category.java

网上拍卖系统

package auction.model;

import java.io.Serializable;
import java.util.*;

/**
 * The CaveatEmptor Category can have child categories and each has items.
 * <p>
 * Categories can be nested, this is expressed as a bidirectional one-to-many
 * relationship that references parent and child categories.
 * <p>
 * Each Category can have many items (and an item can be in many categories). This
 * is a many-to-many relationship. There are four strategies how you can map it.
 * <p>
 * First, the collection <tt>items</tt> is a true many-to-many association, with
 * collections on both sides. There are no additional columns in the underlying
 * many-to-many join table.
 * <p>
 * Second, the collection <tt>categorizedItems</tt> is a one-to-many association
 * to an entity class <tt>CategorizedItem</tt> that represents the link. The
 * <tt>Item</tt> class has the same collection mapped, to make it bidirectional.
 * This intermediate class represents additional columns on the many-to-many
 * join table, such as the user who added the item to the category, and the date
 * of the addition.
 * <p>
 * Third, the collection <tt>categorizedItemComponents</tt> is a collection of
 * value typed elements, of value type <tt>CategorizedItemComponent</tt>. This
 * simplifies management of the link (no intermediate entity class) but allows
 * only unidirectional navigation. The <tt>Item</tt> class does not know anything
 * about this collection or the components - no shared references.
 * <p>
 * Finally, the map <tt>itemsAndUser</tt> represents the many-to-many association
 * with a ternary relationship using a hash map. This map has item objects as keys,
 * and user objects as values. The underlying many-to-many join table has three
 * columns, <tt>CATEGORY_ID</tt>, <tt>ITEM_ID</tt>, and <tt>ADDED_BY_USER_ID</tt>.
 * This strategy allows you to map an additional column (the user foreign key) of
 * a many-to-many join table without writing an intermediate entity or component
 * class.
 *
 * @see Item
 * @see CategorizedItem
 * @see CategorizedItemComponent
 * @author Christian Bauer
 */
public class Category implements Serializable, Comparable {

    private Long id = null;
    private int version = 0;

    private String name;
    private List<Category> childCategories = new ArrayList<Category>(); // A bag with SQL ORDER BY
    private Category parentCategory;

    private List<Item> items = new ArrayList<Item>();
    private Set<CategorizedItem> categorizedItems = new HashSet<CategorizedItem>();
    private Set<CategorizedItemComponent> categorizedItemComponents = new HashSet<CategorizedItemComponent>();
    private Map<Item,User> itemsAndUser = new HashMap<Item,User>();

    private Date created = new Date();

    /**
     * No-arg constructor for JavaBean tools
     */
    public Category() {}

    /**
     * Full constructor
     */
    public Category(String name,
                    List<Category> childCategories,
                    Category parentCategory,
                    List<Item> items,
                    Set<CategorizedItem> categorizedItems,
                    Set<CategorizedItemComponent> categorizedItemComponents,
                    Map<Item, User> itemsAndUser) {
        this.name = name;
        this.childCategories = childCategories;
        this.parentCategory = parentCategory;
        this.items = items;
        this.categorizedItems = categorizedItems;
        this.categorizedItemComponents = categorizedItemComponents;
        this.itemsAndUser = itemsAndUser;
    }

    /**
     * Simple constructors
     */
    public Category(String name) {
        this.name = name;
    }

    public Category(String name, Category parentCategory) {
        this.name = name;
        this.parentCategory = parentCategory;
    }

    // ********************** Accessor Methods ********************** //

    public Long getId() { return id; }
    public int getVersion() { return version; }

    public String getName() { return name; }
    public void setName(String name) { this.name = name; }

    public List getChildCategories() { return childCategories; }
    public void addChildCategory(Category childCategory) {
        if (childCategory == null) throw new IllegalArgumentException("Null child category!");
        if (childCategory.getParentCategory() != null)
            childCategory.getParentCategory().getChildCategories().remove(childCategory);
        childCategory.setParentCategory(parentCategory);
        childCategories.add(childCategory);
    }
    public void removeChildCategory(Category childCategory) {
        if (childCategory == null) throw new IllegalArgumentException("Null child category!");
        childCategory.setParentCategory(null);
        childCategories.remove(childCategory);
    }

    public Category getParentCategory() { return parentCategory; }
    private void setParentCategory(Category parentCategory) { this.parentCategory = parentCategory; }

    // Regular many-to-many
    public List<Item> getItems() { return items; }
    public void addItem(Item item) {
        if (item == null) throw new IllegalArgumentException("Null item!");
        items.add(item);
        item.getCategories().add(this);
    }
    public void removeItem(Item item) {
        if (item == null) throw new IllegalArgumentException("Null item!");
        items.remove(item);
        item.getCategories().remove(this);
    }

    // Many-to-many with additional columns on join table, intermediate entity class
    // To create a link, instantiate a CategorizedItem with the right constructor
    // To remove a link, use getCategorizedItems().remove()
    public Set<CategorizedItem> getCategorizedItems() { return categorizedItems; }

    // Many-to-many with additional columns on join table, intermediate component class
    public Set<CategorizedItemComponent> getCategorizedItemComponents() { return categorizedItemComponents; }

    // Many-to-many with additional columns on join table, ternary hash map representation
    public Map<Item, User> getItemsAndUser() { return itemsAndUser; }

    public Date getCreated() { return created; }

    // ********************** Common Methods ********************** //

    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        final Category category = (Category) o;

        if (!created.equals(category.created)) return false;
        if (!name.equals(category.name)) return false;
        return !(parentCategory != null ?
                !parentCategory.equals(category.parentCategory) :
                category.parentCategory != null);

    }

    public int hashCode() {
        int result;
        result = name.hashCode();
        result = 29 * result + (parentCategory != null ? parentCategory.hashCode() : 0);
        result = 29 * result + created.hashCode();
        return result;
    }

    public int compareTo(Object o) {
        if (o instanceof Category) {
            return this.getName().compareTo( ((Category)o).getName() );
        }
        return 0;
    }

    public String toString() {
        return  "(" + getId() + ") Name: '" + getName();
    }

    // ********************** Business Methods ********************** //

}