Using External Data Sources in Java

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27 Using External Data Sources
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feed by calling its start() function If you want a one-time capture of the feed, you should use the update() function instead
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Atom Feeds
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The Atom feed protocol is newer and more complex than RSS, but for the JavaFX developer, it is just as easy to write an application that works with an Atom feed as it is to handle an RSS feedYou connect to an Atom feed by using the javafxdatafeedatomAtomTask class, which, like RssTask, derives from FeedTask Whereas an RSS feed consists of one or more <item> elements nested inside a <channel> element, in Atom the feed itself is represented by a <feed> element, which is converted to a Feed object, and the individual items in the feed are contained in <entry> elements, which become Entry objectsThe AtomTask class has two callback variables, listed in Table 27-9, that are used to deliver Feed and Entry objects to application code
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Table 27-9 Variable
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onFeed onEntry
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Variables of the AtomTask Class Type
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function (:Feed):Void function (:Entry):Void
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Function to which the feed s Feed object is delivered Function to which Entry objects that hold the feed s content are delivered Class used to convert the XML content of the feed to the corresponding JavaFX objects
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The Twitter Search Feed Twitter has a search API that returns its results in either JSON or Atom format It is convenient to use this API for an example of an Atom feed because the information that it contains is similar to that in the user timeline, which means we can reuse the TwitterEntry class that we used to encapsulate the timeline data earlier in this chapter, and we can also reuse the user interface code with only a minor change, namely the addition of a TextBox that allows you to enter a search term We are not going to discuss the user interface code in this section because our focus is on how to work with the feed, but if you d like to look at it or run the example, you ll find it in the file javafxdata/TwitterAtomSearchfx To perform a Twitter search based on a keyword or keywords, you make a request to a URL that looks like this:
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http://searchtwittercom/searchatom q=javafx&rpp=50
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RSS and Atom Feeds
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The q= parameter specifies the keyword or keywords for the search, and the rpp= parameter is the maximum number of results to return (that is, results per page)You can see part of a typical response to this query in Listing 27-11, which shows the <feed> element and the first of the 50 <entry> elements from the reply, with some of the data anonymized
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Listing 27-11
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40
The Twitter Search Atom Feed
<feed xmlns:google="http://basegooglecom/ns/10" xml:lang="en-US" xmlns:openSearch="http://a9com//spec/opensearch/11/" xmlns=http://wwww3org/2005/Atom xmlns:twitter="http://apitwittercom/"> <id>tag:searchtwittercom,2005:search/javafx</id> <link type="text/html" rel="alternate" href="http://searchtwittercom/search q=javafx"/> <link type="application/atom+xml" rel="self" href="http://searchtwittercom/searchatom q=javafx&rpp=10"/> <title>javafx - Twitter Search</title> <link type="application/opensearchdescription+xml" rel="search" href="http://searchtwittercom/opensearchxml"/> <link type="application/atom+xml" rel="refresh" href="http://searchtwittercom/searchatom q=javafx&rpp=10 &since_id=3250464807"/> <twitter:warning>since_id removed for pagination </twitter:warning> <updated>2009-08-11T19:24:26Z</updated> <openSearch:itemsPerPage>10</openSearch:itemsPerPage> <link type="application/atom+xml" rel="next" href="http://searchtwittercom/searchatom max_id=3250464807& page=2&q=javafx&rpp=10"/> <entry> <id>tag:searchtwittercom,2005:3250464807</id> <published>2009-08-11T19:24:26Z</published> <link type="text/html" rel="alternate" href="http://twittercom/tiainen/statuses/3250464807"/> <title>Installing #netbeans 671 so i can continue my #javafx adventures</title> <content type="html">Installing <a href="http://searchtwittercom/search q=%23netbeans">#netbeans </a> 671 so i can continue my <a href="http://searchtwittercom/search q=%23javafx">#<b>j avafx</b></a> adventures</content> <updated>2009-08-11T19:24:26Z</updated> <link type="image/png" rel="image" href="http://s3amazonawscom/twitter_production/profile_images/46 626732/2_normalgif"/> <twitter:source><a href= data removed/a></twitter:source>
27 Using External Data Sources
41 42 43 44 45 46
<twitter:lang>en</twitter:lang> <author> <name>removed</name> <uri>removed</uri> </author> </entry>
As you can see, there is a mixture of elements with and without namespace prefixesAs with the RSS feed, the elements without a namespace prefix are defined by the Atom specification, while those with namespace prefixes are foreign elements meant to be interpreted by a nonbrowser client specifically written to handle this feedYou can see how each of the standard elements is mapped to variables of the Feed and Entry classes by consulting their API documentation For our example application, we need to extract from each Atom Entry the information necessary to construct a TwitterEntry objectThe values that we need are all available from elements that are defined by the Atom specification itself, so unlike the RSS example in the previous section, we don t need to provide code to extract information from foreign elementsThe values that we need are as follows:
The name of the entry s author, which will be used to set the user variable of the TwitterEntry objectThis value is contained in the <author> element, which you ll find on lines 42 to 45 of Listing 27-11An Atom entry can have more than one author, so the authors variable in the Entry object is actually a sequenceAs you ll see later, we use the first element in the sequence as the user value The entry content, which is taken from the <title> element on lines 28 and 29 of Listing 27-11We use the <title> value rather than the content of the more obvious <content> variable on line 30 because the latter contains the same text, but also has HTML markup, which we do not want the user of our application to seeThe <title> value is used to set the content variable of the TwitterEntry object The publication time of the entry, which we will use to set the time variable of the TwitterEntry objectWe get this from the <published> element shown on line 25 of Listing 27-11, which becomes the value of the published variable of the feed s Entry object The URL of the user s image, which you ll find in the <link> element on line 36 There is more than one <link> element in this feed entry you ll find another one on line 26All the <link> elements are gathered into a sequence of Link objects and stored in the links variable of the feed s Entry objectAs you ll see later, we need to search this sequence to locate the link that refers to the image,
Fetching and Decoding the Feed The code that gets the feed content and converts it to TwitterEntry objects is shown in Listing 27-12 and can be found in the file javafxdata/TwitterAtomSearchClientfx