java reflection issue

Question

I have this code:

public static final <TypeVO extends BaseVo> List<SelectItem> populateSelectBoxForType(
            final Class<TypeVO> voClass, final String fieldName) {
        List<SelectItem> listSelectBox = null;
        final List<TypeVO> vosList = GenericEjbProxyFactory
                .getGenericTopValueObjectProxy(voClass)
                .getAllValueObjects(null);
        System.out.println("loaded vosList!!!!");
        if (vosList != null) {
            listSelectBox = new ArrayList<SelectItem>();
            for (final TypeVO currVo : vosList) {
                listSelectBox.add(new SelectItem(currVo.getInternalId(), currVo.getName()));
            }
        }
        return listSelectBox;
    }

As you see here, I'm using currVo.getName because always, currVo has a name property.

I want to be able to use also other fields from this currVo which has type as voClass, but not all currVo classes will contain this field so I have to use reflection to identify these getField method, something like:

for (final TypeVO currVo : vosList) {
                for (final Method m : voClass.getMethods()) {
                    if (m.getName().contains(fieldName)) {
                        listSelectBox.add(new SelectItem(
                                currVo.getInternalId(), currVo.m));
                    }
                }
            }

What I do not know is HOW I can use that specific method's value when I find it, exactly like currVo.getName (because, of course, currVo.m is wrong)?

Eg: If fieldName is "Age" I want to put in the list: currVo.getAge()... I am simply blocked here...

axtavt · Accepted Answer · 2011-06-02 11:48:32Z

3

m.invoke(currVo);

See also:

Method javadoc

Also note the correct way to look for a method as suggested by Nik and Bohemian.

edited Jun 2, 2011 at 11:48

answered Jun 2, 2011 at 11:32

axtavt

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3 Comments

Mat Over a year ago

invoke takes two arguments.

axtavt Over a year ago

@Mat: It takes vararg as a second argument, which can be empty.

Bohemian Over a year ago

thanks for the new signature tip - didn't realise that reflection had gone varargs

Howard · Accepted Answer · 2011-06-02 11:33:25Z

1

Do I understand it correctly that you want to invoke the method m on your object currVo? Then it's simply

m.invoke(currVo);

answered Jun 2, 2011 at 11:33

Howard

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Comments

Bohemian · Accepted Answer · 2011-06-02 11:39:47Z

1

Use reflection to get the getFieldName method and invoke it, as follows:

 Method method = voClass.getMethod("get" + fieldName); // the getter with no params in the signature
 Object value = method.invoke(currVo}); // invoke with no params
 listSelectBox.add(new SelectItem(currVo.getInternalId(), value));

Note: This assumes that fieldName is leading uppercase, eg "Value", not "value", so prepending it with "get" gives the exact method name, eg "getValue"

answered Jun 2, 2011 at 11:39

Bohemian♦

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Comments

Mat · Accepted Answer · 2011-06-02 11:50:51Z

1

You should use the invoke method from the Method class.

m.invoke(currVo, (Object[]) null);

(Assuming the method takes no parameter.)

This will work for JDK versions 1.4 and later, since they state:

If the number of formal parameters required by the underlying method is 0, the supplied args array may be of length 0 or null

The one-parameter version of that call will not work on older JVMs.

edited Jun 2, 2011 at 11:50

answered Jun 2, 2011 at 11:33

Mat

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4 Comments

Peter Lawrey Over a year ago

This is the same as m.invoke(currVo, new Object[] { null }); which may not be what you intended.

Bohemian Over a year ago

i also disagree - the null is a value and makes the Object[] length 1 - it should be length zero

Peter Lawrey Over a year ago

You are right. null is "cast" to Object[] not as an array of length 0 or 1.

Mat Over a year ago

I was a bit off though, the explicit cast to Object[] is necessary for it to compile without warnings on 1.6 at least.

Buhake Sindi · Accepted Answer · 2011-06-02 11:41:19Z

0

I am not sure if i got ur question right, but what i feel u are asking wud be answered by following code:

// Class is whatever is the type u r using
Method mthd = Class.getMethod("get" + fieldName); //in case method don't have any parameters.
listSelectBox.add(mthd.invoke(currVo));

otherwise ignore.

edited Jun 2, 2011 at 11:41

Buhake Sindi

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answered Jun 2, 2011 at 11:35

Nik

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