Update 09/22/2017: I've been silent for long time (I'm into Golang lately hence putting Java aside) despite the fact that there are lots of interests to make this mini tool better. I'll kick off my effort to improve this tool from now on by reviewing outstanding issues and PRs
InMemoryJavaCompiler 
Samples with utility classes to compile java source code in memory
After taking huge effort to look for example on the internet and found nothing work. I decided to create a very simple version.
Note: Please make sure you use JDK in your runtime
E.g.:
StringBuilder sourceCode = new StringBuilder();
sourceCode.append("package org.mdkt;\n");
sourceCode.append("public class HelloClass {\n");
sourceCode.append(" public String hello() { return \"hello\"; }");
sourceCode.append("}");
Class<?> helloClass = InMemoryJavaCompiler.newInstance().compile("org.mdkt.HelloClass", sourceCode.toString());
If you are looking for more examples, please look at unit tests in the src/test/java folder
Artifact is pushed to Sonatype OSS Releases Repository
https://oss.sonatype.org/content/repositories/releases/
Maven dependency:
<dependency>
<groupId>org.mdkt.compiler</groupId>
<artifactId>InMemoryJavaCompiler</artifactId>
<version>1.3.0</version>
</dependency>
