com.aliyun.odps.data.RecordReader Maven / Gradle / Ivy
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
package com.aliyun.odps.data;
import java.io.Closeable;
import java.io.IOException;
import java.io.UncheckedIOException;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;
/**
* RecordReader用来读取记录
*/
public interface RecordReader extends Closeable, Iterable {
/**
* 读取一条记录
*
* @return 成功读到记录返回{@link Record}对象, 读取完成返回null
* @throws IOException
* 读取过程发生异常, 发生异常后不可重试
*/
public Record read() throws IOException;
/**
* 提供一个迭代器来遍历所有的记录。
*
* 默认实现会创建一个匿名的 {@link Iterator} 对象，
* 该对象的 {@code hasNext} 和 {@code next} 方法依赖于 {@code read} 方法。
*
* @return 一个新的 {@link Iterator} 对象，用于遍历记录。
*/
@Override
default Iterator iterator() {
return new Iterator() {
private Record nextRecord;
{
// 初始化时尝试读取第一条记录。
try {
nextRecord = read();
} catch (IOException e) {
throw new UncheckedIOException(e);
}
}
@Override
public boolean hasNext() {
// 如果 nextRecord 不为 null，则表示还有更多记录。
return nextRecord != null;
}
@Override
public Record next() {
if (!hasNext()) {
throw new NoSuchElementException();
}
Record current = nextRecord;
// 在返回当前记录的同时，尝试读取下一条记录。
try {
nextRecord = read();
} catch (IOException e) {
throw new UncheckedIOException(e);
}
return current;
}
};
}
default Stream stream() {
return StreamSupport.stream(spliterator(), false);
}
}