Rc173 010d-json 2

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Getting Started with
CONTENTS INCLUDE:
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Whats New in JPA 2.0

JPA 2.0
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JDBC Properties
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Access Mode
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Mappings
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Shared Cache
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Additional API and more... By Mike Keith
Getting Started with JPA 2.0

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CONTENTS INCLUDE:
❱ JSON Validation
❱ JSON Modeling
❱ JSON in the Browser
Core JSON
❱ JSON and Ajax The Fat-Free Alternative to XML
❱ JSON and Java
❱ JSON and Ruby...and More! By Tom Marrs

An Object (in this case address) consists of comma-separated name/
JSON OVERVIEW value pairs surrounded by curly braces.

JSON (JavaScript Object Notation) is a standard text-based data
interchange format that enables applications to exchange data over a Array
computer network. Programs written in Ruby, Java/EE, JavaScript, C#/. An Array is a collection of ordered values, and looks like this:
Net, PHP, etc. can easily consume and produce JSON data because it is
independent of languages and computing platforms. The abundance of {
JSON-related APIs and tools make it easy to use JSON from your favorite “people” : [
{ “firstName”: “John”, “lastName”: “Smith”, “age”: 35 },
programming language, IDE, and runtime environment. Additionlly, popular
{ “firstName”: “Jane”, “lastName”: “Smith”, “age”: 32 }
NoSQL databases such as MongoDB and CouchBase are based on JSON. ]
}
JSON was created by Douglas Crockford in 2001, and is specified in RFC
4627 with the IETF (Internet Engineering Task Force) standard; see http://
tools.ietf.org/html/rfc4627. Per the specification, the JSON’s IANA (Internet Value Types
Assigned Numbers Authority) media type is application/json, and the A Value (i.e., the right-hand side of a Name/Value Pair) can be one of the
file type is following:
.json.
• Object
What is JSON? • Array
JSON is a simple data format, and has 3 basic data structures: • String
• Name/Value (or Key/Value) Pair. • Number
• Object. • Boolean
• Arrays. • null

A valid JSON document is always surrounded with curly braces, like this: Number
A number can be an integer or double-precision float. Here are some
{ JSON-Data } examples:

Please note that some members of the JSON community use the term “age”: 29
“string” rather than “document.” “cost”: 299.99
“temperature”: -10.5
“speed_of_light”: 1.23e11
Why JSON? “speed_of_light”: 1.23e+11
JSON is gradually replacing XML as the preferred data exchange format “speed_of_light”: 1.23E11
on the internet because JSON is easy to read and its structures map to “speed_of_light”: 1.23E+11
common programming concepts such as Objects and Arrays. JSON is
more efficient (i.e., faster parsing and network transmission) than XML
because JSON is more compact—there are no begin and end tags. The property name (i.e., age, etc.) is a string surrounded by double quotes,
but the value does not have quotes. A number can be prefixed by a minus
Name/Value Pair sign. The exponent portion (denoted by e or E) comes after the number
A Name/Value pair looks like this: value, and can have an optional plus or minus sign. Neither leading zeroes,
octal, nor hexadecimal values are allowed.
{
“firstName”: “John”
}

A property name (i.e., firstName) is a string that is surrounded by double
quotes. A value can be a string (as in the above example), but this is just
one of several valid data types. (Please see the Data Types section for
further details.) Some well-known technologies claim that they use JSON
data formats, but they don’t surround their strings with quotes. However,
this is not valid JSON; see the JSON Validation section.

Object
An Object is a collection of unordered Name/Value pairs. The following
example shows an address object:

{
Core JSON

“address” : {
“line1” : “555 Main Street”,
“city” : “Denver”,
“stateOrProvince” : “CO”,
“zipOrPostalCode” : “80202”,
“country” : “USA”
}
}


2 Core JSON

Boolean
A Boolean in JSON can either be true or false, as follows:

{
“emailValidated” : true
}

The property name (emailValid) is a string surrounded by double
quotes, but the value (true) does not have quotes.

null
Although technically not a data type, null is a special value to indicate that
a data element has no value. In the following example, the age field has no
value (possibly because the user chose not to enter this information):

{
“age” : null
} JSONLint is also available as a Chrome extension in the Chrome Web Store.

