Java - Reflection setting value at runtime

Question

i try to set values for the field available in a java bean like the following and i want to omit the static final fields:

public Class creatObjectWithDefaultValue(String className) throws IllegalArgumentException, IllegalAccessException {
        DefaultParamValues defaultParamValues = null;
        Class objectClass = null;
        try {
            objectClass = Class.forName(className);
             Field[] fields = objectClass.getDeclaredFields();

             for(Field f:fields){
                 f.setAccessible(true);
                    //if(!f.isAccessible()){
                       // f.setAccessible(true);
                        Class<?> type = f.getType();


                        if(! Modifier.isFinal(f.getModifiers()) && type.equals(Integer.class)){
                            f.set(objectClass, defaultParamValues.INTEGER);  
                        } else if(! Modifier.isFinal(f.getModifiers()) && type.equals(BigInteger.class)){
                            f.set(objectClass, defaultParamValues.BIGINTEGER);  
                        }/*else if(! Modifier.isFinal(f.getModifiers()) && type.equals(LocalDate.class)){
                            f.set(objectClass, defaultParamValues.DATE);  
                        }*/else if(! Modifier.isFinal(f.getModifiers()) && type.equals(Boolean.class)){
                            f.set(objectClass, defaultParamValues.BOOLEAN);  
                        }else if(! Modifier.isFinal(f.getModifiers()) && type.equals(Long.class)){
                            f.set(objectClass, defaultParamValues.LONGVALUE);  
                        }
                        f.setAccessible(false);
                    //}
                        //To print the value set
                        if(! Modifier.isFinal(f.getModifiers()) ){
                             System.out.println(f.get(objectClass));
                        }

                }
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
        return objectClass;
    }

i get the following exception when i run the program : the complete stack strace is :

Exception in thread "main" java.lang.IllegalAccessException: Class com.hexgen.tools.JsonConverter can not access a member of class com.hexgen.ro.request.CreateRequisitionRO with modifiers "private"
    at sun.reflect.Reflection.ensureMemberAccess(Reflection.java:65)
    at java.lang.reflect.Field.doSecurityCheck(Field.java:960)
    at java.lang.reflect.Field.getFieldAccessor(Field.java:896)
    at java.lang.reflect.Field.get(Field.java:358)
    at com.hexgen.tools.JsonConverter.creatObjectWithDefaultValue(JsonConverter.java:89)
    at com.hexgen.tools.JsonConverter.main(JsonConverter.java:181)

what is the problem ? Could somebody help me to fix this?

Best Regards.

JsonConverter.java:89 <-- which line is this?

Adam Arold
– Adam Arold

2013-04-29 12:23:26 +00:00
Commented Apr 29, 2013 at 12:23 — Adam Arold
– Adam Arold, Commented Apr 29, 2013 at 12:23
f.setAccessible(false);

Java Questions
– Java Questions

2013-04-29 12:27:51 +00:00
Commented Apr 29, 2013 at 12:27 — Java Questions
– Java Questions, Commented Apr 29, 2013 at 12:27

Marko Topolnik · Accepted Answer · 2013-04-29 12:22:34Z

2

You revert the accessible property of the field to false and then you go on to access its value.

Don't bother with setting accessible back to false.

answered Apr 29, 2013 at 12:22

Marko Topolnik

201k31 gold badges336 silver badges455 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

Java Questions Over a year ago

Thanks Marko, still i get this

Exception in thread "main" java.lang.IllegalAccessException: Class com.hexgen.tools.JsonConverter can not access a member of class com.hexgen.ro.request.CreateRequisitionRO with modifiers "private"

Adam Arold Over a year ago

I think that this isn't the problem here. Check my answer.

Marko Topolnik Over a year ago

Listen to Adam's advice, he's got it right. You aren't creating an instance of the class, so your current code only works for static fields.

Marko Topolnik Over a year ago

@AdamArold It is not true that this isn't the problem: it just isn't the only problem.

Adam Arold Over a year ago

I see, you are right. We are facing multiple problems here. But hey, it is reflection...

Adam Arold · Accepted Answer · 2013-04-29 12:34:22Z

2

I think that the problem is that you are trying to set fields on a class not an instance of that class.

First you should create an instance of your objectClass and set the values of the instance!

Here:

f.set(objectClass, defaultParamValues.INTEGER);

you are passing the class object, not an instance of that class. The problem occurs when your program encounters a field which is not static, hence your Exception.

If you want to filter for static fields you can use:

java.lang.reflect.Modifier.isStatic(field.getModifiers())

edited Apr 29, 2013 at 12:34

answered Apr 29, 2013 at 12:26

Adam Arold

30.8k25 gold badges124 silver badges226 bronze badges

5 Comments

Java Questions Over a year ago

i created new instance like the following but still i get the same objectClass.newInstance();

Adam Arold Over a year ago

Can you update your code please? With something indicating on which line you get the Exception.

Java Questions Over a year ago

` if(! Modifier.isFinal(f.getModifiers()) ){ System.out.println(f.get(objectClass)); }` is the place where i get exception

Adam Arold Over a year ago

The same exception as before?

Adam Arold Over a year ago

Can you launch your debugger and figure it out that on which method call does it throw the exception?

Collectives™ on Stack Overflow

Java - Reflection setting value at runtime

2 Answers 2

5 Comments

5 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

5 Comments

5 Comments

Your Answer

Sign up or log in

Post as a guest

Related