How can I execute java code from plain text?

Question

How can i execute java code from my java program? Is there a framework I could use to programatically execute them? please help, thanks.

My java class

public class test {

    public static compute(int one, int two){
         // compute goes here
   }

    public static void main(String[] args) {
        //read from file
        //execute the commands
    }
}

my text file : contains java code fragments doesn't consists the whole java file.

   System.out.println("Start of my program");

@do("compute my two int"){
  val = compute(15,25);
  System.out.println(val);
}

Are you just trying to test it? Are you using an IDE like Eclipse? — mdewitt, Jan 23 '14 at 18:16
@mdewitt thanks for the response. the java file is one time compiled to class. Only making changes to plain text file. and executing the java class file at runtime. — Njax3SmmM2x2a0Zf7Hpd, Jan 23 '14 at 18:19
@user2115021 thanks for the comment, it's executed on command prompt java test textfile.txt — Njax3SmmM2x2a0Zf7Hpd, Jan 23 '14 at 18:20
If the plain file has the full class, you can use ProcessBuilder to compile and execute it. — Sujith Surendranathan, Jan 23 '14 at 18:20
@crnlx thanks for the note. I want plain file to be have more clarity. and the class file have lot of functionality. — Njax3SmmM2x2a0Zf7Hpd, Jan 23 '14 at 18:23
What I meant is, it can be a separate class from your calling class. — Sujith Surendranathan, Jan 23 '14 at 18:24
@crnlx is there any mechanism to parse the plain file? without recompile. — Njax3SmmM2x2a0Zf7Hpd, Jan 23 '14 at 18:28
I'll recommend using Java Scripting Engine for this purpose instead http://docs.oracle.com/javase/7/docs/technotes/guides/scripting/programmer_guide/index.html — karakfa, Jan 23 '14 at 18:33
@BrianRoach thanks for response. actually this is a code fragment of java on plain text not full class file. — Njax3SmmM2x2a0Zf7Hpd, Jan 23 '14 at 18:34
Which means the answer is: You don't. At least not getting into runtime bytecode modification, which is extremely complex. — Brian Roach, Jan 23 '14 at 18:36
@karakfa wow!! it looks great! does it mean I can call java-script? or can this be modified to my purpose? — Njax3SmmM2x2a0Zf7Hpd, Jan 23 '14 at 18:36
@karafka: Does it allow Java code also or does it allow only scripting languages? — Sujith Surendranathan, Jan 23 '14 at 18:41
Javascript is bundled with the distribution. If you need proper Java syntax you can alternatively use BeanShell, which can be embedded in your application. This essentially gives you an eval() method. — karakfa, Jan 23 '14 at 19:04

Marko Topolnik · Answer 1 · 2014-01-23T19:23:04.587

0

The JDK contains the JavaCompiler API. You can use it to compile text to a .class file at runtime, and then proceed to make this file available on the classpath—and finally load it using reflection.

The above, if repeated, will result in a "class leak": all the classes you have ever loaded will be stuck in the runtime. To avoid that you'll need to create a new classloader for each class you load dynamically.

edited Jan 23 '14 at 19:23

answered Jan 23 '14 at 18:51

Marko Topolnik

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How can I execute java code from plain text?

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