我正在研究一种使用NamedParameterJdbcTemplate从MySQL数据库获取一些数据的方法. listCurrentRecords应该从数据库返回Customer,Product和SalesOrder的对象类型列表. objectType是从在方法(1 || 2 || 3)内传递的参数定义的,并且在类中更早地定义为public变量.

public static final int TYPE_PRODUCT = 1;

public static final int TYPE_CUSTOMER = 2;

public static final int TYPE_SALESORDER = 3;

下面提供了该方法.

public static List listCurrentRecords(int objectType)

{

// PRODUCT

if ( objectType == 1 ){

}

//CUSTOMER

else if ( objectType == 2 ){

}

// SALESORDER

else if ( objectType == 3 ){

}

return null;

// return new ArrayList();

}

假设objectType == 2,那么它将需要使用getMyCustomer方法(从Product和SalesOrder同样使用它们将使用各自的方法)从Customer表中获取一些数据,如下所示,

public static List getMyCustomer(){

return jdbc.query("select * from Customer", new RowMapper() {

public Customer mapRow(ResultSet rs, int rowNum) throws SQLException {

Customer customer = new Customer();

customer.setCustomerID(rs.getString("CustomerID"));

customer.setName( rs.getString("Name"));

customer.setAddress( rs.getNString("Address"));

customer.setPhone1(rs.getNString("Phone 1"));

customer.setPhone2(rs.getNString("Phone 2"));

customer.setCreditLimit(rs.getDouble("Credit Limit"));

customer.setCurrentCredit(rs.getDouble("Current Credit"));

return customer;

}

});

在else if(objectType == 2){}内部,我想调用getMyCustomer方法并获取List< Customer>.那里.但是,方法listCurrentRecords的返回类型为List< Object>.如何从List< Customer>转换列出< Object>.我提供了以下伪代码,

// customer

else if ( objectType == 2 ){

List myCustomer = getMyCustomer();

// how to convert ***myCustomer*** to List ?

}

感谢您提供一些有关如何用Java正确编写的帮助.

解决方法:

由于需要对象类型(记住泛型是编译时类型检查功能),因此可以使用addAll或采用第二个List的构造函数.喜欢

List myCustomer = new ArrayList<>(getMyCustomer());

要么

List al = new ArrayList<>();

// ...

al.addAll(getMyCustomer());

标签：generics,jdbc,java,mysql,object

来源： https://codeday.me/bug/20191027/1946580.html