Json generation

© 2010 Marty Hall
Automatically
Generating JSON from
Java ObjectsJava Objects
Originals of Slides and Source Code for Examples:
http://courses.coreservlets.com/Course-Materials/ajax.html
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Servlets, JSP, JSF 1.x, JSF 2.0, Struts, Ajax, GWT 2.0, GXT, Spring, Hibernate/JPA, Java 5, Java 6.
Developed and taught by well-known author and developer. At public venues or onsite at your location.
http://courses.coreservlets.com/Course Materials/ajax.html
© 2010 Marty Hall
For live Ajax & GWT training, see training
t htt // l t /courses at http://courses.coreservlets.com/.
Taught by the author of Core Servlets and JSP,
More Servlets and JSP and this tutorial Available atMore Servlets and JSP, and this tutorial. Available at
public venues, or customized versions can be held
on-site at your organization.
C d l d d t ht b M t H ll
• Courses developed and taught by Marty Hall
– Java 6, servlets/JSP (intermediate and advanced), Struts, JSF 1.x, JSF 2.0, Ajax, GWT 2.0 (with GXT), custom mix of topics
– Ajax courses can concentrate on 1 library (jQuery, Prototype/Scriptaculous, Ext-JS, Dojo, Google Closure) or survey several
• Courses developed and taught by coreservlets.com experts (edited by Marty)
– Spring, Hibernate/JPA, EJB3, Web Services, Ruby/Rails
Contact hall@coreservlets.com for details

Topics in This Section
• Using org.json Java utilities
– Building JSON object from bean
– Building JSON array from Java array or List
Building JSON object from Map– Building JSON object from Map
– Other JSON-generation utilities
• Using json2.js JavaScript utilitiesUsing json2.js JavaScript utilities
– Sending JSON objects to server
4
© 2010 Marty Hall
Intro and Setup

Using MVC to Build JSON
• Last section: used MVC to build JSON
– Advantages
• Requires no special server software
• You have full control over resultYou have full control over result
– Disadvantages
• Tedious for complex data structures
Oft i k l d f h ill d t• Often requires knowledge of how server will use data
• This section: turning Java into JSON
– AdvantagesAdvantages
• Can generate complex data easily
• Builds real objects so server can decide what to do
Di d– Disadvantages
• Requires JSON-specific server software
• Sometimes builds objects with unneeded data in them6
Installing the org.json.* Utilities
• Download
– http://www.json.org/java/json.zip
• Or start at http://www.json.org/java/ and follow link that
says “Free source code is available”.y
• Install
– Unzip to get org/json/*.java
– Put into src folder of Eclipse
• Create new package org.json, then copy files there
– They do not supply a JAR file but you could easily build– They do not supply a JAR file, but you could easily build
one yourself, then put JAR file in WEB-INF/lib
• Built org.json-utils.jar and put online at coreservlets.com
• Documentation
– http://www.json.org/java/
7

Configuring Eclipse Project
Used only in last example. Available for download at
http://www.json.org/json2.js. You can also get compressed
version; see http://www.json.org/js.html.version; see http://www.json.org/js.html.
Used in all examples. Available for download at
http://courses coreservlets com/Course-Materials/ajax html
8
http://courses.coreservlets.com/Course-Materials/ajax.html
Downloaded latest .java files from http://www.json.org/java/,
compiled, and put resultant .class files in JAR file. Or, you can put
.java files from http://www.json.org/java/ directly in src/org.json.
Other JSON-Generation
SoftwareSoftware
• org.json utilities (used in this tutorial)
Wid l d– Widely used
• Used within other utilities (e.g., JSON-RPC)
– Limited power
Alt ti• Alternatives
– Google Gson
• Better support for generics
htt // d l / / l /• http://code.google.com/p/google-gson/
– JSON Taglib
• More usable directly from JSP
http://json taglib sourceforge net/• http://json-taglib.sourceforge.net/
– VRaptor
• Uses annotations for much of the work
• http://vraptor org/ajax html• http://vraptor.org/ajax.html
– Many more
• See “Java” entry at http://json.org/
9

© 2010 Marty Hall
Supporting Java CodeSupporting Java Code
(Used in All Examples)
Main Bean: City.java
• Constructor
public City(String name, int timeZone, int pop) {
setName(name);
setTimeZone(timeZone);
setPop(pop);setPop(pop);
}
• Getter methods
– getName
– getTime, getTimeZone
• Assumes server is in US east coasts subtracts 0-3 hoursAssumes server is in US east coasts, subtracts 0 3 hours
based on time zone
– getPop
Raw population as an int• Raw population as an int
– getPopulation
• Formatted population as a String with commas11

