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Struts2 course chapter 19: Decorating Struts2 with Tiles

2010-02-27T00:43:00.012-05:00

In this presentation the topic of decorating Struts2 websites with Apache Tiles is covered. Apache Tiles is a framework built to simplify the development of web application through the use of templates. With Tiles authors can define page fragments which can be assembled into a complete page at runtime. These fragments, called tiles, can be used as simple includes in order to reduce the duplication of common page elements or embedded within other tiles to develop a series of reusable templates. These templates allow the development of a consistent look and feel for an entire application. The integration between Apcahe Tiles and Struts can be difficult and in the slide the details of the configuration are explained. In addition, a working example is presented.

Struts2 course chapter 19: Decorating Struts2 with Tiles

Download the eclipse project with the example of the slide from the following location:

Struts2 Course chapter 19: Decorating Struts2 with Tiles code

Struts2 course chapter 18: Decorating Struts2 with SiteMesh

2010-02-26T20:22:00.014-05:00

In this presentation the topic of decorating Struts2 websites with SiteMesh will be covered. SiteMesh is a framework for web-page layout and decoration as well as for web-application integration. This framework helps to the creation of large sites consisting of many pages for which a consistent look/feel, navigation and layout scheme is required. The integration of SiteMesh and Struts2 can be tricky so all the deails of the configuration will be covered.

Struts2 course chapter 18: Decorating Struts2 with SiteMesh

Download the eclipse projects with the examples of the slide from the following locations:

Struts2 course chapter 18: Decorating Struts2 with SiteMesh code example

'Struts2 Course chapter 17: The Execute and Wait Interceptor

2010-01-07T23:04:00.011-05:00

The Execute And Wait interceptor is useful for running time consuming process in the background while showing the user some feedback with a progress meter. This also prevents the HTTP request from timing out when the action takes more than 5 or 10 minutes.

This interceptor works on a per-session basis. That means that the same action name cannot be run more than once at a time in a given session. On the initial request or any subsequent requests (before the action has completed), the wait result will be returned.

The wait result is responsible for issuing a subsequent request back to the action, giving the effect of a self-updating progress meter.

Using this interceptor is pretty easy but this interceptor is not part of the default stack. Since it's not part of the default stack, actions that need this interceptor must declare it and because of the nature of this interceptor, it must be the last interceptor in the stack.

If no "wait" result is found, Struts will automatically generate a wait result on the fly.

This is the topic of the next slides.

Struts2 Course chapter 17: The Execute and Wait Interceptor

Download the eclipse ready example projects:

Struts2 Course chapter 17: The Execute and Wait Interceptor code example

Struts2 Course chapter 16: Preventing Double Submits

2010-01-07T23:03:00.008-05:00

Double form submits are the nightmare of web application developers. They normally happen by accident or lack of feedback when users wait for a long time process of a form submission.

Double submits may have fatal consequences. For instance, when submitting an online payment in which a credit card will be charged.

Users may click the submit button for a second time if the server's response time is too slow. This may result in his/her credit card being charged twice.

Other less critical examples include forms that add a new product and doubly submitting these forms will cause a product to be added twice causing inconsistencies in the database and inventory.

Fortunately Struts has built-in support for preventing double submits. It employs a technique that you can also find in other web application development technologies.

This technique involves storing a unique token in the server and inserting a copy of the token into a form. When the form is submitted, this token is also sent to the server.

The server application will compare the token with its own copy for the current user. If they match, form submission is considered valid and the token is reset. Subsequent (accidental) submits of the same form will fail because the token on the server have been reset.

This is the topic of the next slides.

Struts2 Course chapter 16: Preventing Double Submits

Download the eclipse ready example projects:

Struts2 Course chapter 16: Preventing Double Submits code example

Struts2 course chapter 15: Custom Result Types

2009-12-28T00:45:00.014-05:00

Struts2 comes with a dozen or more result types, for example: Dispatcher Result, Redirect Result, Chain Result, XSL Result, etc. These results cover the majority of our necesities.

However, what happen if I need a new type of result type? for ejample an Json reult type to deal with Ajax clients? or a Image result?. In these cases, we need to imlement our own results and in the next slides we will show how to make our own custom interceptors.

