org.iq80.leveldb.util.TableIterator Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of SWBTripleStoreLevelDB Show documentation
TripleStore implementation for SemanticWebBuilder using LevelDB
The newest version!
package org.iq80.leveldb.util;

import org.iq80.leveldb.table.Block;
import org.iq80.leveldb.table.BlockIterator;
import org.iq80.leveldb.table.Table;

import java.util.Map.Entry;

public final class TableIterator extends AbstractSeekingIterator
{
    private final Table table;
    private final BlockIterator blockIterator;
    private BlockIterator current;

    public TableIterator(Table table, BlockIterator blockIterator)
    {
        this.table = table;
        this.blockIterator = blockIterator;
        current = null;
    }

    @Override
    protected void seekToFirstInternal()
    {
        // reset index to before first and clear the data iterator
        blockIterator.seekToFirst();
        current = null;
    }

    @Override
    protected void seekInternal(Slice targetKey)
    {
        // seek the index to the block containing the key
        blockIterator.seek(targetKey);

        // if indexIterator does not have a next, it mean the key does not exist in this iterator
        if (blockIterator.hasNext()) {
            // seek the current iterator to the key
            current = getNextBlock();
            current.seek(targetKey);
        }
        else {
            current = null;
        }
    }

    @Override
    protected Entry getNextElement()
    {
        // note: it must be here & not where 'current' is assigned,
        // because otherwise we'll have called inputs.next() before throwing
        // the first NPE, and the next time around we'll call inputs.next()
        // again, incorrectly moving beyond the error.
        boolean currentHasNext = false;
        while (true) {
            if (current != null) {
                currentHasNext = current.hasNext();
            }
            if (!(currentHasNext)) {
                if (blockIterator.hasNext()) {
                    current = getNextBlock();
                }
                else {
                    break;
                }
            }
            else {
                break;
            }
        }
        if (currentHasNext) {
            return current.next();
        }
        else {
            // set current to empty iterator to avoid extra calls to user iterators
            current = null;
            return null;
        }
    }

    private BlockIterator getNextBlock()
    {
        Slice blockHandle = blockIterator.next().getValue();
        Block dataBlock = table.openBlock(blockHandle);
        return dataBlock.iterator();
    }

    @Override
    public String toString()
    {
        final StringBuilder sb = new StringBuilder();
        sb.append("ConcatenatingIterator");
        sb.append("{blockIterator=").append(blockIterator);
        sb.append(", current=").append(current);
        sb.append('}');
        return sb.toString();
    }
}