Java开发基础-JDBC-对其技术的支持—02

JDBC应用中对数据库对象记录的映射JavaBean及增删改查(CRUD)的封装DAO

应用程序中使用数据访问对象(DAO)使我们可以将底层数据访问逻辑与业务逻辑分离开来。构建了为每一个数据源提供 CRUD (创建、读取、更新、删除)操作的 DAO 类。

Dao其实一般没有这个类，一般是指java中MVC架构中的model的概念，主要是访问数据库的一些常用方法。

相关概念：

JavaBean

满足如下规范的类： - 有package - 有无参构造器 - 实现序列化接口 - 有get/set方法

DAO

下面通过简单实例演示如何封装常用数据库操作类Dao

项目目录结构如下图

1.编写实体类：Emp

/**
 * 1.通常实体类和表名一致
 * 2.通常该类中属性名和字段名一致
 * 3.通常该类中属性都使用封装类型
 * @author Cher_du
 *
 */
public class Emp implements Serializable{
	
	private static final long serialVersionUID = 1L;
	
	private Integer empno;
	private String ename;
	private String job;
	private Integer mgr;
	private Date hiredate;
	private Double sal;
	private Double comm;
	private Integer deptno;
	
	
	public Integer getEmpno() {
		return empno;
	}
	public void setEmpno(Integer empno) {
		this.empno = empno;
	}
	public String getEname() {
		return ename;
	}
	public void setEname(String ename) {
		this.ename = ename;
	}
	public String getJob() {
		return job;
	}
	public void setJob(String job) {
		this.job = job;
	}
	public Integer getMgr() {
		return mgr;
	}
	public void setMgr(Integer mgr) {
		this.mgr = mgr;
	}
	public Date getHiredate() {
		return hiredate;
	}
	public void setHiredate(Date hiredate) {
		this.hiredate = hiredate;
	}
	public Double getSal() {
		return sal;
	}
	public void setSal(Double sal) {
		this.sal = sal;
	}
	public Double getComm() {
		return comm;
	}
	public void setComm(Double comm) {
		this.comm = comm;
	}
	public Integer getDeptno() {
		return deptno;
	}
	public void setDeptno(Integer deptno) {
		this.deptno = deptno;
	}
	
}

2.编写数据库操作类EmpDao：【封装CURD】

public class EmpDao {
	
	//查询所有
	public List<Emp> findAll(){
		Connection conn = null;
		List<Emp> empList = new ArrayList<Emp>();
		try {
			conn = DBUtil.getConnection();
			String sql = "select * from emp ";
			PreparedStatement ps = conn.prepareStatement(sql);
			
			ResultSet rs  = ps.executeQuery();
			while(rs.next()){
				Emp e =new Emp();
				e.setEmpno(rs.getInt("empno"));
				e.setEname(rs.getString("ename"));
				e.setJob(rs.getString("job"));
				e.setMgr(rs.getInt("mgr"));
				e.setHiredate(rs.getDate("hiredate"));
				e.setSal(rs.getDouble("sal"));
				e.setComm(rs.getDouble("comm"));
				e.setDeptno(rs.getInt("deptno"));
				empList.add(e);
			}
			return empList;
		} catch (SQLException e) {
			e.printStackTrace();
		}
		return empList;
	}

	public Emp findById(int id){
		
		Connection conn =null;
		try {
			conn = DBUtil.getConnection();
			String sql = "select * from emp "
					    +"where empno =?";
			PreparedStatement ps = conn.prepareStatement(sql);
			ps.setInt(1, id);
			ResultSet rs = ps.executeQuery();
			if(rs.next()){
				Emp e =new Emp();
				e.setEmpno(rs.getInt("empno"));
				e.setEname(rs.getString("ename"));
				e.setJob(rs.getString("job"));
				e.setMgr(rs.getInt("mgr"));
				e.setHiredate(rs.getDate("hiredate"));
				e.setSal(rs.getDouble("sal"));
				e.setComm(rs.getDouble("comm"));
				e.setDeptno(rs.getInt("deptno"));
				return e;
			}
		} catch (SQLException e) {
			e.printStackTrace();
			throw new RuntimeException("根据ID查询员工失败！",e);
		}finally{
			DBUtil.close(conn);
		}	
		return null;	
	}
	
	public boolean save(Emp emp){
		Connection conn = null;
		
