Compile and run a java program through another one

[z.zojaji]

Hi all,
I want to compile and run some run-time generated java code via another one, consider for example the following program:

public class Test {
	public static void main(String[] args) throws IOException {
		 FileOutputStream fos = new FileOutputStream("src/JavaProgram0.java");
	        String s = "\npublic class JavaProgram0 {\n" +
	        		"	public void print() {System.out.println(\"first\");\n	}\n}";
	        fos.write(s.getBytes());
	        fos.close();
	        
		JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
		int result = compiler.run(null, null, null,"src/JavaProgram0.java");
        JavaProgram0 j = new JavaProgram0();
        j.print();
        
    }
}

in this code i write a very simple program defined by a string, to a file and then compile and run it.
it is Ok for one program but if i extend it to compile and run more than one programs it just runs the first one :

public class Test {
	public static void main(String[] args) throws IOException {
		 FileOutputStream fos = new FileOutputStream("src/JavaProgram0.java");
	        String s = "\npublic class JavaProgram0 {\n" +
	        		"	public void print() {System.out.println(\"first\");\n	}\n}";
	        fos.write(s.getBytes());
	        fos.close();
	        
		JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
		int result = compiler.run(null, null, null,"src/JavaProgram0.java");
        JavaProgram0 j = new JavaProgram0();
        j.print();

    FileOutputStream fos1 = new FileOutputStream("src/JavaProgram0.java");
        String s1 = "\npublic class JavaProgram0 {\n" +
        		"	public void print() {System.out.println(\"second\");\n	}\n}";
        fos1.write(s1.getBytes());
        
        result = compiler.run(null, null, null,"src/JavaProgram0.java");
        JavaProgram0 j2 = new JavaProgram0();
        j2.print();
    }
}

in the above example "first" "first" is printed but it is intended to print "first" "second"!
do you have any idea to address this problem?
Thanks in advance,
Z.Zojaji

[Norm]

Where do you close the files?

[z.zojaji]

in the mentioned code i close just the first one (as a mistake) but if I close each after writing and before compile, it will print "second " "second", the code will be as follow:

public class Test {
	public static void main(String[] args) throws IOException {
		 FileOutputStream fos = new FileOutputStream("src/JavaProgram0.java");
	        String s = "\npublic class JavaProgram0 {\n" +
	        		"	public void print() {System.out.println(\"first\");\n	}\n}";
	        fos.write(s.getBytes());
[COLOR="Red"]	        fos.close();[/COLOR]
	        
		JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
		int result = compiler.run(null, null, null,"src/JavaProgram0.java");
                JavaProgram0 j = new JavaProgram0();
                j.print();

    [INDENT]           FileOutputStream fos1 = new FileOutputStream("src/JavaProgram0.java");
        String s1 = "\npublic class JavaProgram0 {\n" +
        		"	public void print() {System.out.println(\"second\");\n	}\n}";
        fos1.write(s1.getBytes());
        
        result = compiler.run(null, null, null,"src/JavaProgram0.java");
        JavaProgram0 j2 = new JavaProgram0();
        j2.print();
[COLOR="Red"][B]        fos1.close();[/B][/COLOR][/INDENT]
    }
}

[JosAH]

What happens if you throw away your JavaProgram0.class file and run again? It won't solve your problem because you're fighting against the ClassLoader (that has already loaded and cached your class after loading it the first time) but start with a clean list first.

kind regards,

Jos

[z.zojaji]

Dear Jos , my opinion is like you my original application generates hundreds of programs automatically and .java file is correctly updated and compiled but all af them run the first .class file. so I add the following code after compile in order to reload the .class files but the problem is not solved yet:

	ClassLoader cl = ToolProvider.getSystemToolClassLoader();
		try {
			cl.loadClass("JavaProgram0");
		} catch (ClassNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}

any alternative solution?

[JosAH]

Dear Jos , my opinion is like you my original application generates hundreds of programs automatically and .java file is correctly updated and compiled but all af them run the first .class file. so I add the following code after compile in order to reload the .class files but the problem is not solved yet:

	ClassLoader cl = ToolProvider.getSystemToolClassLoader();
		try {
			cl.loadClass("JavaProgram0");
		} catch (ClassNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}

any alternative solution?

Class loaders cache the classes they have loaded so you have to write your own non-caching class loader for that purpose. I can't help you there because I've never done it before. It seems quite an achievement though and all I know of is a "rebel class loader" (google for that) that can do it. I wish you success with this project.

kind regards,

Jos

[Norm]

JavaProgram0 j = new JavaProgram0();

Where is JavaProgram0 defined that you can compile this?

[z.zojaji]

Where is JavaProgram0 defined that you can compile this?

JavaProgram0 should be generated and updated in run-time but i initialized it to a java class with an empty "print" method to avoid errors.

[JosAH]

If someone spams a forum I appreciate it if it is spammed correctly, i.e. readable text, fancy pictures here and there (if applicable); but this looks just crappy; the spammer can't even get its character set right; reported.

Jos

[z.zojaji]

Hi all,
I've finally found an alternative solution for the problem, after generating new .class files I run them using "exec()" method and assign the output of process to a bufferdReader for further use, it is some thing like this:

            Runtime rt = Runtime.getRuntime();
            Process pr = rt.exec("java "+outFile);
            BufferedReader input = new BufferedReader(new InputStreamReader(pr.getInputStream()));
            String line=null;
            while((line=input.readLine()) != null) {
                System.out.println(line);

How to compile and execute a Java file from within another Java Program | Rommel Rico