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/*
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* Copyright 2013 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.example.android.basicsyncadapter.net;
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import android.text.format.Time;
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import android.util.Xml;
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import org.xmlpull.v1.XmlPullParser;
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import org.xmlpull.v1.XmlPullParserException;
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import java.io.IOException;
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import java.io.InputStream;
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import java.text.ParseException;
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import java.util.ArrayList;
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import java.util.List;
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/**
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* This class parses generic Atom feeds.
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*
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* <p>Given an InputStream representation of a feed, it returns a List of entries,
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* where each list element represents a single entry (post) in the XML feed.
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*
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* <p>An example of an Atom feed can be found at:
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* http://en.wikipedia.org/w/index.php?title=Atom_(standard)&oldid=560239173#Example_of_an_Atom_1.0_feed
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*/
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public class FeedParser {
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// Constants indicting XML element names that we're interested in
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private static final int TAG_ID = 1;
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private static final int TAG_TITLE = 2;
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private static final int TAG_PUBLISHED = 3;
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private static final int TAG_LINK = 4;
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// We don't use XML namespaces
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private static final String ns = null;
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/** Parse an Atom feed, returning a collection of Entry objects.
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*
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* @param in Atom feed, as a stream.
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* @return List of {@link com.example.android.basicsyncadapter.net.FeedParser.Entry} objects.
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* @throws org.xmlpull.v1.XmlPullParserException on error parsing feed.
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* @throws java.io.IOException on I/O error.
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*/
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public List<Entry> parse(InputStream in)
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throws XmlPullParserException, IOException, ParseException {
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try {
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XmlPullParser parser = Xml.newPullParser();
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parser.setFeature(XmlPullParser.FEATURE_PROCESS_NAMESPACES, false);
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parser.setInput(in, null);
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parser.nextTag();
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return readFeed(parser);
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} finally {
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in.close();
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}
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}
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/**
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* Decode a feed attached to an XmlPullParser.
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*
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* @param parser Incoming XMl
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* @return List of {@link com.example.android.basicsyncadapter.net.FeedParser.Entry} objects.
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* @throws org.xmlpull.v1.XmlPullParserException on error parsing feed.
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* @throws java.io.IOException on I/O error.
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*/
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private List<Entry> readFeed(XmlPullParser parser)
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throws XmlPullParserException, IOException, ParseException {
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List<Entry> entries = new ArrayList<Entry>();
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// Search for <feed> tags. These wrap the beginning/end of an Atom document.
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//
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// Example:
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// <?xml version="1.0" encoding="utf-8"?>
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// <feed xmlns="http://www.w3.org/2005/Atom">
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// ...
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// </feed>
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parser.require(XmlPullParser.START_TAG, ns, "feed");
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while (parser.next() != XmlPullParser.END_TAG) {
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if (parser.getEventType() != XmlPullParser.START_TAG) {
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continue;
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}
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String name = parser.getName();
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// Starts by looking for the <entry> tag. This tag repeates inside of <feed> for each
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// article in the feed.
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//
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// Example:
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// <entry>
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// <title>Article title</title>
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// <link rel="alternate" type="text/html" href="http://example.com/article/1234"/>
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// <link rel="edit" href="http://example.com/admin/article/1234"/>
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// <id>urn:uuid:218AC159-7F68-4CC6-873F-22AE6017390D</id>
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// <published>2003-06-27T12:00:00Z</published>
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// <updated>2003-06-28T12:00:00Z</updated>
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// <summary>Article summary goes here.</summary>
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// <author>
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// <name>Rick Deckard</name>
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// <email>[email protected]</email>
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// </author>
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// </entry>
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if (name.equals("entry")) {
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entries.add(readEntry(parser));
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} else {
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skip(parser);
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}
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}
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return entries;
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}
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/**
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* Parses the contents of an entry. If it encounters a title, summary, or link tag, hands them
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* off to their respective "read" methods for processing. Otherwise, skips the tag.
