Your use case is always going to be as simple as using class fields to build the new field or you need to do any more processing? Like build output based on certain conditions etc? e.g. (age < 18, then set status: minor)
-Priyanka On Wed, Dec 2, 2015 at 4:20 PM, Chinmay Kolhatkar <[email protected]> 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. > >
