1. Chengyu Sun California State University, Los Angeles
CS5220 Advanced Topics in Web Programming Bits and Pieces of Web Programming
Chengyu Sun
California State University, Los Angeles

2. Roadmap Data binding and conversion Internationalization
Input Validation
Sending
Template engine
View template framework
Logging
File upload and download
Task scheduling and execution
Exception handling
Application deployment

3. Data Binding HTML Form Model Attribute Binding
public class User {
String username;
String password; … }
Usename:
Password:
Add User
Bind form fields to properties of the object

4. What About Properties of Class Type?
HTML Form
Model Attribute
Binding
public class User {
String username;
String password;
User manager; … }
Usename:
Password:
Manager: ??
Add User

5. Use Spring Converters …
Tell the framework how to convert one data type to another
Form fields (String)  Properties (Class)
Example: SpringMVC
TextToUser
UserToText

6. … Use Spring Converters
Configure a Conversion Service bean in <servlet-name>-servlet.xml
For example:
<mvc:annotation-driven conversion-service="conversionService" />
<bean id="conversionService"
class="org.springframework.context.support.ConversionServiceFactoryBean">
<property name="converters">
<set>
<bean class="springmvc.web.converter.TextToUser" />
<bean class="springmvc.web.converter.UserToText" />
</set>
</property>
</bean>

7. Exercise: Dropdown List
Use a dropdown list to select manager in Add/Edit User in SpringMVC
Use <form:select>
Support the case where a user does not have a manager

8. Message Bundles
Separate text messages from application code and put them into their own files
E.g. messages.properties
error.username.required=A username is required.
error.password.short=The password is too short.
error.username.taken=The username {0} is already taken.

9. Advantages of Using Message Bundles
Change text messages without modifying the source code
Internationalization (I18N)
messages.properties
messages_en_US.properties
messages_zh_CN.properties …

10. Using Message Bundles with JSTL
<fmt:setBundle basename="messages" />
<fmt:message key="msg1">
<fmt:param value="Chengyu" />
</fmt:message>
<fmt:message key="msg2" />

11. Using Message Bundles with Spring
Declare a messageSource bean
<spring:message> tag
<spring:message code="msg1"
arguments="Chengyu" />
<spring:message code="msg2" />

12. Input Validation in Spring
Add error messages to the message bundle
Implement a Validator and wire it to the controller
Add a BindingResult parameter to the controller method
Use the validator to validate the model attribute
Return the form view if validation fails
Display errors using <form:errors>

13. Example: Validate Add/Edit User
Both username and password fields cannot be empty
Cannot use an existing username

14. Why Input Validation Seems So Complicated
There may be multiple errors in a form submission
Need to identify which error is caused by which field
Internationalization
Remember the correct fields
Separate validation code from application logic
BindingResult
<form:errors>
Message bundle
Model attribute
and other <form>
tags
Validator

15. Other Validation Options
Server-side vs. Client-side Validation
HTML5 validation
JavaScript validation
E.g.
Commons-validator
Provide both declarative and programmatic validation

16. Commons-Validator Declarative Validation Example
<form name=“fooForm">
<field property=“name“ depends="required">
<arg0 key=“fooForm.definition"/>
</field>
<field property="difficultyLevel"
depends="required, integer">
<arg0 key=“fooForm.difficultyLevel"/>
</form>

17. Commons-Validator Routines
Independent of the declarative validation framework
A set of validators to validate
Date and time
Numeric values, currency
...

18. Email Function in Web Applications
Various notifications, e.g. order, payment, shipment, forum post and reply, account activities, and so on
Advertisement campaigns and product promotions
Password reset …

19. How Email Works SMTP, IMAP, POP Email Server A Email Server B ?? ?? ??
Client A
Client B

20. JavaMail http://www.oracle.com/technetwork/java/javamail/index.html
Maven dependency: javax.mail:mail
Properties props = System.getProperties();
props.put("mail.smtp.host", mailhost);
Session session = Session.getInstance( props );
Message msg = new MimeMessage(session);
...
Transport.send( msg );

21. Set Up a Local Email Server for Testing
hMailServer on Windows -
postfix on Linux -

22. Spring Email Support Mail message classes
Need spring-context-support dependency
Declare a mailSender bean
JavaMailSender interface
See CSNS2 for example
Mail message classes
Simpl Message
No attachment, no special character encoding
Mim Message

23. Use Templates Hello ${user.name},
Your order ${order.number} “${order.name}” has
been shipped. You may track your order at the
following URL
We hope to see you again soon.
Your Online Store

24. Template Engine
A template engine combines templates with data to produce documents
Java template engines
Apache Velocity
FreeMarker -
JSP, Apache Tiles …
There is no fundamental difference between template engines and view technologies, but some are more “lightweight” than others