Struts2 course chapter 15: Custom Result Types

Download the code example (yes is file 16):

Struts2 course chapter 10: Model Driven and Prepare Interceptors code example

Struts2 Course chapter 14: Custom Interceptors

2009-12-28T00:34:00.015-05:00

Struts2 comes with a rich set of default interceptors. For example, there is the input validation that is handled by the Validation interceptor. Unplug this interceptor and validation will stop working.

File upload is so easy beacuse of another interceptor, the File Upload interceptor. Some interceptors may prevent from the execution of an action if certain conditions are not met. For instance, the Validation interceptor keeps an action from firing if an error occurs during the validation of that action.

For most applications, the default interceptors are sufficient. However, sometimes you will need to create your own interceptor. This chapter explains how to create custom interceptors.

Struts2 Course chapter 14: Custom Interceptors

Download the code example (yes is file 15)::

Custom Interceptors in Struts2

Struts2 course chatper 13: Securing Struts2 applications

2009-11-17T11:44:00.004-05:00

Security is one of the most critical features in web application development. However, as I said before, Struts2 is the C (controller) in the MVC (model - view - controller) framework. As such, Struts2 has not its own security model. Struts2 is build on the top of the Java Servlet API and the HTTP protocol. Then, the security configuration is the same described for the Servlet API. Yet, other security models such as ACEGI can be implemented with Struts2, but this will be exposed in a future post.

In the next slides I will discuss about the two ways to secure application resources:

by configuring the application and
by writing Java code.

The first is the easier because you only need to edit your deployment descriptor (the web.xml file) to change your security policy without rewriting code. For instance, you can restrict access to certain roles and HTTP methods, determine how users can authenticate themselves, and so forth. Since Struts is based on the Servlet technology, securing a Struts application will center on this configuration plus the security feature in Struts itself.

Remember that to be good at security configuration, you need to be familiar with the concepts of principal and roles, therefore this chapter will start with a review of both. Then, the chapter explains how to write a security policy and deals with authentication methods.

After a section about how to hide resources and another on Struts-specific security features, these slides concludes with the second way of security Servlet applications: by writing code and by the use the Struts2 roles interceptor.

Struts2 course chatper 13: Securing Struts2 applications

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Securing Struts2 applications

Struts2 course chapter 12: File upload and File download

2009-11-08T19:41:00.011-05:00

File upload and file download are common activities of Internet users and these features are usually not well covered in programming books. Struts supports those both features with elegance and easiness.

Before Struts2 to manage file upload or file download you would have to deall with the getInputStream method on HttpServletRequest and parse the resulting InputStream object to retrieve the uploaded file. This is a tedious and error-prone task.

Luckily, Struts2 makes it very easy to retrieve uploaded files. Indeed, Struts make extensive use of the Java Commons FileUpload library and the File Upload interceptor for file uploading. For file downloading Struts2 makes use of the Stream result type.

In the both aforementioned cases Struts2 allow you to make declarative and programmatic implementations providing in this way simplicity with flexibility when you develop these features.

Struts2 course chapter 12: File upload and File download

Downloads projects in eclipse formats

Struts2 File upload and File download

Struts2 course chapter 11: The Persistence Layer

2009-11-08T19:37:00.007-05:00

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Struts2 is a MVC framework where it solves only the C (controller) side of the equation. This means that the developer must implement the V (the view) and the M (the model). Although Struts2 offers OGNL for the V layer, Struts2 is agnostic regarding the M layer. Therefore, we as developers have to implement this layer.

To implement the Model layer you can find many alternatives, JDBC, JPA (Java Persistence API), JDO (Java Data Objects), etc. In this slide I will use a common denominator implementation that is the Data Access Object (DAO) pattern, that the easiest to learn and is sufficient in most applications. Even though I will use JDBC in the examples in the sake of simplicity, it is easy to switch to other persistence framework.

