使用Restlet创建一个简单的web service（Creating a simple web service with Restlet）
Creating a simple web service with RestletPosted by Philippe Van Nuijs at 16:12Restlet是一个轻权的RESt框架。遗憾的是没有很好的示例来描述如何使用它。虽然示例代码包里有一些，但是都比较初级，没有涉及如何创建一个完整的REST web service示例（使用create，update，delete功能）。这里并没有真正的执行数据库操作，你可以再Todo部分填充自己的数据访问代码：
首先，创建一个简单的User类，包含ID和name两个变量：
import java.nio.Buffer;import org.json.JSONObject;public class User {private String id = null;private String name = null;/** * @return Returns the id. */public String getId() { return id;}/** * @param id * The id to set. */public void setId(String id) { this.id = id;}/** * @return Returns the name. */public String getName() { return name;}/** * @param name * The name to set. */public void setName(String name) { this.name = name;}/** * Convert this object to a JSON object for representation */public JSONObject toJSON() {try{ JSONObject jsonobj = new JSONObject(); jsonobj.put("id", this.id); jsonobj.put("name", this.name); return jsonobj;}catch(Exception e){ return null;}}/** * Convert this object to a string for representation */public String toString() { StringBuffer sb = new StringBuffer(); sb.append("id:"); sb.append(this.id); sb.append(",name:"); sb.append(this.name); return sb.toString();}}创建错误展示消息类，用来传递错误信息：
import org.json.JSONObject;public class ErrorMessage {public JSONObject toJSON() { JSONObject jsonobj = new JSONObject(); try { jsonobj.put("error", "An error occured"); return jsonobj; } catch (Exception e) { return null; }}public String toString() { StringBuffer sb = new StringBuffer(); sb.append("error:"); sb.append("An error occured"); return sb.toString();}}Now, let's create our UserResource.好了，现在创建用户资源 UserResource类。
import org.restlet.Context;import org.restlet.data.Form;import org.restlet.data.MediaType;import org.restlet.data.Request;import org.restlet.data.Response;import org.restlet.data.Status;import org.restlet.ext.json.JsonRepresentation;import org.restlet.resource.Representation;import org.restlet.resource.Resource;import org.restlet.resource.ResourceException;import org.restlet.resource.StringRepresentation;import org.restlet.resource.Variant;public class UserResource extends Resource {private User user = null;public UserResource(Context context, Request request, Response response) { super(context, request, response); String userid = null; userid = (String) getRequest().getAttributes().get("id"); this.user = findUser(userid); getVariants().add(new Variant(MediaType.TEXT_PLAIN)); getVariants().add(new Variant(MediaType.APPLICATION_JSON));}/** * Allow a PUT http request * * @return */public boolean allowPut() { return true;}/** * Allow a POST http request * * @return */public boolean allowPost() { return true;}/** * Allow a DELETE http request * * @return */public boolean allowDelete() { return true;}/** * Allow the resource to be modified * * @return */public boolean setModifiable() { return true;}/** * Allow the resource to be read * * @return */public boolean setReadable() { return true;}/** * Find the requested user object * * @param userid * @return */private User findUser(String userid) { try { if (null == userid) return null; // :TODO {do some database lookup here } // user = result of lookup // This part should be replaced by a lookup User u = new User(); u.setId("1"); u.setName("name"); // end replace return u; } catch (Exception e) { return null; }}/** * Represent the user object in the requested format. * * @param variant * @return * @throws ResourceException */public Representation represent(Variant variant) throws ResourceException { Representation result = null; if (null == this.user) { ErrorMessage em = new ErrorMessage(); return representError(variant, em); } else { if (variant.getMediaType().equals(MediaType.APPLICATION_JSON)) { result = new JsonRepresentation(this.user.toJSON()); } else { result = new StringRepresentation(this.user.toString()); } } return result;}/** * Handle a POST Http request. Create a new user * * @param entity * @throws ResourceException */public void acceptRepresentation(Representation entity) throws ResourceException { // We handle only a form request in this example. Other types could be // JSON or XML. try { if (entity.getMediaType().equals(MediaType.APPLICATION_WWW_FORM, true)) { Form form = new Form(entity); User u = new User(); u.setName(form.getFirstValue("user[name]")); // :TODO {save the new user to the database} getResponse().setStatus(Status.SUCCESS_OK); // We are setting the representation in the example always to // JSON. // You could support multiple representation by using a // parameter // in the request like "?response_format=xml" Representation rep = new JsonRepresentation(u.toJSON()); getResponse().setEntity(rep); } else { getResponse().setStatus(Status.CLIENT_ERROR_BAD_REQUEST); } } catch (Exception