25. Basic Features of a Template Engine
Template language
Access objects and properties
Basic expression and control flow statements
For example: EL and JSTL for JSP
Support for I18N

26. FreeMarker Basics Data access Expressions Built-ins Directives
E.g. ${user.username}
Expressions
E.g. ${user.age + 1}
Built-ins
Directives
Mostly the
same as EL

27. Built-ins
Built-ins are some pre-defined functions that can be applied on data
Examples
name?length – number of characters in name
id?c – converts a number to a string
lastUpdated?date – use only the date part of a Java Date object

28. The if Directive <#if x == 1> x is 1 <#elseif x == 2>
x is not 1 or 2
</#if>

29. The list Directive <#list users as user> <tr>
<td>${user.id}</td>
<td>${user.name}</td>
</tr>
</#list>

30. Use FreeMarker with Spring
Create a FreeMarker Configuration bean
Inject the bean to where it’s needed
Combine template with data
FreeMarkerTemplateUtils.processTemplateIntoString(
configuration.getTemplate( template ), data );
Name of the template file
A Map of <key,value> passed to the template engine

31. Apache Tiles http://tiles.apache.org/ A template framework for JSP
Similar to Master Page and Razor in ASP.NET
Dependency
org.apache.tiles:tile-jsp

32. The Need for View Templates
page1.jsp
pageN.jsp
Header
Header
Content 1
Content N
Footer
Footer

33. Why JSP <include> Is Not Enough
It breaks HTML syntax, e.g. <html> in header.jsp and </html> in footer.jsp.
It’s difficult to create and manage multiple complex templates.

34. Basic Tiles Usage Template page = JSP + placeholders (i.e. attributes)
<tiles:insertAttribute>
Content (i.e. attribute values): JSP, string, other tiles
Definition: combine template and content
<put-attribute>
Tiles Tag Library

35. A Tiles Example page1.jsp page2.jsp Header Header Content 1 Content 2
Footer
Footer

36. Tiles – Template Page template.jsp Header Footer
<tiles:insertAttribute name=“content” />
Footer

37. Tiles – Content Pages
page1.jsp
page2.jsp
Content 1
Content 2

38. Tiles – Definitions
<definition name=“page1” template=“template.jsp”>
<put-attribute name=“content” value=“page1.jsp” />
</definition>
<definition name=“page2” template=“template.jsp”>
<put-attribute name=“content” value=“page2.jsp” />
</definition>

39. Use Tiles with Spring <servlet-name>-servlet.xml
<bean class="org.springframework.web.servlet.view.tiles3.TilesViewResolver"/>
<bean class="org.springframework.web.servlet.view.tiles3.TilesConfigurer">
<property name="definitions">
<list>
<value>/WEB-INF/tiles.xml</value>
</list>
</property>
</bean>

40. Use Multiple View Resolvers in Spring
The order of view resolvers specified in <servlet-name>-servlet.xml determines the order they will be used to resolve a view
If a view resolver cannot resolve a view, Spring tries the next one
The JSP view resolver (i.e. InternalResourceViewResolver) should always be the last because it never “fails” to resolve a view (404 is considered a valid view).

41. Tiles Usage in CSNS2
WEB-INF/layout for template and header/footer pages
WEB-INF/content for content pages
WEB-INF/tiles.xml for definitions

42. Logging
Recording events happened during software execution, e.g. using print statements to assist debugging
Why do we want to do that when we have GUI debugger??
public void foo() {
System.out.println( “loop started” );
// some code that might get into infinite loop …
System.out.println( “loop finished” ); }

43. Requirements of Good Logging Tools
Minimize performance penalty
Support different log output
Console, file, database, …
Support different message levels
Fatal, error, warn, info, debug, trace
Easy configuration

44. Java Logging Libraries
Logging implementations
Log4j -
java.util.logging in JDK
Logging API
Apache Commons Logging (JCL) -
Simple Logging Façade for Java (SLF4J) -

45. Choose Your Logging Libraries
Log4j
Widely used
Good performance
Rich features
Easy configuration
java.util.logging
Part of JDK, i.e. no extra library dependency
Commons Logging
Determines logging implementation at runtime
SLF4j
Statically linked to a logging implementation
Cleaner design
Better performance
Less problem

46. Using Log4j and SLF4j Library dependencies Coding Configuration
Creating a Logger
Logging statements
Configuration
Output format

47. Log4j Configuration File
log4j.xml or log4j.properties
Appender
Output type
Output format
Logger
Package or class selection
Message level

48. Log4j PatternLayout

49. Logging in CSNS2 src/main/resources/log4j.xml build.properties
app.log.dir
app.log.level
Use of Log Viewer plugin in Eclipse

50. File Upload and Download in Web Applications
Pictures on online albums and social networking sites
Attachments in web forum posts and web s
Resumes on job search sites
Student homework submissions in learning management systems (LMS)
… …

