JSON manipulation in Java 9 JShell

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In this article I will demonstrate how we can work with JSON based data – for analysis, exploration, cleansing and processing – in JShell, much like we do in Python. I work with a JSON document with entries for all sessions at the Oracle OpenWorld 2017 conference (https://raw.githubusercontent.com/lucasjellema/scrape-oow17/master/oow2017-sessions-catalog.json)

The Java 9 SE specification for the JDK does not contain the JSON-P API and libraries for processing JSON. In order to work with JSON-P in JShell, we need to add the libraries – that we first need to find and download.

I have used a somewhat roundabout way to get hold of the required jar-files (but it works in a pretty straightforward manner):

1. Create a pom.xml file with dependencies on JSON-P

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2. Then run

mvn install dependency:copy-dependencies

as described in this article: https://technology.amis.nl/2017/02/09/download-all-directly-and-indirectly-required-jar-files-using-maven-install-dependencycopy-dependencies/

this will download the relevant JAR files to subdirectory target/dependencies

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3. Copy JAR files to a directory – that can be accessed from within the Docker container that runs JShell – for me that is the local lib directory that is mapped by Vagrant and Docker to /var/www/lib inside the Docker container that runs JShell.

 

4. In the container that runs JShell:

Start JShell with this statement that makes the new httpclient module available, for when the JSON document is retrieved from an HTTP URL resource:

jshell –add-modules jdk.incubator.httpclient

 

5. Update classpath from within jshell

To process JSON in JShell – using JSON-P – we need set the classpath to include the two jar files that were downloaded using Maven.

/env –class-path /var/www/lib/javax.json-1.1.jar:/var/www/lib/javax.json-api-1.1.jar

Then the classes in JSON-P are imported

import javax.json.*;

if we need to retrieve JSON data from a URL resource, we should also

import jdk.incubator.http.*;

 

6. I have made the JSON document available on the file system.

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It can be accessed as follows:

InputStream input = new FileInputStream(“/var/www/oow2017-sessions-catalog.json”);

 

7. Parse data from file into JSON Document, get the root object and retrieve the array of sessions:

JsonReader jsonReader = Json.createReader(input)

JsonObject rootJSON = jsonReader.readObject();

JsonArray sessions = rootJSON.getJsonArray(“sessions”);

 

8. Filter sessions with the term SQL in the title and print their title to the System output – using Streams:

sessions.stream().map( p -> (JsonObject)p).filter(s ->  s.getString(“title”).contains(“SQL”)) .forEach( s -> {System.out.println(s.getString(“title”));})

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One other example: show a list of all presentations for which a slidedeck has been made available for download along with the download URL:

sessions.stream()

.map( p -> (JsonObject)p)

.filter(s -> s.containsKey(“files”) && !s.isNull(“files”) && !(s.getJsonArray(“files”).isEmpty()))

.forEach( s -> {System.out.println(s.getString(“title”)+” url:”+s.getJsonArray(“files”).getJsonObject(0).getString(“url”));})

 

Bonus: Do HTTP Request

As an aside some steps in jshell to execute an HTTP request:

jshell> HttpClient client = HttpClient.newHttpClient();
client ==> jdk.incubator.http.HttpClientImpl@4d339552

jshell> HttpRequest request = HttpRequest.newBuilder(URI.create(“http://www.google.com”)).GET().build();
request ==> http://www.google.com GET

jshell> HttpResponse response = client.send(request, HttpResponse.BodyHandler.asString())
response ==> jdk.incubator.http.HttpResponseImpl@147ed70f

jshell> System.out.println(response.body())
<HTML><HEAD><meta http-equiv=”content-type” content=”text/html;charset=utf-8″>
<TITLE>302 Moved</TITLE></HEAD><BODY>
<H1>302 Moved</H1>
The document has moved
<A HREF=”http://www.google.nl/?gfe_rd=cr&amp;dcr=0&amp;ei=S2XeWcbPFpah4gTH6Lb4Ag”>here</A>.
</BODY></HTML>

 

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About Author

Lucas Jellema, active in IT (and with Oracle) since 1994. Oracle ACE Director and Oracle Developer Champion. Solution architect and developer on diverse areas including SQL, JavaScript, Docker, Machine Learning, Java, SOA and microservices, events in various shapes and forms and many other things. Author of the Oracle Press books: Oracle SOA Suite 11g Handbook and Oracle SOA Suite 12c Handbook. Frequent presenter on community events and conferences such as JavaOne, Oracle Code and Oracle OpenWorld.

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