JSON 参考卡


DZone, Inc. | www.dzone.com By Mike Keith Getting Started with JPA 2.0 Get More Refcardz! Visit refcardz.com #127 CONTENTS INCLUDE: n Whats New in JPA 2.0 n JDBC Properties n Access Mode n Mappings n Shared Cache n Additional API and more... Getting Started with JPA 2.0 DZone, Inc. | www.dzone.com Get More Refcardz! Visit refcardz.com #173 Core JSON By Tom Marrs The Fat-Free Alternative to XML JSON OVERVIEW JSON (JavaScript Object Notation) is a standard text-based data interchange format that enables applications to exchange data over a computer network. Programs written in Ruby, Java/EE, JavaScript, C#/. 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 programming language, IDE, and runtime environment. Additionlly, popular 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 Assigned Numbers Authority) media type is application/json, and the file type is .json. What is JSON? JSON is a simple data format, and has 3 basic data structures: • Name/Value (or Key/Value) Pair. • Object. • Arrays. A valid JSON document is always surrounded with curly braces, like this: { JSON-Data } Please note that some members of the JSON community use the term “string” rather than “document.” Why JSON? JSON is gradually replacing XML as the preferred data exchange format on the internet because JSON is easy to read and its structures map to 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. Name/Value Pair A Name/Value pair looks like this: { “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: { “address” : { “line1” : “555 Main Street”, “city” : “Denver”, “stateOrProvince” : “CO”, “zipOrPostalCode” : “80202”, “country” : “USA” } } An Object (in this case address) consists of comma-separated name/ value pairs surrounded by curly braces. Array An Array is a collection of ordered values, and looks like this: { “people” : [ { “firstName”: “John”, “lastName”: “Smith”, “age”: 35 }, { “firstName”: “Jane”, “lastName”: “Smith”, “age”: 32 } ] } Value Types A Value (i.e., the right-hand side of a Name/Value Pair) can be one of the following: • Object • Array • String • Number • Boolean • null Number A number can be an integer or double-precision float. Here are some examples: “age”: 29 “cost”: 299.99 “temperature”: -10.5 “speed_of_light”: 1.23e11 “speed_of_light”: 1.23e+11 “speed_of_light”: 1.23E11 “speed_of_light”: 1.23E+11 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 sign. The exponent portion (denoted by e or E) comes after the number value, and can have an optional plus or minus sign. Neither leading zeroes, octal, nor hexadecimal values are allowed. CONTENTS INCLUDE: ❱ JSON Validation ❱ JSON Modeling ❱ JSON in the Browser ❱ JSON and Ajax ❱ JSON and Java ❱ JSON and Ruby...and More! Core JSON 2 Core JSON DZone, Inc. | www.dzone.com 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 } Comments JSON does not allow comments. Comments were originally a part of JSON, but developers misused them by putting parsing directives in comments. When Douglas Crockford saw this practice, he removed comments from JSON to preserve interoperability between computing platforms. Style You’ve probably noticed that the property names (i.e., the name on the left- hand side of the colon) use camel case. This is not a rule or standard, but is a convention prescribed in Google’s JSON Style Guide at: http://google- styleguide.googlecode.com/svn/trunk/jsoncstyleguide.xml. Official Syntax Douglas Crockford’s JSON site (http://www.json.org) provides a full description of JSON syntax. Additionally, the JSON Pro Quick Guide (freely available in the iPhone App 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: In this case, the property name for the address Object is missing a closing double quote. After you fix this problem and press the Validate button, JSONLint pretty-prints the JSON document as follows: JSONLint is also available as a Chrome extension in the Chrome Web Store. JSON MODELING Developing valid JSON documents for real applications can be tedious and error-prone. To avoid typographical errors, you can use JSONPad, JSON Editor Online, and JSON Designer to create a logical model (similar to UML) and generate valid JSON documents. JSONPad JSONPad (from http://www.jsonpad.com/en/Home.html) is a GUI tool that eliminates typing JSON text by providing an interface that enables you 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. To create a model, use the green plus key under the text area. The following data types are supported: Key (i.e., Name/Value Pair), Object, and Array. 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 model: 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, and is also available as a Chrome extension. 