Packaging Data for the Web

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Dorthy Thornton
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1 Packaging Data for the Web EN Principles of Enterprise Web Development

2 Overview Both XML and JSON can be used to pass data between remote applications, clients and servers, etc. XML Usually heavier than JSON More difficult to parse JSON Readily parsed by Javascript Faster to process

3 XML Overview Like HTML based on Standard Generalized Markup Language (SGML) XML allows arbitrary definition and use of tags and attributes Well-formed for to faciliate parsing, search and manipulation XML documents have a single root tag that contains the remaining content Every open tag has a corresponding close tag that must match in name (including case) Tags are nested hierarchically Attribute values must be quoted XML comprises many technologies XML Schema XSL/XSLT Extensible Stylesheet Language/Transforms Xpath XML Path Language Others

4 JSON Overview Self-describing format based on syntax used for Javascript objects ECMA-262 standard Completely language independent Easily integrated into Javascript Other languages provide supporting APIs (C/C++, Java, ASP, Python, Ruby ) Lightweight for rapid processing

5 XML JSON Example <?xml version= 1.0 encoding= UTF-8?> <authors> <name> <firstname>larry</firstname> <lastname>brown</lastname> </name> <name> <firstname>bob</firstname> <lastname>evans</lastname> </name> </authors> { authors: { name: [ { firstname: Larry, lastname: Brown }, { firstname: Bob, lastname: Evans } ] }} 235 bytes 146 bytes (38% smaller)

6 JSON versus XML While XML and JSON are both used for the exchange of data over the web, JSON is becoming the defacto format for exchanging data because: More often JSON offers a more lightweight representation that improves performance and processing Javascript s built in mapping into objects make it easy to export and import data from/to the client XML as technology still has much to offer that is not available with JSON. For more information see: Class Additional Resources

7 JSON Syntax Data is in name : value pairs (colon delimited) Names are enclosed in double quotes Values can be Integer or floating point numbers Strings (enclosed in double quotes) Boolean (true or false) Arrays (enclosed in square brackets [] ) Objects (enclosed in curly brackets {}) null (all lowercase, represents empty type) Whitespace (ignored) Data pairs are separated by commas Curly brackets contain objects Square brackets contain arrays

8 JSON Examples Name : Value Pair firstname : Richard age : 30 Objects { firstname : Richard, lastname : Spiegel, age :30 } { id :88421, Experience :17, Reviews:[8,5,7,4] } { InnerObject : { name : Spiegel, years : 10 }, level :4} Arrays [ { firstname : Richard, lastname : Spiegel, age :30 } { firstname : Brian, lastname : Spiegel, age :20} { firstname : Robert, lastname : Evand, age :40 } ]

9 JSON Console Interactive Browser Consoles Chrome : Firefox IE ctrl+shift+j (cmd+shift+j for mac) Select Console tab About:blank in address bar for blank tab Tools->Web Developer->Web Console (ctrl+shift+k) F12 Select console tab Other Firefox tool Scratchpad Jsbin.com Chrome extension JavaScript Editor

10 JSON and JavaScript Creating objects in Javascript Empty object: var sampleobj = {}; New object var sampleobj = new Object(); Initialized object: var sampleobj = { firstname : rich, age :50}; Array object: var samplearray = { directory : [ { firstname : rich, age :35}, { firstname : bob, age :50}, { firstname : emma, age :12} ] };

11 JSON and JavaScript Accessing JSON object fields var x = sampleobj.firstname ; // x = rich var y = sampleobj.age; // y = 50 Accessing JSON array object fields var x = samplearray.directory[2].firstname; // x = emma var y = samplearray.directory[0].age; // y = 35 var z = samplearray.directory[1]; // z = {firstname: bob, age:50}

12 JSON and Java Official standard API, JSR 353 Java API for JSON Processing Several open source APIs existed prior to JSR 353 and are quite popular today FasterXML/Jackson: GSON: (Google) JSON-P: JSON.org: MOXy:

13 FasterXML/Jackson Overview Streaming API that parses and generates JSON in a series of events Low overhead Fast read/writes Tree model for loading and manipulating JSON document as Java objects (JsonNodes) Most flexible for manipulation Data binding converts JSON to plain old Java objects (POJOs) using configurations or annotations and generates JSON from configured POJOs Useful for serializing/deserializing Java Objects Especially for web based application! Full documentation with tutorials and more at:

