Java Reflection Beans Property API

问题

Is there any standard way to access Java Bean Property like

class A {
   private String name;

   public void setName(String name){
       this.name = name;
   }

   public String getName(){
       return this.name;
   }

}

So can I access this java bean property name using Reflection API so that when I change the value of property the methods of getName and setName are called automatically when I set and get values of that property

回答1:

What you need is the BeanInfo / Introspector mechanism (see Bozho's answer). However, it's hell to use this directly, so you can use one of the Libraries that offer property-based access. The best-known is probably Apache Commons / BeanUtils (another one is Spring's BeanWrapper abstraction)

Example code:

A someBean = new A();

// access properties as Map
Map<String, Object> properties = BeanUtils.describe(someBean);
properties.set("name","Fred");
BeanUtils.populate(someBean, properties);

// access individual properties
String oldname = BeanUtils.getProperty(someBean,"name");
BeanUtils.setProperty(someBean,"name","Barny");

回答2:

You question is very unclear, but if I get it:

Yes. The java.beans package has the so called Introspector. There you can read the properties of a bean.

BeanInfo info = Introspector.getBeanInfo(Bean.class);
PropertyDescriptor[] pds = info.getPropertyDescriptors();

You can find the desired PropertyDescriptor by its name and you can call getReadMethod().invoke(..)

回答3:

I have tried BeanUtils as well as PropertyDescriptors because I did not have the information on the class that was passed to my method. I did not even know the data types of the properties passed and so setting values became difficult. I know that BeanUtils should do the conversion automatically for the property and set it but it was not saving the data for me. So finally, I had to rely on getting the fields. Here is what I did:

Field[] fields = className.getDeclaredFields();
for (int i=0; i<fields.length ;i++)
{
  String element = fields[i].getName();
  String propertyType = fields[i].getType().getName();
  fields[i].setAccessible(true);
  if(propertyType.equalsIgnoreCase("java.lang.Integer"))
    {
      fields[i].set(mypojoObj, Integer.parseInt(parameterValue));
    }
    else
    {
      fields[i].set(mypojoObj, parameterValue);
    }
 }

I did a similar switch-case to convert all property types to correct types. When fetching from the page, request.getParameter(paramname) was always returning String so this conversion worked for me. Any better options for direct data conversion will be really helpful.

来源：https://stackoverflow.com/questions/5856895/java-reflection-beans-property-api

标签

java

reflection

javabeans