advanced web technology 13) google web toolkits 2 - gwt ... · advanced web technology 13) google...

Advanced Web Technology13) Google Web Toolkits 2 -GWT, Communication

Emmanuel BenoistFall Term 2016-17

Berner Fachhochschule | Haute cole spcialise bernoise | Berne University of Applied Sciences 1

Table of Contents

� InternationalizationStatic String i18n

� Remote Procedure Code

� JSON


Internationalization


Internationalization : I18N ModuleCore types related to internationalization:

LocaleInfo Provides information about the current locale.

Constants Useful for localizing typed constant values

Messages Useful for localizing messages requiring arguments

ConstantsWithLookup Like Constants but with extra lookupflexibility for highly data-driven applications

Dictionary Useful when adding a GWT module to existinglocalized web pages

Localizable Useful for localizing algorithms encapsulated ina class or when the classes above don’t provide sufficientcontrol

DateTimeFormat Formatting dates as strings. See the sectionon date and number formatting.

NumberFormat Formatting numbers as strings. See thesection on date and number formatting.


Static String i18n


Interantionalizing StringsImplement the Constant Interface

Contains only static stringsVery efficient and compiled once.

Implement the Messages InterfaceAllows to insert values in the stringFor instance numbers or datesEquivalent to the resource bundle in applications.

Dynamic String InternationalizationThe Dictionary class lets your GWT application consumestrings supplied by the host HTML page.Convenient if your existing web server has a localizationsystem that you do not wish to integrate with the static stringinternationalization methods.

Implement the Localizable InterfaceThe most powerful techniqueallows you to go beyond simple string substitutioncreate localized versions of custom types.


Implement the Constants Interface

Create the StockWatcherConstants interfaceUses annotations for the default translationImplements the Constant interface (GWT)Bound automatically to theStockWatcherConstants*.properties files

The java file must contain one method for each of theconstants in the properties files

The right value is found at runtime, corresponding to the locale


Example: the Constants filepackage com.google.gwt.sample.stockwatcher.client;import com.google.gwt.i18n.client.Constants;public interface StockWatcherConstants extends Constants {

@DefaultStringValue(”StockWatcher”)String stockWatcher();@DefaultStringValue(”Symbol”)String symbol();@DefaultStringValue(”Price”)String price();@DefaultStringValue(”Change”)String change();@DefaultStringValue(”Remove”)String remove();@DefaultStringValue(”Add”)String add();}


Translate it to German

Create a file StockWatcherConstants de.properties

stockWatcher = Aktienbeobachtersymbol = Symbolprice = Kurs

change = Anderungremove = Entfernenadd = Hinzufugen


Implement the Messages interface

For Strings containing informationSimilar to resource bundles in JavaCan contain strings with parameters

’’{0}’’ ist kein gultiges Aktiensymbol.

The number is a place holder

myString = First parm is {0}, second parm is {1}, third ↘

→parm is {2}.Usefull for integrating dates, prices, internationalizedresults

I Usefull but less efficient. The strings must be produced atruntime


Messages file

package com.google.gwt.sample.stockwatcher.client;

import com.google.gwt.i18n.client.Messages;

import java.util.Date;

public interface StockWatcherMessages extends Messages {@DefaultMessage(”’’{0}’’ is not a valid symbol.”)String invalidSymbol(String symbol);

@DefaultMessage(”Last update: {0,date,medium} {0,time,↘→medium}”)String lastUpdate(Date timestamp);

}


The corresponding properties file

StockWatcherMessages de.properties file.

lastUpdate = Letzte Aktualisierung: {0,date,medium} {0,time,↘→medium}invalidSymbol = ’’{0}’’ ist kein gultiges Aktiensymbol.


Replace content

Replace the texts with place holders

<body><img src=”images/GoogleCode.png”/><h1 id=”appTitle”></h1>

Replacing strings set programmaticallyCreate the instances of the classes (internationalized)

private ArrayList<String> stocks = new ArrayList<String>();private StockWatcherConstants constants = GWT.create(↘→StockWatcherConstants.class);private StockWatcherMessages messages = GWT.create(↘→StockWatcherMessages.class);


Replace content (Cont)

Set the content:

// Set the window title, the header text, and the Add button ↘

→text.Window.setTitle(constants.stockWatcher());RootPanel.get(”appTitle”).add(new Label(constants.↘→stockWatcher()));addStockButton = new Button(constants.add());// Create table for stock data.stocksFlexTable.setText(0, 0, constants.symbol());stocksFlexTable.setText(0, 1, constants.price());stocksFlexTable.setText(0, 2, constants.change());stocksFlexTable.setText(0, 3, constants.remove());


