Calling URL Browser From Java Application

This program teaches you how you can call the browser in your OS to open the URL that you are passing from your Java application. This program is fully compiled and tested.

package com.kushal.utilities;

/**
 * @author Kushal Paudyal
 * www.sanjaal.com/java
 * Last Modified On: 26th August, 2008
 */
import java.lang.reflect.Method;

import javax.swing.JOptionPane;

public class OpenDefaultBrowserFromJava {
	private static final String errMsg = "ERROR WHILE ATTEMPTEING TO LUNCH WEB BROWSER";
	private static final String errFindingBrowser="COULD NOT FIND THE BROWSER";
	
	public static void main(String args [])
	{
		String urlToOpen="http://www.sanjaal.com/java";
		openURL(urlToOpen);
	}

	/**
	 * This method takes URL as a parameter and tries to
	 * identify Operating system and then lunches the broswer
	 * with the given URL
	 */
	public static void openURL(String url) {
		String operatingSystem = System.getProperty("os.name");
		try {
			/*
			 * Check if it is windows OS 
			 */
			if (operatingSystem.startsWith("Windows"))
				Runtime.getRuntime().exec("rundll32 url.dll,FileProtocolHandler " + url);
			/*
			 * If not windows OS, Check if it is a Mac OS
			 */
			else if (operatingSystem.startsWith("Mac OS")) {
				Class fileManager = Class.forName("com.apple.eio.FileManager");
				Method openURL = fileManager.getDeclaredMethod("openURL",
						new Class[] { String.class });
				openURL.invoke(null, new Object[] { url });
			}
			
			/*
			 * Or, it might be some unix or linux OS
			 */
			else { 
				/**
				 * There are different browsers possible.
				 */
				String[] browsers = { 	"firefox", 
										"netscape",
										"opera", 
										"konqueror", 
										"epiphany", 
										"mozilla"};
				String browser = null;
				
				for (int count = 0; count < browsers.length && browser == null; count++)
					if (Runtime.getRuntime().exec(
							new String[] { "which", browsers[count] })
							.waitFor() == 0)
						browser = browsers[count];

				if (browser == null) 
					throw new Exception(errFindingBrowser);
				else
					Runtime.getRuntime().exec(new String[] { browser, url });
			}

		} catch (Exception e) {
			JOptionPane.showMessageDialog(null, errMsg + ":n" + e.getMessage());
		}
	}

}

Java Reflection Tutorial – List Methods Of A Class

Reflection is a very powerful tool in Java. I will start this tutorial with an excerpt from Sun’s Tutorial Page for Java reflections. It says:

Reflection is commonly used by programs which require the ability to examine or modify the runtime behavior of applications running in the Java virtual machine. This is a relatively advanced feature and should be used only by developers who have a strong grasp of the fundamentals of the language. With that caveat in mind, reflection is a powerful technique and can enable applications to perform operations which would otherwise be impossible.

  • Extensibility Features
    An application may make use of external, user-defined classes by creating instances of extensibility objects using their fully-qualified names.
  • Class Browsers and Visual Development Environments
    A class browser needs to be able to enumerate the members of classes. Visual development environments can benefit from making use of type information available in reflection to aid the developer in writing correct code.
  • Debuggers and Test Tools
    Debuggers need to be able to examine private members on classes. Test harnesses can make use of reflection to systematically call a discoverable set APIs defined on a class, to insure a high level of code coverage in a test suite.

Drawbacks of Reflection
Reflection is powerful, but should not be used indiscriminately. If it is possible to perform an operation without using reflection, then it is preferable to avoid using it. The following concerns should be kept in mind when accessing code via reflection.

  • Performance Overhead
    Because reflection involves types that are dynamically resolved, certain Java virtual machine optimizations can not be performed. Consequently, reflective operations have slower performance than their non-reflective counterparts, and should be avoided in sections of code which are called frequently in performance-sensitive applications.
  • Security Restrictions
    Reflection requires a runtime permission which may not be present when running under a security manager. This is in an important consideration for code which has to run in a restricted security context, such as in an Applet.
  • Exposure of Internals
    Since reflection allows code to perform operations that would be illegal in non-reflective code, such as accessing private fields and methods, the use of reflection can result in unexpected side-effects, which may render code dysfunctional and may destroy portability. Reflective code breaks abstractions and therefore may change behavior with upgrades of the platform.

