<dependency>
    <groupId>com.sparkjava</groupId>
    <artifactId>spark-core</artifactId>
    <version>2.9.4</version>
</dependency>

import static spark.Spark.*;

public class HelloWorld {
    public static void main(String[] arg){
        get("/hello", (request, response) -> "Hello World!");
    }
}

mvn javadoc:javadoc

import static spark.Spark.*;

/**
 * A simple example just showing some basic functionality
 */
public class SimpleExample {

    public static void main(String[] args) {

        //  port(5678); <- Uncomment this if you want spark to listen to port 5678 instead of the default 4567

        get("/hello", (request, response) -> "Hello World!");

        post("/hello", (request, response) ->
            "Hello World: " + request.body()
        );

        get("/private", (request, response) -> {
            response.status(401);
            return "Go Away!!!";
        });

        get("/users/:name", (request, response) -> "Selected user: " + request.params(":name"));

        get("/news/:section", (request, response) -> {
            response.type("text/xml");
            return "<?xml version=\"1.0\" encoding=\"UTF-8\"?><news>" + request.params("section") + "</news>";
        });

        get("/protected", (request, response) -> {
            halt(403, "I don't think so!!!");
            return null;
        });

        get("/redirect", (request, response) -> {
            response.redirect("/news/world");
            return null;
        });

        get("/", (request, response) -> "root");
    }
}

import static spark.Spark.*;

import java.util.HashMap;
import java.util.Map;
import java.util.Random;

/**
 * A simple CRUD example showing how to create, get, update and delete book resources.
 */
public class Books {

    /**
     * Map holding the books
     */
    private static Map<String, Book> books = new HashMap<String, Book>();

    public static void main(String[] args) {
        final Random random = new Random();

        // Creates a new book resource, will return the ID to the created resource
        // author and title are sent in the post body as x-www-urlencoded values e.g. author=Foo&title=Bar
        // you get them by using request.queryParams("valuename")
        post("/books", (request, response) -> {
            String author = request.queryParams("author");
            String title = request.queryParams("title");
            Book book = new Book(author, title);

            int id = random.nextInt(Integer.MAX_VALUE);
            books.put(String.valueOf(id), book);

            response.status(201); // 201 Created
            return id;
        });

        // Gets the book resource for the provided id
        get("/books/:id", (request, response) -> {
            Book book = books.get(request.params(":id"));
            if (book != null) {
                return "Title: " + book.getTitle() + ", Author: " + book.getAuthor();
            } else {
                response.status(404); // 404 Not found
                return "Book not found";
            }
        });

        // Updates the book resource for the provided id with new information
        // author and title are sent in the request body as x-www-urlencoded values e.g. author=Foo&title=Bar
        // you get them by using request.queryParams("valuename")
        put("/books/:id", (request, response) -> {
            String id = request.params(":id");
            Book book = books.get(id);
            if (book != null) {
                String newAuthor = request.queryParams("author");
                String newTitle = request.queryParams("title");
                if (newAuthor != null) {
                    book.setAuthor(newAuthor);
                }
                if (newTitle != null) {
                    book.setTitle(newTitle);
                }
                return "Book with id '" + id + "' updated";
            } else {
                response.status(404); // 404 Not found
                return "Book not found";
            }
        });

        // Deletes the book resource for the provided id
        delete("/books/:id", (request, response) -> {
            String id = request.params(":id");
            Book book = books.remove(id);
            if (book != null) {
                return "Book with id '" + id + "' deleted";
            } else {
                response.status(404); // 404 Not found
                return "Book not found";
            }
        });

        // Gets all available book resources (ids)
        get("/books", (request, response) -> {
            String ids = "";
            for (String id : books.keySet()) {
                ids += id + " ";
            }
            return ids;
        });
    }

    public static class Book {

        public String author, title;

        public Book(String author, String title) {
            this.author = author;
            this.title = title;
        }

        public String getAuthor() {
            return author;
        }

        public void setAuthor(String author) {
            this.author = author;
        }

        public String getTitle() {
            return title;
        }

        public void setTitle(String title) {
            this.title = title;
        }
    }
}

import static spark.Spark.*;

import java.util.HashMap;
import java.util.Map;

