Going Offline with Gears And GWT

Going Offline With GWT and Gears

Tom Peck

AppEngines, LLC

Why?

Web apps are great ... if you can connect

Planes

Trains

Automobiles

Users may not want their data in the cloud

Increase response time for online apps

How? GWT - Google Web Toolkit Google Gears

Google Web Toolkit

Write AJAX Applications in Java

Google Web Toolkit

Program in Java, compile to JavaScript

JavaScript is highly optimized

Programming model similar to Swing

RPC mechanism for calling server

Debug web apps in Eclipse

http://code.google.com/webtoolkit

http://code.google.com/p/gwt-google-apis/

Google Gears

Browser Plugin (FireFox, Internet Explorer)

http://gears.google.com

Features:

LocalServer (“programmable cache”)

SQLite Database

Worker Threads for JavaScript

Take Your App Offline

Manifest file of your app’s resources

Download resources

Create database schema

Go

Manifest File { "betaManifestVersion": 1, "version": "Version 1.0", "entries": [ { "url": "7EEF8FB6BA93DAAD0AB9A64C6D6471FE.cache.html" }, { "url": "7EEF8FB6BA93DAAD0AB9A64C6D6471FE.cache.js" }, { "url": "7EEF8FB6BA93DAAD0AB9A64C6D6471FE.cache.xml" }, { "url": "87AA9AB2FB06214DC10C32E7B35C5F6A.cache.html" }, { "url": "87AA9AB2FB06214DC10C32E7B35C5F6A.cache.js" }, { "url": "87AA9AB2FB06214DC10C32E7B35C5F6A.cache.xml" }, { "url": "884D363F8887607F5180653AA6B10E6D.cache.html" }, { "url": "884D363F8887607F5180653AA6B10E6D.cache.js" }, { "url": "884D363F8887607F5180653AA6B10E6D.cache.xml" }, { "url": "com.company.CompanyApp.nocache.js" }, { "url": "gears_init.js" }, { "url": "gwt.js" }, { "url": "CompanyApp.html" }, { "url": "default.css" }, { "url": "logo1.png" }, ] }

Load Resources LocalServer localServer = new LocalServer();ManagedResourceStore managedRS = localServer.createManagedResourceStore("CompanyApp"); managedRS.setManifestURL(" http://company.com/manifest.json "); managedR.checkForUpdate(); new Timer() { public void run() { switch (managedResourceStore.getUpdateStatus()) { case ManagedResourceStore.UPDATE_OK: statusLabel.setText("Ready for offline access"); break ; case ManagedResourceStore.UPDATE_CHECKING: case ManagedResourceStore.UPDATE_DOWNLOADING: schedule(500); break ; case ManagedResourceStore.UPDATE_FAILED: statusLabel.setText("Unable to go offline); break ; } } }.schedule(500);

Gears Database

Uses SQLite

Simplified SQL syntax

http://sqlite.org

Create Database

“create table if not exists person (id integer, first_name text, last_name text)”

Datatypes: Integer, Real, Text, Blob

Constraints: “primary key”, “not null”, “unique”, etc.

Create Database private Database m_database = null; try { m_database = new Database(“Test”); ResultSet rs = m_database.execute(“create table...”); rs.close(); } // try catch (Exception e) { // Gears not installed } // catch

Queries String sql = “select id, first_name, last_name from person”; ResultSet rs = m_database.execute(sql); ArrayList results = new ArrayList(); while (rs.isValidRow()) { PersonBean person = new PersonBean(); person.setID(rs.getFieldAsInt(0)); person.setFirstName(rs.getFieldAsString(1)); person.setLastName(rs.getFieldAsString(2)); results.add(person); rs.next(); } // while rs.close();

Insert, Update String args[] = new String[3]; args[0] = Integer.toString(person.getID()); args[1] = person.getFirstName(); args[2] = person.getLastName();ResultSet rs = m_database.execute(“insert into person (id, first_name, last_name) values (?,?,?)”, args); rs.close(); args = new String[3]; args[0] = person.getFirstName(); args[1] = person.getLastName();args[2] = Integer.toString(person.getID()); rs = m_database.execute(“update person set first_name=?, last_name=? where id=?)”, args); rs.close();

Demo

Demo Source Code