org.springframework.data.redis.core.ScanCursor Maven / Gradle / Ivy
/*
* Copyright 2014-2018 the original author or authors.
*
* Licensed 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 org.springframework.data.redis.core;
import java.io.IOException;
import java.util.Collections;
import java.util.Iterator;
import java.util.NoSuchElementException;
import org.springframework.dao.InvalidDataAccessApiUsageException;
import org.springframework.lang.Nullable;
import org.springframework.util.CollectionUtils;
/**
* Redis client agnostic {@link Cursor} implementation continuously loading additional results from Redis server until
* reaching its starting point {@code zero}.
* Note: Please note that the {@link ScanCursor} has to be initialized ({@link #open()} prior to usage.
*
* @author Christoph Strobl
* @author Thomas Darimont
* @author Duobiao Ou
* @author Marl Paluch
* @param
* @since 1.4
*/
public abstract class ScanCursor implements Cursor {
private @Nullable CursorState state;
private long cursorId;
private @Nullable Iterator delegate;
private @Nullable final ScanOptions scanOptions;
private long position;
/**
* Crates new {@link ScanCursor} with {@code id=0} and {@link ScanOptions#NONE}
*/
public ScanCursor() {
this(ScanOptions.NONE);
}
/**
* Crates new {@link ScanCursor} with {@code id=0}.
*
* @param options
*/
public ScanCursor(ScanOptions options) {
this(0, options);
}
/**
* Crates new {@link ScanCursor} with {@link ScanOptions#NONE}
*
* @param cursorId
*/
public ScanCursor(long cursorId) {
this(cursorId, ScanOptions.NONE);
}
/**
* Crates new {@link ScanCursor}
*
* @param cursorId
* @param options Defaulted to {@link ScanOptions#NONE} if nulled.
*/
public ScanCursor(long cursorId, ScanOptions options) {
this.scanOptions = options != null ? options : ScanOptions.NONE;
this.cursorId = cursorId;
this.state = CursorState.READY;
this.delegate = Collections. emptyList().iterator();
}
private void scan(long cursorId) {
ScanIteration result = doScan(cursorId, this.scanOptions);
processScanResult(result);
}
/**
* Performs the actual scan command using the native client implementation. The given {@literal options} are never
* {@code null}.
*
* @param cursorId
* @param options
* @return
*/
protected abstract ScanIteration doScan(long cursorId, ScanOptions options);
/**
* Initialize the {@link Cursor} prior to usage.
*/
public final ScanCursor open() {
if (!isReady()) {
throw new InvalidDataAccessApiUsageException("Cursor already " + state + ". Cannot (re)open it.");
}
state = CursorState.OPEN;
doOpen(cursorId);
return this;
}
/**
* Customization hook when calling {@link #open()}.
*
* @param cursorId
*/
protected void doOpen(long cursorId) {
scan(cursorId);
}
private void processScanResult(ScanIteration result) {
if (result == null) {
resetDelegate();
state = CursorState.FINISHED;
return;
}
cursorId = Long.valueOf(result.getCursorId());
if (isFinished(cursorId)) {
state = CursorState.FINISHED;
}
if (!CollectionUtils.isEmpty(result.getItems())) {
delegate = result.iterator();
} else {
resetDelegate();
}
}
/**
* Check whether {@code cursorId} is finished.
*
* @param cursorId the cursor Id
* @return {@literal true} if the cursor is considered finished, {@literal false} otherwise.s
* @since 2.1
*/
protected boolean isFinished(long cursorId) {
return cursorId == 0;
}
private void resetDelegate() {
delegate = Collections. emptyList().iterator();
}
/*
* (non-Javadoc)
* @see org.springframework.data.redis.core.Cursor#getCursorId()
*/
@Override
public long getCursorId() {
return cursorId;
}
/*
* (non-Javadoc)
* @see java.util.Iterator#hasNext()
*/
@Override
public boolean hasNext() {
assertCursorIsOpen();
while (!delegate.hasNext() && !CursorState.FINISHED.equals(state)) {
scan(cursorId);
}
if (delegate.hasNext()) {
return true;
}
if (cursorId > 0) {
return true;
}
return false;
}
private void assertCursorIsOpen() {
if (isReady() || isClosed()) {
throw new InvalidDataAccessApiUsageException("Cannot access closed cursor. Did you forget to call open()?");
}
}
/*
* (non-Javadoc)
* @see java.util.Iterator#next()
*/
@Override
public T next() {
assertCursorIsOpen();
if (!hasNext()) {
throw new NoSuchElementException("No more elements available for cursor " + cursorId + ".");
}
T next = moveNext(delegate);
position++;
return next;
}
/**
* Fetch the next item from the underlying {@link Iterable}.
*
* @param source
* @return
*/
protected T moveNext(Iterator source) {
return source.next();
}
/*
* (non-Javadoc)
* @see java.util.Iterator#remove()
*/
@Override
public void remove() {
throw new UnsupportedOperationException("Remove is not supported");
}
/*
* (non-Javadoc)
* @see java.io.Closeable#close()
*/
@Override
public final void close() throws IOException {
try {
doClose();
} finally {
state = CursorState.CLOSED;
}
}
/**
* Customization hook for cleaning up resources on when calling {@link #close()}.
*/
protected void doClose() {}
/*
* (non-Javadoc)
* @see org.springframework.data.redis.core.Cursor#isClosed()
*/
@Override
public boolean isClosed() {
return state == CursorState.CLOSED;
}
protected final boolean isReady() {
return state == CursorState.READY;
}
protected final boolean isOpen() {
return state == CursorState.OPEN;
}
/*
* (non-Javadoc)
* @see org.springframework.data.redis.core.Cursor#getPosition()
*/
@Override
public long getPosition() {
return position;
}
/**
* @author Thomas Darimont
*/
enum CursorState {
READY, OPEN, FINISHED, CLOSED;
}
}