Struts2 course chapter 11: The Persistence Layer

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Struts2 course chapter 11: Struts2 Persistence Layer

Struts2 course chapter 10: Model Driven and Prepare Interceptors

2009-10-26T16:46:00.009-05:00

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In this slide i will explain one of the most powerful struts2 features. the Model Driven and the Prepare interceptors. These interceptors help with the separation of the action and the model. But the main utility is the automatic population of the properties of the action and transfer objects. No more setters and getter in the middle. That is done by the framework.

Separating the Action and the Model

Web applications are normally multi-tiered. They are the presentation tier, the logic tier, and the data tier. Communication between two tiers is conducted by invoking methods and passing data in the form of transfer objects. Also known as the value object, this transfer object is simple and has no business methods.

In fact, there is a pattern that governs the design and use of transfer objects: the Data Transfer Object (DTO) pattern. Struts resides mainly in the presentation tier and since you can write business logic in Struts actions, you can argue that Struts encapsulates the logic tier too.

However, in an enterprise application, it is not recommendable to write business logic in action classes. Rather, you should call methods in another tier from your action classes. You should do this, even though the Struts actions have methods and properties and can definitely act as a transfer object.

However, why not is appropriate to send an action object to another tier? Because an action class has methods that are useful only in the presentation tier. What would an execute method that returns "success" do in an EJB container, for example? Transferring an action object to another tier is not only awkward but could be dangerous too.

This explain the need of a clear separation between the action and the model in an enterprise application that uses Struts as the front-end. There will be action classes that don't represent model objects and whose functions are limited to serve the presentation tier. The names of such action classes should end with Action.

Model classes, on the other hand, should have no suffix. An action class that manages products should be called ProductAction whereas an instance of a Product class should be used as a transfer object that encapsulates information about a product.

The Model Driven Interceptor

This interceptor helps to map form fields with the transfer object's properties and viceversa. In other words, Struts2 will populate automatically the content fro the form imputs in the DTO object and viceersa.

The Preparable Interceptor

This interceptor helps to map data (from a database for example) fields with the transfer object's properties and viceversa. In other words, Struts2 will populate automatically the content from the source of data in the DTO object and viceersa.

Struts2 course chapter 10: Model Driven and Prepare Interceptors

Download the eclipse project with the code sample

Struts2 Model Driven and Prepare Interceptors example

Struts2 course chapter 9: Message Handling and Internationalization

2009-10-26T16:28:00.006-05:00

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Message handling

Message handling is an important task in professional application. For example, it is almost always mandatory that text and messages be editable without source recompilation. In addition, nowadays it is often a requirement that an application be able to "speak" many languages.

Internationalization

internationalization is a technique for application development that support multiple languages and data formats without having to rewrite programming logic. Internationalization is abbreviated i18n because the word starts with an i and ends with an n, and there are 18 characters between the first i and the last n.

Localization

Localization is a technique for adapting an internationalized application to support a specific locale. A locale is a specific geographical, political, or cultural region. An operation that takes a locale into consideration is said to be locale-sensitive. For example, displaying a date is locale-sensitive because the date must be in the format used by the country or region of the user. The 15th day of November 2005 is written as 11/15/2005 in the US, but printed as 15/11/2005 in Australia. Localization is abbreviated l10n because the word starts with an l and ends with an n and there are 10 letters between the l and the n.

Strus2 easy suport for messaging handling, I18n and i10n

WIth Strus2 you can change visual text in an application quickly and easily. Java has built-in supports for internationalization and Struts makes use of this feature and has been designed from the outset to support easy message handling and internationalization. For instance, the com.opensymphony.xwork2.ActionSupport class, has getText methods for reading messages from a text file and selecting messages in the correct language. A custom tag can display a localized message simply by calling one of these methods.

Struts2 course chapter 9: Message Handling and Internationalization

Download the example code in eclipse project

Struts2 Message Handling and Internationalization

Struts2 course chapter 7: Type Conversion

2009-10-18T11:45:00.016-05:00

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When you transfer data from an HTML form to an action object, conversions are typically from strings to non-strings.

All form inputs are sent to the server as request parameters and each form input is either a String or a String array. This because because HTTP is type neutral.

