Question

我有一个对象类型的列表，如Customer类（属性：customerId，customerName）和一个String数组。

有没有办法从列表中填充/获取包含所有customerName的数组？（除了手动迭代列表）
即

Customer c1 = new Customer(1,"ABC");
Customer c2 = new Customer(2,"DEF");
Customer c3 = new Customer(3,"XYZ");
List<Customer> list = new ArrayList<Customer>();
list.put(c1); list.put(c2); list.put(c3);

String[] allCustomerNames = new String[list.size()];
//Code to get allCustomerNames populated.
//Ofcourse, other than to iterate through list

有没有类似于......的方法。

allCustomerNames = list.toArray(customerNameConvertor);

其中customerNameConveror是假设的转换器类，它会告诉使用customerName来表示数组元素的数量。

Answer 1

您可以使用第三方库，例如Guava或F4J。

这就是Guava的样子：

Function<Customer, String> customerToName = new Function<Customer, String>() {
        public String apply(Customer c) {
            return c.getName();
       };

List<String> allCustomerNamesList = Lists.transform(list, customerToName);

如果您需要数组，则必须使用常规的toArray方法：allCustomerNames = allCustomerNamesList.toArray(allCustomerNames);

Answer 2

您可以编写这样的实用程序类。您可以获得所有字段的值数组。

public class FieldToArrayConvertor {
    public static Object[] getFieldValuesFromEntityList(List list, String fieldName) throws Exception {
        Object[] array = new Object[list.size()];
        int i=0;
        for(Object o : list) {
            Class<? extends Object> aClass = o.getClass();
            Field field = aClass.getDeclaredField(fieldName);
            Object invoke = field.get(o);
            array[i]= invoke;
            i++;
        }
        return array;
    }
    public static void main(String[] args)  {
        try {
            Employee em = new Employee("emp1");
            Employee em1 = new Employee("emp2");
            List<Employee> list1= new ArrayList() ;
            list1.add(em);
            list1.add(em1);
            Object[] field = getFieldValuesFromEntityList(list1, "name");
            for(Object o: field) {
                System.out.println(o);
            }
        } catch (Exception ex) {
            Logger.getLogger(FieldToArrayConvertor.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
}

另请参阅： Uses of Reflection

java.util.list的客户转换器到数组

2 个答案: