This article will explore serving JSON with the Vert.x toolkit. We start with an HTTP microservice. For help creating a microservice see HTTP Microservices With Vert.x in Java.

Open the project in your favorite IDE and edit the MainVerticle class as follows:

src/main/java/com/example/json_hello_world_service/MainVerticle.java

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package com.example.json_hello_world_service;

import io.vertx.core.AbstractVerticle;
import io.vertx.core.Promise;

public class MainVerticle extends AbstractVerticle {

  @Override
  public void start(Promise<Void> startPromise) throws Exception {
    vertx.createHttpServer().requestHandler(req -> {

      req.response()
        .putHeader("content-type", "application/json")
        .end("{\"greeting\":\"hello, world\"}");

    }).listen(8888, http -> {
      if (http.succeeded()) {
        startPromise.complete();
        System.out.println("HTTP server started on port 8888");
      } else {
        startPromise.fail(http.cause());
      }
    });
  }
}
  • Line 13 the content-type header is set to application/json
  • Line 14 writes a raw JSON string

Start the service using the following command:

% ./gradlew run

Test it with curl (or open localhost:8888 in a web browser):

% curl localhost:8888
{"greeting":"hello, world"}

To view the content-type header add the -v (verbose) flag:

% curl -v localhost:8888
*   Trying ::1...
* TCP_NODELAY set
* Connected to localhost (::1) port 8888 (#0)
> GET / HTTP/1.1
> Host: localhost:8888
> User-Agent: curl/7.64.1
> Accept: */*
> 
< HTTP/1.1 200 OK
< content-type: application/json
< content-length: 27
< 
* Connection #0 to host localhost left intact
{"greeting":"hello, world"}* Closing connection 0

JsonObject

Java doesn’t have a native JSON object however the Vert.x library provides a JsonObject to serve JSON. Under the hood, JsonObject is a facade over a LinkedHashMap Java collection. It contains many helper methods for getting or setting values in a JSON structure. In addition Vert.x uses Jackson to parse and serialize to and from the JsonObject.

Modify the MainVerticle class to use a JsonObject:

src/main/java/com/example/json_hello_world_service/MainVerticle.java

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package com.example.json_hello_world_service;

import io.vertx.core.AbstractVerticle;
import io.vertx.core.Promise;
import io.vertx.core.json.JsonObject;

public class MainVerticle extends AbstractVerticle {

  @Override
  public void start(Promise<Void> startPromise) throws Exception {
    vertx.createHttpServer().requestHandler(req -> {

      var json = new JsonObject().put("greeting", "hello, world");

      req.response()
        .putHeader("content-type", "application/json")
        .end(json.encode());

    }).listen(8888, http -> {
      if (http.succeeded()) {
        startPromise.complete();
        System.out.println("HTTP server started on port 8888");
      } else {
        startPromise.fail(http.cause());
      }
    });
  }
}
  • Line 13 a JsonObject was created. Notice the fluent programming interface of the object.
  • Line 17 encode() is called on the JsonObject to produce a UTF-8 encoded string.

Notice the output doesn’t change:

% curl localhost:8888
{"greeting":"hello, world"}%

Admittedly the example is overly simple. It is to isolate the key pieces for serving JSON from a Vert.x HTTP microservice.

Source

GitHub: json-hello-world-service

References

Vert.x Documentation