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*/
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private Entry readEntry(XmlPullParser parser)
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throws XmlPullParserException, IOException, ParseException {
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parser.require(XmlPullParser.START_TAG, ns, "entry");
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String id = null;
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String title = null;
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String link = null;
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long publishedOn = 0;
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while (parser.next() != XmlPullParser.END_TAG) {
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if (parser.getEventType() != XmlPullParser.START_TAG) {
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continue;
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}
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String name = parser.getName();
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if (name.equals("id")){
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// Example: <id>urn:uuid:218AC159-7F68-4CC6-873F-22AE6017390D</id>
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id = readTag(parser, TAG_ID);
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} else if (name.equals("title")) {
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// Example: <title>Article title</title>
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title = readTag(parser, TAG_TITLE);
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} else if (name.equals("link")) {
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// Example: <link rel="alternate" type="text/html" href="http://example.com/article/1234"/>
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//
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// Multiple link types can be included. readAlternateLink() will only return
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// non-null when reading an "alternate"-type link. Ignore other responses.
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String tempLink = readTag(parser, TAG_LINK);
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if (tempLink != null) {
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link = tempLink;
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}
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} else if (name.equals("published")) {
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// Example: <published>2003-06-27T12:00:00Z</published>
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Time t = new Time();
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t.parse3339(readTag(parser, TAG_PUBLISHED));
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publishedOn = t.toMillis(false);
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} else {
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skip(parser);
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}
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}
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return new Entry(id, title, link, publishedOn);
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}
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/**
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* Process an incoming tag and read the selected value from it.
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*/
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private String readTag(XmlPullParser parser, int tagType)
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throws IOException, XmlPullParserException {
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String tag = null;
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String endTag = null;
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switch (tagType) {
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case TAG_ID:
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return readBasicTag(parser, "id");
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case TAG_TITLE:
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return readBasicTag(parser, "title");
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case TAG_PUBLISHED:
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return readBasicTag(parser, "published");
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case TAG_LINK:
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return readAlternateLink(parser);
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default:
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throw new IllegalArgumentException("Unknown tag type: " + tagType);
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}
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}
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/**
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* Reads the body of a basic XML tag, which is guaranteed not to contain any nested elements.
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*
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* <p>You probably want to call readTag().
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*
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* @param parser Current parser object
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* @param tag XML element tag name to parse
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* @return Body of the specified tag
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* @throws java.io.IOException
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* @throws org.xmlpull.v1.XmlPullParserException
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*/
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private String readBasicTag(XmlPullParser parser, String tag)
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throws IOException, XmlPullParserException {
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parser.require(XmlPullParser.START_TAG, ns, tag);
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String result = readText(parser);
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parser.require(XmlPullParser.END_TAG, ns, tag);
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return result;
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}
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/**
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* Processes link tags in the feed.
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*/
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private String readAlternateLink(XmlPullParser parser)
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throws IOException, XmlPullParserException {
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String link = null;
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parser.require(XmlPullParser.START_TAG, ns, "link");
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String tag = parser.getName();
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String relType = parser.getAttributeValue(null, "rel");
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if (relType.equals("alternate")) {
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link = parser.getAttributeValue(null, "href");
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}
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while (true) {
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if (parser.nextTag() == XmlPullParser.END_TAG) break;
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// Intentionally break; consumes any remaining sub-tags.
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}
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return link;
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}
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/**
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* For the tags title and summary, extracts their text values.
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*/
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private String readText(XmlPullParser parser) throws IOException, XmlPullParserException {
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String result = null;
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if (parser.next() == XmlPullParser.TEXT) {
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result = parser.getText();
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parser.nextTag();
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}
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return result;
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}
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/**
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* Skips tags the parser isn't interested in. Uses depth to handle nested tags. i.e.,
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* if the next tag after a START_TAG isn't a matching END_TAG, it keeps going until it
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* finds the matching END_TAG (as indicated by the value of "depth" being 0).
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*/
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private void skip(XmlPullParser parser) throws XmlPullParserException, IOException {
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if (parser.getEventType() != XmlPullParser.START_TAG) {
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throw new IllegalStateException();
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}
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int depth = 1;
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while (depth != 0) {
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switch (parser.next()) {
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case XmlPullParser.END_TAG:
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depth--;
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break;
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case XmlPullParser.START_TAG:
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depth++;
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break;
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}
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}
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}
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/**
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* This class represents a single entry (post) in the XML feed.
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*
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* <p>It includes the data members "title," "link," and "summary."
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*/
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public static class Entry {
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public final String id;
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public final String title;
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public final String link;
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public final long published;
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Entry(String id, String title, String link, long published) {
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this.id = id;
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this.title = title;
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this.link = link;
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this.published = published;
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}
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}
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}