You need to access a simple bean property by name.

Use PropertyUtils.getSimpleProperty() to access a bean property by name; this method takes the name of a property and returns the value of that property. The following example uses this method to retrieve the name property from a Person bean:

import org.apache.commons.beanutils.PropertyUtils;
Person person = new Person( );
person.setName( "Alex" );    
String name = (String) PropertyUtils.getSimpleProperty( person, "name" );
System.out.println( name );

PropertyUtils.getSimpleProperty( ) invokes the public method getName( ) on an instance of Person, returning the value of the name property. The previous example executes and prints out the name "Alex."

A simple bean property is a private member variable that can be accessed with a getter method. If a property can be read via a getter method, that getter method is said to be the read method for the named property. If the property can be modified with a setter method, that setter method is said to be the write method for the named property. The Person bean in Example 3-4 defines two simple bean properties, name and favoriteColor.

package com.discursive.jccook.bean;
public class Person {
    private String name;
    private String favoriteColor;
    public Person( ) {}
    public String getName( ) { return name; }
    public void setName(String name) { 
        this.name = name; 
    }
    public String getFavoriteColor( ) { return favoriteColor; }
    public void setFavoriteColor(String favoriteColor) { 
        this.favoriteColor = favoriteColor;
    }
}

The class defined in Example 3-4 is used in the following sample code, which creates a Person object, sets the name and favoriteColor properties, and demonstrates the use of Property.getSimpleProperty( ) to retrieve both properties by name:

import org.apache.commons.beanutils.PropertyUtils;
// Create a person
Person person = new Person( );
               person.setName( "Alex Wolfe" );
               person.setFavoriteColor( "Green" );
try {
    String name = (String) PropertyUtils.getSimpleProperty( person, "name" );
                   String favoriteColor =
                       (String) PropertyUtils.getSimpleProperty( person, "favoriteColor" );
    System.out.println( "The Person: " + name + " likes " + favoriteColor );
} catch (IllegalAccessException e) {
    System.out.println( "You are not allowed to access a property!" );
} catch (InvocationTargetException e) {
    System.out.println( "There was a problem invoking the method." );
} catch (NoSuchMethodException e) {
    System.out.println( "There is no method to get a property." );
}

Take note of the extensive exception handling required to retrieve two bean properties; three separate exceptions can be thrown by getSimpleProperty( ). The first, IllegalAccessException, is thrown if the getter method is not accessible (not public). InvocationTargetException is thrown if the getter method throws an exception, and NoSuchMethodException is thrown if you specify a bean property that does not exist on an object; for example, attempting to retrieve the numberOfDoors property from the person object above would throw a NoSuchMethodException because there is no getNumberOfDoors( ) method.

Using PropertyUtils.getSimpleProperty( ) when you could simply call a get method might seem like an unwieldy solution to a very simple problem, but the alternative—calling a getter method—locks you into a specific bean property at compile time. This may be unacceptable if you are designing something generic like a templating system or an expression language interpreter; you may need to access an arbitrary property of an arbitrary object known only at runtime. The ability to retrieve the value of a bean property by name lies at the heart of a number of important tools, such as Struts, Apache Velocity, Commons JEXL, and utilities from Commons Collections. Accessing bean properties by name is an appropriate solution for a system that needs a high level of flexibility.

The next three recipes focus on accessing different types of bean properties: nested, indexed, and mapped. Simple properties may also be retrieved with PropertyUtils.getProperty( ); this method is described in Recipe 3.8.

This recipe mentions Apache Struts, a web application MVC framework. For more information about the Struts project, see http://struts.apache.org/. Apache Velocity and Commons JEXL are discussed in Chapter 9, and Commons Collections is discussed in Chapter 5.