The Struts 2 framework comes with built-in support for converting between the HTTP native strings and the following list of Java types:

String Sometimes a string is just a string.
boolean/Boolean True and false strings can be converted to both primitive and object versions of Boolean.
char/Character Primitive or object.
int/Integer, float/Float, long/Long, double/Double Primitives or objects.
Date String version will be in SHORT format of current Locale (for example, 12/10/97).
array Each string element must be convertible to the array's type.
List Populated with Strings by default.
Map Populated with Strings by default.

Struts2 uses the parameters interceptor, one of the interceptors in the default stack, for mapping request parameters with action properties.

Since all request parameters are Strings, and not all action properties are of type String, type conversions must be performed on any non-String action properties.

The Parameters interceptor uses the OGNL API to achieve this.

What happened with failed conversions?

On the other hand, a failed conversion will leave a property unchanged. In other words, int will retain the value of 0 and a Date property will remain null.

If zero or null is a valid property value, there's no way you can find out that a conversion has produced an error other than by comparing the property value with the corresponding request parameter.

Doing so, however, is not recommended. Not only is checking the request parameter an inelegant solution, it also defeats the purpose of using Struts as capable of mapping request parameters to action properties.

So, how does Struts solve this problem? A failed type conversion will not necessarily stop Struts. There are two possible outcomes for this misbehavior. Which one will happen depends on whether or not your action class implements the com.opensymphone.xwork2.ValidationAware interface.

If the action class does not implement this interface, Struts will continue by invoking the action method upon failed type conversions, as if nothing bad had happened.

If the action class does implement ValidationAware, Struts will prevent the action method from being invoked. Rather, Struts will enquiry if the corresponding action element declaration contains an input result. If so, Struts will forward to the page defined in the result element. If no such result was found, Struts will throw an exception.

Struts2 course chapter 7: Type conversion

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Struts2 Type conversion sample code

Struts2 course chapter 8: Input Validation

2009-10-18T11:45:00.010-05:00

Struts makes input validation easy by providing built-in validators that are based on the XWork Validation Framework. By using these validators you won't require programming validation. Instead, you will declare in an XML file how a validator should work. Among the things to declare are what field needs to be validated and what message to send to the browser if a validation fails.

However, in more complex scenarios, built-in validators can help little and you have to write code to validate input. This is called programmatic validation and, along with built-in validators, is discussed in this sessions.

The specific topics to cover in this session are:

Building Built-in validators
Bundled Validators
Visitor Validator
Custom Validators
Programmatic Validation

Struts2 course chapter 8: Input Validation

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Struts2 course chapter 8: Input Validation

Struts2 course chapter 6: Generic Tags

2009-10-14T17:19:00.004-05:00

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Struts comes loaded with a powerful tag library that contains UI and non-UI tags. In this post we will take a look at the non-UI tags, which are also known as generic tags.There two types of generic tags, data tag and control tag. The following are the data tags:

a
action
bean
date
debug
i18n
include
param
push
set
text
url
property

The following are the control tags:

if
elself
else
append
generator
iterator
merge
sort
subset

Struts2 Course chapter 6: Generic Tags

Download eclipse project Struts2 Generic Tags sample code

Struts2 course chapter 5: Form Tags

2009-10-14T17:18:00.005-05:00

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Struts comes with a powerful tag library that incorporates two kinds of tags: User Interface (UI) tags and non-UI tags. The UI tags are further categorized into two groups, those used for data entry and those for displaying error messages. The UI tags in the first group are called the form tags and are the subject of discussion of this post.

The UI tags for displaying error messages are explained in a future post, in the "Input Validation." chapter. Non-UI tags help with control flow and data access and are covered in the next post, "Generic Tags." In addition, there are also tags that assist with AJAX programming and are discussed in the future

The main advantage of using the form tags is when input validation fails and the form is returned to the user. With manual HTML coding, you have to worry about repopulating the input fields with the values the user previously entered. With the form tags, the framework is who take care of this for you.

