6. Building a view: tags

Question 1

What data objects are available to be targeted with OGNL? Think what’s in an ActionContext.

Answer 1

ValueStack, parameters, application, session, attr, request

Question 2

What’s the default data object OGNL will resolve against?

Answer 2

ValueStack

Question 3

How do you have OGNL resolve against a different object?

Answer 3

Use the #object[‘property’] syntax.

Question 4

What are the 4 categories of Struts 2 tags?

Answer 4

1. Data Tags
2. Control-Flow Tags
3. UI Tags
4. Miscellaneous Tags

Question 5

What function do Data Tags perform?

Answer 5

Extracting data from the ValueStack and/or setting values in the ValueStack.

Question 6

What functions do Control-flow tags perform?

Answer 6

Allows you to test values on the ValueStack to conditionally alter the flow of the rendering process.

Question 7

What’s the syntax for including Struts 2 tags into a JSP page?

Answer 7

taglib prefix=”s” uri=”/struts-tags”

Question 8

What is the property tag used for? What’s the syntax for it?

Answer 8

For using OGNL to display value from ValueStack on the page.

s:property value=”OGNL Expression” default=”If null, show instead” escape=”True”

Question 9

Assume image is true, value isn’t on ValueStack. What happens?

Answer 9

Prints out:

nonExistingProperty on the ValueStack =
nonExisting Property on the ValueStack = doesNotExist

Important to note that the first one checks ValueStack, doesn’t find the value so NULL is returned. When NULL turned into a string it becomes empty string “”

Question 10

How could you modify this code so that the default attribute pulls ‘myDefaultString’ from the ValueStack INSTEAD of using the string literal?

Answer 10

Important note is the %{expression} syntax.

Question 11

What is the set tags prupose? What are the attributes available?

Answer 11

Assigning a property to another name. You could use this to basically alias to a deeper, tougher to type out OGNL expression.

Question 12

What is the push tags prupose? What are the attributes available?

Answer 12

Allows you to push properties onto the ValueStack, useful for when you do a lot of work revolving around a single object, push the object and refer to the properties.

Question 13

What is the bean tags purpose? What are the attributes available?

Answer 13

Hybrid of set/push tags except you don’t need to work with an existing object.

Object must conform to JavaBeans standards (zero-arg constructor, properties for fields you intend to intialize with param tags.

Question 14

What syntax would you need to create a bean, pass a parameter to the bean, then invoke a function that outputs a message?

Answer 14

Question 15

What is the action tags purpose? What are the attributes available?

Answer 15

Allows us to invoke another action from our view layer.

Question 16

What is the iterator tags purpose? What are the attributes available?

Answer 16

Allows you to loop over collections or objects easily!

Question 17

What methods are available on the IteratorStatus object?

Answer 17

Question 18

What is the if/else tags purpose? What are the attributes available?

Answer 18

Controls flow of tags. You can use if/elseif/else.

Question 19

What is the include tags purpose? What are the attributes available?

Answer 19

You can use it to include the output of another web resource in the currently rendering page. IMPORTANT: Can include ANY servlet resource.

Question 20

What is the url tags purpose? What are the most important attributes?

Answer 20

Creating URLs, mapping to external or even Actions. Can even pass parameters as part of the URL generation.

–Attributes–

value – Base URL

action – Name of the action to target (no ‘.action’ extension)

Question 21

What’s the OGNL expression for filtering a list of users whos age is greater than 30?

Answer 21

users.{?#this.age > 30}

Notice the {? } is the filter expression. #this is reference THIS user object being evaluated.

Question 22

What’s the OGNL expression for projecting usernames from a collection of users objects?

Answer 22

users.{username}