Create Classes from File with a Jar

Question

Today I asked many questions about Jars & JavaCompiler. Because I haven't been able to achieve my goal I'll ask the whole question now:

I want a ProgramOne.jar which compiles a class out of a file and than loads this class.

Somehow I can't achieve that with the approach which works in Eclipse (the ProgramOne not packed into a Jar).

So the approach which works in eclipse is:

File fRun = new File("someFile.java");
JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
StandardJavaFileManager fileManager = compiler.getStandardFileManager(null, null, null);
Iterable<String> options = Arrays.asList( new String[] { "-d", currentDir+"\\bin\\"} );
Iterable<? extends JavaFileObject> compUnits =  fileManager.getJavaFileObjects(fRun);
Boolean compRes = compiler.getTask(null, fileManager, null, options, null, compUnits).call();           

if(compRes == true){
    System.out.println("Compilation has succeeded");
    fileManager.close();
    ClassLoader cl = Thread.currentThread().getContextClassLoader();
    Class<?> compiledClass = cl.loadClass(someFile);
    cRun = compiledClass;
}else{
    System.out.println("Compilation error");
    fileManager.close();
    throw new Exception("Compilation Error");
}

This creates the class file in the folder <...>/ProgramOne/bin and then loads the class

How can I achieve that with the packed ProgramOne.jar?

use either maven or ant to build the jar (automatically) or run the jar command by hand. — DwB, Mar 12 '12 at 17:56

score 1 · Accepted Answer · edited May 23 '17 at 11:48

1

If I understand what you're trying to do, you'll need to programmatically recreate your ProgramOne.jar file.

So:

java -jar ProgramOne.jar foo.java

1) ProgramOne.jar compiles foo.java

2) ProgramOne.jar reassembles itself to include foo.class

3) ProgramOne.jar executes foo.class

See here for one example of jar file creation.

edited May 23 '17 at 11:48

Community

1
1

answered Mar 12 '12 at 18:07

Dave

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Yes cool, that could be a solution (have to dig in deeper). You understood my question right. Is there a way so that I don't need to reassemble my ProgramOne.jar? For example, can I compile the class to some local folder and than load this class into the ProgramOne.jar from there? – Arian Mar 12 '12 at 19:35
No, unfortunately you can't. It's the same problem you have in your other question; you can't reference an external *.class file (or *.jar) file from inside a runnable jar file. – Dave Mar 12 '12 at 21:05
Can I read a *.java file then into the ProgramOne.jar and then create something like a virtual class? I would need such a class out of a *.java file to run it with a JUnitCore http://junit.sourceforge.net/javadoc/ – Arian Mar 12 '12 at 21:55
I don't know what you mean by 'virtual class' and I'm not sure how the JUnit link is relevant. Can you elaborate? – Dave Mar 12 '12 at 22:10
Well I thought maybe you can think of another way if I tell you the purpose, which is a Class build form a *.java and run with a JUnitCore. With virtual class I mean something like a class which is not in a file and only entity till the ProgrammOne.jar is closed. The User should not need to restart the jar file to execute a new *.java testcase. – Arian Mar 12 '12 at 22:20
I'll have a look at the URIClassloader, maybe this can also provide a solution – Arian Mar 13 '12 at 10:40

Create Classes from File with a Jar

1 Answers1