com.qcloud.cos.model.SelectObjectContentEventStream Maven / Gradle / Ivy
/*
* Copyright 2010-2019 Amazon.com, Inc. or its affiliates. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License").
* You may not use this file except in compliance with the License.
* A copy of the License is located at
*
* http://aws.amazon.com/apache2.0
*
* or in the "license" file accompanying this file. This file 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.
* According to cos feature, we modify some class，comment, field name, etc.
*/
package com.qcloud.cos.model;
import com.qcloud.cos.annotation.NotThreadSafe;
import com.qcloud.cos.exception.SelectObjectContentEventException;
import com.qcloud.cos.internal.ReleasableInputStream;
import com.qcloud.cos.internal.SdkFilterInputStream;
import com.qcloud.cos.internal.eventstreaming.Message;
import com.qcloud.cos.internal.eventstreaming.MessageDecoder;
import com.qcloud.cos.model.SelectObjectContentEvent.RecordsEvent;
import com.qcloud.cos.model.transform.SelectObjectContentEventUnmarshaller;
import com.qcloud.cos.utils.BinaryUtils;
import com.qcloud.cos.utils.ValidationUtils;
import java.io.ByteArrayInputStream;
import java.io.Closeable;
import java.io.IOException;
import java.io.InputStream;
import java.io.SequenceInputStream;
import java.nio.ByteBuffer;
import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;
import java.util.Queue;
/**
* A stream of {@link SelectObjectContentEvent}s, generated as the result of a call
* to {@link com.qcloud.cos.COSClient#selectObjectContent(SelectObjectContentRequest)}.
*
* This stream is usually read by one of {@link #getEventsIterator()}, {@link #visitAllEvents(SelectObjectContentEventVisitor)},
* {@link #getRecordsInputStream()} or (for smaller results) {@link #getAllEvents()}.
*
* @see SelectObjectContentResult#getPayload()
*/
@NotThreadSafe
public class SelectObjectContentEventStream implements Closeable {
private static final InputStream EMPTY_INPUT_STREAM = new ByteArrayInputStream(new byte[0]);
private final SdkFilterInputStream inputStream;
private boolean readOptionChosen = false;
public SelectObjectContentEventStream(SdkFilterInputStream inputStream) {
this.inputStream = ValidationUtils.assertNotNull(inputStream, "inputStream");
}
/**
* Read all of the {@link SelectObjectContentEvent}s from this stream into memory. For large objects, lazy-loading using
* {@link #getEventsIterator()}, {@link #getRecordsInputStream()} or {@link #visitAllEvents(SelectObjectContentEventVisitor)}
* should be used instead.
*
* This will raise a runtime exception if {@link #visitAllEvents(SelectObjectContentEventVisitor)},
* {@link #getRecordsInputStream()} or {@link #getEventsIterator()} have already been used.
*
* After using this method, you still must {@link #close()} this object to release the connection to COS.
*/
public List getAllEvents() throws SelectObjectContentEventException {
List events = new ArrayList();
Iterator eventsIterator = getEventsIterator();
while (eventsIterator.hasNext()) {
events.add(eventsIterator.next());
}
return events;
}
/**
* Apply the provided {@link SelectObjectContentEventVisitor} to each {@link SelectObjectContentEvent} in this stream
* in the order they are returned by COS. This will lazily-load the events from COS, minimizing the amount of memory used.
*
* This will raise a runtime exception if {@link #getAllEvents()}, {@link #getRecordsInputStream()} or {@link #getEventsIterator()}
* have already been used.
*
* After using this method, you still must {@link #close()} this object to release the connection to COS.
*
* @param visitor The visitor that should be applied to each event in this stream.
*/
public void visitAllEvents(SelectObjectContentEventVisitor visitor) throws SelectObjectContentEventException {
Iterator eventsIterator = getEventsIterator();
while (eventsIterator.hasNext()) {
eventsIterator.next().visit(visitor);
}
}
/**
* Retrieve an iterator over the {@link SelectObjectContentEvent}s in this stream, in the order they are returned by COS. This
* will lazily-load the events from COS, minimizing the amount of memory used.
*
* This will raise a runtime exception if {@link #getAllEvents()}, {@link #visitAllEvents(SelectObjectContentEventVisitor)}
* or {@link #getRecordsInputStream()} have already been used.
*
* After using this method, you still must {@link #close()} this object to release the connection to COS.
*/
public Iterator getEventsIterator() throws SelectObjectContentEventException {
readOptionChosen();
return new SelectEventIterator();
}
/**
* Retrieve an input stream to the subset of the COS object that matched the query. This is equivalent to loading the content
* of all {@link SelectObjectContentEvent.RecordsEvent}s into an {@link InputStream}. This will lazily-load the content from
* COS, minimizing the amount of memory used.
*
* This will raise a runtime exception if {@link #getAllEvents()}, {@link #visitAllEvents(SelectObjectContentEventVisitor)}
* or {@link #getEventsIterator()} have already been used.
*
* Like all streams, you should {@link SelectRecordsInputStream#close()} it after the content has been read. This
* is equivalent to calling {@link #close()} on this {@link SelectObjectContentEventStream}.
*
* @see #getRecordsInputStream(SelectObjectContentEventVisitor) to also process non-record events while reading the response.
*/
public SelectRecordsInputStream getRecordsInputStream() throws SelectObjectContentEventException {
return getRecordsInputStream(new SelectObjectContentEventVisitor() {});
}
/**
* Retrieve an input stream to the subset of the COS object that matched the query. This is equivalent to loading the content
* of all {@link SelectObjectContentEvent.RecordsEvent}s into an {@link InputStream}. This will lazily-load the content from
* COS, minimizing the amount of memory used.
