Include Javac in Java applet

Question

I wan't to create an applet that includes the Java compiler and is able to download and compile .java files from the web (or from a textfield for that matter). From what I understand, the Java compiler is based on Java, so this should be possible. However, one thing I wonder is wether the Java compiler is able to store the class file in memory or that it needs explicit disk access. Also, I want to catch the errors javac produces, but this is natural.

Is there an article on this somewhere maybe? I couldn't find much on the case. What troubles could I walk into?

EDIT: I'm planning on using the applet with OpenCL, so I would have to sign the applet.

EDIT: Similar question here: Hosting the Java compiler in an applet or in Google AppEngine?

please have [look at](http://stackoverflow.com/questions/616532/on-the-fly-in-memory-java-code-compilation-for-java-5-and-java-6) the Question, may help you. — Asad Rasheed, Aug 01 '11 at 10:37
What do you mean? Java needs to be compiled to bytecode before it can be ran. — RobotRock, Aug 01 '11 at 11:17

score 1 · Accepted Answer · answered Aug 01 '11 at 10:43

1

Java compiler is always with you. You should use java.lang.Compiler class. But I believe you will have issues with SecurityManager.

If I were you I'd prefer to compile code on server side. It means that I'd develop servlet that is able to get the java source and compile it. The resulted java class should be available over HTTP under path that is configured to be accessible by applet, so your applet will be able to run this class after compilation.

answered Aug 01 '11 at 10:43

AlexR

114,158
16
130
208

I thought about this and I think this is indeed the easier way. However this will cost both bandwidth and time for the user, so if possible I would like to do compilation clientside. Also, it might raise some security concerns. – RobotRock Aug 01 '11 at 10:51
Users will not love you for that (applets are sluggish enough alrady) ;) – Łukasz Bownik Aug 01 '11 at 11:06
Java Webstart would be fine as well. But this won't change the case; it's running from browser. – RobotRock Aug 01 '11 at 11:08
I'm marking this as the answer, because I will probably be using the Compiler class. I'm going to look more into this. – RobotRock Aug 01 '11 at 11:20
Good luck. I'd be glad to know which way succeeded. – AlexR Aug 01 '11 at 11:43
3

Java compiler is always with the JDK. It isn't shipped in the JRE, so it isn't 'always with you'. – user207421 Aug 02 '11 at 03:29
@EJP +1 *..it isn't 'always with you'* Notably not for either JWS launched apps. or applets! – Andrew Thompson Aug 04 '11 at 14:03

score 1 · Answer 2 · answered Aug 03 '11 at 23:20

1

From the documentation on the SSCCE Text Based Compiler:

javax.tools.ToolProvider. The docs for getSystemJavaCompiler() mention that it returns "the compiler provided with this platform or null if no compiler is provided", but do not make clear why it might be null, nor the fact that the compiler will not be available to applets or webstart apps.

answered Aug 03 '11 at 23:20

Andrew Thompson

168,117
40
217
433

There's a webstart link just above the text you cited. I figure it'll work if you provide a tools.jar. – RobotRock Aug 04 '11 at 13:26
1

Yes. If the user has a JDK installed, just do as I did in that code, and get them to identify where it is. See also the notes under [Add the compiler to the application's runtime classpath](http://pscode.org/stbc/help.html#classpath). – Andrew Thompson Aug 04 '11 at 14:00
If I would supply my webstart with OpenJDK's tools.jar, would one be able to compile with only a JRE then? – RobotRock Aug 04 '11 at 14:52
What happened when you tried it? I have not, but would be interested in your report. – Andrew Thompson Aug 04 '11 at 16:11
At the moment I have no dedicated computer to try it on, I will so in a couple of days. Problem is I couldnt find tools.jar online, so have to install the complete JDK first. – RobotRock Aug 04 '11 at 17:03
It worked with the Sun tools.jar as well as the OpenJDK tools.jar, so you might want to incorporate that in your STBC (is that correct?) tool ;) Maybe you could help me out with the Webstart issue that comes impaired with it: http://stackoverflow.com/questions/7093935/java-webstart-attempt-to-sandboxed-jar – RobotRock Aug 17 '11 at 14:02

Include Javac in Java applet

2 Answers2