JAVA EE: How to access the attribute using Java Reflection

Thursday, 2 November 2017

How to access the attribute using Java Reflection | Reflection in java

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Student.java

class Student
{
    private String name;

    public Student(String name)
    {
        this.name = name;
    }

}

ReflectionDemo.java

import java.lang.reflect.Field;

/**
 *
 * Despite the common belief it is actually possible to access private fields
 * and methods of other classes via Java Reflection. It is not even that
 * difficult. This can be very handy during unit testing.
 *
 */
public class ReflectionDemo
{
    public static void main(String[] args)
    {
        try
        {
            Class classObj = Student.class;
            Field privateFieldObj = classObj.getDeclaredField("name");
            /*
             * Set the accessible flag for this object to the indicated boolean
             * value. A value of true indicates that the reflected object should
             * suppress Java language access checking when it is used. A value
             * of false indicates that the reflected object should enforce Java
             * language access checks.
             *
             * First, if there is a security manager, its checkPermission method
             * is called with a ReflectPermission("suppressAccessChecks")
             * permission.
             *
             * By calling Field.setAcessible(true) you turn off the access
             * checks for this particular Field instance, for reflection only.
             * Now you can access it even if it is private, protected or package
             * scope, even if the caller is not part of those scopes.
             */
            privateFieldObj.setAccessible(true);
            Student student = new Student("Peter");
            String fieldValue = (String) privateFieldObj.get(student);
            System.out.println("privateNameField value = " + fieldValue);
        }
        catch (NoSuchFieldException | SecurityException
                | IllegalArgumentException | IllegalAccessException e)
        {
            e.printStackTrace();
        }

    }

}