For this class exercise, you will write a Java program to consume data from the MusicBrainz Web Service, which provides a RESTful web service interface to the MusicBrainz Databse. The database can be searched by recording and artist as well as many other fields.

The example program with which you have been provided is hard coded to search for recordings with titles that that match the query "Carry on Wayward Son". When you run it, it will print out a very large string of XML, the beginning of which you can see in the example below.

java MBSimpleRequestAPIExample <?xml version="1.0" encoding="UTF-8" standalone="yes"?><metadata created="2020-01-26T18:33:51.293Z" xmlns="http://musicbrainz.org/ns/mmd-2.0#" xmlns:ns2="http://musicbrainz.org/ns/ext#-2.0"><recording-list count="86" offset="0"><recording id="34608c81-c15f-4f97-9146-cf7f25789ff9" ns2:score="100"><title>Carry on Wayward Son</title><length>259000</length><artist-credit><name-credit><name>Tufts University Amalgamates</name><artist id="47f61709-da5d-437c-ac0f-366332a66fa9"><name>Tufts University Amalgamates</name><sort-name>Tufts University Amalgamates</sort-name></artist></name-credit></artist-credit><release-list><release id="f2bc1557-94b2-44a8-850a-e41f37669000"><title>Hands Off The Mannequin!</title><status>Official</status><release-group id="f9edb063-44ea-4bf0-829e-2bbb67e4696f" type="Album" type-id="f529b476-6e62-324f-b0aa-1f3e33d313fc"><title>Hands Off The Mannequin!</title><primary-type id="f529b476-6e62-324f-b0aa-1f3e33d313fc">Album</primary-type></release-group><date>2011</date><country>US</country><release-event-list><release-event><date>2011</date><area id="489ce91b-6658-3307-9877-795b68554c98"><name>United States</name><sort-name>United States</sort-name><iso-3166-1-code-list><iso-3166-1-code>US</iso-3166-1-code></iso-3166-1-code-list></area></release-event></release-event-list><medium-list count="1"><track-count>13</track-count><medium><position>1</position><track-list count="13" offset="9"><track id="f9d76101-67bd-4f9a-94e3-37fe6a251d51"><number>10</number><title>Carry on Wayward Son</title><length>259000</length></track></track-list></medium></medium-list></release></release-list></recording>...

You will modify the program to make a number of changes:

• The title of the song will be specified as a program argument, e.g. java MBSimpleRequestAPIExample smells like teen spirit. You will need to replace the spaces with the %20 URL encoding.
• Request that the response to the query be returned in JSON format rather than XML.
• Use Google's Gson library to deserialize the JSON into plain old Java objects.
• Print the number, name, and performing artist for each of the results returned by the query.

When finished, your output should look similar to the example below.

java MBSimpleRequestAPIExample smells like teen spirit 1) Smells Like Teen Spirit by Le Bang Bang 2) Smells Like Teen Spirit by Tori Amos 3) Smells Like Teen Spirit by The Arrogant Sons of Bitches 4) Smells Like Teen Spirit by Tori Amos 5) Smells Like Teen Spirit by Cássia Eller 6) Smells Like Teen Spirit by Hammerschmitt 7) Smells Like Teen Spirit by René Amesz Baggi Begovic 8) Smells Like Teen Spirit by Kevin Devine 9) Smells Like Teen Spirit by Tori Amos 10) Smells Like Teen Spirit by Mountain Men 11) Smells Like Teen Spirit by Tori Amos 12) Smells Like Teen Spirit by MAN WITH A MISSION 13) Smells Like Teen Spirit by Tori Amos 14) Smells Like Teen Spirit by Deep Schrott 15) Smells Like Teen Spirit by Ben Wild and the Wild Band 16) Smells Like Teen Spirit by Young Widows 17) Smells Like Teen Spirit by Ben Williams 18) Smells Like Teen Spirit by Robert Glasper 19) Smells Like Teen Spirit by ONE OK ROCK 20) Smells Like Teen Spirit by DJ MAGIC DRAGON 21) Smells Like Teen Spirit by The International Classic Rock Orchestra 22) Smells Like Teen Spirit by Phish 23) Smells Like Teen Spirit by Tori Amos 24) Smells Like Teen Spirit by Nirvana 25) Smells Like Teen Spirit by Nirvana

Generating the request and obtaining the response

Your request to the webservice is based on a URL. For the MusicBrainz Web Service, the URL is "https://musicbrainz.org/ws/2/recording?query="{query string}". You specify the desired response format using an &fmt={value} attribute at the end of the URL with a value of json or xml.

The example program shows how to use Java's HTTP support to open an HttpURLConncection to the URL for the web service. Readers are wrapped around the connection to facilitate access to the response text.

How are you going to parse the response?

The first design decision that you have to make is to choose to work with either JSON or XML responses. You may make that choice based on the approach you want to use for parsing the response string. In no particular order, you can consider doing:

• With a JSON response, use the Gson library that you used on your SWEN-261 project to place data into POJOs (Plain Old Java Objects). You will be able to use the BufferedReader wrapped around the URL connection directly in the fromJson() call. You will have to create classes that have a similar structure to the JSON message. There are many Gson tutorial websites available. One of them is here.
  • Hint 1: Your data class attributes must exactly match the case of element identifiers in the JSON response.
  • Hint 2: [] in the JSON response indicates an array which you will have to capture as a List even if there is only one array element.
  • Hint 3: {} in the JSON response indicates a class which you will have to capture as a class that you create with attributes for the elements within that {} structure.
• With an XML response, there are a few different methods for parsing XML data in Java.
• With either response, you could consider manually scanning the response string for the data that you need.
  • If you assume that the ordering of elements will always be consistent, one java.util.regex.Pattern operation can capture the values for all the elements that you are interested in.
  • If the elements may be in different order, or sometimes are missing, you can use multiple Java regex, StringMatcher, or String substring operations to extract the values that you want.

More GSon Hints

• Adding Gson to an IntelliJ IDEA project is easy if you have Maven installed (your project does not need to be a Maven project).
  1. Open the Project Structure configuration dialog.
  2. Click the Libraries tab.
  3. Click the + button to add a new library and choose Maven from the pop-up.
  4. In the dialog, type "gson" and press enter to search. The search usually takes several seconds.
  5. Scroll through the list and choose the latest version of the com.google.code.gson library (e.g. 2.8.6 as of the time of this writing).
• You may name your "top level" class whatever you'd like, e.g. RecordingsSearch. When you are ready to parse the JSON, you simply need to pass your class as a parameter, e.g.

  RecordingSearch search = gson.fromJson(json, RecordingSearch.class);

• Gson makes sophisticated use of Java's powerful reflection apis, and will look for any fields in your class that correspond to one of the attributes in the JSON structure. If the field is named correctly, Gson will find it even if it is private and there is no setter.
• In some cases, you may not be able to name a field exactly the same as it is in the JSON, e.g. the artist-credit attribute. In these cases (or any other, really) you may add a @SerializedName annotation to the field, to help Gson find it, e.g.

  @SerializedName("artist-credit")
  private List<ArtistCredit> credits;

• If Gson cannot find a field in your class to match one of the JSON attributes, it will skip the attribute. This means that you can build your Java class slowly, one field at a time as you test it.

Writing the program

Once you have decided on the approach that you will use for parsing the input, start with MBSimpleRequestAPIExample.java as the initial base.

Submission Instructions

Submit a ZIP file (.zip file extension) that includes your Java source files and example of the output generated by the program when it runs.