Compile, instantiate and use a Java class from source code

CompileTest

package org.amicofragile.etude.compiling;

import java.io.File;
import java.io.FileWriter;
import java.net.URL;
import java.net.URLClassLoader;

import javax.tools.JavaCompiler;
import javax.tools.ToolProvider;

import org.junit.Assert;
import org.junit.Test;

public class CompileTest {
	public static interface Hello {
		public abstract String sayHello();
	}
	
	@Test
	public void compileAndExecuteSource() throws Exception {
            final String src =	"package test; public class Test implements org.amicofragile.etude.compiling.CompileTest.Hello {" + 
            	"public String sayHello() { return \"Hello, World!\";}" +
            "}";
	    final File tempDir = new File(System.getProperty("java.io.tmpdir") + "/sources");
	    final File pkg = new File(tempDir, "test");
	    pkg.mkdirs();
	    final File source = new File(pkg, "Test.java");
	    new FileWriter(source).append(src).close();
	
	    JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
	    compiler.run(null, null, null, source.getPath());
	
	    URLClassLoader classLoader = URLClassLoader.newInstance(new URL[] { tempDir.toURI().toURL() });
	    Class<Hello> cls = (Class<Hello>) Class.forName("test.Test", true, classLoader);
	    Hello hello = cls.newInstance();
	    Assert.assertEquals("Hello, World!", hello.sayHello());
	}
}