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;
}