Code in the Cloud, Programming Google App Engine

306 Pages·2011·3.54 MB·English

by  Mark C. Chu-Carroll

What readers are saying about Code in the Cloud
This is a great book if you want to learn about the cloud and how to
use App Engine. It was nice to see examples in both Python and Java.
Mark does an excellent job of explaining the technologies involved in a
down-to-earth, less-hype–more-facts way that I found engaging. Very
nice read indeed!
Fred Daoud
Author, Stripes:...andJavaWebDevelopmentIsFunAgain
and Getting StartedwithApacheClick
When you think about the distinction between essential and acciden-
tal complexity in web application development, chores like acquiring
server hardware, installing an operating system, and worrying about
how well those infrastructure choices are going to serve your applica-
tion’s needs down the road definitely fall into the latter group. Code
intheCloud explains how developers can use the services provided by
the Google App Engine platform to write highly flexible and scalable
web-based applications without worrying about a lot of the low-level
deployment details that have plagued developers in the past.
Lyle Johnson
Senior Analyst, Sentar Inc.
Compact, well-commented code, and clear explanations—what more
could a new cloud developer want?
Dorothea Salo
University of Wisconsin–Madison
Code in the Cloud
Programming Google App Engine
Mark C. Chu-Carroll
The Pragmatic Bookshelf
Raleigh,NorthCarolina Dallas,Texas
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Version:2011-4-14
Contents
I Getting Started with Google App Engine 9
1 Introduction 10
1.1 What’s Cloud Computing? . . . . . . . . . . . . . . . 10
1.2 Cloud Computing Programming Systems . . . . . . 16
1.3 Acknowledgments . . . . . . . . . . . . . . . . . . . . 19
2 Getting Started 20
2.1 Setting Up a Google App Engine Account . . . . . . 20
2.2 Setting Up Your Development Environment . . . . . 22
2.3 Starting to Program in Python with App Engine . . 25
2.4 Monitoring Your Application . . . . . . . . . . . . . . 32
II Programming Google App Engine with Python 36
3 A First Real Cloud Application 37
3.1 The Basic Chat Application . . . . . . . . . . . . . . 37
3.2 The Basics of HTTP . . . . . . . . . . . . . . . . . . . 41
3.3 Mapping Chat into HTTP . . . . . . . . . . . . . . . . 45
4 Managing Data in the Cloud 53
4.1 Why Didn’t Chat Work?. . . . . . . . . . . . . . . . . 53
4.2 Making Chat Persistent. . . . . . . . . . . . . . . . . 56
5 Google App Engine Services for Login Authentication 65
5.1 Introducing the Users Service . . . . . . . . . . . . . 65
5.2 The Users Service . . . . . . . . . . . . . . . . . . . . 66
5.3 Integrating the Users Service into Chat . . . . . . . 67
6 Organizing Code: Separating UI and Logic 70
6.1 Getting Started with Templates . . . . . . . . . . . . 70
6.2 Building Related Views with Templates . . . . . . . 75
6.3 Multiple Chat Rooms . . . . . . . . . . . . . . . . . . 81
CONTENTS 6
7 Making the UI Pretty: Templates and CSS 87
7.1 Introducing CSS . . . . . . . . . . . . . . . . . . . . . 88
7.2 Styling Text Using CSS . . . . . . . . . . . . . . . . . 89
7.3 Page Layouts Using CSS . . . . . . . . . . . . . . . . 94
7.4 Building Our Interface Using Flowed Layout . . . . 102
7.5 Including CSS Files in App Engine Applications . . 105
8 Getting Interactive 107
8.1 Interactive Web Services: The Basics . . . . . . . . . 107
8.2 The Model-View-Controller Design Pattern . . . . . 110
8.3 Talking to the Server without Disruption . . . . . . 113
8.4 References and Resources . . . . . . . . . . . . . . . 121
III Programming Google App Engine with Java 122
9 Google App Engine and Java 123
9.1 Introducing GWT . . . . . . . . . . . . . . . . . . . . 125
9.2 Getting Started with Java and GWT . . . . . . . . . 127
9.3 RPC in GWT . . . . . . . . . . . . . . . . . . . . . . . 135
9.4 Testing and Deploying with GWT . . . . . . . . . . . 140
10 Managing Server-Side Data 141
10.1 Data Persistence in Java . . . . . . . . . . . . . . . . 141
10.2 Storing Persistent Objects in GWT . . . . . . . . . . 145
10.3 Retrieving Persistent Objects in GWT. . . . . . . . . 149
10.4 Gluing the Client and the Server Together . . . . . . 151
10.5 References and Resources . . . . . . . . . . . . . . . 153
11 Building User Interfaces in Java 154
11.1 Why Use GWT? . . . . . . . . . . . . . . . . . . . . . 154
11.2 Building GWT UIs with Widgets . . . . . . . . . . . . 155
