JavaCompiler API: access functions/variables outside the compiled program while it's running? - java-compiler-api

Question

Adapting this the following code takes a class and function name, a string of Java code, compiles the code and runs the function.
public class Compile {
static void compileAndRun(final String className, final String methodName, final String code) {
JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
DiagnosticCollector<JavaFileObject> diagnostics = new DiagnosticCollector<>();
JavaFileObject file = new JavaSourceFromString(className, code);
Iterable<? extends JavaFileObject> compilationUnits = Arrays.asList(file);
JavaCompiler.CompilationTask task = compiler.getTask(null, null, diagnostics, null, null, compilationUnits);
boolean success = task.call();
for (Diagnostic diagnostic : diagnostics.getDiagnostics()) {
System.out.println(diagnostic.getCode());
System.out.println(diagnostic.getKind());
System.out.println(diagnostic.getPosition());
System.out.println(diagnostic.getStartPosition());
System.out.println(diagnostic.getEndPosition());
System.out.println(diagnostic.getSource());
System.out.println(diagnostic.getMessage(null));
}
System.out.println("Success: " + success);
if (success) {
try {
URLClassLoader classLoader = URLClassLoader.newInstance(new URL[] { new File("").toURI().toURL() });
Class.forName("HelloWorld", true, classLoader).getDeclaredMethod(methodName, new Class[] { String[].class }).invoke(null, new Object[] { null });
} catch (ClassNotFoundException e) {
System.err.println("Class not found: " + e);
} catch (NoSuchMethodException e) {
System.err.println("No such method: " + e);
} catch (IllegalAccessException e) {
System.err.println("Illegal access: " + e);
} catch (InvocationTargetException e) {
System.err.println("Invocation target: " + e);
} catch (MalformedURLException e) {
e.printStackTrace();
}
}
}
}
class JavaSourceFromString extends SimpleJavaFileObject {
final String code;
JavaSourceFromString(String name, String code) {
super(URI.create("string:///" + name.replace('.','/') + Kind.SOURCE.extension),Kind.SOURCE);
this.code = code;
}
#Override
public CharSequence getCharContent(boolean ignoreEncodingErrors) {
return code;
}
}
You might call this using:
StringWriter writer = new StringWriter();
PrintWriter out = new PrintWriter(writer);
out.println("public class HelloWorld {");
out.println(" public static void main(String args[]) {");
out.println(" System.out.println(\"Hello World !\");");
out.println(" }");
out.println("}");
out.close();
Compile.compileAndRun("HelloWorld", "main", writer.toString());
Is it possible from inside the compiled program to call external functions and variables? e.g.
class SomeClass {
int x = 123;
void myFunc() {
StringWriter writer = new StringWriter();
PrintWriter out = new PrintWriter(writer);
out.println("public class HelloWorld {");
out.println(" public static void main(String args[]) {");
out.println(" y = foo(x);");
out.println(" }");
out.println("}");
out.close();
Compile.compileAndRun("HelloWorld", "main", writer.toString());
}
void foo(int x) {
}
}
or maybe with the foo and x in another class? Obviously I tried this, but it fails to compile. Is there a way to achieve this?

Answer 1

In the end I was able to use Groovy, which is a superset of the Java language, to achieve my goal, so you can write a script in Java or Groovy. Passing in variables and classes, which can of course contain variables and functions, was straight-forward, e.g.
class MyClass {
int x = 100;
void myFunc(int r) {
System.out.println("value from inside script = " + r + " !");
}
}
void groovy() {
MyClass q = new MyClass();
StringWriter writer = new StringWriter();
PrintWriter out = new PrintWriter(writer);
out.println(" System.out.println(\"Hello world\" + q.x);");
out.println(" q.x += 100;");
out.println(" q.myFunc(123)");
out.close();
// call groovy expressions from Java code
Binding binding = new Binding();
binding.setVariable("q", q);
GroovyShell shell = new GroovyShell(binding);
Object value = shell.evaluate(writer.toString());
System.out.println("new value = " + q.x);
}