java如何将ArrayList中的元素分组并分成三个列表

Question

我有一门实体课

    class Entity {
        private String customer;
        private String product;
        private String productDetail;
    }

我有一个ArrayList<Entity>包括许多记录，例如我列表中的记录：

customer    product    productDetail
   A          A1            A11
   A          A1            A12
   A          A2            A21
   A          A2            A22
   B          B1            B11
   B          B2            B21
   C          C1            C11
   C          C1            C12

我下面有3个实体

   class ProductDetail{
       private String details;
   }

   class Product{
       private String product;
       private List<ProductDetail> detailList;
   }

   class Customer{
       private String customer;
       private List<Product> productList;
   }

我想把我的ArrayList<Entity>和分组记录循环到Customer类Customer类包括productList，以及productList包括detailList

请给我一个解决方案

更新我的代码：

客户实体：

public class CustomerEntity {
    private int customer;

    private List<ProductEntity> productList;

    public int getCustomer() {
        return customer;
    }

    public void setCustomer(int customer) {
        this.customer = customer;
    }

    public List<ProductEntity> getProductList() {
        return productList;
    }

    public void setProductList(List<ProductEntity> productList) {
        this.productList = productList;
    }

}

产品实体：

public class ProductEntity {

    private int product;
    private List<ProductDetailEntity> detailList;

    public int getProduct() {
        return product;
    }

    public void setProduct(int product) {
        this.product = product;
    }

    public List<ProductDetailEntity> getDetailList() {
        return detailList;
    }

    public void setDetailList(List<ProductDetailEntity> detailList) {
        this.detailList = detailList;
    }

}

产品详细信息实体：

public class ProductDetailEntity {
    private int details;

    public int getDetails() {
        return details;
    }

    public void setDetails(int details) {
        this.details = details;
    }

}

我的虚拟代码测试：

public class TestList {
    public static void main(String[] args) {
        TestEntity testEntity;
        List<TestEntity> list = new ArrayList<TestEntity>();

        // Create Dummy Data
        testEntity = new TestEntity();
        testEntity.setCustomer("A");
        testEntity.setProduct("A1");
        testEntity.setProductDetail("A11");
        list.add(testEntity);

        testEntity = new TestEntity();
        testEntity.setCustomer("A");
        testEntity.setProduct("A1");
        testEntity.setProductDetail("A12");
        list.add(testEntity);

        testEntity = new TestEntity();
        testEntity.setCustomer("A");
        testEntity.setProduct("A2");
        testEntity.setProductDetail("A21");
        list.add(testEntity);

        testEntity = new TestEntity();
        testEntity.setCustomer("A");
        testEntity.setProduct("A2");
        testEntity.setProductDetail("A22");
        list.add(testEntity);

        testEntity = new TestEntity();
        testEntity.setCustomer("B");
        testEntity.setProduct("B1");
        testEntity.setProductDetail("B11");
        list.add(testEntity);

        testEntity = new TestEntity();
        testEntity.setCustomer("B");
        testEntity.setProduct("B2");
        testEntity.setProductDetail("B21");
        list.add(testEntity);

        testEntity = new TestEntity();
        testEntity.setCustomer("C");
        testEntity.setProduct("C1");
        testEntity.setProductDetail("C11");
        list.add(testEntity);

        testEntity = new TestEntity();
        testEntity.setCustomer("C");
        testEntity.setProduct("C1");
        testEntity.setProductDetail("C12");
        list.add(testEntity);

        Map<String, List<TestEntity>> groupByCustomerMap = new LinkedHashMap<String, List<TestEntity>>();
        List<TestEntity> tempEntityList;
        TestEntity tempEntity;

        // Group record by customer
        for (TestEntity item : list) {
            String customer = item.getCustomer();

            tempEntityList = new ArrayList<TestEntity>();
            tempEntity = new TestEntity();

            tempEntity.setCustomer(customer);
            tempEntity.setProductDetail(item.getProductDetail());
            tempEntity.setProduct(item.getProduct());

            tempEntityList.add(tempEntity);

            if (!groupByCustomerMap.containsKey(customer)) {
                groupByCustomerMap.put(customer, tempEntityList);
            } else {
                groupByCustomerMap.get(customer).addAll(tempEntityList);
            }
        }

        // I think from groupByCustomerMap, read ProductDetail and group by product
        // Pleaes suggest me next solution
    }
}