Java-反射。 设置动态创建的类对象的值

Question

Hi have a class[many] for which I create object dynamically during run time. now I want to set value for the fields which are private fields . How do I set them.

I have seen many examples which explain this but we need to know the field name and only than the values can be set.

for my case I have some set of default values for set of primitive and non primitive types and find the field type during run time and set the default values for them.

For example:

LoginBean loginBean = new LoginBean();
Method setUserName = loginBean.getClass().getMethod("setUserName", new Class[]{String.class});
setUserName.invoke(loginBean, "myLogin");

My case is different and i don't even know the field name but have to set the default value according to field type.

how to do this using reflection or even better in spring.

Answer 1

You can say yourBean.class.getFields(); which will give array of Field .

Using Field you can find its name and type , and do the desired work (setting some value, if its type is == some primitive type)

Answer 2

This example sets default values on several fields within a class using reflection. The fields have private access, which is toggled on and off via reflection. Field.set() is used to set the values of the field on a particular instance instead of using the setter method.

import java.lang.reflect.Field;
import java.util.Date;


public class StackExample {

    private Integer field1 = 3;
    private String field2 = "Something";
    private Date field3;

    public static void main(String[] args) throws IllegalArgumentException, IllegalAccessException {
        StackExample se = new StackExample();

        Field[] fields = se.getClass().getDeclaredFields();

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

                if(type.equals(Integer.class)){
                    f.set(se, 100); //Set Default value
                }else if(type.equals(String.class)){
                    f.set(se, "Default");
                }else if (type.equals(Date.class)){
                    f.set(se, new Date());
                }
                f.setAccessible(false);
            }
            System.out.println(f.get(se)); //print fields with reflection
        }
    }
}

Answer 3

1) By Using Spring Constructor/Setter Injection. You dont need to know the attribute name , just type will do. Like as following:

<bean id="myBean" class="myBean">
  <constructor-arg type="int"><value>1</value></constructor-arg>
</bean>