简单Java程序的JavaScript包装器

Question

I want to arrange to have a computer simulation with super simple IO (just print statements), than can run in a browser. I can program in java, but know very little about Javascript. I have a feeling (correct me if I'm wrong) that it may be possible to arrange some HTML/Javascript such that it could neatly wrap a separated chunk of pure java - either in a file on its own, or perhaps inside a larger file with a region marked with...

** START JAVA HERE **

** END JAVA HERE **

...such that someone who only knew java could write a java program there and view it in the browser - so long as the IO was restricted to simple print statements.

Is this possible? Has it been done already?

EDIT: A bit more background... I have written a computer simulation of a real world phenomenon which I want academics to be able to play with and modify. Academics are more likely to know java than javascript - so I want to hide away all the javascript stuff and let the user just see java.

Answer 1

it may be possible to arrange some html/javascript such that it could neatly wrap a separated chunk of pure java

No. Java is to Javascript as a car is to a carpet. Browsers are not guaranteed co contain a Java runtime no matter how well they support Javascript. They might, but there's about the same chance of Java being supported as of Flash being supported (with Flash winning). It's just a plugin.

Unless you wrap the entire Java compiler and interpreter in javascript (compile them to javascript), you can't do this entirely client-side. Even then, it would be pretty slow. What you can do:

Option 1:

1. Let the user write a chunk of Java code
2. Send the chunk to the server
3. Add bunch of Java code around, and store into a file. Namely: includes, class header, method header, two closing braces
4. Invoke the java compiler on the server. This requires you to have a JDK installed on your server.
5. Once the class is compiled, pack this into a jar file with bunch of other, static, classes and a manifest file.
6. Respond to the client with a URL of this JAR file.
7. The client creates a new applet or object tag that refers to this JAR, which the server then feeds to the client.
8. If the user has a JRE on his machine and allows the Java plugin and the applet itself to run, you're done.

This is the easiest way to do it, but it's heavily sub-optimal (especially with all the security warnings the client has to confirm). You could do this instead:

Option 2:

• Feed an entirely static applet to the client
• Do not pack several more classes with the compiled one
• Instead of creating a new applet element at run time, pass the URL to the existing applet
• The applet then loads the compiled class only , and then restarts the simulation with the new implementation.

Also:

• Jars can take up a lots of space (especially if you don't classload), so if the uploaded source code is not saved visibly, you may wish to delete the jars automatically upon serving as well.

Option 3:

You could compile the Java into Javascript, but only a very limited subset of Java would be supported.

One such compiler is an integral part of the Google Web Toolkit , designed to write entire websites from Java. The user would not need to have a Java Runtime Environment on his machine, but would need to restrict himself to a subset of Java that is efficiently compilable to Javascript (you'd need to scratch half of java.util, if I remember correctly).

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Bottom line: You can let the user write Java and then let him observe the results, but the heavy lifting of Java compilation should be done by the server. If the user doesn't have the Java plugin, then he can't write just any Java code and expect it to run. Also, you better know how to code in Java, including classloading and Javasript -> applet communication.