How to make sure you're Java examples in a README compiles and runs.

DocTest.java

package com.sillelien.dollar;

import org.apache.commons.io.FileUtils;
import org.junit.Test;
import org.pegdown.Extensions;
import org.pegdown.PegDownProcessor;
import org.pegdown.ast.RootNode;

import java.io.File;
import java.io.IOException;

import static com.sillelien.dollar.api.DollarStatic.$;

/**
 * @author hello@neilellis.me
 */
public class DocTest {

    @Test
    public void test() throws IOException {
        PegDownProcessor processor = new PegDownProcessor(Extensions.FENCED_CODE_BLOCKS);
        RootNode rootNode = processor.parseMarkdown(FileUtils.readFileToString(new File("README.md")).toCharArray());
        rootNode.accept(new DocTestingVisitor());

    }
}

DocTestingVisitor.java

package com.sillelien.dollar;
/*
 * Copyright (c) 2014-2015 Neil Ellis
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import org.apache.commons.io.FileUtils;
import org.jetbrains.annotations.NotNull;
import org.pegdown.ast.*;

import javax.tools.DiagnosticCollector;
import javax.tools.JavaCompiler;
import javax.tools.StandardJavaFileManager;
import javax.tools.ToolProvider;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLClassLoader;

public class DocTestingVisitor implements Visitor {
    @Override
    public void visit(AbbreviationNode node) {

    }

//    @Override
//    public void visit(AnchorLinkNode anchorLinkNode) {
//
//    }

    @Override
    public void visit(AutoLinkNode node) {

    }

    @Override
    public void visit(BlockQuoteNode node) {

    }

    @Override
    public void visit(BulletListNode node) {

    }

    @Override
    public void visit(CodeNode node) {

    }

    @Override
    public void visit(DefinitionListNode node) {

    }

    @Override
    public void visit(DefinitionNode node) {

    }

    @Override
    public void visit(DefinitionTermNode node) {

    }

    @Override
    public void visit(ExpImageNode node) {

    }

    @Override
    public void visit(ExpLinkNode node) {

    }

    @Override
    public void visit(HeaderNode node) {

    }

    @Override
    public void visit(HtmlBlockNode node) {

    }

    @Override
    public void visit(InlineHtmlNode node) {

    }

    @Override
    public void visit(ListItemNode node) {

    }

    @Override
    public void visit(MailLinkNode node) {

    }

    @Override
    public void visit(OrderedListNode node) {

    }

    @Override
    public void visit(@NotNull ParaNode node) {

        visitChildren(node);
    }

    @Override
    public void visit(QuotedNode node) {

    }

    @Override
    public void visit(ReferenceNode node) {

    }

    @Override
    public void visit(RefImageNode node) {

    }

    @Override
    public void visit(RefLinkNode node) {

    }

    @Override
    public void visit(@NotNull RootNode node) {
        node.getReferences().forEach(this::visitChildren);
        node.getAbbreviations().forEach(this::visitChildren);
        visitChildren(node);
    }

    @Override
    public void visit(SimpleNode node) {

    }

    @Override
    public void visit(SpecialTextNode node) {
    }

    @Override
    public void visit(StrikeNode node) {

    }

    @Override
    public void visit(StrongEmphSuperNode node) {

    }

    @Override
    public void visit(TableBodyNode node) {

    }

    @Override
    public void visit(TableCaptionNode node) {

    }

    @Override
    public void visit(TableCellNode node) {

    }

    @Override
    public void visit(TableColumnNode node) {

    }

    @Override
    public void visit(TableHeaderNode node) {

    }

    @Override
    public void visit(TableNode node) {

    }

    @Override
    public void visit(TableRowNode node) {

    }

    @Override
    public void visit(@NotNull VerbatimNode node) {
        if ("java".equals(node.getType())) {
            try {
                String name = "DocTemp"+System.currentTimeMillis();
                File javaFile = new File("/tmp/" + name + ".java");
                File clazzFile = new File("/tmp/" + name + ".class");
                clazzFile.getParentFile().mkdirs();
                FileUtils.write(javaFile,
                        "import com.sillelien.dollar.api.*;\n" +
                                "import static com.sillelien.dollar.api.DollarStatic.*;\n" +
                                "public class " + name + " implements java.lang.Runnable{\n" +
                                "    public void run() {\n" +
                                "        " + node.getText() + "\n" +
                                "    }\n" +
                                "}");
                final JavaCompiler javac
                        = ToolProvider.getSystemJavaCompiler();
                final StandardJavaFileManager jfm
                        = javac.getStandardFileManager(null, null, null);
                JavaCompiler.CompilationTask task;

                try (FileOutputStream fileOutputStream = FileUtils.openOutputStream(clazzFile)) {
                    task = javac.getTask(new OutputStreamWriter(fileOutputStream), jfm, new DiagnosticCollector<>(), null, null,
                            jfm.getJavaFileObjects(javaFile));
                }
                task.call();

                try {
                    // Convert File to a URL
                    URL url = clazzFile.getParentFile().toURL();
                    URL[] urls = new URL[]{url};
                    ClassLoader cl = new URLClassLoader(urls);
                    Class cls = cl.loadClass(name);
                    ((Runnable) cls.newInstance()).run();
                } catch (MalformedURLException e) {
                    e.printStackTrace();
                } catch (ClassNotFoundException e) {
                    e.printStackTrace();
                } catch (InstantiationException e) {
                    e.printStackTrace();
                } catch (IllegalAccessException e) {
                    e.printStackTrace();
                }
                System.out.println("Parsed: " + node.getText());
            } catch (IOException e) {
                throw new RuntimeException(e);
            }

        }
    }

    @Override
    public void visit(WikiLinkNode node) {

    }

    @Override
    public void visit(TextNode node) {

    }

    @Override
    public void visit(@NotNull SuperNode node) {
        visitChildren(node);
    }

    @Override
    public void visit(Node node) {

    }

    void visitChildren(@NotNull SuperNode node) {
        for (Node child : node.getChildren()) {
            child.accept(this);
        }
    }
}