Comments JSON MODELING
JSON does not allow comments. Comments were originally a part of JSON,
but developers misused them by putting parsing directives in comments. Developing valid JSON documents for real applications can be tedious and
When Douglas Crockford saw this practice, he removed comments from error-prone. To avoid typographical errors, you can use JSONPad, JSON
JSON to preserve interoperability between computing platforms. Editor Online, and JSON Designer to create a logical model (similar to UML)
and generate valid JSON documents.
Style
You’ve probably noticed that the property names (i.e., the name on the left- JSONPad
hand side of the colon) use camel case. This is not a rule or standard, but JSONPad (from http://www.jsonpad.com/en/Home.html) is a GUI tool
is a convention prescribed in Google’s JSON Style Guide at: http://google- that eliminates typing JSON text by providing an interface that enables you
styleguide.googlecode.com/svn/trunk/jsoncstyleguide.xml. to create Objects, Keys (i.e., Name/Value Pairs), and Arrays. JSONPad is
available as a Windows or Mac GUI, and online at the JSONPad web site.
Official Syntax To create a model, use the green plus key under the text area. The following
Douglas Crockford’s JSON site (http://www.json.org) provides a full data types are supported: Key (i.e., Name/Value Pair), Object, and Array.
description of JSON syntax. After the model is complete, press the blue up-arrow button (under the
Tree tab) to generate a valid, pretty-printed JSON document based on the
Additionally, the JSON Pro Quick Guide (freely available in the iPhone App model:
Store) provides examples and an overview of JSON syntax.

JSON VALIDATION

A textual document MUST follow the JSON syntax rules to be considered
a valid JSON document. Valid JSON is important because it ensures
interoperability between applications and JSON-related tools. Although
the JSON.org web site shows JSON syntax, sometimes it’s easier to see
JSON validation in action. JSONLint (http://www.jsonlint.com) provides an
interactive, web-based JSON validator. To use it, type or paste some text
into the main text area and press the Validate button. If the text isn’t valid
JSON, you’ll see an error message as follows:

The end result is a valid JSON document that is usable in your application.
You can also generate a model by pasting JSON text into the text area and
pressing the green down arrow in the Tree tab. Under the Format tab, you
can either compress or pretty print a JSON document. JSONPad validates
the JSON document in the text are when you press the JSON button in the
Tools tab.

JSON Editor Online
JSON Editor Online (http://jsoneditoronline.org/) is an online JSON modeler,
In this case, the property name for the address Object is missing a and is also available as a Chrome extension.
closing double quote. After you fix this problem and press the Validate
button, JSONLint pretty-prints the JSON document as follows:
JSON IN THE BROWSER

Firefox and Chrome provide excellent extensions (i.e., add-ons and plugins)
that make it easier to work with JSON.


3 Core JSON

REST Client The JSONView Chrome extension provides a bit more functionality than its
Rest Client is a Firefox extension that provides the ability to debug and Firefox counterpart – it enables a user to search a JSON document using
test RESTful Web Services from the browser. The ability to test from the the JSONQuery language. For example, entering ..bib_key in the Query
browser isn’t new, but the output formatting is much more readable. text box displays all the bib_key fields in the text:

The above example uses the Books service from the Open Library API. JSONQuery is one of several technologies that can search JSON
After entering the service URI, the Response Body (Highlight) tab shows the documents and return the desired element(s).
JSON output.
JSON Beautification with JSON SH
Pretty Printing with JSONView JSON SH is a Chrome extension (available in the Google Chrome Web
JSON is not very readable when displayed natively in a browser. JSONView Store) that acts as a pretty-printer and a validator. Paste a valid (but not
is a Firefox and Chrome extension that pretty-prints JSON. pretty) JSON document into the text area at the top of the page, and JSON
SH beautifies the text into a human-readable format.
JSONView in Firefox
After installing this extension and re-starting Firefox, the JSON response
JSON AND AJAX
from the Open Library Books service URI is readable, and you can expand/
collapse objects on the page:
AJAX (Asynchronous JavaScript and XML) was one of the original use
cases for JSON, and the following jQuery example shows how a JavaScript
client makes an HTTP Get request to a RESTful Web Service and processes
a JSON response:

$.getJSON(‘http://example/service/addresses/home/1’,
function(data) {
var address = JSON.parse(data);

console.log(“Address Line 1 = “ + address.line1);
}
);

In the code above, $.getJSON() (a shorthand version of the main
jQuery $.ajax() call) makes an HTTP GET request. The (anonymous)
success callback function receives the JSON response and parses it into
a JavaScript object using JSON.parse(), which is part of the ECMA-
262 standard (beginning with the 5th edition) – please see http://www.
ecmascript.org/ for further information). The console.log() method
JSONView in Chrome then logs line 1 of the address to the browser console. Conversely, the
JSONView is also available as a Chrome extension from the Chrome Web JSON.stringify() method converts a JavaScript value to a JSON string
Store: (with optional pretty-printing).

