设计模式【十二】-迭代器模式

1. 作用

比如List的iterator，可以迭代获取存放的对象，一般存放的时候可以直接用List。

但是如果需要进行特殊定制化处理，我们可以参考迭代器模式进行设计

2. 代码

2.1 迭代器对象

package com.hz.design.iterator;

/**
 * @fileName: BusinessIterator
 * @version:
 * @description:
 * @author: pp_lan
 * @date: 2022/3/29
 */
public interface BusinessIterator<T> {

    boolean hasNext();

    T next();

}

package com.hz.design.iterator;

/**
 * @fileName: Container
 * @version:
 * @description:
 * @author: pp_lan
 * @date: 2022/3/29
 */
public interface Container {

    BusinessIterator iterator();

}

package com.hz.design.iterator;

import com.hz.model.CommonException;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

/**
 * @fileName: UserStore
 * @version:
 * @description:
 * @author: pp_lan
 * @date: 2022/3/29
 */
public class UserStore implements Container {

    private final List<User> userList;

    public UserStore(User... users) {
        this.userList = new ArrayList<>(Arrays.asList(users));
    }

    public void addUser(User user) {
        this.userList.add(user);
    }


    @Override
    public BusinessIterator iterator() {
        return new UserIterator();
    }


    static class User {
        private String name;

        private Integer age;

        public User(String name, Integer age) {
            this.name = name;
            this.age = age;
        }

        public String getName() {
            return name;
        }

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

        public Integer getAge() {
            return age;
        }

        public void setAge(Integer age) {
            this.age = age;
        }

        @Override
        public String toString() {
            return "IteratorUser{" +
                    "name='" + name + '\'' +
                    ", age='" + age + '\'' +
                    '}';
        }
    }


    class UserIterator implements BusinessIterator<User> {

        private int count = 0;

        @Override
        public boolean hasNext() {
            return count < userList.size();
        }

        @Override
        public User next() {
            if (count < userList.size()) {
                User user = userList.get(count++);

                // 模拟比较特殊的业务
                if (user.getAge() == null) {
                    System.out.format("%s年龄缺失，查询其年龄.\n", user.getName());
                    user.setAge(20);
                }

                return user;
            }
            throw new CommonException("超出大小，无法获取");
        }
    }
}

2.2 测试类（调用）

package com.hz.design.iterator;

/**
 * @fileName: IteratorTest
 * @version:
 * @description:
 * @author: pp_lan
 * @date: 2022/3/29
 */
public class IteratorTest {

    public static void main(String[] args) {
        UserStore userStore = new UserStore(new UserStore.User("王丽", 29), new UserStore.User("李丹丹", null), new UserStore.User("藏兵", 32));

        userStore.addUser(new UserStore.User("王珊珊", null));

        for(BusinessIterator<UserStore.User> it = userStore.iterator(); it.hasNext();) {
            UserStore.User user = it.next();
            System.out.println(user);
        }
    }
}

3. 执行结果

Connected to the target VM, address: '127.0.0.1:60166', transport: 'socket'
IteratorUser{name='王丽', age='29'}
李丹丹年龄缺失，查询其年龄.
IteratorUser{name='李丹丹', age='20'}
IteratorUser{name='藏兵', age='32'}
王珊珊年龄缺失，查询其年龄.
IteratorUser{name='王珊珊', age='20'}
Disconnected from the target VM, address: '127.0.0.1:60166', transport: 'socket'