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 DZone, Inc. | www.dzone.com REST Client Rest Client is a Firefox extension that provides the ability to debug and test RESTful Web Services from the browser. The ability to test from the browser isn’t new, but the output formatting is much more readable. The above example uses the Books service from the Open Library API. After entering the service URI, the Response Body (Highlight) tab shows the JSON output. Pretty Printing with JSONView JSON is not very readable when displayed natively in a browser. JSONView is a Firefox and Chrome extension that pretty-prints JSON. JSONView in Firefox After installing this extension and re-starting Firefox, the JSON response from the Open Library Books service URI is readable, and you can expand/ collapse objects on the page: JSONView in Chrome JSONView is also available as a Chrome extension from the Chrome Web Store: Click on the minus sign to collapse each element, and press the Toggle Collapsed link to show/hide each collapsed element. The JSONView Chrome extension provides a bit more functionality than its Firefox counterpart – it enables a user to search a JSON document using the JSONQuery language. For example, entering ..bib_key in the Query text box displays all the bib_key fields in the text: JSONQuery is one of several technologies that can search JSON documents and return the desired element(s). JSON Beautification with JSON SH JSON SH is a Chrome extension (available in the Google Chrome Web Store) that acts as a pretty-printer and a validator. Paste a valid (but not pretty) JSON document into the text area at the top of the page, and JSON SH beautifies the text into a human-readable format. JSON AND AJAX 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 then logs line 1 of the address to the browser console. Conversely, the JSON.stringify() method converts a JavaScript value to a JSON string (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() { return line1; } 4 Core JSON DZone, Inc. | www.dzone.com public void setLine1(line1) { this.line1 = line1; } // Remaining getters and setters ... } Address addrOut = new Address(); // Call setters to populate addrOut … ObjectMapper mapper = new ObjectMapper(); // Reuse this. // Marshal Address object to JSON String. Writer writer = new StringWriter(); mapper.writeValue(writer, addrOut); System.out.println(writer.toString()); // Unmarshal Address object from JSON String. String addrJsonStr = “{“ + “\”address\” : {“ + “\”line1\” : \”555 Main Street\”,” + “\”city\” : \”Denver\”,” “\”stateOrProvince\” : \”CO\”,” “\”zipOrPostalCode\” : \”80202\”,” + “\”country\” : \”USA\”” + “}” + “}”; Address addrIn = mapper.readValue(addrJsonStr, Address.class); In addition to Jackson, other well-known Java-based JSON APIs include: API Source Google GSON http://code.google.com/p/google-json/ SOJO http://sojo.sourceforge.net/ org.json (by Douglas Crockford) http://www.json.org/java json-lib http://sourceforge.net/projects/json-lib/ json-io http://code.google.com/p/json-io jsontools http://jsontools.berlios.de/ jsonbeans http://code.google.com/p/jsonbeans/ JSON AND RUBY There are many JSON-related libraries for Ruby. Here’s an example using the JSON gem that comes standard with Ruby. require ‘json’ class Address attr_accessor :line1, :city, :state_or_province, :zip_or_postal_code, :country def initialize(line1=’’, city=’’, state_or_province=’’, zip_or_postal_code=’’, country=’’) @line1 = line1 @city = city @state_or_province = state_or_province @zip_or_postal_code = zip_or_postal_code @country = country end def to_json to_hash.to_json end def from_json!(str) JSON.parse(str).each { |var, val| send(“#{var}=”, val) } end private def to_hash Hash[instance_variables.map { |var| [var[1..-1].to_sym, send(var[1..-1])] }] end end The JSON gem’s to_json method converts a String or Hash to JSON. The 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: addr1 = Address.new(‘555 Main Street’, ‘Denver’, ‘CO’, ‘80231’, ‘US’) puts addr1.to_json # Outputs the following … {“line1”:”555 Main Street”,”city”:”Denver”,”state_or_ province”:”CO”,”zip_or_postal_code”:”80231”,”country”:”US”} The JSON gem’s JSON.parse method converts a JSON String to a Hash. The Address object’s from_json! method takes a JSON String, calls JSON.parse to convert to a Hash, and sets each corresponding data member from the Hash as follows: json_addr = < person} end end end The Rails ApplicationController takes care of marshalling/ unmarshalling objects to/from JSON, so there’s no need to write a to_ json method here. JSON SCHEMA 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 RESTful Web Service. JSON Schemas are written in JSON. The main JSON Schema site can be found at: http://json-schema.org. JSON Schema is a work in progress – the JSON Schema team has just 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 DZone, Inc. | www.dzone.com