Java反射-获取现有对象中的当前字段值

Question

I have a constructed object of the type below,

public class Form {
   private String a;
   private String b;
   private Boolean c;

   public String getA() { return a; }
   public void setA (String a) { this.a = a; }
   public String getB() { return b; }
   public void setB (String b) { this.b = b; }
   public Boolean getC() { return c; }
   public void setC (Boolean c) { this.c = c; }
}

I'm using reflection to examine an existing object, eg this Form: ("testA", "testB", False)

How do I get the current value of a particular field, let's say String b ?

// Assume "form" is my current Form object
Field[] formFields = form.getClass().getDeclaredFields();
if (formFields != null) {
   for (Field formField : formFields) { 
       Class type = formField.getType();
       // how do I get the current value in this current object?
   }
}

Answer 1

Use methods of java.lang.reflect.Field :

// Necessary to be able to read a private field
formField.setAccessible(true);

// Get the value of the field in the form object
Object fieldValue = formField.get(form);

Answer 2

This is a situation where I am a big proponent of using an external library. Apache Commons BeanUtils is excellent for this purpose and hides a lot of the core java.lang.reflect complexity. You can find it here: http://commons.apache.org/proper/commons-beanutils/

Using BeanUtils, the code to satisfy your need would be the following:

Object valueOfB = PropertyUtils.getProperty( formObject, "b" );

Another benefit of using BeanUtils is that it does all of the checking to ensure that you have a proper accessor method for "b" -- getB(). There are also other utility methods in the BeanUtils library which enable you to handle all sorts of Java bean property manipulation.