Restlet 2.0 边学边写（七）Restlet返回xml和json数据格式

 上一次实践实现了html form来访问Restlet的PUT和DELETE方法，但返回数据都是string，仅能作为演示使用。本次实践将使各方法返回xml和json格式的数据，方便页面、程序的读取和展示。

1.xml库
首先是基础的xml数据格式。Restlet的扩展包org.restlet.ext.xml.jar提供各种xml相关类库。包中的抽象类XmlRepresentation作为父类提供接口和方法，但不能创建该父类的实例，而是需要使用SaxRepresentation和DomRepresentation类的实例来执行操作。

将Restlet安装目录\Edition Java EE\2.0.10\lib下的org.restlet.ext.xml.jar包加入Build Path。

2.Resource
修改com.sunny.restlet.order.CustomersResource类，代码如下：

@Override
protected Representation get() throws ResourceException {
// TODO Auto-generated method stub
Map customers = orderDao.getAllCustomers();
DomRepresentation representation;
try {
representation = new DomRepresentation();
Document dom = representation.getDocument();
Element all = dom.createElement("customers");
dom.appendChild(all);
for (Object object : customers.entrySet()) {
Entry<String, Customer> entry = (Entry) object;
String id = entry.getKey();
Customer customer = entry.getValue();
Element root = dom.createElement("customer");
root.setAttribute("id", id);
all.appendChild(root);
Element namElement = dom.createElement("name");
namElement.appendChild(dom.createTextNode(customer.getName()));
root.appendChild(namElement);
Element addressElement = dom.createElement("address");
addressElement.appendChild(dom.createTextNode(customer
.getAddress()));
root.appendChild(addressElement);
}
dom.normalizeDocument();
return representation;
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return null;
}

@Override
protected Representation post(Representation entity)
throws ResourceException {
// TODO Auto-generated method stub
Form form = new Form(entity);
String name = form.getFirstValue("name");
String address = form.getFirstValue("address");
Customer customer = new Customer(name, address);
String id = orderDao.addCustomer(customer);
customer = orderDao.getCustomerById(id);
if (customer == null) {
return null;
}
DomRepresentation representation;
try {
representation = new DomRepresentation();
Document dom = representation.getDocument();
Element root = dom.createElement("customer");
root.setAttribute("id", id);
dom.appendChild(root);
Element namElement = dom.createElement("name");
root.appendChild(namElement);
namElement.appendChild(dom.createTextNode(customer.getName()));
Element addressElement = dom.createElement("address");
root.appendChild(addressElement);
addressElement.appendChild(dom
.createTextNode(customer.getAddress()));
dom.normalizeDocument();
return representation;
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return null;
}