		try {
			conn = DBUtil.getConnection();
			String sql = "insert into emp values("
					     +"?,?,?,?,?,?,?,?)";
			PreparedStatement ps = conn.prepareStatement(sql);
			ps.setInt(1, emp.getEmpno());
			ps.setString(2, emp.getEname());
			ps.setString(3, emp.getJob());
			ps.setInt(4, emp.getMgr());
			ps.setDate(5, emp.getHiredate());
			ps.setDouble(6,emp.getSal());
			ps.setDouble(7, emp.getComm());
			ps.setInt(8, emp.getDeptno());
			
		    int count = ps.executeUpdate();
			
		    if(count>0){
		    	return true;
		    }else{
		    	return false;
		    }
			
		} catch (SQLException e) {
			e.printStackTrace();
			throw new RuntimeException("保存员工失败！",e);
		}finally{
			DBUtil.close(conn);
		}
	}
	
	public void update(Emp emp){
		Connection conn = null;
		
		try {
			conn = DBUtil.getConnection();
			String sql = "update emp set "
					     +"ename =?,"
					     +"job =?,"
					     +"mgr =?,"
					     +"hiredate =?,"
					     +"sal =?,"
					     +"comm =?,"
					     +"deptno =? "
					     +"where empno=?";
			PreparedStatement ps = conn.prepareStatement(sql);
			ps.setString(1, emp.getEname());
			ps.setString(2, emp.getJob());
			ps.setInt(3, emp.getMgr());
			ps.setDate(4, emp.getHiredate());
			ps.setDouble(5,emp.getSal());
			ps.setDouble(6, emp.getComm());
			ps.setInt(7, emp.getDeptno());
			ps.setInt(8, emp.getEmpno());
			ps.executeUpdate();
			
		} catch (SQLException e) {
			e.printStackTrace();
			throw new RuntimeException("修改员工失败！",e);
		}finally{
			DBUtil.close(conn);
		}
		
		
	}
	
	public boolean delete(int id){
		Connection conn =null;
		try {
			conn = DBUtil.getConnection();
			String sql = "delete from emp "
					    +"where empno =?";
			PreparedStatement ps = conn.prepareStatement(sql);
			ps.setInt(1, id);
			int count = ps.executeUpdate();
			
			if(count>0){
				return true;
			}else{
				return false;
			}
		} catch (SQLException e) {
			e.printStackTrace();
			throw new RuntimeException("根据ID删除员工失败！",e);
		}finally{
			DBUtil.close(conn);
		}	
	}
}

3.编写EmpDao测试类

public class EmpDaoTest {
	
	public static void main(String[] args) {
//		EmpDao dao = new EmpDao();
//		Emp emp = new Emp();
//		emp.setEmpno(1000);
//		emp.setEname("Jimmy");
//		emp.setJob("经理");
//		emp.setHiredate(new Date(System.currentTimeMillis()));
//		emp.setSal(10000.00);
//		emp.setComm(2000.00);
//		emp.setDeptno(20);
//		emp.setMgr(45);
//		
//		boolean  b = dao.save(emp);
//		System.out.println(b);
		
//		EmpDao dao = new EmpDao();
//		Emp emp = new Emp();
//		emp.setEmpno(1000);
//		emp.setEname("Jimmy");
//		emp.setJob("高级经理");
//		emp.setHiredate(new Date(System.currentTimeMillis()));
//		emp.setSal(10000.00);
//		emp.setComm(2000.00);
//		emp.setDeptno(20);
//		emp.setMgr(45);
//		
//		dao.update(emp);
		
//		EmpDao dao = new EmpDao();
//		Emp emp = new Emp();
//		
//		emp =dao.findById(1000);
//		System.out.println(emp.getEname());
		
//		EmpDao dao = new EmpDao();
//		Emp emp = new Emp();
//		
//		boolean b =dao.delete(1000);
//		System.out.println(b);
		
		EmpDao dao = new EmpDao();
		List<Emp> empList =dao.findAll();
        for(Emp e :empList){
        	System.out.println(e.getEname());
        }
		
	}

}

总结: DAO常用于MVC开发模式中

DAO层一般有接口和该接口的实现类! 接口用于规范实现类! 实现类一般用于用于操作数据库! 一般操作修改，添加，删除数据库操作的步骤很相似，就写了一个公共类DAO类 ，修改，添加，删除数据库操作时 直接调用公共类DAO类