13
Sat, Apr
5 New Articles

TechTip: Call JavaMail from ILE RPG or CL

RPG
Typography
  • Smaller Small Medium Big Bigger
  • Default Helvetica Segoe Georgia Times
Q: Can the example used in Michael J. Floyd's article "Java Journal: You've Got JavaMail" be called from ILE RPG or CL?

A: Yes, there are actually a couple of different ways of going about this. The first way is to call the class using either the JAVA or Run Java (RUNJVA) command. The second is by calling the Java classes/methods from the JavaMail API directly from RPG.

Using JAVA or RUNJVA

One of the first things you would probably want to do if calling one of the examples in Michael's article would be to change the hard-coding of the addresses, subject, and body of the message to be parameter driven.

For example, change this:

public static void main(String[] argv)    
    {
      String to = "This email address is being protected from spambots. You need JavaScript enabled to view it.";
      String from = "This email address is being protected from spambots. You need JavaScript enabled to view it.";
      String subject = "Test Message";
      String myMessage = "Hello";


to something like this:

public static void main(String[] argv)    
    {
      String to        = argv[0];
      String from      = argv[1];
      String subject   = argv[2];
      String myMessage = argv[3];

In this code example, we're assigning the incoming parameters (the argv array) to our String variables. Obviously, we would have to ensure that we called this class with a parameter list that matched this order.

This is what a CL program call to this class might look like using RUNJVA:.:

PGM PARM(&to &from &subject &myMessage)

DCL        VAR(&to)        TYPE(*CHAR) LEN(256)
DCL        VAR(&from)      TYPE(*CHAR) LEN(256)
DCL        VAR(&subject)   TYPE(*CHAR) LEN(256)
DCL        VAR(&myMessage) TYPE(*CHAR) LEN(256)

RUNJVA CLASS(SimpleExample) PARM(&to &from &subject &myMessage) +  CLASSPATH('/java')                                                                     

ENDPGM


When using this method to run a Java class, there are a couple of things to note:

  • The RUNJVA and Java classes have a 256-character limit on any single parameter that you wish to pass. This typically is not a problem with an Internet email address or subject, but it is most definitely one when dealing with the body of the email.
  • When the command is executed, another job will be submitted to the subsystem it is running in--that is, the Java Virtual Machine (JVM). This can be a problem if the command is running in a subsystem that only allows one job to run at a time. The command will fail.
  • The command will also produce a spool file that details the status of the Java class you just called. If it runs normal, you will find it just tells you "Java program completed."


You can find these commands documented in the iSeries Information Center by searching on RUNJVA.

Calling Java Classes/Methods Directly from RPG

When using this method, you would make calls to the JavaMail API directly from RPG instead of having a Java class do it for you and then having to call that class from RPG or CL.

For example, let's look at a piece of code from one of Michael's examples in his article:

String host = "mail.yourwork.com"; 

Properties props = new Properties(); props.put("mail.smtp.host", host);  

In the last two lines of code, we are creating a Properties object and putting the name value pair of our SMTP server in our Properties object for later use by the Session class.

To do this same thing from within RPG, we would code it something like this:

D keyName        S               O  CLASS(*JAVA:'java.lang.String')
D smtpSvr        S               O  CLASS(*JAVA:'java.lang.String')
D propFile       S               O  CLASS(*JAVA:'java.util.Properties')

/free

            smtpSvr = crtString('mail.yourwork.com');       
            keyName = crtString('mail.smtp.host');

            propFile = crtPropFile();

            addProp(propFile:keyName:smtpSvr);

/end-free


As you can see, we have defined three new String objects (the Object data type is new as of V5R1 and is what allows us to deal directly with Java). We will be using these to put our character values in, since the methods to create the Properties file and add the name value pair accept String objects.

The next couple of lines create the String objects for the SMTP server and the key value for the name value pair that you will be putting in the Properties file.

The last couple of lines create the Properties object, assign it to the propFile object variable, and then add the name value pairs to the propFile object.

