Dynamic compile java source code and reflection invoke issue

Question

I got the following code which copy from a tutorial:

package com.tom.labs;

import java.io.IOException;
import java.lang.reflect.Method;
import java.net.URI;
import java.net.URISyntaxException;
import java.util.Arrays;

import javax.tools.JavaCompiler;
import javax.tools.JavaCompiler.CompilationTask;
import javax.tools.SimpleJavaFileObject;
import javax.tools.StandardJavaFileManager;
import javax.tools.ToolProvider;

public class CompilerTest {

    /**
     * @param args
     */
    public static void main(String[] args) throws Exception {
        String source = "public class Main { " +
                " public static void main(String[] args) {" +
                "   System.out.println(\"Hello World!\");" +
                " }" +
                " public static void test() { " +
                " System.out.println(\"Hello World!\");" +
                " } " +
                "}";
        JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
        StandardJavaFileManager fileManager = compiler.getStandardFileManager(null, null, null);
        StringSourceJavaObject sourceObject = new CompilerTest.StringSourceJavaObject("Main", source);
        Iterable fileObjects = Arrays.asList(sourceObject);
        CompilationTask task = compiler.getTask(null, fileManager, null, null, null, fileObjects);
        boolean result = task.call();
        if (result) {
            ClassLoader loader = CompilerTest.class.getClassLoader();
            Class<?> clazz = loader.loadClass("com.tom.labs.Main");
            Method method = clazz.getMethod("test", new Class<?>[] {});
            method.invoke(null, new Object[] {});
        }
    }

    static class StringSourceJavaObject extends SimpleJavaFileObject {
        private String content = null;
        public StringSourceJavaObject(String name, String content) throws URISyntaxException {
            super(URI.create("string:///" + name.replace('.', '/') + Kind.SOURCE.extension), Kind.SOURCE);
            this.content = content;
        }
        public CharSequence getCharContent(boolean ignoreEncodingErrors) throws IOException {
            return content;
        }
    }
}

However，it doesn't work. Getting error: Exception in thread "main" java.lang.NoSuchMethodException: com.tom.labs.Main.test() at java.lang.Class.getMethod(Class.java:1622) at com.tom.labs.CompilerTest.main(CompilerTest.java:38)

Can anybody help me out? Updte:

I printed out the output of getMethods: [public static void com.tom.labs.Main.main(java.lang.String[]), public final void java.lang.Object.wait(long,int) throws java.lang.InterruptedException, public final native void java.lang.Object.wait(long) throws java.lang.InterruptedException, public final void java.lang.Object.wait() throws java.lang.InterruptedException, public boolean java.lang.Object.equals(java.lang.Object), public java.lang.String java.lang.Object.toString(), public native int java.lang.Object.hashCode(), public final native java.lang.Class java.lang.Object.getClass(), public final native void java.lang.Object.notify(), public final native void java.lang.Object.notifyAll()]

It's very strange, method test is not in there.

there is no class called "Main" and as no class is there, there is no method called "test". — Alpesh Prajapati
@AlpeshPrajapati I don't think so,if no class,the exception should be: java.lang.ClassNotFoundException: — Tom
Did you try it without the 2nd parameter to getMethod() and invoke()? (I don't think you need to specify them at all if they are empty.) — Turix

Gergely Szilagyi Gergely Szilagyi · Accepted Answer · 2012-06-29T08:49:50

Your 'source'

String source = "public class Main { " +
                " public static void main(String[] args) {" +
                "   System.out.println(\"Hello World!\");" +
                " }" +
                " public static void test() { " +
                " System.out.println(\"Hello World!\");" +
                " } " +
                "}";

has no namespace. Either you should add a package keyword to it, or change

Class<?> clazz = loader.loadClass("com.tom.labs.Main");

to

Class<?> clazz = loader.loadClass("Main");

Dynamic compile java source code and reflection invoke issue

2 Answers