Utilities for Finding Beans:
CityUtils javaCityUtils.java
• Map that associates city name with City
private static Map<String,City> biggestAmericanCities =
new HashMap<String,City>();
• Populate it with largest US cities
L k f ti• Lookup functions
public static City getCity(String name) {
name = name.toUpperCase();
return(biggestAmericanCities.get(name));
}
12
Utilities for Finding Beans:
CityUtils java ContinuedCityUtils.java Continued
• Map that associates category of cities with
icity names
private static Map<String,String[]> cityTypeMap;
• Lookup function
public static List<City> findCities(String cityType) {
String[] cityNames = cityTypeMap get(cityType);String[] cityNames cityTypeMap.get(cityType);
if (cityNames == null) {
String[] twoCities = { "New York", "Los Angeles" };
cityNames = twoCities;
}
List<City> cities = new ArrayList<City>();
for(String cityName: cityNames) {
cities add(getCity(cityName));cities.add(getCity(cityName));
}
return(cities);
}13

Parent Servlet Class:
ShowCities javaShowCities.java
public abstract class ShowCities extends HttpServlet {
public void doGet(HttpServletRequest request,public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
response.setHeader("Cache-Control", "no-cache");
response.setHeader("Pragma", "no-cache");
response.setContentType("text/javascript");
List<City> cities = getCities(request);
outputCities(cities, request, response);
}
protected List<City> getCities(HttpServletRequest request) {protected List<City> getCities(HttpServletRequest request) {
String cityType = request.getParameter("cityType");
return(CityUtils.findCities(cityType));
}}
14
Parent Servlet Class:
ShowCities java ContinuedShowCities.java Continued
public void doPost(HttpServletRequest request,
HttpServletResponse response)HttpServletResponse response)
doGet(request, response);
}
public abstract void outputCities
(List<City> cities,
HttpServletRequest request,
throws ServletException, IOException;
}}
15

© 2010 Marty Hall
General Approach
Steps for Servlet Using JSON
UtilitiesUtilities
• Set normal response headers
tH d f P d C h C t l– response.setHeader for Pragma and Cache-Control
• Set Content-Type to text/javascript
– response.setContentType("text/javascript");
• Get PrintWriter in normal manner
– PrintWriter out = response.getWriter
• Get result as bean array or Map• Get result as bean, array, or Map
– Call normal business logic code
• Turn Java object into JSONObject
– JSONObject result = new JSONObject(bean);
– JSONArray result = new JSONArray(arrayOfBeans, false);
– JSONObject result = new JSONObject(map);j j ( p)
• Output JSONObject with print
– out.print(result);
17

Steps for Using JSON Utilities:
Sample Servlet CodeSample Servlet Code
public void doPost(HttpServletRequest request,
HttpServletResponse response)HttpServletResponse response)
response.setHeader("Cache-Control", "no-cache");
PrintWriter out = response.getWriter();
SomeBean javaResult = callSomeBusinessLogic(…);
JSONObject jsonResult = new JSONObject(javaResult);
out.print(jsonResult);p (j );
}
These two lines are the only ones that typically change
f li ti t li ti Oth li t tl i
18
from application to application. Other lines stay exactly as is.
© 2010 Marty Hall
Turning Java BeansTurning Java Beans
into JSONObjectj

Turning Beans into JSON
• org.json defines JSONObject
I S i h d b ild JSON f– Its toString method builds JSON format
• Most important constructor takes a bean
– JSONObject json = new JSONObject(myBean);JSONObject json new JSONObject(myBean);
• Second arg of “true” means to include superclass info
– Result
• Uses reflection on myBean to find all public methods of the• Uses reflection on myBean to find all public methods of the
form getBlah (any return type) or isBlah (boolean return)
• Calls each getter method
• If myBean has getFoo and getBar, it builds object of theIf myBean has getFoo and getBar, it builds object of the
form { "foo": "getFoo() result", "bar": "getBar() result"}
• Other capabilities
Can turn Map into JSONObject (keys become properties)– Can turn Map into JSONObject (keys become properties)
– Can add properties one at a time with “put”
20
JSONObject from Bean:
Example CodeExample Code
package coreservlets;
import org.json.*;
public class CityTest1 {public class CityTest1 {
public static void main(String[] args) {
City sf = CityUtils.getCity("San Francisco");
JSONObj t fJSON JSONObj t( f)JSONObject sfJSON = new JSONObject(sf);
System.out.println("JSON version of SF is:n" +
sfJSON);
}
}
21
Note: toString is automatically called when you print an
Object in Java. It is the toString method of JSONObject that
builds the JSON representation.

