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A trivial use case would be adding a 'replace' function that is callable from a DFDL expression. In the DFDL Schema, we might call call something like the below; where transformedElem will contain "Hello_World", if someElement resolves to "Hello World".
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@UserDefinedFunctionIdentification( name = "replace", namespacenamespaceURI = "urn:example:com:ext:udfunction:stringfunctions" ) public class Replace { public String evaluate(String orig, String pre, String post) { //implementation... } } |
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Another use case would be implementing the normalization of elevation above Mean-Sea-Level (MSL) to Height-Above-Ellipsoid (HAE) for Link16F1 data. In the DFDL schema, we might call something like the below; where the functions will return the result of the conversion.
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xmlns:mhdf="http://extOther.UDFunction.ElevationConversions.com" ... dfdl:outputValueCalc="{ mhdf:convert_to_hae(../lat, ../lon, ../msl) }" |
The function userDefinedFunction class would look something like the below
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@UserDefinedFunctionIdentification( name = "convert_to_hae", namespacenamespaceURI = "http://extOther.UDFunction.ElevationConversions.com" ) public class MSLConversions { public double evaluate(double latitude, double longitude, double msl) { //implementation.. } } |
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The Daffodil solution will use a combination of JAVA's ServiceLoader and Reflection APIs.
Daffodil Provided
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Classes
Daffodil will provide a UserDefinedFunction interface, a UserDefinedFunctionProvider abstract class, a UserDefinedFunctionIdentification annotation class, and two exception classes: UserDefinedFunctionFatalException and UserDefinedFunctionProcessingError.
Each UDF must implement the UserDefinedFunction interface. This marks it as a UDf UDF to Daffodil and gives it some properties such as Serializability.
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The UserDefinedFunctionProcessingError exception can be thrown when an implementer wishes to throw a recoverable error that'll induce backtracking. The UserDefinedFunctionFatalException exception can be thrown to halt processing all together and abort Daffodil.
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The implementer will be expected to implement at least 2 two classes: a provider class and at least one UDF class.
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The UDF classes will contain the functionality of the UDF embodied in an evaluate method. The UDF class will be expected to implement an evaluate method as well as apply the Daffodil provided UserDefinedFunctionIdentification annotation to the class . Because the parameter types and the return types of the evaluate function are dependent on the functionality, and we really only care about the name, we will not provide an abstract function for it. Each function that the implementer wishes to expose must implement the UserDefinedFunction interface, contain an evaluate function, and have the UserDefinedFunctionIdentification annotation. See Use Cases/Examples 135859640 for a sample UDF class.
Daffodil Service Loader
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ID | Description | Test Data |
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1 | Tests when there are no providers found by the ServiceLoader API due to missing or empty meta-inf file | No META-INF file on classpath |
2 | Tests when there is an error thrown from ServiceLoader API | META-INF file contains class that doesn’t exit |
3 | Tests when UDF Provider has no function classes | UDFP whose getUDF func returns null |
4 | Tests when UDF Provider has empty function class | UDFP whose getUDF func returns empty array of classes |
5 | Tests when function classes don’t implement UserDefinedFunction interface | UDF with function class that doesn’t implement UserDefinedFunction interface |
6 | Tests when function classes don’t have annotations | UDF with function class that doesn’t have UserDefinedFunctionIdentification annotation |
7 | Tests when function classes have empty/invalid annotation fields | UDF with function class that has annotation function with empty fields |
8 | Tests when function classes have no evaluate function | UDF with function class whose doesn’t have method called evaluate |
9 | Tests when function can’t be found | Function call from schema with no matching UDF loaded |
10 | Tests when function class have overloaded evaluate function | UDF with overloaded evaluate function |
11 | Tests when arguments number incorrect | Function call from schema with incorrect arg number |
12 | Tests when argument types incorrect | Function call from schema with incorrect arg type |
13 | Tests when argument types unsupported | Function call from schema with unsupported type (such as Array of String) |
14 | Tests when return type unsupported | UDF with unsupported return type such as Array of Arrays |
15 | Tests UDF with no args | UDF with no params |
16 | Tests UDF with no return type | UDF with void return type |
17 | Tests UDF with primitive int params and returns | UDF with primitive params and return |
18 | Tests UDF with primitive byte params and returns | UDF with primitive params and return |
19 | Tests UDF with primitive byte array params and returns | UDF with primitive params and return |
20 | Tests UDF with primitive short params and returns | UDF with primitive params and return |
21 | Tests UDF with primitive long params and returns | UDF with primitive params and return |
22 | Tests UDF with primitive double params and returns | UDF with primitive params and return |
23 | Tests UDF with primitive float params and returns | UDF with primitive params and return |
24 | Tests UDF with primitive boolean params and returns | UDF with primitive params and return |
25 | Tests UDF with Boxed Integer params and returns | UDF with boxed params and return |
26 | Tests UDF with Boxed Byte params and returns | UDF with boxed params and return |
27 | Tests UDF with Boxed Short params and returns | UDF with boxed params and return |
28 | Tests UDF with Boxed Long params and returns | UDF with boxed params and return |
29 | Tests UDF with Boxed Double params and returns | UDF with boxed params and return |
30 | Tests UDF with Boxed Float params and returns | UDF with boxed params and return |
31 | Tests UDF with Boxed Boolean params and returns | UDF with boxed params and return |
32 | Tests UDF with Java Big Integer params and returns | UDF with specified params and returns |
33 | Tests UDF with Java Big Decimal params and returns | UDF with specified params and returns |
34 | Tests UDF with String params and returns | UDF with specified params and returns |
35 | Tests when no UDFs called, and no UDFs available to be loaded | No UDFs on classpath, no UDF in schema |
36 | Tests when UDFs called, but no UDFs loaded | No UDFs on classpath, UDF in schema |
37 | Tests when UDF called with default namespace | Default namespace set to UDF namespaceURI; UDF calls with no prefix |
38 | Tests when exceptions thrown during loading UDFP | UDFP classes throws exception in class |
39 | Tests when exceptions thrown during loading UDFP’s UDF classes | UDFP throws exception in getUDFs function |
40 | Tests when exceptions thrown during loading UDF | UDF throws exception in class |
41 | Tests when custom exceptions thrown during evaluating (FatalError) | UDF throws exception in evaluate function |
42 | Tests when UDFProcessingError thrown during evaluating (ProcessingError) | UDF throws UDFProcessingError in evaluate function |
43 | Tests when UDF initializer returns object of wrong type | UDFP’s initialization function creates UDF object of different type |
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Pull Requests
UDF Jars: HAEMSLConversions.jar and UDFunctionProviderImpl.jar. Both extend UDFunctionProvider.jar.
MockDaffodil.jar contains a Scala app, that also contains a JAVA class that uses ServiceLoader. It needs UDFunctionProviderImpl.jar & UDFunctionProvider.jar
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https://github.com/apache/incubator-daffodil/pull/273 - Initial Proposal
https://github.com/apache/incubator-daffodil/pull/279 - Final Product
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