Question

Hi I have requirement to create ,compile and load java classes run time. Using FTL i am creating java source files , and able to compile the source if there is no dynamic dependency.

To elaborate with an instance, I have two java source file, one interface and its implementation class. I am able to compile the interface using java compiler api as follows

String classpath=System.getProperty("java.class.path");
        String testpath =classpath+";"+rootPath+"/lib/is_wls_client.jar;"+rootPath+"/rtds_wls_proxyclient.jar;.;";
        File javaFile =  new File(javaFileName+".java");
        JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
        List<String> optionList = new ArrayList<String>();
        optionList.addAll(Arrays.asList("-classpath",testpath));
        StandardJavaFileManager sjfm = compiler.getStandardFileManager(null, null, null);
        Iterable fileObjects = sjfm.getJavaFileObjects(javaFile);
        JavaCompiler.CompilationTask task = compiler.getTask(null, null, null,optionList,null,fileObjects);
        task.call();
        sjfm.close();

I set class path for static classes which are already in the classpath , but this approach do not work for dynamically created classes? Any custom class loader will do the fix? My final implementation will be in web/app server

Any feedback will be highly appreciated

Satheesh

Answer 1

I was able to solve this issue by compiling all the java files together. Using FTL I generate the java classes, and then compile it using java compiler api and load classes with custom class loader

Java Complier

private  void compile(File[] files) throws IOException{
        String classpath=System.getProperty("java.class.path");
        String rootPath=getServletContext().getRealPath("/");
        System.out.println("--> root Path "+rootPath);
        String testpath=classpath+";.;xx.jar;yy.jar";
        JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
        List<String> optionList = new ArrayList<String>();
        optionList.addAll(Arrays.asList("-classpath",testpath));
//      optionList.addAll(Arrays.asList("-d",rootPath+"/target"));
        StandardJavaFileManager sjfm = compiler.getStandardFileManager(null, null, null);
        Iterable fileObjects = sjfm.getJavaFileObjects(files);
        JavaCompiler.CompilationTask task = compiler.getTask(null, null, null,optionList,null,fileObjects);
        task.call();
        sjfm.close();

    }

Below code snippet shows how to use custom class loader

class CustomClassLoader extends ClassLoader {

     public CustomClassLoader(ClassLoader parent) {
            super(parent);
     }

    public Class findClass(String className,String path) {
        byte[] classData = null;
        try {
            FileInputStream f = new FileInputStream(path);
            int num = f.available();
            classData = new byte[num];

            f.read(classData);
        } catch (IOException e) {
            System.out.println(e);
        }
        Class x = defineClass(className, classData, 0, classData.length);
        return x;
    }
}

thanks
Satheesh