*
* Unlike {@link #getRecordsInputStream()}, this allows you to provide a "listener" {@link SelectObjectContentEventVisitor}
* that intercepts the events returned by COS while the thread that called {@link SelectRecordsInputStream#read()} blocks
* waiting for COS to return a response.
*
* This will raise a runtime exception if {@link #getAllEvents()}, {@link #visitAllEvents(SelectObjectContentEventVisitor)}
* or {@link #getEventsIterator()} have already been used.
*
* Like all streams, you should {@link SelectRecordsInputStream#close()} it after the content has been read. This
* is equivalent to calling {@link #close()} on this {@link SelectObjectContentEventStream}.
*
* @param listener A visitor for monitoring the progress of the query between {@link RecordsEvent}s.
* @see #getRecordsInputStream()
*/
public SelectRecordsInputStream getRecordsInputStream(SelectObjectContentEventVisitor listener)
throws SelectObjectContentEventException {
InputStream recordInputStream = new SequenceInputStream(new EventStreamEnumeration(getEventsIterator(), listener));
// Ignore close() calls to the record stream. The sequence input stream would read the whole stream to close all of the
// streams in the enum, and the streams in the enum aren't needed because they're byte array input streams.
recordInputStream = ReleasableInputStream.wrap(recordInputStream).disableClose();
return new SelectRecordsInputStream(recordInputStream, inputStream);
}
/**
* Abort this stream, potentially before all events have been read. This should be used before {@link #close()} if there are
* still events pending on the stream. Using this method has a performance impact, because it will forcibly close the active
* connection to COS, whereas reading to end of the stream before calling {@link #close()} will still allow the connection to
* be reused.
*/
public void abort() {
inputStream.abort();
}
/**
* Close this stream, after all events have been read. If there are still pending events, an error will be logged. To prevent
* error logging on incomplete reads, you can call {@link #abort()} to signal an intent to only partially read events in the
* stream.
*/
public void close() throws IOException {
inputStream.close();
}
private void readOptionChosen() {
if (readOptionChosen) {
throw new IllegalStateException("Reading of the select event stream was already started by another method.");
}
readOptionChosen = true;
}
/**
* An implementation of {@link LazyLoadedIterator} that returns events one-by-one from the underlying event stream.
*/
private class SelectEventIterator extends LazyLoadedIterator {
private final MessageDecoder decoder = new MessageDecoder();
@Override
protected Collection getNext() throws IOException {
List next = new ArrayList();
byte[] payload = new byte[256];
while (next.isEmpty()) {
int read = inputStream.read(payload);
if (read == -1) {
if (decoder.hasPendingContent()) {
throw new SelectObjectContentEventException("Service stream ended before an event could be entirely decoded.");
}
break;
}
List messages = decoder.feed(payload, 0, read);
for (Message message : messages) {
next.add(SelectObjectContentEventUnmarshaller.unmarshalMessage(message));
}
}
return next;
}
}
/**
* An implementation of {@link LazyLoadedIterator} that returns an input stream to any {@link RecordsEvent} content from the
* underlying event stream. Also implements {@link Enumeration} for use in a {@link SequenceInputStream}.
*/
private class EventStreamEnumeration extends LazyLoadedIterator implements Enumeration {
private final Iterator selectEventIterator;
private final SelectObjectContentEventVisitor additionalVisitor;
private boolean initialized = false;
private EventStreamEnumeration(Iterator selectEventIterator,
SelectObjectContentEventVisitor additionalVisitor) {
this.selectEventIterator = selectEventIterator;
this.additionalVisitor = additionalVisitor;
}
@Override
protected Collection getNext() {
// Always return a single empty input stream at first. This allows the user to wrap this in a sequence input stream
// without taking forever to initialize (sequence input streams are not lazily loaded).
if (!initialized) {
initialized = true;
return Collections.singleton(EMPTY_INPUT_STREAM);
}
final Collection result = new ArrayList();
while (selectEventIterator.hasNext()) {
SelectObjectContentEvent event = selectEventIterator.next();
// If they have an additional visitor interested in events as they are encountered, notify them of this event.
event.visit(additionalVisitor);
// Create an input stream to the content of any records events we find.
event.visit(new SelectObjectContentEventVisitor() {
@Override
public void visit(RecordsEvent event) {
ByteBuffer records = event.getPayload();
if (records != null) {
result.add(new ByteArrayInputStream(BinaryUtils.copyBytesFrom(records)));
}
}
});
// Don't load all results in memory. Stop if we've found one.
if (!result.isEmpty()) {
return result;
}
}
// Couldn't find anything - no results.
return result;
}
@Override
public boolean hasMoreElements() {
return super.hasNext();
}
@Override
public InputStream nextElement() {
return super.next();
}
}
/**
* An implementation of {@link Iterator} that maps the Iterator contract into a lazily-loaded, simpler-to-implement
* {@link #getNext()} method.
*/
private abstract class LazyLoadedIterator implements Iterator {
private final Queue next = new ArrayDeque();
private boolean isDone = false;
@Override
public boolean hasNext() {
advanceIfNeeded();
return !isDone;
}
@Override
public T next() {
advanceIfNeeded();
if (isDone) {
throw new NoSuchElementException();
}
return next.poll();
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
private void advanceIfNeeded() {
if (!isDone && next.isEmpty()) {
try {
this.next.addAll(getNext());
this.isDone = this.next.isEmpty();
} catch (IOException e) {
throw new SelectObjectContentEventException("Failed to read COS select event.", e);
}
}
}
/**
* Load any newly-available events. This can return any number of events, in the order they should be encountered by the
* user of the iterator. This should return an empty collection if there are no remaining events in the stream.
*/
protected abstract Collection getNext() throws IOException;
}
}
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