Automatically generating-json-from-java-objects-java-objects268

© 2010 Marty Hall

Automatically
Generating JSON from
Java Objects
Originals of Slides and Source Code for Examples:
http://courses.coreservlets.com/Course Materials/ajax.html
http://courses.coreservlets.com/Course-Materials/ajax.html
Customized Java EE Training: http://courses.coreservlets.com/
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.

© 2010 Marty Hall

For live Ajax & GWT training, see training
courses at http://courses.coreservlets.com/.
t htt // l t /
Taught by the author of Core Servlets and JSP,
More Servlets and JSP and this tutorial. Available at
JSP, tutorial
public venues, or customized versions can be held
on-site at your organization.
•C
Courses d
developed and t
l d d taught b M t H ll
ht 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 1EE Training: http://courses.coreservlets.com/ or survey several
Customized Java library (jQuery, Prototype/Scriptaculous, Ext-JS, Dojo, Google Closure)
• 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
– Other JSON-generation utilities
• Using 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 result
– Disadvantages
• Tedious for complex data structures
• Oft requires knowledge of how server will use data
Often i k l d fh ill d t
• This section: turning Java into JSON
– Advantages
• Can generate complex data easily
• Builds real objects so server can decide what to do
– Di d
Disadvantages
• Requires JSON-specific server software
6 • Sometimes builds objects with unneeded data in them

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
file,
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.

Used in all examples. Available for download at
http://courses.coreservlets.com/Course-Materials/ajax.html
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.
8

Other JSON-Generation
Software
• org.json utilities (used in this tutorial)
– Wid l used
Widely d
• Used within other utilities (e.g., JSON-RPC)
– Limited power
• Alt
Alternatives
ti
– Google Gson
• Better support for generics
• htt // d
http://code.google.com/p/google-gson/
l / / l /
– 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 Code
(Used in All Examples)


Main Bean: City.java
• Constructor
public City(String name, int timeZone, int pop) {
setName(name);
setTimeZone(timeZone);
setPop(pop);
}

• Getter methods
– getName
– getTime, getTimeZone
• Assumes server is in US east coasts subtracts 0-3 hours
coasts, 03
based on time zone
– getPop
• Raw population as an int
– getPopulation
11 • Formatted population as a String with commas

Utilities for Finding Beans:
CityUtils.java
CityUtils 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
Lookup f
functions
ti
public static City getCity(String name) {
name = name.toUpperCase();
return(biggestAmericanCities.get(name));
}

12

Utilities for Finding Beans:
CityUtils.java
CityUtils java Continued
• Map that associates category of cities with
city names
i
private static Map<String,String[]> cityTypeMap;

• Lookup function
public static List<City> findCities(String cityType) {
String[] cityNames = cityTypeMap get(cityType);
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.java
ShowCities java
public abstract class ShowCities extends HttpServlet {
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) {
String cityType = request.getParameter("cityType");
return(CityUtils.findCities(cityType));
}

14

Parent Servlet Class:
ShowCities.java
ShowCities java Continued
public void doPost(HttpServletRequest request,
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
Utilities
• Set normal response headers
– response.setHeader f P
tH d for Pragma and C h C t l
d 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
bean, array,
– 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 Code
public void doPost(HttpServletRequest request,
response.setHeader("Cache-Control", "no-cache");
PrintWriter out = response.getWriter();
SomeBean javaResult = callSomeBusinessLogic(…);
JSONObject jsonResult = new JSONObject(javaResult);
p (j );
out.print(jsonResult);
}

These two lines are the only ones that typically change
from application t application. Oth li
f li ti to li ti Other lines stay exactly as iis.
t tl

18

© 2010 Marty Hall

Turning Java Beans
j
into JSONObject


Turning Beans into JSON
• org.json defines JSONObject
– I toString method builds JSON f
Its S i h d b ild format
• Most important constructor takes a bean
– 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
form getBlah (any return type) or isBlah (boolean return)
• Calls each getter method
• If 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 add properties one at a time with “put”
20

JSONObject from Bean:
Example Code
package coreservlets;

import org.json.*;

public class CityTest1 {
public static void main(String[] args) {
City sf = CityUtils.getCity("San Francisco");
JSONObject fJSON
JSONObj t sfJSON = new JSONObj t( f)
JSONObject(sf);
System.out.println("JSON version of SF is:n" +
sfJSON);
}
}

Note: toString is automatically called when you print an
Object in Java. It is the toString method of JSONObject that
builds the JSON representation.