As you can see, calling a Java class or method is very similar to calling a prototyped procedure in RPG. These methods are actually ones from the java.lang and java.util packages that have been prototyped for our use, as follows:

D crtString       PR            O   EXTPROC(*JAVA:                 
D                                   'java.lang.String':            
D                                   *CONSTRUCTOR)                  
D                                   CLASS(*JAVA:'java.lang.String')
D                          32000A   CONST VARYING                   
 
D crtPropFile     PR            O   EXTPROC(*JAVA:                   
D                                   'java.util.Properties':              
D                                   *CONSTRUCTOR)                 
D                      CLASS(*JAVA:'java.util.Properties')
D                                   STATIC

D addProp         PR            O   EXTPROC(*JAVA:                 
D                                   'java.util.Properties':        
D                                   'setProperty')                 
D                                   CLASS(*JAVA:'java.lang.Object')
D                               O   CLASS(*JAVA:'java.lang.String')
D                               O   CLASS(*JAVA:'java.lang.String')


Similar to procedure prototypes, these prototypes define the interface to the Java methods (procedures) we wish to call from our RPG program. (We define a name for our method/procedure, a return value, and its parameters.)

Let me explain what's in the first prototype:

  • The crtString is the name you will use in the RPG program.
  • The PR defines this code as a prototype.
  • The O tells us that the return type of this method call is an object.
  • The code after the EXTPROC tells us that we are dealing with a method written in Java (*JAVA), that the qualified class name that the method resides in is ('java.lang.String'), and that the actual call will be to the constructor of that class (*CONSTRUCTOR).
  • By qualifying the name of the class, the CLASS keyword further defines the return and parameter values by specifying what objects we will be returning/sending.
  • The last line defines a character field that will not be changed by our method call.


I have just brushed the surface on calling Java directly from RPG, but you can find more information concerning this subject in the WebSphere Development Studio: V5R1 ILE RPG Programmer's Guide in chapter 11,"RPG and the eBusiness World."

In summary, it's easy enough to get around the issues discussed in calling the Java class with either the RUNJVA or JAVA command (with a little extra coding). But I have found that calling the Java classes/methods directly from RPG gives you more control and tends to be more flexible as you decide to use more that the JavaMail API has to offer.

--Brandon Wahl
This email address is being protected from spambots. You need JavaScript enabled to view it.





BLOG COMMENTS POWERED BY DISQUS

LATEST COMMENTS

Support MC Press Online

$0.00 Raised:
$

Book Reviews

Resource Center

  • SB Profound WC 5536 Have you been wondering about Node.js? Our free Node.js Webinar Series takes you from total beginner to creating a fully-functional IBM i Node.js business application. You can find Part 1 here. In Part 2 of our free Node.js Webinar Series, Brian May teaches you the different tooling options available for writing code, debugging, and using Git for version control. Brian will briefly discuss the different tools available, and demonstrate his preferred setup for Node development on IBM i or any platform. Attend this webinar to learn:

  • SB Profound WP 5539More than ever, there is a demand for IT to deliver innovation. Your IBM i has been an essential part of your business operations for years. However, your organization may struggle to maintain the current system and implement new projects. The thousands of customers we've worked with and surveyed state that expectations regarding the digital footprint and vision of the company are not aligned with the current IT environment.

  • SB HelpSystems ROBOT Generic IBM announced the E1080 servers using the latest Power10 processor in September 2021. The most powerful processor from IBM to date, Power10 is designed to handle the demands of doing business in today’s high-tech atmosphere, including running cloud applications, supporting big data, and managing AI workloads. But what does Power10 mean for your data center? In this recorded webinar, IBMers Dan Sundt and Dylan Boday join IBM Power Champion Tom Huntington for a discussion on why Power10 technology is the right strategic investment if you run IBM i, AIX, or Linux. In this action-packed hour, Tom will share trends from the IBM i and AIX user communities while Dan and Dylan dive into the tech specs for key hardware, including:

  • Magic MarkTRY the one package that solves all your document design and printing challenges on all your platforms. Produce bar code labels, electronic forms, ad hoc reports, and RFID tags – without programming! MarkMagic is the only document design and print solution that combines report writing, WYSIWYG label and forms design, and conditional printing in one integrated product. Make sure your data survives when catastrophe hits. Request your trial now!  Request Now.