Add a supported locale:

Inside StockWatcher.gwt.xml add the property

<entry−point class=’com.google.gwt.sample.↘→stockwatcher.client.StockWatcher’/>

<extend−property name=”locale” values=”de”/></module>

Load the german version by adding &locale=de


Client Server Communication

Remote Procedure CodeFrom Java To JavaSupported by the languageOptimized and easy to test

JSONFor communicating with the same server

JSONPFor cross server communicationOvergoes the Same Origin Policy


Remote Procedure Code


GWT Remote Procedure CallRPC contains:

the service that runs on the serverthe method you are calling

the client code that invokes the service

the Java data objects that pass between the client andserver

Both (client and server) must serialize and deserialize theobjects

You need to write three componentsDefine the interface StockPriceService that extendsRemoteService and lists all your RPC methodsCreate a class StockPriceServiceImpl that extendsRemoteServiceServlet and implements the interface youcreated above.Define an asynchronous interface StockPriceServiceAsync

to your service to be called from the client-side code.


GWT Remote Procedure Call1

1Source: code.google.comBerner Fachhochschule | Haute cole spcialise bernoise | Berne University of Applied Sciences 19

StockPriceService interface

In the packagecom.google.gwt.sample.stockwatcher.client


import com.google.gwt.user.client.rpc.RemoteService;import com.google.gwt.user.client.rpc.↘→RemoteServiceRelativePath;

@RemoteServiceRelativePath(”stockPrices”)public interface StockPriceService extends RemoteService {

StockPrice[] getPrices(String[] symbols);}


StockPriceServiceImpl classpackage com.google.gwt.sample.stockwatcher.server;import com.google.gwt.sample.stockwatcher.client.StockPrice;import com.google.gwt.sample.stockwatcher.client.StockPriceService;import com.google.gwt.user.server.rpc.RemoteServiceServlet;import java.util.Random;public class StockPriceServiceImpl extends RemoteServiceServlet implements↘→ StockPriceService {

private static final double MAX PRICE = 100.0; // $100.00private static final double MAX PRICE CHANGE = 0.02; // +/− 2%public StockPrice[] getPrices(String[] symbols) {

Random rnd = new Random();StockPrice[] prices = new StockPrice[symbols.length];for (int i=0; i<symbols.length; i++) {

double price = rnd.nextDouble() ∗ MAX PRICE;double change = price ∗ MAX PRICE CHANGE ∗ (rnd.nextDouble() ↘

→∗ 2f − 1f);prices[i] = new StockPrice(symbols[i], price, change);}return prices;}}Berner Fachhochschule | Haute cole spcialise bernoise | Berne University of Applied Sciences 21

Include the server-side code in theGWT moduleDefine new servlets in the web.xml

<web−app><welcome−file−list>

<welcome−file>StockWatcher.html</welcome−file></welcome−file−list><servlet>

<servlet−name>stockPriceServiceImpl</servlet−name><servlet−class>com.google.gwt.sample.stockwatcher.server.↘→StockPriceServiceImpl</servlet−class>

</servlet><servlet−mapping><servlet−name>stockPriceServiceImpl</servlet−name><url−pattern>/stockwatcher/stockPrices</url−pattern>

</servlet−mapping></web−app>


Invoking the service from the client

Making asynchronous calls to the server


import com.google.gwt.user.client.rpc.AsyncCallback;

public interface StockPriceServiceAsync {

void getPrices(String[] symbols, AsyncCallback<StockPrice[]>↘

→ callback);

}


Making the remote procedure callprivate void refreshWatchList() {

// Initialize the service proxy.if (stockPriceSvc == null) {

stockPriceSvc = GWT.create(StockPriceService.class);}// Set up the callback object.AsyncCallback<StockPrice[]> callback = new AsyncCallback<↘

→StockPrice[]>() {public void onFailure(Throwable caught) {// TODO: Do something with errors.}public void onSuccess(StockPrice[] result) {

updateTable(result);}};// Make the call to the stock price service.stockPriceSvc.getPrices(stocks.toArray(new String[0]), callback);}


Serializing Java objects

GWT RPC requires that all service method parametersand return types be serializable.


import java.io.Serializable;

public class StockPrice implements Serializable {

private String symbol;private double price;private double change;

...