JSONObject from Bean:
Example ResultExample Result
JSON version of SF is:
{"time": "06:00:55 AM"{"time": "06:00:55 AM",
"name": "San Francisco",
"timeZone": -3,
"pop": 744041,
"population": " 744,041"}
• (White space added for readability)
22
Building Arrays of JSON Info
• org.json defines JSONArray
– Its toString method outputs array in JSON format
• Most important constructors
JSONA (j A O C ll i )– new JSONArray(javaArrayOrCollection)
• Assumes javaArrayOrCollection contains primitives,
Strings, or JSONObjects
– new JSONArray(javaArrayOrCollection, false)
• Assumes javaArrayOrCollection contains beans that
should be converted as in previous section, but you don’tp , y
want to include superclass info
– new JSONArray(javaArrayOrCollection, true)
• Assumes javaArrayOrCollection contains beans that• Assumes javaArrayOrCollection contains beans that
should be converted as in previous section, but you do
want to include superclass info
23

JSONArray: Example Code
import org.json.*;
import java.util.*;
public class CityTest2 {
List<City> biggestUSCities =List<City> biggestUSCities
CityUtils.findCities("top-5-cities");
JSONArray citiesJSON =
new JSONArray(biggestUSCities, false);e JSO ay(b ggestUSC t es, a se);
System.out.println("JSON version of biggest " +
"US cities is:n" +
citiesJSON););
}
}
24
JSONArray: Example Result
JSON version of biggest US cities is:
[{"time":"09:14:16 AM" "name":"New York"[{"time":"09:14:16 AM", "name":"New York",
"timeZone":0,"pop":8250567,"population":"8,250,567"},
{"time":"06:14:16 AM", "name":"Los Angeles",
"timeZone": 3 "pop":3849368 "population":"3 849 368"}"timeZone":-3,"pop":3849368,"population":"3,849,368"},
{"time":"08:14:16 AM", "name":"Chicago",
"timeZone":-1,"pop":2873326,"population":"2,873,326"},
{"ti " "08 14 16 AM" " " "H t "{"time":"08:14:16 AM", "name":"Houston",
"timeZone":-1,"pop":2144491,"population":"2,144,491"},
{"time":"07:14:16 AM", "name":"Phoenix",
"ti Z " 2 " " 1512986 " l ti " "1 512 986"}]"timeZone":-2,"pop":1512986,"population":"1,512,986"}]
• (White space added for readability)(White space added for readability)
25

© 2010 Marty Hall
C i M l dComparing Manual and
Automatic JSON Generation
Developed and taught by well-known author and developer. At public venues or onsite at your location.26
Manual Generation: Server Code
(Servlet)(Servlet)
public class ShowCities1 extends ShowCities {
public void outputCities(List<City> citiespublic void outputCities(List<City> cities,
throws ServletException IOException {throws ServletException, IOException {
request.setAttribute("cities", cities);
String outputPage =
"/WEB INF/ lt / iti j j ""/WEB-INF/results/cities-json.jsp";
RequestDispatcher dispatcher =
request.getRequestDispatcher(outputPage);
di t h i l d ( t )dispatcher.include(request, response);
}
}
27

Manual Generation: Server Code
(JSP)(JSP)
{ headings: ["City", "Time", "Population"],
cities: [["${cities[0] name}" "${cities[0] time}"cities: [["${cities[0].name}", "${cities[0].time}",
"${cities[0].population}"],
["${cities[1].name}", "${cities[1].time}",
["${cities[4].name}", "${cities[4].time}",[ ${ [ ] } , ${ [ ] } ,
"${cities[4].population}"]]
}
28
Manual Generation: Client Code
function cityTable1(address, inputField, resultRegion) {
var data = "cityType=" + getValue(inputField);var data = "cityType=" + getValue(inputField);
ajaxPost(address, data,
function(request) {
showCityInfo1(request resultRegion);showCityInfo1(request, resultRegion);
});
}
• Note:
– ajaxPost shown in previous tutorial sectionajaxPost shown in previous tutorial section
• Sends data via POST and passes result to handler
function
29

