DAO数据访问对象
本文主要讲述DAO层，数据访问对象的含义与使用
一. 图解DAO层
二. 代码结构
1. dao
2. domain
3. utils
4.test做测试
三. 具体实现
1.1 dao中的BasicDAO
/** * 处理sql语句，返回结果 */ public class BasicDAO<T> { private QueryRunner queryRunner = new QueryRunner(); private Connection connection; /** * * @param sql sql语句 * @param aClass aClass反射对象 * @param params params可变参数，对?赋值 * @return */ // 查询多行结果 // 方法中的泛型，必须是类中声明过的，没有声明的不能使用。 public List<T> queryMultiple(String sql, Class<T> aClass, Object... params){ List<T> result = null; try { connection = JDBCUtilsByDruid.getConnection(); result = queryRunner.query(connection,sql, new BeanListHandler<T>(aClass), params); } catch (SQLException e) { throw new RuntimeException(e); // 方法默认抛出运行时异常机制 } finally { JDBCUtilsByDruid.Close(null,null,connection); } return result; } // 查询单行数据 public T querySingle(String sql,Class<T> aClass,Object... params){ T t = null; try { connection = JDBCUtilsByDruid.getConnection(); System.out.println("@2:" + connection); t = queryRunner.query(connection,sql,new BeanHandler<T>(aClass),params); } catch (SQLException e) { e.printStackTrace(); } finally { JDBCUtilsByDruid.Close(null,null,connection); } return t; } // 查询单行单列的数据 public Object queryScalar(String sql,Object... params){ Object obj = null; try { connection = JDBCUtilsByDruid.getConnection(); obj = queryRunner.query(connection, sql, new ScalarHandler(), params); } catch (SQLException e) { throw new RuntimeException(e); } finally { JDBCUtilsByDruid.Close(null,null,connection); } return obj; } // 执行DML语句 public int update(String sql,Object...params){ int update = 0; try { connection = JDBCUtilsByDruid.getConnection(); update = queryRunner.update(connection,sql, params); } catch (SQLException e) { new RuntimeException(e); } finally { JDBCUtilsByDruid.Close(null,null,connection); } return update; } }
注意：这里的泛型使用，方法中所使用的泛型，必须是在该类中实现声明的，如：
BasicDAO类声明泛型T
public class BasicDAO<T> {}
BasicDAO类的方法使用泛型T
ublic List<T> queryMultiple(String sql, Class<T> aClass, Object... params){}
1.2 dao中的AdminDAO
public class AdminDAO extends BasicDAO<Admin> { // 1.继承BasicDAO的所有方法 // 2.可以写特有的方法 }
2 domain中的Admin
public class Admin { private Integer id; private String name; private String pwd; public Admin() { } public Admin(Integer id, String name, String pwd) { this.id = id; this.name = name; this.pwd = pwd; } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getPwd() { return pwd; } public void setPwd(String pwd) { this.pwd = pwd; } @Override public String toString() { return "Admin{" + "id=" + id + ", name='" + name + '\'' + ", pwd='" + pwd + '\'' + '}'; } }
注意：domain中的类的无参构造器不能省略【反射机制】
3. utils中的 JDBCUtilsByDruid
public class JDBCUtilsByDruid { private static DataSource druid; static { Properties properties = new Properties(); try { properties.load(new FileInputStream("src\\druid.properties")); druid = DruidDataSourceFactory.createDataSource(properties); } catch (Exception e) { e.printStackTrace(); } } public static Connection getConnection(){ Connection connection = null; try { connection = druid.getConnection(); } catch (SQLException e) { e.printStackTrace(); } return connection; } @SuppressWarnings({"all"}) public static boolean Close(ResultSet resultSet, Statement statement,Connection connection){ try { if(resultSet != null){ resultSet.close(); } if(statement != null){ statement.close(); } if(connection != null){ connection.close(); } } catch (SQLException e) { throw new RuntimeException(); } return true; } }
参看 jdbc+Druid工具类 - zwGitOne - 博客园 (cnblogs.com)这篇博客
4. test测试
public class TestDAO { @Test public void testAdmin(){ // 1.查询多行记录 String all = "select * from admin "; AdminDAO adminDAO = new AdminDAO(); List<Admin> adminList = adminDAO.queryMultiple(all, Admin.class, null); System.out.println("===显示表中所有的数据==="); Iterator<Admin> iterator = adminList.iterator(); while (iterator.hasNext()) { Admin admin = iterator.next(); System.out.println(admin); } // 2.查询单行记录 String single = "select * from admin where id = ?"; Admin admin = adminDAO.querySingle(single, Admin.class, 8); System.out.println("===显示单行对象==="); System.out.println(admin); // 3.查询单行单个对象 String scalar = "select name from admin where id = ?"; int id = 8; Object o = adminDAO.queryScalar(scalar, id); System.out.println("===显示单行单个对象==="); System.out.println("id:" + id + "的name是" + o); // 增加 String insert = "insert into admin values(null,?,?)"; int row = adminDAO.update(insert, "张山峰", "123456"); // 修改 String update = "update admin set name = ? where id = ?"; row = adminDAO.update(update, "张三丰", 16); // 删除 String delete = "delete from admin where id = ?"; row = adminDAO.update(delete,16); } }
运行结果如下：
===显示表中所有的数据=== Admin{id=3, name='Tom3', pwd='123'} Admin{id=5, name='Tom2', pwd='123'} Admin{id=6, name='Tom3', pwd='123'} Admin{id=8, name='Tom2', pwd='123'} Admin{id=9, name='Tom3', pwd='123'} Admin{id=11, name='zw', pwd='123'} Admin{id=12, name='郑为', pwd='1234'} Admin{id=13, name='郑威', pwd='1234'} Admin{id=14, name='郑为', pwd='1234'} Admin{id=15, name='郑威', pwd='1234'} Admin{id=17, name='张山峰', pwd='123456'} Admin{id=18, name='张山峰', pwd='123456'} Admin{id=19, name='张山峰', pwd='123456'} Admin{id=20, name='张山峰', pwd='123456'} @2:com.mysql.cj.jdbc.ConnectionImpl@10aa41f2 ===显示单行对象=== Admin{id=8, name='Tom2', pwd='123'} ===显示单行单个对象=== id:8的name是Tom2 Process finished with exit code 0
四. 总结
理解AdminDAO与BasicDAO的继承关系，为什么抽象出BasicDAO这一父类？
将XXxxDAO类的公共操作提取出来，作为父类BasicDAO，使得XXxxDAO代码简化。