/**
 * Example showing a very simple (and stupid) authentication filter that is
 * executed before all other resources.
 *
 * When requesting the resource with e.g.
 *     http://localhost:4567/hello?user=some&password=guy
 * the filter will stop the execution and the client will get a 401 UNAUTHORIZED with the content 'You are not welcome here'
 *
 * When requesting the resource with e.g.
 *     http://localhost:4567/hello?user=foo&password=bar
 * the filter will accept the request and the request will continue to the /hello route.
 *
 * Note: There is a second "before filter" that adds a header to the response
 * Note: There is also an "after filter" that adds a header to the response
 */
public class FilterExample {

    private static Map<String, String> usernamePasswords = new HashMap<String, String>();

    public static void main(String[] args) {

        usernamePasswords.put("foo", "bar");
        usernamePasswords.put("admin", "admin");

        before((request, response) -> {
            String user = request.queryParams("user");
            String password = request.queryParams("password");

            String dbPassword = usernamePasswords.get(user);
            if (!(password != null && password.equals(dbPassword))) {
                halt(401, "You are not welcome here!!!");
            }
        });

        before("/hello", (request, response) -> response.header("Foo", "Set by second before filter"));

        get("/hello", (request, response) -> "Hello World!");

        after("/hello", (request, response) -> response.header("spark", "added by after-filter"));

        afterAfter("/hello", (request, response) -> response.header("finally", "executed even if exception is throw"));

        afterAfter((request, response) -> response.header("finally", "executed after any route even if exception is throw"));
    }
}

import static spark.Spark.after;
import static spark.Spark.get;

/**
 * Example showing the use of attributes
 */
public class FilterExampleAttributes {

    public static void main(String[] args) {
        get("/hi", (request, response) -> {
            request.attribute("foo", "bar");
            return null;
        });

        after("/hi", (request, response) -> {
            for (String attr : request.attributes()) {
                System.out.println("attr: " + attr);
            }
        });

        after("/hi", (request, response) -> {
            Object foo = request.attribute("foo");
            response.body(asXml("foo", foo));
        });
    }

    private static String asXml(String name, Object value) {
        return "<?xml version=\"1.0\" encoding=\"UTF-8\"?><" + name +">" + value + "</"+ name + ">";
    }
}

import static spark.Spark.*;

public class StaticResources {

    public static void main(String[] args) {

        // Will serve all static file are under "/public" in classpath if the route isn't consumed by others routes.
        // When using Maven, the "/public" folder is assumed to be in "/main/resources"
        staticFileLocation("/public");

        get("/hello", (request, response) -> "Hello World!");
    }
}

import static spark.Spark.*;

public class JsonAcceptTypeExample {

    public static void main(String args[]) {

        //Running curl -i -H "Accept: application/json" http://localhost:4567/hello json message is read.
        //Running curl -i -H "Accept: text/html" http://localhost:4567/hello HTTP 404 error is thrown.
        get("/hello", "application/json", (request, response) -> "{\"message\": \"Hello World\"}");
    }
} 

public class FreeMarkerTemplateEngine extends TemplateEngine {

    private Configuration configuration;

    protected FreeMarkerTemplateEngine() {
        this.configuration = createFreemarkerConfiguration();
    }

    @Override
    public String render(ModelAndView modelAndView) {
        try {
            StringWriter stringWriter = new StringWriter();

            Template template = configuration.getTemplate(modelAndView.getViewName());
            template.process(modelAndView.getModel(), stringWriter);

            return stringWriter.toString();
        } catch (IOException e) {
            throw new IllegalArgumentException(e);
        } catch (TemplateException e) {
            throw new IllegalArgumentException(e);
        }
    }

    private Configuration createFreemarkerConfiguration() {
        Configuration retVal = new Configuration();
        retVal.setClassForTemplateLoading(FreeMarkerTemplateEngine.class, "freemarker");
        return retVal;
    }
}

public class FreeMarkerExample {

    public static void main(String args[]) {

        get("/hello", (request, response) -> {
            Map<String, Object> attributes = new HashMap<>();
            attributes.put("message", "Hello FreeMarker World");

            // The hello.ftl file is located in directory:
            // src/test/resources/spark/examples/templateview/freemarker
            return modelAndView(attributes, "hello.ftl");
        }, new FreeMarkerTemplateEngine());
    }
}

public class JsonTransformer implements ResponseTransformer {

	private Gson gson = new Gson();

	@Override
	public String render(Object model) {
		return gson.toJson(model);
	}
}

public class TransformerExample {

    public static void main(String args[]) {
        get("/hello", "application/json", (request, response) -> {
            return new MyMessage("Hello World");
        }, new JsonTransformer());
    }
}