Manual Generation: Client Code
(Continued)(Continued)
// Data that arrives is JSON object with two properties:
// headings (an array of strings for the th elements)// - headings (an array of strings for the th elements)
// - cities (an array of array of strings
// matching the heading names)
function showCityInfo1(request, resultRegion) {
if ((request.readyState == 4) &&
( t t t 200)) {(request.status == 200)) {
var rawData = request.responseText;
var data = eval("(" + rawData + ")");
t bl tT bl (d t h di d t iti )var table = getTable(data.headings, data.cities);
htmlInsert(resultRegion, table);
}
}
30
Manual Generation: HTML Code
<fieldset>
<legend>JSON Data: Original MVC Approach</legend>g g pp / g
<form action="#">
<label for="city-type-1">City Type:</label>
<select id="city-type-1">
/<option value="top-5-cities">Largest Five US Cities</option>
<option value="second-5-cities">Second Five US Cities</option>
…
</select>/se ect
<br/>
<input type="button" value="Show Cities"
onclick='cityTable1("show-cities-1", "city-type-1",
/"json-city-table-1")'/>
</form>
<p/>
<div id="json-city-table-1"></div><div id json city table 1 ></div>
</fieldset>
31

Manual Generation: Results
32
Manual Generation:
Pros and ConsPros and Cons
• Advantages
– Requires no JSON-specific software on server
– Java code is moderately simple
Client code is simple– Client code is simple
• Disadvantages
– JSP code is complexJSP code is complex
– JSP code cannot adapt to arbitrary number of cities
• This can be fixed with JSTL – see next tutorial section
– Server code needs to know a lot about how client code
will use results. Server code essentially pre-processed the
data and put it in form ready for presentation.p y p
• If you are going to do that, why bother with data-centric
Ajax? Why not just send HTML table from the server?
33

Automatic Generation: Server
Code (Servlet)Code (Servlet)
public void outputCities(List<City> citiespublic void outputCities(List<City> cities,
throws ServletException IOException {throws ServletException, IOException {
PrintWriter out = response.getWriter();
out.println(new JSONArray(cities, false));
}}
}
34
Automatic Generation: Server
Code (JSP)Code (JSP)
• None!
35

Automatic Generation: Client
CodeCode
function cityTable2(address, inputField, resultRegion) {
var data = "cityType=" + getValue(inputField);var data = "cityType=" + getValue(inputField);
function(request) {
showCityInfo2(request resultRegion);showCityInfo2(request, resultRegion);
});
}
• Note:
– Only difference from previous example is that result isOnly difference from previous example is that result is
passed to showCityInfo2 instead of ShowCityInfo1
36
Automatic Generation: Client
Code (Continued)Code (Continued)
// Data that arrives is an array of city objects.
// City objects contain (among other things)// City objects contain (among other things)
// name, time, and population properties.
function showCityInfo2(request, resultRegion) {
if ((request.readyState == 4) &&
(request.status == 200)) {
var cities = eval("(" + rawData + ")");var cities = eval( ( + rawData + ) );
var headings = ["City", "Time", "Population"];
var rows = new Array();
for(var i=0; i<cities.length; i++) {
var city = cities[i];
rows[i] = [city.name, city.time, city.population];
}
t bl tT bl (h di )var table = getTable(headings, rows);
htmlInsert(resultRegion, table);
}
}37

Automatic Generation:
HTML CodeHTML Code
<fieldset>
<legend>JSON Data: Automatic Conversion of Lists</legend>g / g
<form action="#">
<label for="city-type-2">City Type:</label>
<select id="city-type-2">
/<option value="top-5-cities">Largest Five US Cities</option>
<option value="second-5-cities">Second Five US Cities</option>
…
</select>/se ect
<br/>
<input type="button" value="Show Cities"
onclick='cityTable2("show-cities-2", "city-type-2",
/"json-city-table-2")'/>
</form>
<p/>
<div id="json-city-table-2"></div><div id json city table 2 ></div>
</fieldset>
38
Automatic Generation: Results
39

Automatic Generation:
Pros and ConsPros and Cons
• Advantages
J d i i l– Java code is very simple
– No JSP whatsoever
– Server code can adapt to arbitrary number of citiesp y
– Server code does not need to know how client code will
use the result
– Client code has “real” data so can do logic based on itClient code has real data so can do logic based on it
• Disadvantages
– Requires JSON-specific software on server
– Client code is more complex
• It needs to extract data from objects before sending it to
table-building function
– Extra fields were sent
• Client did not use timeZone and pop properties, but they
were sent anyway40
© 2010 Marty Hall
Turning Java MapsTurning Java Maps
into JSONObjectj

