Is it possible automatically instantiation of a nested Property with Commons Bean Utils?

Question

I'm using PropertyUtils.setProperty(object, name, value) method of Apache Commons Bean Utils:

Giving these classes:

public class A {
    B b;
}

public class B {
    C c;
}

public class C {
}

And this:

A a = new A();
C c = new C();
PropertyUtils.setProperty(a, "b.c", c); //exception

If I try that I get: org.apache.commons.beanutils.NestedNullException: Null property value for 'b.c' on bean class 'class A'

Is it possible to tell PropertyUtils that if a nested property has a null value try to instantiate it (default constructor) before trying to go deeper?

Any other approach?

Thank you

Answer 1

I solved it by doing this:

private void instantiateNestedProperties(Object obj, String fieldName) {
    try {
        String[] fieldNames = fieldName.split("\\.");
        if (fieldNames.length > 1) {
            StringBuffer nestedProperty = new StringBuffer();
            for (int i = 0; i < fieldNames.length - 1; i++) {
                String fn = fieldNames[i];
                if (i != 0) {
                    nestedProperty.append(".");
                }
                nestedProperty.append(fn);

                Object value = PropertyUtils.getProperty(obj, nestedProperty.toString());

                if (value == null) {
                    PropertyDescriptor propertyDescriptor = PropertyUtils.getPropertyDescriptor(obj, nestedProperty.toString());
                    Class<?> propertyType = propertyDescriptor.getPropertyType();
                    Object newInstance = propertyType.newInstance();
                    PropertyUtils.setProperty(obj, nestedProperty.toString(), newInstance);
                }
            }
        }
    } catch (IllegalAccessException e) {
        throw new RuntimeException(e);
    } catch (InvocationTargetException e) {
        throw new RuntimeException(e);
    } catch (NoSuchMethodException e) {
        throw new RuntimeException(e);
    } catch (InstantiationException e) {
        throw new RuntimeException(e);
    }
}

Answer 2

I know the question is about apache commons PropertyUtils.setProperty but there is very similar functionality available in Spring Expression Language "SpEL" which does exactly what you want. Better still it deals with lists and arrays too. The doc link above is for spring 4.x but the code below works for me in spring 3.2.9.

    StockOrder stockOrder = new StockOrder(); // Your root class here

    SpelParserConfiguration config = new SpelParserConfiguration(true,true);   // auto create objects if null
    ExpressionParser parser = new SpelExpressionParser(config);
    StandardEvaluationContext modelContext = new StandardEvaluationContext(stockOrder);

    parser.parseExpression("techId").setValue(modelContext, "XXXYYY1");
    parser.parseExpression("orderLines[0].partNumber").setValue(modelContext, "65498");
    parser.parseExpression("orderLines[0].inventories[0].serialNumber").setValue(modelContext, "54686513216");

    System.out.println(ReflectionToStringBuilder.toString(stockOrder));

Answer 3

A little correction:

String fn = fieldNames[i];
if (i != 0) {
        nestedProperty.append(".");
}
nestedProperty.append(fn);
Object value = PropertyUtils.getProperty(obj, nestedProperty.toString());