The tags to cover are:

Form
Label
TextField
TextArea
CheckBox
CheckBox2
CheckBoxList
ComboBox
DoubleSelect
OptGroup
OptionTransferSelect
Radio
Select
UpDownSelect

Struts2 Course 5: Form Tags

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Struts2 Form Tags Example code

Struts2 course chapter 4: OGNL - Object graph notation language

2009-10-10T12:35:00.006-05:00

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OGNL stands for the Object-Graph Navigation Language. In despite of its name, OGNL is a simple and powerful technology that's been integrated into the Struts 2 framework to help with data transfer and type conversion.

OGNL is the glue between the framework's string-based HTTP input and output and the Java-based internal processing. While it seems that you can use the framework without really knowing about OGNL, your development efforts will be made many times more efficient by spending a few moments with this oddly named power utility.

From the point of view of a developer building applications on the Struts 2 framework, OGNL consists of two things: an expression language and type converters.

OGNL: Object graph notation language

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Struts2 course chapter 4: OGNL (Object graph notation language)

Struts2 course chapter 3: Actions and results

2009-10-10T12:26:00.009-05:00

Actions are the units of work of the framework. Essentially, the action maps an identifier to a handler class. When a request matches the action's name, the framework uses the mapping to determine how to process the request.

Results are the response of the framework to indicate what view will be rendered to the user. If there are a few type of actions, there are many types of results . All of them will be covered here in the slides below.

In the following slides you will read more about actions and results in detail with several examples.

Struts2 course chapter 3: Actions and results

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Struts2 Actions and Results sample code

Struts2 course chapter 2: Installation and configuration

2009-10-04T20:46:00.005-05:00

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I this chapter I will explain how to install and configure Struts2. In fact, Installing and configuring Struts is pretty strightforward. As of the version 2.6.x of Struts2 just download the binary files from http://struts.apache.org/download.cgi#struts217 and drop in the classpath of the server or the one of the web application. See the details in the slide below:

Struts2 course chapter 2: Installation and configuration

Download the ready to use eclipse projects

Struts2 course chapter 2: installation and configuration sample code

Struts2 course chapter 1: Evolution of web applications

2009-10-04T20:43:00.014-05:00

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This is the first of a series of slides trying of spread the word about Struts2, a powerful, easy to use, but still unknown MVC framework for most the Java developers.

You should already know that Struts is the most popular framework for developing Java web applications. However, with the years, this framework has became short of features to meet the emerging paradigms of computer programming such as dependency injection, aspect oriented programming, REST, etc. Struts2 include these features and more, but some training is necessary. Thus, in the following weeks I will try to synthesize the most important aspects of this framework.

I must say that Struts 2 is not only a new version of the popular Struts framework but it is a brand-new, state-of-the-art web application framework. In includes the following advantages:

Is based on Java and therefore you can use your former Java talent pool
Is uses the convention over configuration paradigm
Is uses dependency injection (DI)
It uses aspect oriented programming (AOP)
Easy testability
Easy extensibility (plug-ins)
Portal support
AJAX support
Intelligent defaults
Among others.

One of the best things about Struts2 is that you do not need to be an expert of the last paradigms of computer programming such as DI or AOP and take advantage of them. Struts2 includes them inside the framework.

In summary, Struts 2 isn't just a new release of the older Struts 1 framework. It is a completely re-engineering new framework, based on the OpenSymphony WebWork framework.

In this chapter I will explain about the evolution of the MVC framework and its different implementations and comparing them:

Life without MVC
Using the mediator pattern
MVC model 1
MVC model 2
Struts1 implementation of MVC2
Struts2 implementation of MVC2

Struts2 Course Chapter 1: Evolution of web applications

Download the ready to use eclipse projects

Evolution of web applications sample code

Javaee trainer

Struts2 course chapter 19: Decorating Struts2 with Tiles

Struts2 course chapter 18: Decorating Struts2 with SiteMesh

'Struts2 Course chapter 17: The Execute and Wait Interceptor

Struts2 Course chapter 16: Preventing Double Submits

Struts2 course chapter 15: Custom Result Types

Struts2 Course chapter 14: Custom Interceptors

Struts2 course chatper 13: Securing Struts2 applications

Struts2 course chapter 12: File upload and File download

Struts2 course chapter 11: The Persistence Layer

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