Building JSONObject from Map
• Most important JSONObject constructors
– new JSONObject(bean)
• Uses reflection on myBean to find all public methods of the
form getBlah (any return type) or isBlah (boolean return)g ( y yp ) ( )
• Calls each getter method
• If myBean has getFoo and getBar, it builds object of the
form { "foo": "getFoo() result", "bar": "getBar() result"}form { foo : getFoo() result , bar : getBar() result }
– new JSONObject(bean, true)
• Same as above but includes inherited methods
Oth t t• Other constructors
– new JSONObject(map)
• Map keys become JSON property namesMap keys become JSON property names
– new JSONObject(string)
• Useful when passing JSON to the server42
JSONObject from Map:
Example CodeExample Code
import org.json.*;
import java.util.*;
public class CityTest3 {
M <St i St i []> itiMap<String,String[]> cities =
CityUtils.getCityTypeMap();
JSONObject citiesJSON =
( )new JSONObject(cities);
System.out.println("JSON version of map of " +
"US cities is:n" +
citiesJSON);
}
}43

JSONObject from Map:
Example ResultExample Result
JSON version of map of US cities is:
{"superbowl-hosts":{ superbowl hosts :
["Phoenix","Miami",
"Detroit","Jacksonville","Houston"],
"top-5-cities":top 5 cities :
["New York","Los Angeles",
"Chicago","Houston","Phoenix"],
"cities-starting-with-s":cities starting with s :
["San Antonio","San Diego",
"San Jose","San Francisco","Seattle"],
"second-5-cities":seco d 5 c t es :
["Philadelphia","San Antonio",
"San Diego","Dallas","San Jose"]}
• (White space added for readability)
44
Converting Maps: Server Code
public class ShowCityTypes extends HttpServlet {
public void doGet(HttpServletRequest requestpublic void doGet(HttpServletRequest request,
response setHeader("Cache-Control" "no-cache");response.setHeader( Cache Control , no cache );
PrintWriter out = response.getWriter();PrintWriter out response.getWriter();
JSONObject cityTypes =
new JSONObject(CityUtils.getCityTypeMap());
out.println(cityTypes);out.p t (c ty ypes);
}
45

Converting Maps: Server Code
public void doPost(HttpServletRequest requestpublic void doPost(HttpServletRequest request,
doGet(request response);doGet(request, response);
}
}
46
Converting Maps: Client Code
function cityTypeList(address, resultRegion) {
ajaxPost(address nullajaxPost(address, null,
function(request) {
showCityTypeInfo(request, resultRegion);
});});
}
// Data that arrives is an object where the
// properties are city categories and the
// associated values are arrays of city names.// assoc ated a ues a e a ays o c ty a es.
47

Converting Maps:
HTML CodeHTML Code
<fieldset>
<legend>JSON Data: Automatic Conversion of Maps</legend><legend>JSON Data: Automatic Conversion of Maps</legend>
<form action="#">
<input type="button" value="Show City Types"
onclick='cityTypeList("show-city-types",onclick cityTypeList( show city types ,
"city-types")'/>
</form>
<p/>p/
<div id="city-types"></div>
</fieldset>
50
Converting Maps: Results
51

© 2010 Marty Hall
Sending JSON DataSending JSON Data
from Client to Server
Using JSON.stringify
• Download json2.js
h // j /j 2 j– http://www.json.org/json2.js
– Or, start at http://www.json.org/js.html and follow links
at bottom of page
• Install in your project
– E.g., in Eclipse, drop in WebContent/scripts
Load json2 js in your HTML file– Load json2.js in your HTML file
• Call JSON.stringify on JavaScript object
– Produces string in JSON format representing objectg p g j
• Call escape on result
– URL-encode characters for transmission via HTTP
S d i POST t li t• Send in POST to client
– Data might be large, so POST is better than GET
53

Utility Function
function makeJsonString(object) {function makeJsonString(object) {
return(escape(JSON.stringify(object)));
}
54
Receiving JSON Objects on
ServerServer
• Pass string to JSONObject or JSONArray
constructor
– String jsonString = request.getParameter(…);
JSONArray myArray = new JSONArray(jsonString);– JSONArray myArray = new JSONArray(jsonString);
• Access elements with getBlah methods
– PrimitivesPrimitives
• getInt, getDouble, getString, getBoolean, isNull
• double d = myArray.getDouble(0);
S d t k th t th t ill b t f li t– Server needs to know the types that will be sent from client
– High-level
• getJSONObject, getJSONArray
55