JSON


Retrieving JSON DataJSON stands for JavaScript Object Notation

Language independant formatVery light

Example

[{

”symbol”: ”ABC”,”price”: 87.86,”change”: −0.41},{

”symbol”: ”DEF”,”price”: 62.79,”change”: 0.49}

]Berner Fachhochschule | Haute cole spcialise bernoise | Berne University of Applied Sciences 27

Server part

JSON can be generated by a servlet

out.println(” {”);out.print(” \”symbol\”: \””);out.print(stockSymbol);out.println(”\”,”);out.print(” \”price\”: ”);out.print(price);out.println(’,’);out.print(” \”change\”: ”);out.println(change);out.println(” },”);


JSON generated by PHP<?php

header(’Content−Type: text/javascript’);define(”MAX PRICE”, 100.0); // $100.00define(”MAX PRICE CHANGE”, 0.02); // +/− 2%echo ’[’;$q = trim($ GET[’q’]);if ($q) {

$symbols = explode(’ ’, $q);for ($i=0; $i<count($symbols); $i++) {

$price = lcg value() ∗ MAX PRICE;$change = $price ∗ MAX PRICE CHANGE ∗ (lcg value() ∗ 2.0 − ↘

→1.0);echo ’{’;echo ”\”symbol\”:\”$symbols[$i]\”,”;echo ”\”price\”:$price,”;echo ”\”change\”:$change”;echo ’}’;if ($i < (count($symbols) − 1)) {

echo ’,’;}}}echo ’]’;

?>


Transform JSON object intoJavaScript

use the built in JavaScript function eval

The function will receive a response.getText() as aparameter

private final native JsArray<StockData> asArrayOfStockData(↘→String json) /∗−{

return eval(json);}−∗/;


Manipulate JSON objects

Create a JavaScriptObject StockData to manipulate the data inputin Java

package com.google.gwt.sample.stockwatcher.client;import com.google.gwt.core.client.JavaScriptObject;class StockData extends JavaScriptObject {// Overlay types always have protected, zero argument constructors.protected StockData() {}// JSNI methods to get stock data.public final native String getSymbol() /∗−{ return this.symbol; }−∗/;public final native double getPrice() /∗−{ return this.price; }−∗/;public final native double getChange() /∗−{ return this.change; }−∗/;// Non−JSNI method to return change percentage.public final double getChangePercent() {

return 100.0 ∗ getChange() / getPrice();}}


Connect the Web serverPrepare the list of stocks

private void refreshWatchList() {if (stocks.size() == 0) {

return;}String url = JSON URL;// Append watch list stock symbols to query URL.Iterator iter = stocks.iterator();while (iter.hasNext()) {

url += iter.next();if (iter.hasNext()) {

url += ”+”;}}url = URL.encode(url);// TODO Send request to server and handle errors.}


Connect the Web Server (Cont.)

// Send request to server and catch any errors.RequestBuilder builder = new RequestBuilder(RequestBuilder.GET, url);try {

Request request = builder.sendRequest(null, new RequestCallback() {public void onError(Request request, Throwable exception) {

displayError(”Couldn’t retrieve JSON”);}public void onResponseReceived(Request request, Response response↘→) {

if (200 == response.getStatusCode()) {updateTable(asArrayOfStockData(response.getText()));} else {

displayError(”Couldn’t retrieve JSON (” + response.↘→getStatusText()

+ ”)”); } } });} catch (RequestException e) {

displayError(”Couldn’t retrieve JSON”);}


Conclusion GWT

Google Web ToolkitsOne Application = one languageDevelopment in JavaScript is made easyClient Server Communication is hidden

Security IssuesCommunication is bluredWhat is tested where?Who does what?


Conclusion AWTJava on a Server

Servlet : for small programms (alternative to PHP)Java Server Faces : For large programms with a huge Middletier

Web SecurityVery important to test and validate inputsEncode outputsVerify everythingDo not allow access to your intern kitchen to attackersRemove error messages

GWTOnly one language from the client to the server

Quality Management

Can you please fill out the given questionnairePurely informative, for my use only


References

Google Codehttp://code.google.com/intl/fr-FR/webtoolkit/

overview.html

Tutorial for Client Server communicationhttp://code.google.com/intl/fr-FR/webtoolkit/doc/

latest/tutorial/clientserver.html


http://code.google.com/intl/fr-FR/webtoolkit/overview.html

http://code.google.com/intl/fr-FR/webtoolkit/overview.html

http://code.google.com/intl/fr-FR/webtoolkit/doc/latest/tutorial/clientserver.html

http://code.google.com/intl/fr-FR/webtoolkit/doc/latest/tutorial/clientserver.html

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