ps = conn.prepareStatement(sql_dept, Statement.RETURN_GENERATED_KEYS);
            ps.setString(1, emp.getDept().getName());
            ps.executeUpdate();
            //获取保存部门自增长的主键
            rs = ps.getGeneratedKeys();
            if(rs.next())
                deptid = rs.getInt(1);
            ps = conn.prepareStatement(sql_emp);
            ps.setString(1, emp.getName());
            ps.setInt(2,deptid);
            ps.executeUpdate();
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }finally {
            JdbcUtil.close(conn, ps, rs);
        }
    }
    
    public static void main(String[] args)
    {
        Dept dept = new Dept();
        dept.setName("市场部");
        Employee employee = new Employee();
        employee.setName("柳柳");
        employee.setDept(dept);
        Dao dao = new Dao();
        dao.save(employee);
    }

 

4、事务

一组最小逻辑操作单元，里面有多个操作组成。组成事务的每一部分要同时提交成功，如果一个操作失败，则整个操作回滚。通俗的讲，类似于银行转账系统，到了转账的最后一步，但是转账失败，则前面的操作全部返回，需要再次从头开始

原子性：要么都发生，要么都不发生；

一致性：事务过程中，数据处于一致状态

隔离性：多个并发事务之间要相互隔离

持久性：事务一旦提交成功，对数据库中数据的改变是持久性的

参照账户表

private Connection connection;
    private java.sql.PreparedStatement ps;
    
    //转账，没有使用事务
    public void trans1(){
        String sql_z = "update account set money = money + 1000 where name = ‘张三‘";
        String sql_l = "update account set money = money - 1000 where name = ‘李四‘";
        try
        {
            connection = JdbcUtil.getConnection();
            //默认开启隐士事务
            connection.setAutoCommit(true);
            ps = connection.prepareStatement(sql_l);
            ps.executeUpdate();
            ps = connection.prepareStatement(sql_z);
            ps.executeUpdate();
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }finally {
            JdbcUtil.close(connection, ps, null);
        }
    }
    
    //转账，使用事务
    public void trans2(){
        String sql_z = "update account set money = money + 1000 where name = ‘张三‘";
        String sql_l = "update account set money = money - 1000 where name = ‘李四‘";
        try
        {
            connection = JdbcUtil.getConnection();
            //设置事务为手动提交
            connection.setAutoCommit(false);
            ps = connection.prepareStatement(sql_z);
            ps.executeUpdate();
            ps = connection.prepareStatement(sql_l);
            ps.executeUpdate();
            //设置事务回滚位置
            //Savepoint sp = connection.setSavepoint();
        }
        catch (Exception e)
        {
            try
            {
                //出现异常，回滚事务
                connection.rollback();
                //connection.rollback(savepoint);  回滚到指定代码
            }
            catch (SQLException e1)
            {
                e1.printStackTrace();
            }
            e.printStackTrace();
        }finally {
            try
            {
                //所有操作执行成功，提交事务
                connection.commit();
                JdbcUtil.close(connection, ps, null);
            }
            catch (SQLException e)
            {
                e.printStackTrace();
            }
        }
    }

 

5、jdbc中大文本类型的处理（涉及到流的问题，后面统一处理）

Oracle ：Clob 长文本类型；Bolb 二进制类型

mysql：Text  长文本类型；Blob  二进制类型