3.19. Getting and Setting Properties as Strings

You need to persist a bean to a text file, or populate a bean's properties from a String.

Use BeanUtils to get and set bean properties with strings. This utility contains many of the same functions as PropertyUtils with one major exception; instead of returning the Object value of the property, BeanUtils returns and expects a string representation of a value. The following code uses BeanUtils to populate a bean that is dependent on user input:

import java.util.*;
import org.apache.commons.beanutils.*;
Person person = new Person( );
person.setAge( new Integer( 45 ) );
person.setName( "Donald" );
person.setOccupation( "Salesman" );
// Get the Age as a String
               String ageString = BeanUtils.getProperty( person, "age" );
               // Set the Age from a String
               BeanUtils.setProperty( person, "age", "50" );

BeanUtils come in handy when a bean is populated from a user-supplied input like standard input or the parameters of an HTTP request. In fact, BeanUtils started as the mechanism used to populate a Struts ActionForm from the contents of an HTTP request. When the Struts ActionServlet receives a request that is mapped to an Action, the ActionServlet calls a method in RequestUtils, which examines the request and sets any properties on the relevant ActionForm. Because the inner workings of Struts are outside the scope of this book, Example 3-7 takes a String input from System.in and sets the age property of Person.

import java.io.*;
public class ReadAge {
    public static void main (String[] args) throw Exception {
        //  Prompt for an Age
        System.out.print("Enter Age: ");
        //  open up standard input
        BufferedReader br =
            new BufferedReader(new InputStreamReader(System.in));
        String ageString = null;
        ageString = br.readLine( );
        // Set the Integer property with a String
                          Person person = new Person( );
                          BeanUtils.setProperty( person, "age", ageString );
   }
}

When BeanUtils sets the age property, it uses a set of registered Converter instances that are available to translate between a String and an Object. Behind the scenes, BeanUtils used the IntegerConverter class to convert the user-supplied String to an Integer object. For a full list of converters, read the documentation for the org.apache.commons.beanutils.converters package.

The BeanUtils Javadoc is available at http://commons.apache.org/beanutils/api/index.html.