What is Spark? If we take a look to the project’s web page, it says something like “Spark is a simple and lightweight Java web framework built for rapid development“. In other words, it proposes us a simple way to build web applications without dealing with XML or annotations.
I recognize I do not usually use it but I have found it very useful when I need to prepare some REST services for a quick demo. Do not missunderstanding me, I think that use the Java EE platform is amazing and you can develop with it very fast, but you need a server, a couple of classes with the JAX-RS configuration and a few annotations to make everything work. With Spark, you only need to add a dependency in you .pom file and write a few lines of code.
For the example, I am going to implement a little application offering REST services with the CRUD operations for a User. This entity is going to have:
- id
- name
- surname
In first place, we should create a java application in our favorite IDE using maven.
In second place, we are going to add the correct maven dependency for the Spark library.
<dependencies>
<dependency>
<groupId>com.sparkjava</groupId>
<artifactId>spark-core</artifactId>
<version>2.1</version>
</dependency>
</dependencies>
In third place, we should create our entity object.
public class User {
private String id;
private String name;
private String surname;
// Getters and setters
}
Now, we need to start to write our main class. In this main class we are going to add a couple of things:
- A Map to simulate our data store.
- A main method that it is going to contain our REST services.
The main class looks like:
public class Users {
private static Map<String, User> users = new HashMap<String, User>();
public static void main(String[] args) {
final Random random = new Random();
// Services here
}
}
Now, we are going to start with the services.
/users?name=Foo&surname=Bar (POST)
Spark.post("/users", (request, response) -> {
String name = request.queryParams("name");
String surname = request.queryParams("surname");
User user = new User(name, surname);
int id = random.nextInt(Integer.MAX_VALUE);
users.put(String.valueOf(id), user);
response.status(201); // 201 Created
return id;
});
/users/:id (GET)
Spark.get("/users/:id", (request, response) -> {
User user = users.get(request.params(":id"));
if (user != null) {
return "Name: " + user.getName() + ", Surname: " + user.getSurname();
} else {
response.status(404); // 404 Not found
return "User not found.";
}
});
/users/:id (PUT)
Spark.put("/users/:id", (request, response) -> {
String id = request.params(":id");
User user = users.get(id);
if (user != null) {
String newName = request.queryParams("name");
String newSurname = request.queryParams("surname");
if (newName != null) {
user.setName(newName);
}
if (newSurname != null) {
user.setSurname(newSurname);
}
return "User with id '" + id + "' has been updated.";
} else {
response.status(404); // 404 Not found
return "User not found.";
}
});
/users/:id (DELETE)
Spark.delete("/users/:id", (request, response) -> {
String id = request.params(":id");
User user = users.remove(id);
if (user != null) {
return "User with id '" + id + "'has been deleted";
} else {
response.status(404); // 404 Not found
return "User not found.";
}
});
/users (GET)
Spark.get("/users", (request, response) -> {
String ids = "";
for (String id : users.keySet()) {
ids += id + " ";
}
return ids;
});
Now, we only need to execute our application and check if everything is working correctly. To do this, we can use cURL or our browser with the URL:
http://localhost:4567/users
The next steps are on you. Implement a front-end with Javascript or consuming the services with a mobile app or… whatever you prefer.
See you.
Binary Coders 
[…] As its web page describes “Spark – A tiny Sinatra inspired framework for creating web applications in Java 8 with minimal effort“. You can see a previous example I implemented in this blog called: Quick REST demo with Spark. […]
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