泛型的使用

目前这个项目使用的jsp+servlet+javabean,没有使用其它的框架。在处理数据库的时候，多张表就对应多个dao，而每个dao都有增删改查的方法，显得很冗余。于是写了一个CommonDao，其中包含了其他dao里面共有的一些方法。然后让其他的dao类继承CommonDao，servlet中直接使用CommonDao中的相应方法。那么这个时候遇到了一个问题，怎样判断需要对哪张表执行相应的操作。这时可以从servlet向dao类传入相应的sql，同时也需要判断传入的JavaBean对象，因为需要向sql中赋值。那么这个时候就需要使用泛型达到这一目的。

使用泛型时：

public class CommonDao<T> {
    private ExecuteStatement executeStatement = new ExecuteStatement();
    private ReturnList returnList = new ReturnList();
    private T t;
    
    //添加数据到数据库
    public void add(T t, String sql) {
        Connection conn = null;
        PreparedStatement stmt = null;
        try {
            conn = DataBaseUtil.getConnection();
            stmt = conn.prepareStatement(sql);
            if(t instanceof Customer) {                            //判断泛型t的类型
                Customer customer = (Customer) t;
                stmt = executeStatement.setStatement(customer,stmt);
            }
            else if(t instanceof Person) {
                Person person = (Person) t;
                stmt = executeStatement.setStatement(person,stmt);
            }
            else if(t instanceof Department) {
                Department department = (Department) t;
                stmt = executeStatement.setStatement(department,stmt);
            }
            stmt.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            DataBaseUtil.close(stmt, conn);
        }
    }

对应的其他dao:

public class CustomerDao<T> extends CommonDao<T>{
    
    public CustomerDao() {
        
    }
    
    public void add(Customer customer) {
        Connection conn = null;
        PreparedStatement stmt = null;
        String sql = "insert into SYSCUSTOMER(cuscode,cusname,cusdepcode,cuspercode,devdate,busdate,exitdate," +
                "cellphone,email,address,tenid,ufts) values(?,?,?,?,?,?,?,?,?,?,?,?)";
        try {
            conn = DataBaseUtil.getConnection();
            stmt = conn.prepareStatement(sql);
            stmt.setString(1, customer.getCusCode());
            stmt.setString(2, customer.getCusName());
            stmt.setString(3, customer.getCusDepCode());
            stmt.setString(4, customer.getCusPerCode());
            stmt.setString(5, customer.getDevDate());
            stmt.setString(6, customer.getBusDate());
            stmt.setString(7, customer.getExitDate());
            stmt.setString(8, customer.getCellphone());
            stmt.setString(9, customer.getEmail());
            stmt.setString(10, customer.getAddress());
            stmt.setString(11, customer.getTenId());
            long currentTime = System.currentTimeMillis();            //获取当前时间，毫秒级别，距离1970年
            Timestamp deptIsEnd = new Timestamp(currentTime);        //获取时间戳
            stmt.setTimestamp(12, deptIsEnd);
            stmt.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            if(stmt != null) {
                DataBaseUtil.closeStatement(stmt);
            }
            if(conn != null) {
                DataBaseUtil.closeConnection(conn);
            }
        }
    }

executeStatement.setStatement(customer,stmt)代码：

//为customer表执行PreparedStatement方法
    public PreparedStatement setStatement(Customer customer, PreparedStatement stmt) {
        try {
            stmt.setString(1, customer.getCusCode());
            stmt.setString(2, customer.getCusName());
            stmt.setString(3, customer.getCusDepCode());
            stmt.setString(4, customer.getCusPerCode());
            stmt.setString(5, customer.getDevDate());
            stmt.setString(6, customer.getBusDate());
            stmt.setString(7, customer.getExitDate());
            stmt.setString(8, customer.getCellphone());
            stmt.setString(9, customer.getEmail());
            stmt.setString(10, customer.getAddress());
            stmt.setString(11, customer.getTenId());
            long currentTime = System.currentTimeMillis();            //获取当前时间，毫秒级别，距离1970年
            Timestamp deptIsEnd = new Timestamp(currentTime);        //获取时间戳
            stmt.setTimestamp(12, deptIsEnd);
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return stmt;
    }

CustomerServlet的add方法:

/*
     * 功能：添加数据并返回到customer.jsp页面
     */
    @SuppressWarnings("unchecked")
    public void add(HttpServletRequest request, HttpServletResponse response) 
            throws ServletException, IOException {
        String cusCode = request.getParameter("cuscode");
        String cusName = null;
        try {
            cusName = new String(request.getParameter("cusname").getBytes("ISO-8859-1"),"utf-8");
        } catch (UnsupportedEncodingException e1) {
            e1.printStackTrace();
        }
        String cusDepCode = request.getParameter("cusdepcode");
        String cusPerCode = request.getParameter("cuspercode");
        String devDate = request.getParameter("devdate");
        String busDate = request.getParameter("busdate");
        String exitDate = request.getParameter("exitdate");
        Customer customer = new Customer();
        customer.setCusCode(cusCode);
        customer.setCusName(cusName);
        customer.setCusDepCode(cusDepCode);
        customer.setCusPerCode(cusPerCode);
        customer.setDevDate(devDate);
        customer.setBusDate(busDate);
        customer.setExitDate(exitDate);
        String sql = "insert into SYSCUSTOMER(cuscode,cusname,cusdepcode,cuspercode,devdate,busdate,exitdate," +
                "cellphone,email,address,tenid,ufts) values(?,?,?,?,?,?,?,?,?,?,?,?)";
        //customerDao.add(customer);
        customerDao.add(customer, sql);
        select(request, response);
        try {
            response.sendRedirect("common/customer.jsp");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

这样就很好的解决了代码冗余的问题，当然后面还可以再优化。