How can i generate xml from an object hierarchy?

Question

I have object, tree/model/hierarchy, whatever the correct term is. It consists of what could be characterized as a one-to-one mapping of the desired XML.

That is i have the following (in a non-standard UML sort of syntax)

class A {
    class B b[*]
    class C
    class D
}

class B {
    class C c[*]
    string AttributeFoo = "bar"
}

class C {
    string AttributeThis = "is"
}

class D {
    string AttributeName = "d"
}

Desired output is something like this:

<?xml version="1.0"?>
<a>
    <b attribute-foo="bar">
        <c attribute-this="is"/>
    </b>
    <c attribute-this="is"/>
    <d attribute-name="d"/>
</a>

What would you propose to be the best, and/or the simplest way of achieving this goal?

Answer 1

I would look at JAXB because a) you get it in the standard library and b) it isn't that complicated. This code requires Java 6:

@XmlRootElement public static class A {
  public List<B> b = new ArrayList<B>();
}

public static class B {
  public List<C> c = new ArrayList<C>();
  @XmlAttribute(name = "attribute-foo") public String attributeFoo = "foo";
}

public static class C {
  @XmlAttribute(name = "attribute-this") public String attributeThis = "is";
}

public static void main(String[] args) {
  A a = new A();
  a.b.add(new B());
  a.b.get(0).c.add(new C());
  JAXB.marshal(a, System.out);
}
//TODO: getters/setters, error handling and so on

Output:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<a>
    <b attribute-foo="foo">
        <c attribute-this="is"/>
    </b>
</a>

Answer 2

The simplest way is to use XStream. See here for an idea what it does. It can be a bit buggy, but for simple tasks its great. For a more comprehensive (and reliable) technology, then JAXB (part of Java6, see javax.xml.bind) is the better option.

Answer 3

I think it is the purpose of JAXB (http://jaxb.java.net/) to map Objects to/from XML

Answer 4

If you want to use tools, have a look at jaxb. Marshalling/Unmarshalling is what your're doing here, it's a common problem with a lot of solutions available.

I think it's the best (not reinventing the wheel) and it's the simplest (I've done it manually and it's really no fun - object graphs can be cyclic...)

Answer 5

I like XMLBeans.

Answer 6

In my opinion if your not too bothered about performance I would stay away from Jaxb and take a look at some of the simpler frameworks. If performance is an issue I tend to favour jibx over jaxb for most situations.

In this situation I tend to use the simple project.

http://simple.sourceforge.net/download/stream/doc/tutorial/tutorial.php#start

Just annotate your object model and away you go..... :-)

@Root
public class Example {

   @Element
   private String text;

   @Attribute
   private int index;

   public Example() {
      super();
   }  

   public Example(String text, int index) {
      this.text = text;
      this.index = index;
   }

   public String getMessage() {
      return text;
   }

   public int getId() {
      return index;
   }
}