120 lines
4.0 KiB
Java
120 lines
4.0 KiB
Java
package org.schabi.newpipe.extractor;
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import org.schabi.newpipe.extractor.exceptions.ExtractionException;
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import javax.annotation.Nonnull;
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import java.io.IOException;
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import java.util.Collections;
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import java.util.List;
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/**
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* Base class to extractors that have a list (e.g. playlists, users).
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*/
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public abstract class ListExtractor<R extends InfoItem> extends Extractor {
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public ListExtractor(StreamingService service, String url) {
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super(service, url);
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}
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/**
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* A {@link InfoItemsPage InfoItemsPage} corresponding to the initial page where the items are from the initial request and
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* the nextPageUrl relative to it.
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*
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* @return a {@link InfoItemsPage} corresponding to the initial page
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*/
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@Nonnull
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public abstract InfoItemsPage<R> getInitialPage() throws IOException, ExtractionException;
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/**
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* Returns an url that can be used to get the next page relative to the initial one.<br/>
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* <p>Usually, these links will only work in the implementation itself.</p>
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*
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* @return an url pointing to the next page relative to the initial page
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* @see #getPage(String)
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*/
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public abstract String getNextPageUrl() throws IOException, ExtractionException;
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/**
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* Get a list of items corresponding to the specific requested page.
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*
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* @param nextPageUrl any next page url got from the exclusive implementation of the list extractor
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* @return a {@link InfoItemsPage} corresponding to the requested page
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* @see #getNextPageUrl()
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* @see InfoItemsPage#getNextPageUrl()
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*/
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public abstract InfoItemsPage<R> getPage(final String nextPageUrl) throws IOException, ExtractionException;
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public boolean hasNextPage() throws IOException, ExtractionException {
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final String nextPageUrl = getNextPageUrl();
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return nextPageUrl != null && !nextPageUrl.isEmpty();
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}
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/*//////////////////////////////////////////////////////////////////////////
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// Inner
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//////////////////////////////////////////////////////////////////////////*/
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/**
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* A class that is used to wrap a list of gathered items and eventual errors, it
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* also contains a field that points to the next available page ({@link #nextPageUrl}).
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*/
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public static class InfoItemsPage<T extends InfoItem> {
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private static final InfoItemsPage<InfoItem> EMPTY =
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new InfoItemsPage<>(Collections.<InfoItem>emptyList(), "", Collections.<Throwable>emptyList());
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/**
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* A convenient method that returns a representation of an empty page.
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*
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* @return a type-safe page with the list of items and errors empty and the nextPageUrl set to an empty string.
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*/
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public static <T extends InfoItem> InfoItemsPage<T> emptyPage() {
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//noinspection unchecked
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return (InfoItemsPage<T>) EMPTY;
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}
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/**
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* The current list of items of this page
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*/
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private final List<T> itemsList;
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/**
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* Url pointing to the next page relative to this one
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*
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* @see ListExtractor#getPage(String)
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*/
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private final String nextPageUrl;
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/**
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* Errors that happened during the extraction
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*/
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private final List<Throwable> errors;
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public InfoItemsPage(InfoItemsCollector<T, ?> collector, String nextPageUrl) {
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this(collector.getItems(), nextPageUrl, collector.getErrors());
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}
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public InfoItemsPage(List<T> itemsList, String nextPageUrl, List<Throwable> errors) {
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this.itemsList = itemsList;
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this.nextPageUrl = nextPageUrl;
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this.errors = errors;
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}
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public boolean hasNextPage() {
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return nextPageUrl != null && !nextPageUrl.isEmpty();
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}
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public List<T> getItems() {
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return itemsList;
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}
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public String getNextPageUrl() {
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return nextPageUrl;
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}
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public List<Throwable> getErrors() {
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return errors;
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}
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}
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}
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