14 FasterXML/Jackson Databinding Getting and Installing Download from URLs provided to included in Maven builds Links to jar files with library files, source code and api docs Three library jar files required for minimal access jackson-core jackson-databind jackson-annotations API Usage com.fasterxml.jackson.databind.objectmapper Primary class to facilitate the marshalling and unmarshalling of java objects to and from JSON Constructor and supporting methods com.fasterxml.jackson.core package core classes used by databind package (aka ObjectMapper) Exception classes thrown by class methods throughout Jackson com.fasterxml.jackson.annotations package All supported annotations used for java class mapping to JSON formats Helper classes that are used by ObjectMapper

15 ObjectMapper Provides function of converting Java objects to JSON and vice versa Wraps other Jackson objects (from core library) for reading/writing JSON import com.fasterxml.jackson.databind.objectmapper Constructor: new ObjectMapper() Methods: readvalue: several methods for moving data sources (streams, files, Strings) into Java objects readvalue(string content, Class<T> valuetype) : deserializes JSON content into object of type valuetype writevalue: several methods for serializing Java objects into JSON output into Strings, files, streams writevalueasstring : serializes Java object to String enable: methods for configuring the mapper for parsing JSON or generating JSON Exceptions IOException JsonGenerationException JsonMappingException JsonProcessingException JsonParseException

16 Annotations Meta data to control how Java classes map to JSON documents and vice versa Added to either property or one of the accessor/mutator methods on that property Some have additional properties that can be value: provides a name of the property in the JSON or just use name of java filed defaultvalue: value for the property if one is not value: root name to use around object if root-level wrapping @JsonPropertyOrder

17 Using JSON with ReST The JAX-RS API (aka Jersey) interfaces with the JAX-B (JSON/XML binding) API inherently when necessary JSON passed in conjunction with annotation will use JAX-B to deserialize JSON into objects. Java objects passed in conjunction with annotation will use JAX-B to serialize objects into JSON. Jersey projects must have a JAX-B implementation to support those API calls or they will fail Will use default JAX-B API implementation packaged with Jersey (MOXy) Can replace MOXy with alternative JAX-B implementations through library manipulation

18 FasterXML/Jackson with ReST FasterXML/Jackson libraries are required for processing the underlying POJOs and JSON mappings jackson-core jackson-databind jackson-annotations Need additional libraries that account for Jackson under the Java API for RESTful Web Services (JAX-RS) jackson-jaxrs-base jackson-jaxrs-json-provider Out of the box, Jersey provides another JAXB API (Moxy) that must be removed in order to use Jackson. Remove jersey-media-moxy.jar file from classpath

19 Netbeans Project View Default libraries provided by Jersey Library with jersey-media-moxy jar file removed FasterXML/Jackson libraries for use under JAX-RS Basic FasterXML/Jackson JAX-B libraries

20 Using JSON Binding in ReST Create POJOs that will be mapped to desired JSON (and vice-versa) Objects create from JSON passed from client JSON serialized from objects used on server Optionally, employ Jackson annotations on object to dictate mapping features (field names, order, etc) Employ the objects in ReST service methods as parameters or return variables in conjunction with annotations

21 @GET Example JSON /record public Record getrecord() { } Record r = new Record(); r.setfirstname( Rich ); r.setlastname( Spiegel ); r.setage(35); return r; public class Record first ) private String last ) private String age ) private int age; A ReST call to will return content of type application/json that will look as follows: { first : rich, last : spiegel, age :35} } :

22 Example /new public Response newrecord(record record) { } // record is initialized from the // json content provided in the POST // request public class Record first ) private String last ) private String age ) private int age; : } A POST to with attached JSON content will automatically create record and initialize it with fields from the JSON passed.

CSC Web Technologies, Spring Web Data Exchange Formats

CSC Web Technologies, Spring Web Data Exchange Formats CSC 342 - Web Technologies, Spring 2017 Web Data Exchange Formats Web Data Exchange Data exchange is the process of transforming structured data from one format to another to facilitate data sharing between