PropertyExpressionEvaluation returns null for certain generics
--------------------------------------------------------------
Key: STS-884
URL: http://www.stripesframework.org/jira/browse/STS-884
Project: Stripes
Issue Type: Bug
Components: ActionBean Dispatching
Affects Versions: Release 1.5.7
Reporter: Martin Cortez
I have a Stripes project where my domain objects have several layers of
generics. It seems that in a certain combination, calling
{{PropertyExpressionEvaluation.getType()}} returns {{null}}. This seems to be
the simplest scenario where it fails:
{code:title=Main.java|borderStyle=solid}
import net.sourceforge.stripes.util.bean.PropertyExpression;
import net.sourceforge.stripes.util.bean.PropertyExpressionEvaluation;
public final class Main {
public static void main(final String... args) throws Throwable {
printType(new Bean(), "listValues");
printType(new Bean(), "listValues.values");
printType(new Bean(), "listValues.values[0]");
printType(new Bean(), "listValues.values[0].alpha");
printType(new Bean(), "listValues.values[0].beta");
}
private static void printType(Object bean, String expression) {
PropertyExpression exp =
PropertyExpression.getExpression(expression);
PropertyExpressionEvaluation eval = new
PropertyExpressionEvaluation(
exp, bean);
Class<?> clazz = eval.getType();
System.out.println("Expression: " + expression);
System.out.println("Object: " + bean);
System.out.println("Type: " + clazz);
System.out.println();
}
}
{code}
{code:title=Bean.java|borderStyle=solid}
public class Bean {
public ListValues<Child> getListValues() { return null; }
}
{code}
{code:title=ListValues.java|borderStyle=solid}
public class ListValues<V> {
public java.util.List<V> getValues() { return null; }
}
{code}
{code:title=Parent.java|borderStyle=solid}
public class Parent<A> {
public A getAlpha() { return null; }
public Beta getBeta() { return null; }
}
{code}
{code:title=Child.java|borderStyle=solid}
public class Child extends Parent<Alpha> {}
{code}
{code:title=Alpha.java|borderStyle=solid}
public class Alpha {}
{code}
{code:title=Beta.java|borderStyle=solid}
public class Beta {}
{code}
Running Main prints the following output:
{noformat}
Expression: listValues
Object: Bean@4d20a47e
Type: class ListValues
Expression: listValues.values
Object: Bean@2b86c6b2
Type: interface java.util.List
Expression: listValues.values[0]
Object: Bean@593d93f4
Type: class Child
Expression: listValues.values[0].alpha
Object: Bean@635b9e68
Type: null
Expression: listValues.values[0].beta
Object: Bean@13fcf0ce
Type: class Beta
{noformat}
Without understanding the {{PropertyExpressionEvaluation}} code too much, I
think the problem is at the following line:
{code:title=PropertyExpressionEvaluation.java|borderStyle=solid}
type = getBeanPropertyType(clazz, property);
// XXX What do we do if type is a generic type?
{code}
The type returned by {{getBeanPropertyType()}} is a {{TypeVariable}} and,
according to the comment, it seems like this scenario isn't handled yet. For
now, I guess I can just create a few concrete classes without using so many
generics... but it would be nice if this worked. Maybe my test classes will
help someone figure out the correct logic?
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