14、基于JDBC的BaseDao的实现

青旅半醒 2022-07-24 03:17 156阅读 0赞

1、jdbc.properties的配置文件如下

driver=com.mysql.jdbc.Driver
    url=jdbc:mysql://localhost/bjsxteasyui
    username=root
    password=root

2、BaseDao.java

public interface BaseDao<Entity> {
    
    	
    	void save(Entity obj) throws Exception ; 
    	
    	void update (Entity obj) throws Exception; 
    	
    	void delete(int id) throws Exception; 
    	
    	List<Entity> findAll() throws Exception;
    	
    	Entity findById( int id) throws Exception;
    	
    	
    }

3、BaseDaoImpl.java

/**
     * jdbc连接 ： 1创建连接对象  2拼sql 3 preparedstatemenet
     *
     * @param <Entity>
     */
    public class BaseDaoImpl<Entity> implements BaseDao<Entity>{
    
    	//public 
    	protected Class clazz ;
    	
    
    	public BaseDaoImpl(){
    
    		//System.out.println(this.getClass());
    		ParameterizedType pt = (ParameterizedType) this.getClass().getGenericSuperclass();
    		//带有真实类型参数的对象
    		clazz = (Class)pt.getActualTypeArguments()[0];
    		System.out.println(clazz);
    	}
    	
    	
    	
    	/**
    	 * 保存方法
    	 */
    	public void save(Entity obj) throws Exception {
    		
    		//obj.getSimpleName();
    		Connection conn = DBUtils.createConn();
    		String sql = "insert into " + clazz.getSimpleName() + " values(null ";
    		// 可以获取本类所声明的变量
    		Field[] fs = clazz.getDeclaredFields();
    		//System.out.println(fs.length);
    		
    		for (int i = 1; i < fs.length; i++) {
    			sql += ",? " ;
    		}
    		sql = sql + ")";
    		System.out.println(sql);
    		
    		//进行预编译
    		PreparedStatement ps = DBUtils.getPs(conn, sql);
    		
    		//ps.setString(1, user.getName());
    		
    		for (int i = 1; i < fs.length; i++) {
    			//拼接方法的名称
    			String MethodName = "get" +Character.toUpperCase(fs[i].getName().charAt(0)) + fs[i].getName().substring(1) ;
    			Method m = clazz.getMethod(MethodName);
    			ps.setObject(i, m.invoke(obj));
    		}
    		ps.executeUpdate();
    		DBUtils.close(ps);
    		DBUtils.close(conn);
    		
    	}
    	
    	/**
    	 * 更新方法
    	 */
    	public void update(Entity obj) throws Exception {
    
    			Connection conn = DBUtils.createConn();
    			// update user set name = ? , age = ? where id = ?
    			String sql = " update " + clazz.getSimpleName() + " set  ";
    			Field[] fs = clazz.getDeclaredFields();
    			for (int i = 1; i < fs.length; i++) {
    				sql += fs[i].getName() + "=?,";
    			}
    			sql = sql.substring(0, sql.length()-1) + " where id = ? ";
    			
    			PreparedStatement ps = DBUtils.getPs(conn, sql);
    			
    			for (int i = 1; i < fs.length; i++) {
    				String methodName = "get" + Character.toUpperCase(fs[i].getName().charAt(0)) + fs[i].getName().substring(1);
    				Method m  = clazz.getMethod(methodName);
    				ps.setObject(i, m.invoke(obj));// user.getName();
    			}
    			Method m2 = clazz.getMethod("getId");
    			ps.setInt(fs.length,(Integer)m2.invoke(obj));
    			
    			ps.executeUpdate();
    			DBUtils.close(ps);
    			DBUtils.close(conn);			
    			
    	}
    
    	/**
    	 * 根据一个id 查找对象
    	 */
    	public Entity findById(int id) throws Exception {
    		Connection conn = DBUtils.createConn();
    		String sql = " select * from  " + clazz.getSimpleName() +  " where id = " + id ;
    		PreparedStatement ps = DBUtils.getPs(conn, sql);
    		ResultSet rs = ps.executeQuery();
    		Entity entity =  (Entity) clazz.newInstance();
    		if(rs.next()){
    			Field[]  fs = clazz.getDeclaredFields();
    			for (int i = 0; i < fs.length; i++) {
    				
    				String methodName = "set" + Character.toUpperCase(fs[i].getName().charAt(0)) + fs[i].getName().substring(1);
    				Method m = clazz.getDeclaredMethod(methodName, fs[i].getType());
    				m.invoke(entity, rs.getObject(fs[i].getName()));
    			}
    		}
    		DBUtils.close(rs);
    		DBUtils.close(ps);
    		DBUtils.close(conn);
    		return entity;
    	}
    
    	/**
    	 * 查询所有
    	 */
    	public List<Entity> findAll() throws Exception {
    		Connection conn = DBUtils.createConn();
    		String sql =" select * from " + clazz.getSimpleName();
    		PreparedStatement ps = DBUtils.getPs(conn, sql);
    		
