io.github.lukehutch.fastclasspathscanner.matchprocessor

Interface StaticFinalFieldMatchProcessor

Functional Interface:

This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.

@FunctionalInterface
public interface StaticFinalFieldMatchProcessor

The method to run when a class with the matching class name and with a final static field with the matching field name is found on the classpath. The constant value of the final static field is obtained directly from the constant pool of the classfile. Field values are obtained directly from the constant pool in classfiles, not from a loaded class using reflection. This allows you to detect changes to the classpath and then run another scan that picks up the new values of selected static constants without reloading the class. (Class reloading is fraught with issues, see: http://tutorials.jenkov.com/java-reflection/dynamic-class-loading-reloading.html ) Note: Only static final fields with constant-valued literals are matched, not fields with initializer values that are the result of an expression or reference, except for cases where the compiler is able to simplify an expression into a single constant at compiletime, such as in the case of string concatenation (see https://docs.oracle.com/javase/specs/jvms/se7/html/jvms-5.html#jvms-5.1 ). The following are examples of constant static final fields: public static final int w = 5; public static final String x = "a"; static final String y = "a" + "b"; // Referentially equal to the interned String object "ab" private static final int z = 1; // Private field values are also returned static final byte b = 0x7f; // Primitive constants are autoboxed, e.g. byte -> Byte whereas the following fields are non-constant assignments, so these fields cannot be matched: public static final Integer w = 5; // Non-constant due to autoboxing static final String y = "a" + w; // Non-constant expression, because x is non-constant static final int[] arr = {1, 2, 3}; // Arrays are non-constant static int n = 100; // Non-final final int N = 100; // Non-static

Method Summary

Modifier and Type	Method and Description
void	processMatch(String className, String fieldName, Object fieldConstantValue)

Method Detail

processMatch

void processMatch(String className,
                  String fieldName,
                  Object fieldConstantValue)