Hi Vlad,
Sure. Here is the example of than one POJO used:
Consider a input POJO as following:
class InputPOJO {
int id;
Date dob;
}
Consider another POJO object, for the sake of discussion is, comming from a
database:
class InputDB {
int id;
Date dob;
}
Requirement is that I want to find the age of the person under following
circumstances:
1) Input POJO may or may not have it. It might be null.
2) If input POJO has it, it should be picked up over DB one.
In such a case, lets say I have 2 placeholder: “inp” & “db” for Input POJO
and DB object respectively.
The expression would now become:
(${inp.dob} == null) ? (new Date().getYear() - ${db.dob}.getYear()) :
(new Date().getYear() - ${inp.dob}.getYear())
The code using the ExpressionEvaluator.java I pasted before would look like
following:
InputPOJO inp = new InputPOJO();
inp.dob = null;
DBPOJO db = new DBPOJO();
db.dob = new Date(1988-1900, 2, 11);
ExpressionEvaluator ee = new ExpressionEvaluator();
ee.addDefaultImports(new String[]{"java.util.Date"});
ee.setInputObjectPlaceholders(new String[]{"inp", "db"}, new
Class[]{InputPOJO.class, DBPOJO.class});
String expression = "(${inp.dob} == null) ? (new Date().getYear()
- ${db.dob}.getYear()) : (new Date().getYear() -
${inp.dob}.getYear())";
ExpressionEvaluator.DataGetter<Integer> getter =
ee.createGetter(expression, Integer.class);
// null dob
inp.dob = null;
Integer age = getter.get(inp, db);
System.out.println("Age is: " + age);
// same dob
inp.dob = new Date(1988-1900, 2, 11);
age = getter.get(inp, db);
System.out.println("Age is: " + age);
I hope this clarifies the case. As of now I see requirement for only 2 such
objects being input. But in future I might have more than 2 of them as well.
Can above be done using POJOUtils?
Considering such a use case, would you suggest the approach I took is
correct one OR suggest any better approach is there?
Thanks,
Chinmay.
~ Chinmay.
On Thu, Dec 3, 2015 at 12:28 AM, Vlad Rozov <[email protected]> wrote:
> In the example there is only one Pojo object. Can you please provide an
> example/use case with two Pojo objects?
>
> Thank you,
>
> Vlad
>
>
> On 12/2/15 10:00, Chinmay Kolhatkar wrote:
>
>> Hi Vlad,
>>
>> I had a look at pojoutils. It can cater for getter method taking a single
>> pojo object as param.
>> What I need is atleast 2 pojo objects from which final result will be
>> derived as per expression.
>> Hence I wrote getter using janino which can takes 'n' number of pojo
>> objects as params as work off the expression.
>> This might possibly be a extension to pojoutils.
>>
>> Please correct me if I'm wrong.
>>
>> - Chinmay.
>> On 2 Dec 2015 22:07, "Vlad Rozov" <[email protected]> wrote:
>>
>> The use case is already fully covered by PojoUtils that is part of Malhar.
>>> Please take a look and let me know if you have any questions how to use
>>> it.
>>>
>>> Thank you,
>>>
>>> Vlad
>>>
>>> On 12/2/15 02:50, Chinmay Kolhatkar wrote:
>>>
>>> Hi All,
>>>>
>>>> We’re evaluating a expression evaluator for our use case.
>>>>
>>>> *Example Use Case:*
>>>> The expressions needs to contain Java specific code for evaluating once
>>>> and running the same for every tuple.
>>>> For e.g. a POJO has following definition:
>>>>
>>>> |public class POJO { String firstname; // Firstname String lastname; //
>>>> Lastname Date dob; // Date of birth } |
>>>>
>>>> From this POJO, we need to generate fullname as concatenation of
>>>> firstname & lastname and age which will be derived from dob field.
>>>> The expressions for those might look like following:
>>>> For full name : ${inp.firstname} + “ “ + ${inp.lastname}
>>>> For Age : new Date().getYear() - ${inp.dob}.getYear()
>>>>
>>>> Currently, I have a implementation using Janino library for expression
>>>> evaluation. Code (ExpressionEvaluator.java) and Test code (Main.java)
>>>> attached.
>>>> As performance is an important concern, we chose a custom evaluator
>>>> using
>>>> Janino’s fast script evaluator.
>>>>
>>>> *Design of the custom expression evaluator:*
>>>>
>>>> /ExpressionEvaluator class is used for evaluating expressions
>>>> which takes multiple parameter object and the result is returned
>>>> for that expression./
>>>> /
>>>> /
>>>> /The way to reference a variable in an object is
>>>> ${placeholder.varname}./
>>>> /The variable will be resolved to its accessible variable or
>>>> getter method in order. After this the variable can be used as if
>>>> its a Java variable./
>>>> /
>>>> /
>>>> /ExpressionEvaluator also allows you to set extra imports that
>>>> needs to be added over default is java.lang.*/
>>>> /
>>>> /
>>>> /ExpressionEvaluator needs to be configured with following
>>>> configurations as minimal configuration:/
>>>> /1. Mapping of input object place holders to it corresponding
>>>> types./
>>>> / This can be done with setInputObjectPlaceholders method./
>>>> /2. Return type of of expression eveluation./
>>>> /3. Expression to be evaluated. This is a standard java expression
>>>> except for referencing the variable inside object JEL syntax needs
>>>> to be used i.e. ${objectPlaceHolder.varName}/
>>>>
>>>> *Example Use of custom expression evaluator:*
>>>>
>>>> |ExpressionEveluator ee = new ExpressionEvaluator(); // Let expression
>>>> evaluator know what are the object mappings present in expressions and
>>>> their class types. ee.setInputObjectPlaceholders(new String[]{"input"},
>>>> new
>>>> Class[]{Test.class}); // Generate expression for finding age from Date
>>>> object. String expression = "${input.firstname} + \" \" +
>>>> ${input.lastname}"; ExpressionEvaluator.DataGetter<String> getter4 =
>>>> ee.createGetter(expression, String.class); inp1.firstname = "ABC";
>>>> inp1.lastname = "XYZ"; String fullname = getter4.get(inp1);
>>>> System.out.println("Fullname is: " + fullname); |
>>>>
>>>> *Output:*
>>>>
>>>> |Fullname is: ABC XYZ |
>>>>
>>>>
>>>> Can you please suggest for any improvements in this OR is there a better
>>>> option to achieve expression evaluation?
>>>>
>>>> Can this code possibly go into Malhar library?
>>>>
>>>> ~ Chinmay.
>>>>
>>>>
>>>>
>>>>
>>>
>
