Weblog for the AMIS Technology corner
Posts tagged json
Create simple Java application to post JSON message to CometD Bayeux Channel using Apache HttpClient and Maven style NetBeans project
Jan 20th
The objective discussed in this article is to post messages to a CometD Bayeux Channel with a standalone Java Class – without dependencies on CometD. For example to control from Java the Slideshow introduced in the synchronized Slideshow demo application created using CometD (see previous articles Push based synchronized Slideshow demo application implemented using CometD and jQuery running on Tomcat and Publishing to CometD Bayeux Channel from inside the Oracle Database – PL/SQL based push to CometD Web Client ).
This article describes the creation of a simple Java Class leveraging Apache HttpClient to post HTTP requests (JSON messages) to a CometD Bayeux Channel. The main point is to show working code with the lest dependencies, not an optimal program (it is far from optimal). The article demonstrates how NetBeans and Maven conspire here to make the task as simple as possible. The Maven support in NetBeans allows me to simply create a new Maven style project of (arche)type Java Application.
Push-based synchronized slideshow web application – implemented using WebSockets and Kaazing WebSocket Gateway
Jan 7th
In the last few articles, I have discussed downloading, installing and running demos for a number of different tools, frameworks and libraries that support push-style (web) applications in one way or another. I have looked into ‘classic’ comet with Grizzly, Atmosphere and CometD as well as ADF Active Data Service and WebLogic Pub/Sub (Bayeux) Channels. I have also looked to WebSockets with jWebSocket, again Atmosphere and CometD and also with Kaazing. I intend to now take a closer look at some of these frameworks, by taking a simple push-style application and implementing it using each of these frameworks. The functionality I will be implementing is simple:
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through the web client (HTML 5/javaScript), a user can select an image from a list of ’slides’
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the selection of the image is communicated to the server (background WebSocket based or alternatively regular AJAX)Comet (Bayeux)/Long Poll style)
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the server informs all connected clients about the selected image through a pushed message (background WebSocket based or alternatively Comet (Bayeux)/Long Poll style); these clients all synchronize that slide selection
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a Java (server side) component can also connect to the server and listen in to image selection events as well as publish image selection messages of its own
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bonus: it may also broadcast ‘new image available’ events to allow the web clients to update the list of images presented to the user
In this article, I will present an implementation using the Kaazing WebSocket Gateway. The application parts that I created or configured are a static HTML page with some JavaScript elements, the Kaazing gateway-config.xml file and a single Java Class. Maybe 50 lines of code in total, to get a fully operaional push style WebSocket application. Not a bad start for this series. Note: I would like to thank Matthias Wessendorf from Kaazing for his help.
Absolutely Typical – The whole story on Types and how they power PL/SQL Interoperability (UKOUG, 2011)
Dec 12th
This presentation will hopefully convince database developers that types in the Oracle Database are worth their salt – and more. With the recent improvements in 11gR2, the pieces are available to complete the puzzle of structured and modern programming with a touch of OO and more importantly to create a decoupled, reusable API that exposes services based on tables and views to clients that speak SQL, AQ, PL/SQL, Types, XML or RESTful, through SQL*Net, JDBC or HTTP.
This session shows through many demonstrations how types and collections are defined, how they are used between SQL and PL/SQL and how they can be converted to and from XML and JSON and how they drive Native WebServices as well as RESTful services based on the Embedded PL/SQL Gateway. Everyone doing PL/SQL programming will benefit immediately from this session. Every Database Developer should be aware of Types and Collections. For structured programming, for optimal SQL to PL/SQL integration and for interoperability to client application. This session introduces Types and Collections, their OO capabilities, the conversion to XML and JSON, their use in Native and RESTful WebServices and the pivotal role they can play in encapsulation and decoupling.
The slides can be reviewed here:
View more presentations from Lucas Jellema.
Resources
Download Slides plus Demoscripts here: AbsolutelyTypical_UKOUG2011_jellema.zip.
Creating JSON document straight from SQL query – using LISTAGG and With Clause
Jun 14th
This very brief article demonstrates how a fairly complex, nested JSON document can be created using a single SQL query. The main features used in the SQL statement are the WITH clause to define the inline views per object (Department, Manager, Employee), Scalar Subquery to retrieve the result from an inline view as string into the overall JSON string and LISTAGG to collect multiple elements into a JSON list.
The article shows a very simple application of this JSON creation through a simple HTML page – served by a PL/SQL package. This page does not contain any data. Right after loading, the onLoad event triggers a listener that invokes – through AJAX – the PL/SQL package’s other procedure. This procedure returns the JSON object – courtesy of that fabulous SQL query – and uses it to write the company details on the fly into the page.
No JDBC based data retrieval in Java applications – RESTstyle, JSON formatted HTTP based interaction from Java to Database
Jan 30th
This article demonstrates how Java application can query data from relational databases (well, in this case more specifically the Oracle RDBMS) without the use of plain old JDBC but instead through a simple HTTP interaction with a RESTful service that returns the data in JSON format.
In this way, issues with JDBC drivers, database connections, data sources and firewall and other network complications are avoided and the Java application does not contain a single bit of SQL.
This article will demonstrate how easy it is to set up the RESTful API from the database – using Oracle’s dbms_epg package – and how this API can be accessed from Java using JAX-RS (Jersey) and the json-lib utility library.
This topic is one of many to be discussed in Friday’s (4th February) Masterclass on Leveraging the Oracle Database in Java Application (some seats are available – go to http://www.amis.nl/trainingen/oracle-database-in-java-applications for registration and details).
Leveraging RESTful Services from Java applications using Jersey (Introduction)
Dec 14th
While researching for the Oracle SOA Suite 11g Handbook, I wanted to take a quick look at REST(ful) WebServices and see how those can be integrated into the SCA based SOA Composite Applications that we create with the Oracle SOA Suite. Currently, it does not have the HTTP binding that the 10.1.3 release of the SOA Suite used to have. So what are the alternatives? But first, how does one call a simple HTTP only (no SOAP/WS*) service from a piece of Java code? With as little programming and as much framework lifting as possible.
One of the frameworks available for RESTful operations is Jersey – a framework that should be more REST aware than plain HTTP communication oriented libraries like Apache HTTP Client, as well as offer some support for typical formats used in RESTful interactions, such as JSON, XML, RSS, CSV. So let’s create the simples Java application consuming a RESTful service – the Google Translation service – using the Jersey library.