JSON AND JAVA

The Jackson (http://jackson.codehaus.org/) library is a popular Java-based
JSON API. Here’s an example of how to marshal/unmarshal an Address
object to/from JSON:

import java.io.Writer;
import java.io.StringWriter;
import org.codehaus.jackson.map.ObjectMapper;

public class Address {
private String line1;
private String city;
private String stateOrProvince;
private String zipOrPostalCode;
private String country;

public Address() {}

public String getLine1() {
Click on the minus sign to collapse each element, and press the Toggle return line1;
Collapsed link to show/hide each collapsed element. }

4 Core JSON

public void setLine1(line1) { The JSON gem’s to_json method converts a String or Hash to JSON. The
this.line1 = line1; Address object’s to_json method converts an Address to JSON format
} by converting its data members to a Hash and then calling to to_json on

the Hash. To convert the Address to JSON, do the following:
// Remaining getters and setters ...
}
addr1 = Address.new(‘555 Main Street’, ‘Denver’, ‘CO’, ‘80231’,
Address addrOut = new Address(); ‘US’)
// Call setters to populate addrOut … puts addr1.to_json
ObjectMapper mapper = new ObjectMapper(); // Reuse this. # Outputs the following …
{“line1”:”555 Main Street”,”city”:”Denver”,”state_or_
// Marshal Address object to JSON String. province”:”CO”,”zip_or_postal_code”:”80231”,”country”:”US”}
Writer writer = new StringWriter();
mapper.writeValue(writer, addrOut);
System.out.println(writer.toString());
The JSON gem’s JSON.parse method converts a JSON String to a Hash.
// Unmarshal Address object from JSON String. The Address object’s from_json! method takes a JSON String, calls
String addrJsonStr = JSON.parse to convert to a Hash, and sets each corresponding data
“{“ + member from the Hash as follows:
“”address” : {“ +
“”line1” : ”555 Main Street”,” +
“”city” : ”Denver”,” json_addr = <<END
“”stateOrProvince” : ”CO”,” {
“”zipOrPostalCode” : ”80202”,” + “line1” : “999 Broadway”, “city” : “Anytown”,
“”country” : ”USA”” + “state_or_province” : “CA”, “zip_or_postal_code” : “90210”,
“}” + “country” : “USA”
“}”; }
END
Address addrIn = mapper.readValue(addrJsonStr, Address.class);
addr2 = Address.new
addr2.from_json!(json_addr)
In addition to Jackson, other well-known Java-based JSON APIs include:
In addition to the JSON gem, other JSON-related gems include:
API Source
Google GSON http://code.google.com/p/google-json/ API Source
ActiveSupport JSON http://api.rubyonrails.org/classes/
SOJO http://sojo.sourceforge.net/
ActiveSupport/JSON.html
org.json (by Douglas http://www.json.org/java
Yajl https://github.com/brianmario/yajl-ruby
Crockford)
Oj https://github.com/ohler55/oj
json-lib http://sourceforge.net/projects/json-lib/
json-io http://code.google.com/p/json-io
JSON AND RUBY ON RAILS
jsontools http://jsontools.berlios.de/
jsonbeans http://code.google.com/p/jsonbeans/ Ruby on Rails provides additional functionality that makes it easier
to convert Ruby objects to JSON. The following controller uses the
ActionController’s render method to output an Address object to JSON:
JSON AND RUBY
class Person
There are many JSON-related libraries for Ruby. Here’s an example using attr_accessor :first_name, :last_name
the JSON gem that comes standard with Ruby.
def initialize(first_name=nil, last_name=nil)
@first_name = first_name
require ‘json’ @last_name = last_name
end
class Address end

attr_accessor :line1, :city, :state_or_province, class MyController < ApplicationController
:zip_or_postal_code, :country def index
person = Person.new(‘John’, ‘Doe’)
def initialize(line1=’’, city=’’, state_or_province=’’, respond_to do |format|
zip_or_postal_code=’’, country=’’) format.html # index.html.erb
@line1 = line1 format.json { render :json => person}
@city = city end
@state_or_province = state_or_province end
@zip_or_postal_code = zip_or_postal_code end
@country = country
end
The Rails ApplicationController takes care of marshalling/
def to_json unmarshalling objects to/from JSON, so there’s no need to write a to_
to_hash.to_json
end
json method here.

def from_json!(str)
JSON.parse(str).each { |var, val| send(“#{var}=”, val) } JSON SCHEMA
end

private JSON Schema specifies the structure of a JSON document. JSON Schema
can be used to validate the content of JSON sent to/received from a
def to_hash RESTful Web Service. JSON Schemas are written in JSON.
Hash[instance_variables.map { |var| [var[1..-1].to_sym,
send(var[1..-1])] }] The main JSON Schema site can be found at: http://json-schema.org.
end
JSON Schema is a work in progress – the JSON Schema team has just
end
published version 0.4, which can be found at: http://tools.ietf.org/html/
draft-zyp-json-schema-04.

