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Tags/Keywords : Spring Reflection, Spring POC, Spring, Java,Questions, Example, Code, Tutorial, Article
Author : ISHTEK
Date (Year/Month/Date): 2009-07-17
An idea to use new operator for instantiating a JavaBean while using SpringFramework

Please be informed that NONE of the design/code from this
page is claiming to be some sort of best practices and we DO NOT expect
any of our visitor/reader of this page to assume this as some sort of
best practice for any context and should not be using this 
as it is without appropriate evaluation to their, so to say, 
specific programming context.

This page intends only to provide bit and piece of known ways  for
doing some sort of example and may not be fit for any other purpose.


While using SpringFramework we have to use appropriate concrete class
that implements some form of ApplicationContext interface

Like for example I have used ClassPathXmlApplicationContext class
that implements AbstractXmlApplicationContext interface.
This interface extends from a Interface hierarchy that will
lead us to the ApplicationContext as the base interface.

Once ClassPathXmlApplicationContext is instantiated, then we can retrieve
any bean that is already defined in the applicationContext.xml file,
by using getBean method from AbstractApplicationContext.

To the best of my understanding of Springframework, this could be
one of the many ways we can use SpringFramework to retrieve bean
instance that is already defined in the applicationContext or 
any other configuration XML file.



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But generally being a Software Professional, working on Java Technology,
I tend to use "new" operator for creating instance of any
JavaBean class.

But while using SpringFramework for creating Object from some form of
dependency injection to prepopulate values or state with other dependent
objects, I may not be able to use "new" operator.

On one fine day, as idea came to my mind to find ways by which I can still
use quot;new" operator to create an instance of a class, but should be
able to construct an object similar enough if I would have used 
SpringFramework application context to retrieve that bean.

Let me discuss this very idea with you all:
If I could use Reflection from Java API, to find out all the setter methods
existing in any object, and retrieve corresponding values/objects from 
SpringFramework application context, and populate those to the new bean.

POC (Proof of concept for this very thought of mine), as follows:

Suppose the service bean in question is TestServiceBean.java
TestServiceBean.java

package example;

public class TestServiceBean {
	//Mandatory transient private instance variable
	//that does all the trick, using Reflection from
	//Java API.
	//This variable should not have any public
	//accessor getter or setter methods.
  private transient TestBeanValueSetter testBeanValueS
	                    = new TestBeanValueSetter(this);

  private TestService testService;

  public TestService getTestService() {
	return testService;
  }

  public void setTestService(TestService testService) {
	this.testService = testService;
  }
}



And the dependent Javabean as follows:
TestService.java

package example;

public class TestService {
  public String serviceName;

public String getServiceName() {
	return serviceName;
}

public void setServiceName(String serviceName) {
	this.serviceName = serviceName;
}
}




Client program will use "new" operator to instantiate
this TestServiceBean JavaBean.
Client program is as follows:
TestClient.java

package test;

import example.TestServiceBean;

public class TestClient {
    
    public TestClient() {
    	TestServiceBean testServBean = new TestServiceBean();
    	System.out.println(testServBean.getTestService());
    }
	/**
	 * @param args
	 */
	public static void main(String[] args) {
      new TestClient();
	}
}



Looking at the above two lines (marked as red and bold), one can
think that the output on console or command prompt would be
null

As testService instance variable of type TestService, is having
default initialization of null value.

But this is wrong, instead when I ran this client in my local
development environment with all the other dependent class files,
I found output as follows:
example.TestService@1f6a7b9
This means that testService variable is already intialized with some
value from some other class file.

Now let us look at the "TestBeanValueSetter.java" class file:

TestBeanValueSetter.java

package example;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

public class TestBeanValueSetter {
    public TestBeanValueSetter(Object obj) {
    	TestBeanValueProvider beanValue = 
		                new TestBeanValueProvider(obj);
    	Method[] methods = obj.getClass().getMethods();

    	for(int i=0;i<methods.length;i++) {
    		try {

    			if(methods[i].getName().startsWith("set")) {
        	       Object[] objs = new Object[1];
        	       objs[0] = beanValue
				         .getObject(methods[i].getName());
        	 
				  methods[i].invoke(obj, objs);
    			}
			} catch (IllegalArgumentException e) {
				e.printStackTrace();
			} catch (IllegalAccessException e) {
				e.printStackTrace();
			} catch (InvocationTargetException e) {
				e.printStackTrace();
			}
    	}
    }
}



TestBeanValueProvider class is the interfacing or abstracting
all operations related to SpringFramework:
TestBeanValueProvider.java

package example;

public class TestBeanValueProvider {

	//assuming that this class will be using SpringFramework
	//application context to retrieve bean with the name
	//as that of the package.classname. This has to be the
	//same in applicationContext.xml file as key value.
	
	private String key;
	public TestBeanValueProvider(Object obj) {
		key = obj.getClass().toString();
	}
  public Object getObject(String methodName) {

	  //Retrieve corresponding value from SpringFramework
	  //application context getBean method for this corresponding
	  //methodName, with some String manipulation done as per
	  //suitability, like if the methodName is "setTestService",
	  //then using String manipulation on this methodName, to
	  //extract appropriate variable name as "testService".
	  
	  return new TestService();
  }
}



I shall be enhancing this example to include all the SpringFramework
related code and try to complete this concept appropriately.

Can I expect comments and suggestions on this from reader of this
idea?



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to help or guide users with any technical difficulties he/she faces
while working with the example code environment setting up, running
and resolving any such exception raised during compile or at runtime.
You may ask for any technical doubt or seek technical help related to
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from the Author for FREE.

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