Sending JSON to Server:
Client CodeClient Code
function randomCityTable(address, resultRegion) {
var data = "cityNames=" +var data = cityNames= +
makeJsonString(getRandomCities());
function(request) {function(request) {
showCityInfo2(request, resultRegion);
});
}}
This is the same showCityInfo2 function used earlier.
Takes an array of city objects and makes HTML tableTakes an array of city objects and makes HTML table
from their names, times, and populations.
56
Client Code (Continued)Client Code (Continued)
var cityNames =
["New York", "Los Angeles", "Chicago", "Houston",[ New York , Los Angeles , Chicago , Houston ,
"Phoenix", "Philadelphia", "San Antonio", "San Diego",
"Dallas", "San Jose", "Detroit", "Jacksonville",
"Indianapolis", "San Francisco", "Columbus", "Austin",p , , , ,
"Memphis", "Fort Worth", "Baltimore", "Charlotte",
"El Paso", "Milwaukeee", "Boston", "Seattle",
"Washington DC", "Denver", "Louisville", "Las Vegas",
"Nashville", "Oklahoma City", "Miami"];
57

Client Code (Continued)Client Code (Continued)
function getRandomCities() {
var randomCities = new Array();var randomCities new Array();
var j = 0;
for(var i=0; i<cityNames.length; i++) {
if(Math.random() < 0.25) {( () ) {
randomCities[j++] = cityNames[i];
}
}
return(randomCities);
}
58
HTML CodeHTML Code
<script src="./scripts/ajax-utils.js"
type="text/javascript"></script>type text/javascript ></script>
<script src="./scripts/json-generation-examples.js"
type="text/javascript"></script>
<script src="./scripts/json2.js"p p j j
type="text/javascript"></script>
…
<fieldset>
<legend>JSON Data: Sending JSON <i>to</i>
Server</legend>
<form action="#">
<input type="button" value="Show Random Cities"<input type="button" value="Show Random Cities"
onclick='randomCityTable("show-cities-3",
"json-city-table-3")'/>
</form></form>
<p/>
<div id="json-city-table-3"></div>
</fieldset>59

Server CodeServer Code
protected List<City> getCities(HttpServletRequest request) {p y g ( p q q ) {
String cityNames = request.getParameter("cityNames");
if ((cityNames == null) || (cityNames.trim().equals(""))) {
cityNames = "['New York', 'Los Angeles]";
}
try {
JSONArray jsonCityNames = new JSONArray(cityNames);
List<City> cities = new ArrayList<City>();st C ty c t es e ay st C ty ();
for(int i=0; i<jsonCityNames.length(); i++) {
City city =
CityUtils.getCityOrDefault(jsonCityNames.getString(i));
cities.add(city);
}
return(cities);
} catch(JSONException jse) {} catch(JSONException jse) {
return(CityUtils.findCities("top-5-cities"));
}
}60
ResultsResults
61

© 2010 Marty Hall
Wrap-up
Preview of Next Section:
JSON-RPCJSON-RPC
• Simpler designation of server-side resource
– Client-side code acts as if it is calling a server-side
function (not a URL)
• Simpler client side code• Simpler client-side code
– Client-side code passes and receives regular arguments
• Passing: no need to escape data or build param stringsg p p g
• Receiving: no need to use responseText or eval
• Simpler server-side code
S id d i d l– Server-side code receives and returns regular arguments
• Receiving: no need to call request.getParamter & convert
• Returning: results automatically converted with
JSONObject and JSONArray
63

Summary
• Building JSON from Java
– new JSONObject(bean)
– new JSONArray(arrayOrCollectionOfBeans, false)
new JSONObject(map)– new JSONObject(map)
• Outputting JSON String
– myJSONObject toString() myJSONArray toString()myJSONObject.toString(), myJSONArray.toString()
• When you do out.print, toString is invoked automatically
• Sending JSON to server
– escape(JSON.stringify(javaScriptObject))
• Receiving JSON on server
– new JSONObject(string) or new JSONArray(string)
– myArray.getString(i), myArray.getDouble(i), etc.
64
© 2010 Marty Hall
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Json generation

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