Some important JSON Schema constructs include:


5 Core JSON

Construct Description “phoneNumber”: {
“type”: “object”,
type The data type object, array, string, number, etc. “id”: “phoneNumber”,
“required”: true,
$schema The URI that provides the schema version. “properties”: {
required true/false “channel”: {
“type”: “string”,
id Data element id “id”: “channel”,
properties Validation properties for a data element include type (see “enum”: [
above), minimum (minimum value), maximum (maximum “cell”,
“work”,
value), enum, etc. “home”
]
Here is a sample JSON Schema for a portion of an online gift registry: },
“number”: {
“type”: “object”, “type”: “string”,
“$schema”: “http://json-schema.org/draft-03/schema”, “id”: “number”,
“id”: “#”, “required”: true
“required”: true, }
“properties”: { }
“registrants”: { }
“type”: “array”, }
“id”: “registrants”, }
“required”: true, }
“items”: { }
“type”: “object”, }
“required”: false,
“properties”: {
“address”: { The above schema:
“type”: “object”,
“id”: “address”,
“required”: true, • Requires an array of registrant objects.
“properties”: { • Limits the phoneNumber.channel field to the following values:
“city”: { cell, work, fax, or home.
• Limits the address.premise field to these values: home, work, or
“id”: “city”,
“required”: true other.
},
“country”: { A Web Service consumer could use this schema to validate the following
JSON document:
“id”: “country”,
“required”: false
},
{
“line1”: {
“registrants”: [
{
“id”: “line1”,
“firstName”: “Fred”,
“required”: true
“lastName”: “Smith”,
},
“phoneNumber”: {
“line2”: {
“channel”: “cell”,
“number”: “303-555-1212”
“id”: “line2”,
},
“required”: false
“address”: {
},
“premise”: “home”,
“postalCode”: {
“line1”: “555 Broadway NW”,
“line2”: “# 000”,
“id”: “postalCode”,
“city”: “Denver”,
“stateOrProvince”: “CO”,
},
“postalCode”: “88888”,
“premise”: {
“country”: “USA”
}
“id”: “premise”,
}
]
“enum”: [
}
“work”,
“home”,
“other”
]
}, JSON Schema Generator
“stateOrProvince”: { Creating a JSON Schema is tedious and error-prone. Use a JSON Schema
“type”: “string”, Generator to generate a Schema from any valid JSON document. Visit the
“id”: “stateOrProvince”, online JSON Schema Generator (www.jsonschema.net/) and generate a
} schema by doing the following:
}
}, • Paste the JSON document into the right-hand text area.
“firstName”: { • Choose the JSON Input option
“id”: “firstName”, • Press the Generate Schema button.
},
“lastName”: {
JSON Schema Validator
“type”: “string”, An application uses a JSON Schema Validator to ensure that a JSON
“id”: “lastName”, document conforms to the structure specified by the Schema. JSON
“required”: true Schema Validators are available for most modern programming languages:
},

JSON Schema Language Source
Validator
JSV JavaScript https://github.com/garycourt/JSV
Ruby JSON Schema Ruby https://github.com/hoxworth/json-
<!============Snippet con’t on next page------------------>
Validator schema


6 Core JSON

JSON Schema Language Source
Validator
json-schema- Java https://github.com/fge/json-
validator schema-validator
php-json-schema PHP https://github.com/hasbridge/php-
(by MIT) json-schema
JSON.Net .NET http://james.newtonking.com/
projects/json-net.aspx

Besides the language-specific tools, there is an excellent online JSON
Schema Validator at: http://json-schema-validator.herokuapp.com. To use
this site, enter the JSON document and Schema into the corresponding text
boxes and press the Validate button.

IN CONCLUSION

We’ve covered the basics of JSON, but we’ve just scratched the surface.
Although JSON is a simple data format, there are many tools to streamline
the design and development process. JSON is a standard, it has replaced
XML as the preferred data interchange format on the Internet, and it
enables developers to create efficient, interoperable enterprise-class
applications.

ABOUT THE AUTHORS RECOMMENDED BOOK
Tom Marrs is a Principal Architect at Ciber, where he With JavaScript: The Good Parts, you’ll discover a
specializes in Service-Oriented Architecture (SOA) He beautiful, elegant, lightweight and highly expressive
designs and implements mission-critical web and language that lets you create effective code, whether
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Rails, REST, HTML5, JavaScript, Java/EE, and Open Ajax to run fast. If you develop sites or applications for
Source technologies. Tom is also the author of the the Web, this book is an absolute must.
upcoming JSON at Work, and a founder of the Denver
Open Source User Group (DOSUG)
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