21

JSONObject from Bean:
Example Result
JSON version of SF is:
{"time": "06:00:55 AM"
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
– new JSONA
JSONArray(javaArrayOrCollection)
(j A O C ll i )
• 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’t
p , y
want to include superclass info
– new JSONArray(javaArrayOrCollection, true)
• 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.*;

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"
AM", 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",
{"time":"08:14:16 AM", "
{"ti " "08 14 16 AM" "name":"Houston",
" "H t "
{"time":"07:14:16 AM", "name":"Phoenix",
"timeZone":-2,"pop":1512986,"population":"1,512,986"}]
"ti Z " 2 " " 1512986 " l ti " "1 512 986"}]


25

© 2010 Marty Hall

Comparing M
C i Manual and
l d
Automatic JSON Generation

26 Developed and taught by well-known author and developer. At public venues or onsite at your location.

Manual Generation: Server Code
(Servlet)
public class ShowCities1 extends ShowCities {
public void outputCities(List<City> cities
cities,
throws ServletException IOException {
ServletException,
request.setAttribute("cities", cities);
String outputPage =
"/WEB-INF/results/cities-json.jsp";
"/WEB INF/ lt / iti j j "
RequestDispatcher dispatcher =
request.getRequestDispatcher(outputPage);
dispatcher.include(request, response);
di t h i l d ( t )
}
}

27

Manual Generation: Server Code
(JSP)
{ headings: ["City", "Time", "Population"],
cities: [["${cities[0] name}" "${cities[0] time}"
[["${cities[0].name}", "${cities[0].time}",
"${cities[0].population}"],
["${cities[1].name}", "${cities[1].time}",
[ ${
[ ] } , ${ [ ] } ,
"${cities[4].population}"]]
}

28

Manual Generation: Client Code
function cityTable1(address, inputField, resultRegion) {
var data = "cityType=" + getValue(inputField);
ajaxPost(address, data,
function(request) {
showCityInfo1(request,
showCityInfo1(request resultRegion);
});
}

• Note:
– ajaxPost shown in previous tutorial section
• Sends data via POST and passes result to handler
function

29

Manual Generation: Client Code
(Continued)
// Data that arrives is JSON object with two properties:
// - 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) &&
(request.status == 200)) {
( t t t
var rawData = request.responseText;
var data = eval("(" + rawData + ")");
var t bl = getTable(data.headings, d t
table tT bl (d t h di data.cities);
iti )
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>
…
/se ect
</select>
<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>
id json city table 1 ></div>
</fieldset>

31

Manual Generation: Results

32

Manual Generation:
Pros and Cons
• Advantages
– Requires no JSON-specific software on server
– Java code is moderately simple
– Client code is simple
• Disadvantages
– JSP 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 p
p y presentation.
• 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)
public void outputCities(List<City> cities
cities,
throws ServletException IOException {
ServletException,
out.println(new JSONArray(cities, false));
}
}

34

Automatic Generation: Server
Code (JSP)
• None!

35

Automatic Generation: Client
Code
function cityTable2(address, inputField, resultRegion) {
var data = "cityType=" + getValue(inputField);
function(request) {
showCityInfo2(request,
showCityInfo2(request resultRegion);
});
}

• Note:
– Only difference from previous example is that result is
passed to showCityInfo2 instead of ShowCityInfo1

36

Automatic Generation: Client
Code (Continued)
// Data that arrives is an array of city objects.
// City objects contain (among other things)
// name, time, and population properties.

function showCityInfo2(request, resultRegion) {
var cities = eval("(" + rawData + ")");
eval( ( ) );
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];
}
var t bl = getTable(headings, rows);
table tT bl (h di )
htmlInsert(resultRegion, table);
}
37
}

Automatic Generation:
HTML 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>
…
/se ect
</select>
<br/>
<input type="button" value="Show Cities"
onclick='cityTable2("show-cities-2", "city-type-2",
/
</form>
<p/>
id json city table 2 ></div>
</fieldset>

38

Automatic Generation: Results

39

Automatic Generation:
Pros and Cons
• Advantages
– Java code i very simple
J d is i l
– No JSP whatsoever
– Server code can adapt to arbitrary number of cities
p 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 it
real
• 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
40
were sent anyway

