5. Data transfer: OGNL and type conversion

Question 1

What does OGNL stand for?

Answer 1

Object Graph Navigation Language

Question 2

What’s the OGNL escape sequence?

Answer 2

%{expression}

Question 3

What’s the difference between these fields when OGNL converts them to Java?

Answer 3

• ages – Sets the whole array.
• names – Sets individual index with value (calls get, then sets value). SO array MUST be initialized!

Question 4

How do we tell OGNL what types to convert values to?

Answer 4

Create a ClassName-conversion.properties file next to the Java Class.

Question 5

Regarding OGNL convertions properties file, how would you convert values named ‘weights’ from a generic list to a list of Doubles?

Answer 5

Add a line:

Element-weights=java.lang.Double

Note: Prefix of ‘Element-‘ and the full path to the Type.

Question 6

What’s the syntax for using OGNL to populate a map from HTML?

Answer 6

Two ways you can do it:

map.key

or

map[‘key’]

Question 7

Regarding HTML -> Java OGNL is the -conversion.properties NEEDED when dealing with List/Set/Map?

Answer 7

If you’re not using a typed generic, yet. But you should be using generics in which case it will work wihtout the properties file!

Ex: Map

Question 8

What interface must be implemented to give OGNL ability to convert types? What 2 methods need to be implemented?

Answer 8

–Interface–

StrutsTypeConverter

–Methods–

convertFromString(Map context, String[] values, Class toClass)

String convertToString(Map context, Object o)

Question 9

What is the OGNL properties file that’s used globally? Where should it be located?

Answer 9

xwork-conversion.properties

Place it in the root of the classpath.