Java Json pretty print javax.json

Question

I'm trying to pretty print json with the javax.json API

The code I'm currently using is as follows:

private String prettyPrint(String json) {
        StringWriter sw = new StringWriter();

        try {
            JsonReader jr = Json.createReader(new StringReader(json));

            JsonObject jobj = jr.readObject();



            Map<String, Object> properties = new HashMap<>(1);
            properties.put(JsonGenerator.PRETTY_PRINTING, true);


            JsonGeneratorFactory jf = Json.createGeneratorFactory(properties);
            JsonGenerator jg = jf.createGenerator(sw);

            jg.write(jobj).close();


        } catch (Exception e) {
        }

        String prettyPrinted = sw.toString();

        return prettyPrinted;
    }

I'm getting the following exception:

11:47:08,830 ERROR [stderr] (EJB default - 1) javax.json.stream.JsonGenerationException: write(JsonValue) can only be called in array context
11:47:08,835 ERROR [stderr] (EJB default - 1)   at org.glassfish.json.JsonGeneratorImpl.write(JsonGeneratorImpl.java:301)
11:47:08,838 ERROR [stderr] (EJB default - 1)   at org.glassfish.json.JsonPrettyGeneratorImpl.write(JsonPrettyGeneratorImpl.java:55)
11:47:08,841 ERROR [stderr] (EJB default - 1)   at org.proactive.rest.VideoFeedService.prettyPrint(VideoFeedService.java:247)
11:47:08,843 ERROR [stderr] (EJB default - 1)   at org.proactive.rest.VideoFeedService.requestVideoFeedData(VideoFeedService.java:124)
11:47:08,845 ERROR [stderr] (EJB default - 1)   at org.proactive.rest.VideoFeedService.run(VideoFeedService.java:86)
11:47:08,848 ERROR [stderr] (EJB default - 1)   at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
11:47:08,850 ERROR [stderr] (EJB default - 1)   at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
11:47:08,852 ERROR [stderr] (EJB default - 1)   at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
11:47:08,854 ERROR [stderr] (EJB default - 1)   at java.lang.reflect.Method.invoke(Method.java:483)

Answer 1

You should be using JsonWriter instead of JsonGenerator.

Replace these lines:

JsonGeneratorFactory jf = Json.createGeneratorFactory(properties);
JsonGenerator jg = jf.createGenerator(sw);

jg.write(jobj).close();

with these:

JsonWriterFactory writerFactory = Json.createWriterFactory(properties);
JsonWriter jsonWriter = writerFactory.createWriter(sw);

jsonWriter.writeObject(jobj);
jsonWriter.close();

Answer 2

You can achieve pretty printing by utilizing the JsonWriterFactory . This takes a configuration map of properties.

Use the JsonWriter to write to the StringWriter .

I added a convenience method which already passes the PRETTY_PRINTING flag for you.

public static String prettyPrint(JsonStructure json) {
    return jsonFormat(json, JsonGenerator.PRETTY_PRINTING);
}

public static String jsonFormat(JsonStructure json, String... options) {
    StringWriter stringWriter = new StringWriter();
    Map<String, Boolean> config = buildConfig(options);
    JsonWriterFactory writerFactory = Json.createWriterFactory(config);
    JsonWriter jsonWriter = writerFactory.createWriter(stringWriter);

    jsonWriter.write(json);
    jsonWriter.close();

    return stringWriter.toString();
}

private static Map<String, Boolean> buildConfig(String... options) {
    Map<String, Boolean> config = new HashMap<String, Boolean>();

    if (options != null) {
        for (String option : options) {
            config.put(option, true);
        }
    }

    return config;
}

Answer 3

Here's a solution for pretty printing (indenting) JSON with javax.json and javax.ws.rs using Jersey:

@GET
@Path("stuff")
public Response getStuff(@QueryParam("pretty") boolean pretty) {
    JsonArrayBuilder stuff = Json.createArrayBuilder().add("foo").add("bar");
    JsonObject jsonObject = Json.createObjectBuilder()
            .add("status", "OK")
            .add("data", stuff).build();
    if (pretty) {
        Map<String, Boolean> config = new HashMap<>();
        config.put(JsonGenerator.PRETTY_PRINTING, true);
        JsonWriterFactory jwf = Json.createWriterFactory(config);
        StringWriter sw = new StringWriter();
        try (JsonWriter jsonWriter = jwf.createWriter(sw)) {
            jsonWriter.writeObject(jsonObject);
        }
        // return "Content-Type: application/json", not "text/plain"
        MediaType mediaType = MediaType.APPLICATION_JSON_TYPE;
        return Response.ok(sw.toString(), mediaType).build();
    } else {
        return Response.ok(jsonObject).build();
    }

}

Sample curl output:

$ curl -i http://localhost:8080/api/stuff?pretty=true
HTTP/1.1 200 OK
Content-Type: application/json
Date: Fri, 08 Aug 2014 14:32:40 GMT
Content-Length: 71


{
    "status":"OK",
    "data":[
        "foo",
        "bar"
    ]
} 
$ curl http://localhost:8080/api/stuff
{"status":"OK","data":["foo","bar"]}

See also:

• JSR 353: Java API for JSON Processing: https://jsonp.java.net
• Java API for JSON Processing (JSON-P): https://json-processing-spec.java.net
• Jersey: https://jersey.java.net
• The Java EE 7 Tutorial:JSON in Java EE RESTful Web Services | Java EE Documentation