51. File Upload – The Form <form action="FileUploadHandler"
method="post"
enctype="multipart/form-data">
First file: <input type="file" name="file1" /> <br />
Second file: <input type="file" name="file2" /> <br />
<input type="submit" name="upload" value="Upload" />
</form>

52. File Upload – The Request
POST / HTTP/1.1
Host: cs.calstatela.edu:4040
[…]
Cookie: SITESERVER=ID=289f7e a2d7d1e6e44f931195
Content-Type: multipart/form-data; boundary=
Content-Length: 509
Content-Disposition: form-data; name="file1"; filename="test.txt"
Content-Type: text/plain
this is a test file.
Content-Disposition: form-data; name="file2"; filename="test2.txt.gz"
Content-Type: application/x-gzip
?????????UC

53. Apache commons-fileupload
Maven dependency:
commons-fileupload:commons-fileupload
FileItemFactory fileItemFactory = DiskFileItemFactory();
ServletFileUpload fileUpload = new ServletFileUpload( fileItemFactory );
List items = fileUpload.parseRequest( request );
for( Object o : items ) {
FileItem item = (FileItem) items;
if( ! item.isFormFiled() ) {...} }

54. Handle File Upload in Spring
multipartResolver bean
Support multiple request parser libraries
See CSNS2 for example
Add argument of type MultipartFile to the controller method

55. Store Uploaded Files In database On disk Pros and Cons?? BLOB, CLOB
BINARY VARCAR, VARCHAR
On disk
Pros and Cons??

56. File Download Generate an HTTP response directly Understand Java IO
Add an HttpServletResponse argument to the controller method
Return null for view
Understand Java IO
Reader and Writer
InputStream and OutputStream
Use of the Content-Disposition header

57. Examples of Scheduled Tasks
Periodic s, e.g.
Information about weekly sale
Forum daily digests
Member newsletters
Payment reminders
Batch data processing

58. Concepts in Task Scheduling and Execution …
Executor
Use one thread for each task
Use one thread for all tasks
Use a thread pool
Schedule (a.k.a. Trigger)
E.g. every 5 minutes, every day at midnight, every first Sunday of each month at 8am …

59. … Concepts in Task Scheduling and Execution
Scheduler
Task
Schedule/Trigger
Executor

60. Spring Configuration <task> namespace
<task:scheduler id="scheduler" />
<task:executor id="executor"
pool-size="5"/>
<task:annotation-driven
scheduler="scheduler"
executor="executor" />
Creates a scheduler
Creates a thread pool
Based executor
Enables annotations
@Scheduled and
@Async

61. @Scheduled

62. Cron Expression Six field separated by space Seconds (0-59)
Minutes (0-59)
Hours (0-23)
Day of month (1-31)
Month (1-12 or JAN-DEC)
Day of week (1-7 or MON-SUN)

63. Cron Field Values Single value, e.g. 12 Set of values, e.g. 0,15,30,45
Range, e.g. 1-12,MON-FRI,* (first-last)
Range with step, e.g. 1-12/3

64. Cron Expression Examples
Every hour at the beginning
of the hour
0 0 * * * *
0 */10 * * * *
0 0 8 * * MON-FRI
,15 * *
Every 10 minutes
Every weekday at 8AM
Every 1st and 15th of each
month at 1AM

65. Problem with Java Exceptions
Too many checked exceptions
Checked vs. Runtime exceptions
Require lots of boilerplate exception handling code

66. Spring’s Solution to the Exception Problem
Use primarily runtime exceptions
Separate exception handling code into exception handlers

67. Controller Exception Handing in Spring
An Exception Resolver handles all runtime exceptions thrown by controllers
SimpleMappingExceptionResolver maps different exceptions to different views

68. ExceptionResolver in CSNS2
<bean id="exceptionResolver“
class="csns.web.resolver.ExceptionResolver">
<property name="exceptionMappings">
<props>
<prop key="AccessDeniedException">exception/access</prop>
<prop key=“MailException">exception/mail</prop>
</props>
</property>
<property name="defaultErrorView" value="exception/default" />
</bean>
A SimpleMappingExceptionResolver with additional logging.

69. Application Deployment
Deploy Application
Computer for
Development
Server Hosting the
Web Application

70. Directory Structure of a Java Web Application
Application Root Directory
JSPs and static resources
WEB-INF
web.xml
classes
Compiled Java classes
lib
Additional Java libraries

71. WAR Files Web application ARchive
A JAR file for packaging, distributing, and deploying Java web applications
Create WAR files
The command line tool jar
Eclipse Export -> Web -> WAR file
mvn package

72. Deploy WAR Files to a Tomcat Server
Copy the WAR file to the webapps folder
Use the Manager App
Need a user with the manager-gui role
More options at