com.github.azbh111.utils.java.iterable.model.MergedLazyIterator Maven / Gradle / Ivy

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package com.github.azbh111.utils.java.iterable.model;

import java.io.Closeable;
import java.io.IOException;
import java.util.Arrays;
import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 * @author: zyp
 * @since: 2021/7/27 17:49
 */
public class MergedLazyIterator implements Iterator {
    private final Iterator> sources;
    private Iterator curSource;
    /**
     * 设置这个值, 指定最多迭代多少条数据
     *
     * @author zhengyongpan
     * @since 2021/6/25 10:40
     */
    private long limit = Long.MAX_VALUE;
    private long count = 0;

    public MergedLazyIterator(Iterator... sources) {
        if (sources == null || sources.length == 0) {
            this.sources = new EmptyIterator();
        } else {
            this.sources = (Iterator>) Arrays.asList(sources).iterator();
        }

    }

    public MergedLazyIterator(Iterator> sources) {
        if (sources == null) {
            this.sources = new EmptyIterator();
        } else {
            this.sources = sources;
        }
    }

    private void prepareNext() {
        while (curSource == null || !curSource.hasNext()) {
            closeCurrentSource();
            if (sources.hasNext()) {
                curSource = sources.next();
            } else {
                curSource = null;
                break;
            }
        }
    }

    @Override
    public boolean hasNext() {
        if (count >= limit) {
            closeCurrentSource();
            return false;
        }
        if (curSource != null) {
            if (curSource.hasNext()) {
                return true;
            }
            closeCurrentSource();
        }
        prepareNext();
        return curSource != null && curSource.hasNext();
    }

    private void closeCurrentSource() {
        if (curSource != null && curSource instanceof Closeable) {
            try {
                ((Closeable) curSource).close();
                curSource = null;
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
    }

    @Override
    public T next() {
        if (curSource == null) {
            throw new NoSuchElementException();
        }
        T t = curSource.next();
        count++;
        return t;
    }

    public void setLimit(long limit) {
        this.limit = limit;
    }
}