使用策略模式加標籤來解決商品顯示的一級分層

假設咱們要在一個商品顯示對象中放入商品對象的任何一個屬性ide

商品顯示類的定義以下this

@Data
public class ProductShow {
    private String title;
}

商品類的定義以下spa

@AllArgsConstructor
@Data
public class Product {
    private String name;
    private BigDecimal amount;
    private LocalDate date;
}

商品工廠類定義以下對象

public class ProductFactory {
    public static Product createProduct() {
        Product product = new Product("football",new BigDecimal("36.4"), LocalDate.now());
        return product;
    }
}

顯示的枚舉Tag定義以下接口

public enum Tag {
    Name,Amount,Date;
}

咱們寫一個管理類來打印商品顯示類要顯示商品的哪一個屬性ci

public class ProductManager {
    public static ProductShow showProduct(Tag tag) {
        Product product = ProductFactory.createProduct();
        ProductShow productShow = new ProductShow();
        if (tag.equals(Tag.Name)) {
            productShow.setTitle(product.getName());
        }else if (tag.equals(Tag.Amount)) {
            productShow.setTitle(product.getAmount().toString());
        }else if (tag.equals(Tag.Date)) {
            productShow.setTitle(product.getDate().toString());
        }
        return productShow;
    }

    public static void main(String[] args) throws Exception {
        ProductShow show = ProductManager.showProduct(Tag.Name);
        System.out.println(show.getTitle());
    }
}

運行結果:get

footballit

這裏咱們能夠看到不少if...else if....else if,若是這裏商品的屬性很是多,就會不斷的增長else if,這顯然不是一個好主意,增長了強耦合。io

如今咱們把它進行拆分解耦,由標籤來決定顯示哪個屬性。class

咱們的策略接口爲

public interface ShowProduct {
    public ProductShow showProduct(Product product);
}

各自的實現類分別爲

@NoArgsConstructor
public class ShowName implements ShowProduct{
    @Override
    public ProductShow showProduct(Product product) {
        ProductShow productShow = new ProductShow();
        productShow.setTitle(product.getName());
        return productShow;
    }
}
@NoArgsConstructor
public class ShowAmount implements ShowProduct {
    @Override
    public ProductShow showProduct(Product product) {
        ProductShow productShow = new ProductShow();
        productShow.setTitle(product.getAmount().toString());
        return productShow;
    }
}
@NoArgsConstructor
public class ShowDate implements ShowProduct {
    @Override
    public ProductShow showProduct(Product product) {
        ProductShow productShow = new ProductShow();
        productShow.setTitle(product.getDate().toString());
        return productShow;
    }
}

咱們將枚舉Tag作一下修改

public enum Tag {
    Name("com.guanjian.product.ShowName"),
    Amount("com.guanjian.product.ShowAmount"),
    Date("com.guanjian.product.ShowDate");
    private final String value;
    private Tag(String value) {
        this.value = value;
    }
    public String getValue() {
        return this.value;
    }
}

定義一個標籤

@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface ShowTag {
    Tag value();
}

給商品顯示類的title字段打上標籤

@Data
public class ProductShow {
    @ShowTag(value = Tag.Amount)
    private String title;
}

這個時候咱們在商品管理類中添加方法

public static ProductShow showProduct() throws Exception {
    Product product = ProductFactory.createProduct();
    ProductShow productShow = new ProductShow();
    Field title = productShow.getClass().getDeclaredField("title");
    ShowTag tag = title.getAnnotation(ShowTag.class);
    Object showProduct = Class.forName(tag.value().getValue()).newInstance();
    productShow = ((ShowProduct) showProduct).showProduct(product);
    return productShow;
}

修改main方法

public static void main(String[] args) throws Exception {
    ProductShow show = ProductManager.showProduct();
    System.out.println(show.getTitle());
}

運行結果:

36.4

這樣咱們只須要替換商品顯示類的title字段的標籤的枚舉value,就能夠顯示商品的哪個屬性了。根據這一思想之後還須要作進一步的擴展,考慮多級分層。

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