A Simple Example

This is a simple example to help those new to betwixt. It shows how a simple bean can be converted to xml and back again. A round trip, no less!

In order to run these simple examples, the classpath needs to contain Betwixt and all its dependencies . Note that any JAXP (1.1 or later) compliant parser can be used to replace xerces and xml-apis. JUnit is not required to run betwixt (but is needed if you want to run the unit tests in CVS).

This example is based around a very simple bean representing a person:

public class PersonBean {
    private String name;
    private int age;
    /** Need to allow bean to be created via reflection */
    public PersonBean() {}
    public PersonBean(String name, int age) {
        this.name = name;
        this.age = age;
    public String getName() {
        return name;
    public void setName(String name) {
        this.name = name;
    public int getAge() {
        return age;
    public void setAge(int age) {
        this.age = age;
    public String toString() {
        return "PersonBean[name='" + name + "',age='" + age + "']";

The basic usage pattern for writing beans using Betwixt is to create a BeanWriter, configure it and then pass a bean into the write method. Pretty easy.

Here's a simple application which converts a person bean to xml which is then sent to System.out:

import java.io.StringWriter;

import org.apache.commons.betwixt.io.BeanWriter;

public class WriteExampleApp {

     * Create an example bean and then convert it to xml.
    public static final void main(String [] args) throws Exception {
        // Start by preparing the writer
        // We'll write to a string 
        StringWriter outputWriter = new StringWriter(); 
        // Betwixt just writes out the bean as a fragment
        // So if we want well-formed xml, we need to add the prolog
        outputWriter.write("<?xml version='1.0' ?>");
        // Create a BeanWriter which writes to our prepared stream
        BeanWriter beanWriter = new BeanWriter(outputWriter);
        // Configure betwixt
        // For more details see java docs or later in the main documentation

        // If the base element is not passed in, Betwixt will guess 
        // But let's write example bean as base element 'person'
        beanWriter.write("person", new PersonBean("John Smith", 21));
        // Write to System.out
        // (We could have used the empty constructor for BeanWriter 
        // but this way is more instructive)
        // Betwixt writes fragments not documents so does not automatically close 
        // writers or streams.
        // This example will do no more writing so close the writer now.

The basic usage pattern for reading beans is only a little more complex. This time, you need to create a BeanReader, configure it, register the bean classes that the xml will be mapped to and then parse should be called.

Here's a simple application that converts some xml to a person bean. The bean is then converted to string and the result sent to System.out:

import java.io.StringReader;

import org.apache.commons.betwixt.io.BeanReader;

public class ReadExampleApp {
    public static final void main(String args[]) throws Exception{
        // First construct the xml which will be read in
        // For this example, read in from a hard coded string
        StringReader xmlReader = new StringReader(
                    "<?xml version='1.0' ?><person><age>25</age><name>James Smith</name></person>");
        // Now convert this to a bean using betwixt
        // Create BeanReader
        BeanReader beanReader  = new BeanReader();
        // Configure the reader
        // If you're round-tripping, make sure that the configurations are compatible!
        // Register beans so that betwixt knows what the xml is to be converted to
        // Since the element mapped to a PersonBean isn't called the same 
        // as Betwixt would have guessed, need to register the path as well
        beanReader.registerBeanClass("person", PersonBean.class);
        // Now we parse the xml
        PersonBean person = (PersonBean) beanReader.parse(xmlReader);
        // send bean to system out

A Rich Site Summary Mapping

In the RSS example from Digester there's a bean which matches this pattern.

public class Channel

    public Item[] getItems();

    public void addItem(Item item);

This means that the following bean does not match this naming convention, since the plural property name does not start with the singular name.

public class Foo {
    public Collection getPeople();
    public void addPerson(Person person);

Though these two beans do match

public class Foo {
    public Collection getPersonCollection();
    public void addPerson(Person person);
public class Foo {
    public Iterator getPersonIterator();
    public void addPerson(Person person);

The following are other valid examples of composite-getter methods and their matching adder methods.

Composite getter method Adder method
getChildren() addChild()
getPersonList() addPerson()
getItems() addItem()
getChannels() addChannel()
getSheep() addSheep()