Construct Description type The data type object, array, string, number, etc. $schema The URI that provides the schema version. required true/false id Data element id properties Validation properties for a data element include type (see above), minimum (minimum value), maximum (maximum value), enum, etc. Here is a sample JSON Schema for a portion of an online gift registry: “type”: “object”, “$schema”: “http://json-schema.org/draft-03/schema”, “id”: “#”, “required”: true, “properties”: { “registrants”: { “type”: “array”, “id”: “registrants”, “required”: true, “items”: { “type”: “object”, “required”: false, “properties”: { “address”: { “type”: “object”, “id”: “address”, “required”: true, “properties”: { “city”: { “type”: “string”, “id”: “city”, “required”: true }, “country”: { “type”: “string”, “id”: “country”, “required”: false }, “line1”: { “type”: “string”, “id”: “line1”, “required”: true }, “line2”: { “type”: “string”, “id”: “line2”, “required”: false }, “postalCode”: { “type”: “string”, “id”: “postalCode”, “required”: true }, “premise”: { “type”: “string”, “id”: “premise”, “required”: true, “enum”: [ “work”, “home”, “other” ] }, “stateOrProvince”: { “type”: “string”, “id”: “stateOrProvince”, “required”: true } } }, “firstName”: { “type”: “string”, “id”: “firstName”, “required”: true }, “lastName”: { “type”: “string”, “id”: “lastName”, “required”: true }, “phoneNumber”: { “type”: “object”, “id”: “phoneNumber”, “required”: true, “properties”: { “channel”: { “type”: “string”, “id”: “channel”, “required”: true, “enum”: [ “cell”, “work”, “home” ] }, “number”: { “type”: “string”, “id”: “number”, “required”: true } } } } } } } } The above schema: • Requires an array of registrant objects. • Limits the phoneNumber.channel field to the following values: cell, work, fax, or home. • Limits the address.premise field to these values: home, work, or other. A Web Service consumer could use this schema to validate the following JSON document: { “registrants”: [ { “firstName”: “Fred”, “lastName”: “Smith”, “phoneNumber”: { “channel”: “cell”, “number”: “303-555-1212” }, “address”: { “premise”: “home”, “line1”: “555 Broadway NW”, “line2”: “# 000”, “city”: “Denver”, “stateOrProvince”: “CO”, “postalCode”: “88888”, “country”: “USA” } } ] } JSON Schema Generator Creating a JSON Schema is tedious and error-prone. Use a JSON Schema Generator to generate a Schema from any valid JSON document. Visit the 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. • Choose the JSON Input option • Press the Generate Schema button. JSON Schema Validator An application uses a JSON Schema Validator to ensure that a JSON document conforms to the structure specified by the Schema. JSON Schema Validators are available for most modern programming languages: JSON Schema Validator Language Source JSV JavaScript https://github.com/garycourt/JSV Ruby JSON Schema Validator Ruby https://github.com/hoxworth/json- schema Browse our collection of over 150 Free Cheat Sheets Upcoming Refcardz Free PDF 6 Core JSON DZone, Inc. 150 Preston Executive Dr. Suite 201 Cary, NC 27513 888.678.0399 919.678.0300 Refcardz Feedback Welcome refcardz@dzone.com Sponsorship Opportunities sales@dzone.com Copyright © 2012 DZone, Inc. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by means electronic, mechanical, photocopying, or otherwise, without prior written permission of the publisher. Version 1.0 $7.95 DZone communities deliver over 6 million pages each month to more than 3.3 million software developers, architects and decision makers. DZone offers something for everyone, including news, tutorials, cheat sheets, blogs, feature articles, source code and more. “"DZone is a developer's dream",” says PC Magazine. JSON Schema Validator Language Source json-schema- validator Java https://github.com/fge/json- schema-validator php-json-schema (by MIT) PHP https://github.com/hasbridge/php- 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. Tom Marrs is a Principal Architect at Ciber, where he specializes in Service-Oriented Architecture (SOA) He designs and implements mission-critical web and business applications using the latest SOA, Ruby on Rails, REST, HTML5, JavaScript, Java/EE, and Open Source technologies. Tom is also the author of the upcoming JSON at Work, and a founder of the Denver Open Source User Group (DOSUG) With JavaScript: The Good Parts, you’ll discover a beautiful, elegant, lightweight and highly expressive language that lets you create effective code, whether you’re managing object libraries or just trying to get Ajax to run fast. If you develop sites or applications for the Web, this book is an absolute must. Buy Here. ABOUT THE AUTHORS RECOMMENDED BOOK Debugging Patterns Clean Code Cypher Object-Oriented JS
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