public abstract class Par {
  @XmlTransient
  public String name;

  @XmlAttribute(name="name")
  public String getName() {
    return name;
  }

  public void setName(String n) {
    name = n;
  }
}

@XmlRootElement(name="int")
public class IntegerPar extends Par {
    @XmlTransient
    public int value;

    @XmlAttribute(name="value")
    public int getValue() {
      return value;
    }

    public void setValue(int v) {
      value = v;
    }
}

@XmlRootElement(name="string")
public class StringPar extends Par { ... }

<root>
  <int name="x" value="1"/>
  <string name="s" value="hello"/>
</root>

@XmlRootElement(name="root")
public class ParamRequest {
  @XmlAnyElement
  public ArrayList<Par> params;
}

myRequest.params    [[int: null], [string: null]]