© 2010 Marty Hall

Turning Java Maps
into JSONObject
j


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 }
foo : getFoo() result", bar : getBar() result"}
– new JSONObject(bean, true)
• Same as above but includes inherited methods
• Oth constructors
Other t t
– new JSONObject(map)
• Map keys become JSON property names
– new JSONObject(string)
42
• Useful when passing JSON to the server

JSONObject from Map:
Example Code

import org.json.*;
import java.util.*;

Map<String,String[]> cities =
M <St i St i []> iti
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 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"],
seco d 5 c t es :
"second-5-cities":
["Philadelphia","San Antonio",
"San Diego","Dallas","San Jose"]}

44

Converting Maps: Server Code
public class ShowCityTypes extends HttpServlet {
public void doGet(HttpServletRequest request
request,
response.setHeader( Cache Control
response setHeader("Cache-Control", "no-cache");
no cache );
JSONObject cityTypes =
new JSONObject(CityUtils.getCityTypeMap());
out.p
out.println(cityTypes);
t (c ty ypes);
}

45

Converting Maps: Server Code
(Continued)
public void doPost(HttpServletRequest request
request,
doGet(request,
doGet(request response);
}
}

46

Converting Maps: Client Code
function cityTypeList(address, resultRegion) {
ajaxPost(address, null,
ajaxPost(address null
function(request) {
showCityTypeInfo(request, resultRegion);
});
}

// Data that arrives is an object where the
// properties are city categories and the
// assoc ated values a e a ays o c ty names.
associated a ues are arrays of city a es.

47

(Continued)
function showCityTypeInfo(request, resultRegion) {
var cityTypes = eval("(" + rawData + ")");
var headings = new Array();
Object property names are city
var row1Entries = new Array(); categories like “top-5-cities”
var i = 0;
for(var cityType in cityTypes) {
headings[i] = cityType;
row1Entries[i] = getBulletedList(cityTypes[cityType]);
i++;
}
var rows = [row1Entries];
var result = getTable(headings, rows); Object property values are
arrays of city names (
y y (cities
htmlInsert(resultRegion, result);
ht lI t( ltR i lt) that match the category)
}
}
48

(Continued)
function getBulletedList(listItems) {
var list = "<ul>n";
for(var i=0; i<listItems.length; i++) {
list = list + " <li>" + listItems[i] + "</li>n";
}
list = list + "</ul>"
return(list);
}

49

Converting Maps:
HTML Code
<fieldset>
<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 Data
from Client to Server


Using JSON.stringify
• Download json2.js
– h //
http://www.json.org/json2.js
j /j 2 j
– 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
json2 js
• Call JSON.stringify on JavaScript object
– Produces string in JSON format representing object
g p g j
• Call escape on result
– URL-encode characters for transmission via HTTP
• S d in POST to client
Send i t li t
– Data might be large, so POST is better than GET
53

Utility Function

function makeJsonString(object) {
return(escape(JSON.stringify(object)));
}

54

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

55

Sending JSON to Server:
Client Code
function randomCityTable(address, resultRegion) {
var data = "cityNames=" +
cityNames=
makeJsonString(getRandomCities());
function(request) {
showCityInfo2(request, resultRegion);
});
}

This is the same showCityInfo2 function used earlier.
Takes an array of city objects and makes HTML table
from their names, times, and populations.

56

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)
function getRandomCities() {
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 Code
<script src="./scripts/ajax-utils.js"
type text/javascript ></script>
type="text/javascript"></script>
<script src="./scripts/json-generation-examples.js"
<script src="./scripts/json2.js"
p p j j
…
<fieldset>
<legend>JSON Data: Sending JSON <i>to</i>
Server</legend>
<form action="#">
<input type="button" value="Show Random Cities"
onclick='randomCityTable("show-cities-3",
</form>
<p/>
59 </fieldset>

Server Code
p
protected List<City> getCities(HttpServletRequest request) {
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> c t es = new ArrayList<City>();
st C ty cities 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) {
return(CityUtils.findCities("top-5-cities"));
}
60
}

Results

61

© 2010 Marty Hall

Wrap-up


Preview of Next Section:
JSON-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
client-side
– Client-side code passes and receives regular arguments
• Passing: no need to escape data or build param strings
g p p g
• Receiving: no need to use responseText or eval
• Simpler server-side code
–S
Server-side code receives and returns regular arguments
id d i d l
• 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)
• 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

Questions?


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