The following tutorial will use the class called Student and display all the methods of that class using the Java Reflection technology.

package com.kushal.utils;
/**
 * @Author Kushal Paudyal
 * www.sanjaal.com/java
 * Last Modified On 10th August 2009
 *
 * A Simple class that lists the method of another
 * class using the reflections mechanism.
 */
import java.lang.reflect.Method;

public class MethodsListViaReflection {

	public void listMethods() {

		Class myStudentClass = Student.class;

		Method[] methods = myStudentClass.getDeclaredMethods();

		for (Method method : methods) {
			System.out.println(method.getName());
		}
	}

	public static void main(String[] args) {
		new MethodsListViaReflection().listMethods();
	}
}

class Student {

private String _firstname;
private String _lastname;
private String _address;
private int _rollNumber;

public String getFirstname() {
return _firstname;
}

public void setFirstname(String firstname) {
_firstname = firstname;
}

public String getLastname() {
return _lastname;
}

public void setLastname(String lastname) {
_lastname = lastname;
}

public String getAddress() {
return _address;
}

public void setAddress(String address) {
_address = address;
}
public int getRollNumber() {
return _rollNumber;
}

public void setRollNumber(int rollNumber) {
_rollNumber= rollNumber;
}
}[/java]
=======================
The following is the output of this program:
getFirstname
setFirstname
getLastname
setLastname
getAddress
setAddress
getRollNumber
setRollNumber

Java Reflections Tutorial

This tutorial gives an insight on how Java Reflection can be used to load Java classes dynamically at the run time. Reflection is commonly used by programs which require the ability to examine or modify the runtime behavior of applications running in the Java virtual machine.

package com.kushal.utilities;

/**
 * @author Kushal Paudyal
 * 08/05/2008
 * 
 * Simple demonstration of Java Reflection mechanism to
 * instantiate a class, get it's method and call that
 * method with proper parameter passing.
 */
import java.lang.reflect.*;

public class JavaReflectionsDemo {

	public static void main(String args[]) {
		try {
			/*
			 * Step 1 Define a class loader
			 */
			ClassLoader myClassLoader = ClassLoader.getSystemClassLoader();
			/*
			 * Step 2: Define a class to be loaded.
			 */
			String classNameToBeLoaded = "com.kushal.utilities.DemoClassToBeLoaded";

			/*
			 * Step 3: Load the class
			 */
			Class myClass = myClassLoader.loadClass(classNameToBeLoaded);

			/*
			 *Step 4: create a new instance of that class
			 */
			Object whatInstance = myClass.newInstance();

			String methodParameter = "ABC";
			/*
			 * Step 5: get the method, with proper parameter signature.
			 * The second parameter is the parameter type.
			 * There can be multiple parameters for the method we are trying to call, 
			 * hence the use of array.
			 */

			Method myMethod = myClass.getMethod("myMethod123",
					new Class[] { String.class });

			/*
			 *Step 6:
			 *Calling the real method. Passing methodParameter as
			 *parameter. You can pass multiple paramters based on 
			 *the signature of the method you are calling. Hence
			 *there is an array. 
			 */
			String returnValue = (String) myMethod.invoke(whatInstance,
					new Object[] { methodParameter });

			System.out.println("The value returned from the method is:"
					+ returnValue);

			/*
			 * Catching Probable Exceptions
			 * You can simply catch the Generic 'Exception' to reduce your coding.		 
			 */
		} catch (ClassNotFoundException e1) {
			System.out.println("EXCEPTION:CLASS NOT FOUND");
		} catch (IllegalAccessException e2) {
			System.out.println("EXCEPTION:ILLEGAL ACCESS");
		} catch (InstantiationException e3) {
			System.out.println("EXCEPTION:INSTANTIATION EXCEPTION");
		} catch (NoSuchMethodException e4) {
			System.out.println("EXCEPTION:NO SUCH METHOD");
		} catch (InvocationTargetException e5) {
			System.out.println("EXCEPTION: INVOCATION TARGET");

		}
	}

}
/**
 * @author Kushal Paudyal
 * 08/05/2008
 * www.sanjaal.com/java
 */

/*
 * This is the demo class that we will use to load and invoke method
 * using Java Reflection.
 */
class DemoClassToBeLoaded {
	public static String myMethod123(String someParam) {
		System.out.println("You Are Calling myMethod()");
		System.out.println("You Passed " + someParam + " as Parameter");

		/*
		 * Just returning the current class name
		 * This is just an example method. 
		 */
		return DemoClassToBeLoaded.class.getName();
	}

}