Cover your bases with TweetMe4i and JSON

Search for and log twitter messages using open source Java and RPG

The world of audits is a reality that more financial companies are learning to live with. One of the things being audited are the texts sent to social media sites like Twitter, LinkedIn and Facebook. This tutorial will guide you through how to do Twitter searches from RPG on IBM i and record the results into a DB2 table.


Aaron Bartell (, Software Developer, Krengel Tech

Aaron Bartell PhotoAaron Bartell is a senior software developer for Krengel Technology Inc. Aaron focuses much of his development on creating modern applications using RPG and Java™ on the IBM i and Android platforms. He is the lead developer of RPG-XML Suite and the primary "pusher" of He enjoys being part of the strong IBM i community through forum participation, article writing and providing open source software on his personal website, He has most recently pursued how to use his abilities to benefit those in need. He started the site as a mechanism to raise money for digging clean water wells in Africa and also feeding starving children. Aaron lives with his wife and five children in southern Minnesota and enjoys playing electric and bass guitar in his band, Scattered Showers.

21 February 2012

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Where it makes sense

I am a big fan of keeping everything in RPG when dealing with programming on IBM i. I figure the less languages and runtimes I have to deal with the more I can focus on meeting business needs vs. focusing on fixing technology. Don't get me wrong, I LOVE learning about new things outside of the RPG landscape - been diving into PhoneGap and Apache Callback lately - but I've learned that the adoption of technology should be done with a full understanding of the longterm ramifications (i.e. it doubles the half-life of information an IT shop needs to keep track of). I digress into this preamble because in this article I am going to show how to query Twitter from RPG with Java in the middle. The reason I am going this route (vs. RPG direct to Twitter) is because there are a handful of things missing from RPG that would make this much more doable - specifically an RPG implementation of the OAuth mechanism of authenticating to Twitter. OAuth is a new(er) mechanism to do authentication from one site or service to another. Learn more about the OAuth authentication protocol from Twitter's perspective.

Twitter4j makes it happen

One of the reasons Java usage is so attractive in today's software eco-system is that it is so prevalent - there are MANY open source Java projects out there that are quite solid and free for you to use. For the purposes of this article, the free and open source Twitter4j project is being used. It should be noted that there are other Java libraries for Twitter. I chose Twitter4j because it seems to be the most promising library (seemed to be active, had a wide breadth of API's, looked to be well thought out and included things like debugging needs, and had a license that works well in commercial situations - Apache License 2.0). If you have no idea why you should be concerned about which license is used on an open source project then you should take a few minutes to read up on licensing. I have learned that not all open source projects are created equal and there is definitely an art to picking "safe" and good projects. It is something most programmers will need to be knowledgeable on as litigation increases concerning some licenses (i.e. GPLv3).

Twitter4j has many features that allow you to connect with Twitter on a number of fronts, but the purpose of this article is to focus solely on doing Twitter searches. Specifically, we are going to be diving into the Advanced Search capabilities found on this Twitter page so we can learn what profile "aaronbartell" is tweeting within a certain timeframe.

At this point, it would be good to rewind to a few months ago when I released a new open source project named TweetMe4i. The initial code base for TweetMe4i focused on sending status updates to a Twitter account. On the TweetMe4i webpage you can find documentation on how to register for the various aspects of Twitter and also how to configure your IBM i. This article adds to that initial code base, specifically, by providing search functionality as shown in Listing 1 with the search() Java method. You can find the full source for in the file provided with this article.

Listing 1. Search Java Code
public static String search(String searchStr) {
  String result = "";
  StringBuilder jsonTweet = new StringBuilder();
  try {
    System.setOut(new PrintStream(new FileOutputStream("TweetMe4iLog.txt")));

    Twitter twitter = new TwitterFactory().getInstance();
    QueryResult qryResult = Query(searchStr));

    boolean firstTime = true;
    jsonTweet.append("{ \"tweets\": [");
    for (Tweet tweet : qryResult.getTweets()) {
        firstTime = false;
    jsonTweet.append("] }");
    result = resultDS("SUCCESS", jsonTweet.toString());
  } catch (Exception te) {
    result = resultDS("FAIL", "Java Exception:" + stackTraceToString(te));
  return result;

As you can see, the search() Java method receives and returns a String object. An example of a search string is as follows:

"from:aaronbartell since:2011-11-01 until:2001-11-30"

The basic concept of the search() Java method is to call Twitter with the search string and then return the result of that search as a JSON string to the calling program. In this case, the calling program is written in RPG, which we will be reviewing in a next section. JSON is utilized as the result set return mechanism because it is less laborious to process on the RPG end of things - especially when we have access to a free and open source JSON parser and serializer in RPG - more on that later.

In the search() method, you'll notice the code making a call to System.setOut(). This call is done so that the program can redirect System.out messages to a stream file to make my debugging efforts significantly easier. Please note that the code doesn't specify a fully qualified path with TweetMe4iLog.txt. This means that the stream file will be written to the current directory. You can view your current directly by simply entering WRKLNK onto the IBM i command line with no other options.

Next in Listing 1, the code obtains a new instance of a Twitter object using the TwitterFactory.getInstance() call. The code then invokes and passes the search string that was provided in the call to this method. Underneath the covers an HTTP request is being made to to submit the search request and retrieve the results back into the qryResult object. The program then iterates over the qryResult object and starts composing the JSON string that will be passed back to the RPG program. The reason that the composition logic hard codes some of the JSON string is because an enveloping structure is required for the JSON value provided by the call to DataObjectFactory.getRawJSON(tweet) which is used to get the JSON representation of the twitter result set. A sample of the resulting JSON output is shown in Listing 2.

To make DataObjectFactory.getRawJSON(tweet) work successfully, you need to add an entry to the existing file, which if you installed TweetMe4i from it will exist at location /java/tweetme4i/ The addition to the file is jsonStoreEnabled=true.

Listing 2. JSON Result from search () method
         "text":"Opps, wrong url on that last one ( though a great Christmas
            song :-)  Try this one:",
         "created_at":"Wed, 07 Dec 2011 19:55:47 +0000",
         "text":"Give feedback for next #RPGNextGen 2.0 features
    #opensource #free #RPG #IBMi editor
            #eclipse based",
         "created_at":"Wed, 07 Dec 2011 19:51:21 +0000",
         "text":"RT @SystemiNetwork: Maxed Out: New IBM Tools Uses POWER
            to Crush Commodity Server Architectures: .
         "from_user_name":"Aaron Bartell",
         "created_at":"Mon, 05 Dec 2011 20:32:47 +0000",

If this is your first exposure to JSON, then you can learn more about it here. JSON stands for Javascript Object Notation and was made popular in the web browser programming world as a way to easily serialize and de-serialize Javascript objects so they could be communicated to and from the server. For example, in the past I have used it extensively with OpenRPGUI and ExtJS. Lately, I have been extending JSON beyond Javascript scenarios. For example, JSON has used it to communicate with an Android application in my DynaDroid4i efforts where Javascript wasn't involved at all. However, JSON was still used to send messages to and from the IBM i to the Android mobile device.

RPG side of things

Now it's time to move to the RPG side of the solution to see how to invoke the Java search() method. Listing 3 shows the mainline of RPG program TM4ISEARCH. Note the full source for TM4ISEARCH can be found in this article's accompanying zip file.

Listing 3. TM4ISEARCH mainline
            qte +
            '/java/tweetme4i' +
            ':/java/tweetme4i/TweetMe4i.jar' +
            ':/java/tweetme4i/twitter4j-core-2.2.5.jar' +
            qte + ')';

         QCMDEXC(%trimr(cmd): %len(%trimr(cmd)) );

           'REPLACE(*YES) VALUE(' + qte + '-Djava.version=1.5;' + qte + ')';

         QCMDEXC(%trimr(cmd): %len(%trimr(cmd)) );
       gSrchStr = 'from:aaronbartell since:2011-10-01';
       jStr = TweetMe4i_search( newStr(gSrchStr) );
       gResult = getBytes(jStr);
       if gResult.code = 'SUCCESS';

In Listing 3 I have bolded the areas that we will be discussing. First we see the CLASSPATH environment variable being added to include both TweetMe4i.jar and twitter4j-core-2.2.5.jar. The TweetMe4i.jar contains the search() function discussed earlier and twitter4j-core-2.2.5.jar is the latest version of Twitter4j as of this writing. Next, look at the formulation of the search string being applied to the gSrchStr variable which is then used on the call to TweetMe4i_search(). The RPG prototype for the TweetMe4i_search API can be seen in Listing 4.

Listing 4. TweetMe4i_search prototype
D TweetMe4i_search...
D                 pr              o   class(*java: jStrConst) static
D                                     extproc(
D                                     *java:
D                                     'com.mowyourlawn.twitter.TweetMe4i':
D                                     'search')
D  pTxt                           o   class(*java: jStrConst) const

After the RPG program receives the JSON response back, the last bit of important code in Listing 3 is the call to jsonToDB(). The jsonToDB() sub procedure can be seen in Listing 5 and its purpose is to take the inputted JSON string, parse it and write the contents to a DB2 table, TWTHST (short for Tweet History).

Listing 5. jsonToDB sub procedure
 P jsonToDB        b
 D jsontoDB        pi
 D  pStr                      65535a

 D jRoot           S               *
 D jTweets         S               *
 D jObj            S               *
 D tweetCount      S             10i 0
 D x               S             10i 0

   jRoot = json_parse(%addr(pStr));

   jTweets = json_getArray(jRoot: 'tweets');
   tweetCount = jsona_size(jTweets);

   for x = 0 to (tweetCount - 1);
     jObj = jsona_getObject(jTweets: x);

     if jObj = *null;

     clear TWTHSTR;
     ID = json_getLong(jObj: 'id');
     chain ID TWTHST;
     if not %found(TWTHST);
       TXT = %str( json_get(jObj: 'text'));
       FRMUSRID = json_getInt(jObj: 'from_user_id');
       FRMUSR = %str( json_get(jObj: 'from_user'));
       CRTDAT = %str( json_get(jObj: 'created_at'));
       write TWTHSTR;


 P                 e

This sub procedure introduces the JSON *SRVPGM object from Mihael Schmidt of All of the sub procedure calls that start with json_ or jsona_ are from Mihael's JSON *SRVPGM and the variables that start with a lower case j are meant to represent the JSON *SRVPGM's objects (pointers, actually). You should definitely take a look at if you haven't already done so. Mihael has been very busy and generous towards the RPG community with his many open source tools.

The first step in the jsonToDB sub procedure is calling the json_parse() routine which will take the JSON string and store it in a specialized pointer array under the covers. This operation allows the RPG program to subsequently access the various JSON parts by name. The code uses json_getArray() to obtain the tweets portion of the array and store reference to it in the jTweets pointer - if necessary, go back to Listing 2 for a review of the structure. After obtaining the total number of tweets with jsona_size(), the code logic starts iterating through the results starting at an index of zero. The open source contributor, Mihael, must have had Java on the mind the day he created this part of the tool - we all know RPG people like to start indexes at 1! The call to jsona_getObject() retrieves a tweets iteration and stores it in jObj. After determining whether or not the jObj is null (i.e. was the retrieval successful and did the entry exist), the code starts obtaining the various portions of the JSON tweets result using json_* API calls and populate them into the DB2 record. If you dig into the json_* prototypes you'll find that there are generic "getters" like json_get(), and more specific ones like json_getString() or json_getInt(). Either approach works fine, though the more generic ones require a type-cast as shown (i.e. %str() ).

The TWTHST table definition is shown in Listing 6. Each of the columns in TWTHST are occupied with data from Twitter, including the unique key of the table. The column label values correspond to the actual name of the JSON entity that Twitter and Twitter4j provided.

Listing 6. TTHST table definition

(    ID TEXT IS 'ID' ,

The last required step in jsonToDB() is to clean up all of the allocated memory by calling json_dispose(). At this point ,the coding is complete and there are now results in the TWTHST DB2 table as shown in Figure 1 via a screen shot from Squirrel SQL (a great tool to check out if you aren't already using it).

Figure 1. TWTHST Content via Squirrel SQL
TWTHST Content via Squirrel SQL


So that's it! You have officially done a Twitter search from your IBM i and stored the results in our beloved DB2. Note that there are also API's for the other social networks like LinkedIn and Facebook, but those offerings also require more permission to see the content that is being sent back and forth (i.e. on Facebook you need to be somebody's friend to see their content). If you would find value in seeing an API for Facebook or LinkedIn, then please email me and I will see what effort it would take to put something together and subsequently write about it.



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