11.3 Making the UI Active: Handling Events . . . . . . . 162
11.4 Making the UI Active: Updating the Display . . . . . 167
11.5 Wrapping Up with GWT . . . . . . . . . . . . . . . . 169
11.6 References and Resources . . . . . . . . . . . . . . . 170
12 Building the Server Side of a Java Application 171
12.1 Filling in Gaps: Supporting Chat Rooms . . . . . . . 171
12.2 Proper Interactive Design: Being Incremental . . . . 176
12.3 Updating the Client . . . . . . . . . . . . . . . . . . . 184
12.4 Chat Administration . . . . . . . . . . . . . . . . . . 185
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12.5 Running and Deploying the Chat Application . . . . 187
12.6 Wrapping Up the Server Side . . . . . . . . . . . . . 189
IV Advanced Google App Engine 190
13 Advanced Datastore: Property Types 191
13.1 Building a Filesystem Service . . . . . . . . . . . . . 191
13.2 Modeling the Filesystem: A First Cut . . . . . . . . . 195
13.3 Property Types Reference. . . . . . . . . . . . . . . . 212
13.4 Wrapping Up Property Types . . . . . . . . . . . . . 215
14 Advanced Datastore: Queries and Indices 216
14.1 Indices and Queries in Datastore . . . . . . . . . . . 217
14.2 More Flexible Models . . . . . . . . . . . . . . . . . . 223
14.3 Transactions, Keys, and Entity Groups . . . . . . . 224
14.4 Policy and Consistency Models . . . . . . . . . . . . 226
14.5 Incremental Retrieval . . . . . . . . . . . . . . . . . . 230
15 Google App Engine Services 232
15.1 The Memcache Service . . . . . . . . . . . . . . . . . 233
15.2 Accessing Other Stuff: The URL Fetch Service . . . 238
15.3 Communicating with People: Mail and Chat Services 239
15.4 Sending and Receiving Email . . . . . . . . . . . . . 243
15.5 Wrapping Up Services . . . . . . . . . . . . . . . . . 246
16 Server Computing in the Cloud 248
16.1 Scheduling Jobs with App Engine Cron . . . . . . . 249
16.2 Running Jobs Dynamically Using the Task Queue . 253
16.3 Wrapping Up Server Computing . . . . . . . . . . . . 259
17 Security in App Engine Services 260
17.1 What Is Security? . . . . . . . . . . . . . . . . . . . . 260
17.2 Basic Security . . . . . . . . . . . . . . . . . . . . . . 261
17.3 Advanced Security . . . . . . . . . . . . . . . . . . . 269
18 Administering Your App Engine Deployment 277
18.1 Monitoring . . . . . . . . . . . . . . . . . . . . . . . . 277
18.2 Peeking at the Datastore . . . . . . . . . . . . . . . . 281
18.3 Logs and Debugging . . . . . . . . . . . . . . . . . . 282
18.4 Managing Your Application . . . . . . . . . . . . . . 284
18.5 Paying for What You Use . . . . . . . . . . . . . . . . 285
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19 Wrapping Up 287
19.1 Cloud Concepts . . . . . . . . . . . . . . . . . . . . . 287
19.2 Google App Engine Concepts . . . . . . . . . . . . . 288
19.3 Where to Go from Here . . . . . . . . . . . . . . . . . 290
19.4 References and Resources . . . . . . . . . . . . . . . 292
Index 293
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Part I
Getting Started with Google
App Engine
Chapter 1
Introduction
Cloud computing is an innovative and exciting style of programming
and using computers. It creates tremendous opportunities for software
developers: cloud computing can provide an amazing new platform for
building new kinds applications. In this chapter, we’ll look at the basic
concepts: what cloud computing is, when and why you should use it,
andwhatkindsofcloud-basedservicesareavailabletoyouasanappli-
cation developer.
1.1 What’s Cloud Computing?
BeforewelookathowtowritecloudprogramswithGoogleAppEngine,
let’s start at the very beginning and ask just what we mean by cloud
computing?Whatisthecloud?Howisitdifferentfromdesktopcomput-
ing or old-fashioned client-server computing? And most importantly,
why should you, as a software developer, care about the cloud? When
should you use it, and what should you use it for?
The Cloud Concept
In the modern world of the Internet and the World Wide Web, there
are thousands upon thousands of computers sitting in data centers,
scattered around the world. We use those computers constantly—for
chatting with other people, sending email, playing games, and reading
and writing blogs. When we’re doing one of these everyday activities,
we’re accessing a program running on a server, using our browser as a
client.
But where is the program actually running? Where is the data? Where
are the servers? They’re somewhere out there, somewhere in some