  • SB HelpSystems ROBOT GenericForms of ransomware has been around for over 30 years, and with more and more organizations suffering attacks each year, it continues to endure. What has made ransomware such a durable threat and what is the best way to combat it? In order to prevent ransomware, organizations must first understand how it works.

  • SB HelpSystems ROBOT GenericIT security is a top priority for businesses around the world, but most IBM i pros don’t know where to begin—and most cybersecurity experts don’t know IBM i. In this session, Robin Tatam explores the business impact of lax IBM i security, the top vulnerabilities putting IBM i at risk, and the steps you can take to protect your organization. If you’re looking to avoid unexpected downtime or corrupted data, you don’t want to miss this session.

  • SB HelpSystems ROBOT GenericCan you trust all of your users all of the time? A typical end user receives 16 malicious emails each month, but only 17 percent of these phishing campaigns are reported to IT. Once an attack is underway, most organizations won’t discover the breach until six months later. A staggering amount of damage can occur in that time. Despite these risks, 93 percent of organizations are leaving their IBM i systems vulnerable to cybercrime. In this on-demand webinar, IBM i security experts Robin Tatam and Sandi Moore will reveal:

  • FORTRA Disaster protection is vital to every business. Yet, it often consists of patched together procedures that are prone to error. From automatic backups to data encryption to media management, Robot automates the routine (yet often complex) tasks of iSeries backup and recovery, saving you time and money and making the process safer and more reliable. Automate your backups with the Robot Backup and Recovery Solution. Key features include:

  • FORTRAManaging messages on your IBM i can be more than a full-time job if you have to do it manually. Messages need a response and resources must be monitored—often over multiple systems and across platforms. How can you be sure you won’t miss important system events? Automate your message center with the Robot Message Management Solution. Key features include:

  • FORTRAThe thought of printing, distributing, and storing iSeries reports manually may reduce you to tears. Paper and labor costs associated with report generation can spiral out of control. Mountains of paper threaten to swamp your files. Robot automates report bursting, distribution, bundling, and archiving, and offers secure, selective online report viewing. Manage your reports with the Robot Report Management Solution. Key features include:

  • FORTRAFor over 30 years, Robot has been a leader in systems management for IBM i. With batch job creation and scheduling at its core, the Robot Job Scheduling Solution reduces the opportunity for human error and helps you maintain service levels, automating even the biggest, most complex runbooks. Manage your job schedule with the Robot Job Scheduling Solution. Key features include:

  • LANSA Business users want new applications now. Market and regulatory pressures require faster application updates and delivery into production. Your IBM i developers may be approaching retirement, and you see no sure way to fill their positions with experienced developers. In addition, you may be caught between maintaining your existing applications and the uncertainty of moving to something new.

  • LANSAWhen it comes to creating your business applications, there are hundreds of coding platforms and programming languages to choose from. These options range from very complex traditional programming languages to Low-Code platforms where sometimes no traditional coding experience is needed. Download our whitepaper, The Power of Writing Code in a Low-Code Solution, and:

  • LANSASupply Chain is becoming increasingly complex and unpredictable. From raw materials for manufacturing to food supply chains, the journey from source to production to delivery to consumers is marred with inefficiencies, manual processes, shortages, recalls, counterfeits, and scandals. In this webinar, we discuss how:

  • The MC Resource Centers bring you the widest selection of white papers, trial software, and on-demand webcasts for you to choose from. >> Review the list of White Papers, Trial Software or On-Demand Webcast at the MC Press Resource Center. >> Add the items to yru Cart and complet he checkout process and submit

  • Profound Logic Have you been wondering about Node.js? Our free Node.js Webinar Series takes you from total beginner to creating a fully-functional IBM i Node.js business application.

  • SB Profound WC 5536Join us for this hour-long webcast that will explore:

  • Fortra IT managers hoping to find new IBM i talent are discovering that the pool of experienced RPG programmers and operators or administrators with intimate knowledge of the operating system and the applications that run on it is small. This begs the question: How will you manage the platform that supports such a big part of your business? This guide offers strategies and software suggestions to help you plan IT staffing and resources and smooth the transition after your AS/400 talent retires. Read on to learn: