Small Aside: Writing Agents With Java 5+ Features

Nov 26, 2019 10:46 AM

Tags: designer java

The topic of using Java 5+ language features in agents came up recently in the OpenNTF Slack room (use this invitation link if you haven't already joined!), and I think that it's one of those topics that's worth making a post about for posterity's sake.

For historical and compatibility reasons, the default compiler language level for newly-created agents, at least in the absence of the JavaCompilerTarget notes.ini setting, is Java 1.3:

Java Agent Compiler Properties

This is laughably out-of-date, and doesn't even support 15-year-old features like generics. Accordingly, if you take a piece of code from my last post, you'll end up with a couple errors:

Java agent compilation problems

It recognizes the Java 7+ classes, since it's still backed by a Java 8 JDK, but it complains about try-with-resources and the use of varargs.

Setting the Compiler Level

The fix for this is to change the compiler compliance level for your agent project. Depending on the type of problem, you may be given an Eclipse quick fix option if you hover over the red-underlined text:

Eclipse quick fix

If you don't have that option (for example, there's no such option for the Files.createTempFile vararg problem), you can alternatively go to the "Package Explorer" view, find the temporary project for the agent (named something like "foo.nsf.Some Agent.ja"), and go to Properties. In there, you can go to the "Java Compiler" settings, make sure the "Compiler compliance level" is the level you want, and then check "Use default compliance settings":

Project compiler at 1.8

When you do this and next save the agent, you'll be greeted with this Designer-specific message box:

Java compiler backward compatibility warning

This is good to see, since it shows that Designer picked up the change and will write it into the agent note in items named $JavaCompilerSource and $JavaCompilerTarget. That's the part that really counts, since it's what Designer uses to re-construct the Eclipse project in the future.

Note, though, that the title of the message box is a reminder about an important aspect: if you set the target compiler level to 1.7 or above, then your agent will not run on Domino servers before 9.0.1 FP8. So, if you're using one of those for some reason, take care about the language features you're using. The other breakpoints, if you're working with some really-legacy servers, are Java 1.4 being added in 7, 1.5 added in 8, and 1.6 added in 8.5.

Dealing With Errors

Depending on your Notes version (I suspect this problem cropped up in 9.0.1FP10 and seems to be gone in the V11 beta), changing your compiler level may result in "forbidden reference" errors for basic things like the lotus.domino classes.

If you hit this, the quickest fix is to modify your settings in Designer's preferences, in the "Java" → "Compiler" → "Errors/Warnings" section:

Setting to ignore forbidden references

If you set "Forbidden reference (access rules)" in the "Deprecated and restricted API" section to "Ignore", the problems should go away. I'm not actually sure why this problem crops up (perhaps something to do with the structure of Notes.jar), but it was fairly consistent for me for a while.

With all that set, though, you should be free to use up to Java 8 features in agents (and web services, probably) to your heart's content.

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