JarCastingCursor Iterator
一个简单的适合移动端无限下拉构建数据的后端支持组件
使用方法
public class UserDAO {
private static final int MAX_USER_ID = 938;
// A fake DAO for test
public static List<User> getUsersAscById(Integer startId, int limit) {
if (startId == null) {
startId = 0;
}
List<User> result = IntStream.range(startId, Math.min(startId + limit, MAX_USER_ID))
.mapToObj(User::new)
.collect(Collectors.toList());
System.out.println("get users asc by id, startId:" + startId + ", limit:" + limit
+ ", result:" + result);
return result;
}
}
// 声明
CursorIterator<Integer, User> users = CursorIterator.newGenericBuilder()
.start(startId)
.cursorExtractor(User::getId)
.bufferSize(countPerFetch)
.buildEx(UserDAO::getUsersAscById);
// jdk1.8 Stream方式
List<User> collect = users.stream()
.filter(user -> user.getId() % 11 == 0)
.limit(5)
.collect(Collectors.toList());
// 传统迭代器模式
List<User> finalResult = new ArrayList<>();
for (User user : users) {
if (user.getId() % 11 == 0) { // filter
System.out.println("add to final result:" + user);
finalResult.add(user);
} else {
System.out.println("ignore add user:" + user);
}
if (finalResult.size() == 50) {
break;
}
}
注意事项
- GetByCursorDAO返回的元素不能有null，因为如果结尾的元素是null，CursorIterator将无法根据null计算下一次迭代滑动窗口时的起始位置