    		List<Entity> list = new ArrayList<Entity>();
    		
    		ResultSet rs =  ps.executeQuery();
    		
    		while(rs.next()){
    			Entity entity = (Entity)clazz.newInstance();
    			
    			Field[] fs = clazz.getDeclaredFields();
    			for (int i = 0; i < fs.length; i++) {
    				String methodName = "set"+ Character.toUpperCase(fs[i].getName().charAt(0)) + fs[i].getName().substring(1);
    				Method m = clazz.getMethod(methodName, fs[i].getType());
    				m.invoke(entity, rs.getObject(fs[i].getName()));
    			}
    			
    			list.add(entity);
    		}
    		DBUtils.close(rs);
    		DBUtils.close(ps);
    		DBUtils.close(conn);
    		return list;
    	}
    
    	/**
    	 * 删除方法
    	 */
    	public void delete(int id) throws Exception {
    			Connection conn = DBUtils.createConn();
    			String sql = " delete from " + clazz.getSimpleName() + " where id =" +id;
    			PreparedStatement ps = DBUtils.getPs(conn, sql);
    			ps.executeUpdate(sql);
    			DBUtils.close(ps);
    			DBUtils.close(conn);	
    	}
    
    
    	
    	/**
    	 * 条件查询的反射封装方法
    	 * @param sql
    	 * @param params
    	 * @return
    	 */
    	public  List<Entity> queryListForParams(String sql,Object[] params ) throws Exception{
    		Connection conn  = DBUtils.createConn();
    		PreparedStatement ps = null;
    		ResultSet rs = null;
    		List list = new ArrayList();
    		try {
    			// 建立statement对象(封装了sql)
    			ps = conn.prepareStatement(sql); // select * from org where id = ? and name = ?  [1 , z3]
    			if(params!=null){
    				for(int i=0;i<params.length;i++){
    					ps.setObject(i+1, params[i]);
    				}
    			}
    			Field[] fs = clazz.getDeclaredFields();
    			rs = ps.executeQuery();
    			while(rs.next()){
    				Object obj = clazz.getConstructor().newInstance();
    				for(int i = 0 ; i <fs.length;i++ ){
    					String methodName = "set" +fs[i].getName().substring(0, 1).toUpperCase()+fs[i].getName().substring(1);
    					Method m = clazz.getMethod(methodName, fs[i].getType());			
    					Object value = rs.getObject(fs[i].getName());  
    					m.invoke(obj, value); 
    				}
    				list.add(obj);
    			}				
    
    		} catch (Exception e) {
    			e.printStackTrace();
    		}finally{
    			DBUtils.close(rs);
    			DBUtils.close(ps);
    			DBUtils.close(conn);
    		}
    		return list;
    	}		
    	
    	
    }

4、DButils.java

public class DBUtils {
    	
    	private static Properties props = new Properties();
    	
    	static{
    		InputStream is = null;
    		
    		is = DBUtils.class.getClassLoader().getResourceAsStream("jdbc.properties");
    		try {
    			props.load(is);
    		} catch (IOException e) {
    			e.printStackTrace();
    		} finally{
    			if(is!=null){
    				try {
    					is.close();
    				} catch (IOException e) {
    					e.printStackTrace();
    				}
    			}
    		}
    		
    	}
    	
    	
    		
    	//获得连接
    	public static Connection createConn(){
    		Connection conn = null; 
    		try {
    			Class.forName((String)props.get("driver"));
    			//ip地址 + 数据库名称
    			conn = DriverManager.getConnection((String)props.get("url"), (String)props.get("username"), (String)props.get("password"));
    		} catch (ClassNotFoundException e) {
    			e.printStackTrace();
    		} catch (SQLException e) {
    			e.printStackTrace();
    		}
    		return conn;
    	}
    	
    	//编译执行
    	public static PreparedStatement getPs(Connection conn , String sql){
    		PreparedStatement ps = null; 
    		try {
    			ps = conn.prepareStatement(sql);
    		} catch (SQLException e) {
    			e.printStackTrace();
    		}
    		return ps ; 
    	}
    
    	public static void close(Connection conn){
    			if(conn != null){
    				try {
    					conn.close();
    				} catch (SQLException e) {
    					e.printStackTrace();
    				}
    			}
    	}
    	
    	public static void close(ResultSet rs){
    		if(rs != null){
    			try {
    				rs.close();
    			} catch (SQLException e) {
    				e.printStackTrace();
    			}
    		}
    	}
    	
    	public static void close(PreparedStatement ps){
    		if(ps != null){
    			try {
    				ps.close();
    			} catch (SQLException e) {
    				e.printStackTrace();
    			}
    		}
    	}
    		
    }

5、UserDao.java

public interface UserDao extends BaseDao<User> {
    
    }

6、UserDaoImpl.java

public class UserDaoImpl extends BaseDaoImpl<User> implements UserDao {
        //加入属于自己的方法
    
    }