e) { getResponse().setStatus(Status.SERVER_ERROR_INTERNAL); }}/** * Handle a PUT Http request. Update an existing user * * @param entity * @throws ResourceException */public void storeRepresentation(Representation entity) throws ResourceException { try { if (null == this.user) { ErrorMessage em = new ErrorMessage(); Representation rep = representError(entity.getMediaType(), em); getResponse().setEntity(rep); getResponse().setStatus(Status.CLIENT_ERROR_BAD_REQUEST); return; } if (entity.getMediaType().equals(MediaType.APPLICATION_WWW_FORM, true)) { Form form = new Form(entity); this.user.setName(form.getFirstValue("user[name]")); // :TODO {update the new user in the database} getResponse().setStatus(Status.SUCCESS_OK); // We are setting the representation in this example always to // JSON. // You could support multiple representation by using a // parameter // in the request like "?response_format=xml" Representation rep = new JsonRepresentation(this.user.toJSON()); getResponse().setEntity(rep); } else { getResponse().setStatus(Status.CLIENT_ERROR_BAD_REQUEST); } } catch (Exception e) { getResponse().setStatus(Status.SERVER_ERROR_INTERNAL); }}/** * Handle a DELETE Http Request. Delete an existing user * * @param entity * @throws ResourceException */public void removeRepresentations() throws ResourceException { try { if (null == this.user) { ErrorMessage em = new ErrorMessage(); Representation rep = representError(MediaType.APPLICATION_JSON, em); getResponse().setEntity(rep); getResponse().setStatus(Status.CLIENT_ERROR_BAD_REQUEST); return; } // :TODO {delete the user from the database} getResponse().setStatus(Status.SUCCESS_OK); } catch (Exception e) { getResponse().setStatus(Status.SERVER_ERROR_INTERNAL); }}/** * Represent an error message in the requested format. * * @param variant * @param em * @return * @throws ResourceException */private Representation representError(Variant variant, ErrorMessage em) throws ResourceException { Representation result = null; if (variant.getMediaType().equals(MediaType.APPLICATION_JSON)) { result = new JsonRepresentation(em.toJSON()); } else { result = new StringRepresentation(em.toString()); } return result;}protected Representation representError(MediaType type, ErrorMessage em) throws ResourceException { Representation result = null; if (type.equals(MediaType.APPLICATION_JSON)) { result = new JsonRepresentation(em.toJSON()); } else { result = new StringRepresentation(em.toString()); } return result;}}And implement a restlet server, listening on port 8100. 同时，我们事先一个restlet 服务器，监听8100端口：
import org.restlet.Application;import org.restlet.Component;import org.restlet.Context;import org.restlet.Restlet;import org.restlet.Router;import org.restlet.data.MediaType;import org.restlet.data.Protocol;import org.restlet.data.Request;import org.restlet.data.Response;import org.restlet.resource.StringRepresentation;public class WebServiceApplication extends Application { public static void main(String[] args) throws Exception { // Create a component Component component = new Component(); component.getServers().add(Protocol.HTTP, 8100); WebServiceApplication application = new WebServiceApplication( component.getContext()); // Attach the application to the component and start it component.getDefaultHost().attach(application); component.start(); } public WebServiceApplication() { super(); } public WebServiceApplication(Context context) { super(context); } @Override public Restlet createRoot() { Router router = new Router(getContext()); router.attach("/users", UserResource.class); router.attach("/users/{id}", UserResource.class); Restlet mainpage = new Restlet() { @Override public void handle(Request request, Response response) { StringBuilder stringBuilder = new StringBuilder(); stringBuilder.append("<html>"); stringBuilder .append("<head><title>Sample Application Servlet Page</title></head>"); stringBuilder.append("<body bgcolor=white>"); stringBuilder.append("<table border=\"0\">"); stringBuilder.append("<tr>"); stringBuilder.append("<td>"); stringBuilder.append("<h1>2048Bits.com example - REST</h1>"); stringBuilder.append("</td>"); stringBuilder.append("</tr>"); stringBuilder.append("</table>"); stringBuilder.append("</body>"); stringBuilder.append("</html>"); response.setEntity(new StringRepresentation(stringBuilder .toString(), MediaType.TEXT_HTML)); } }; router.attach("", mainpage); return router; }}You can test the restlet web service with any internet browser except for the PUT and DELETE requests. I prefer curl to test a Restful web service.你可以使用任何浏览器测试restlet web service的服务（出了PUT和DELETE请求）。最好使用curl来测试，具体方法如下：
GET REQUEST - Show the information of a user:
curl http://localhost:8100/users/1POST REQUEST - Create a new user:
curl -d "user[name]=John" http://localhost:8100/usersPUT REQUEST - Update an existing user:
curl -X PUT -d "user[name]=Jane" http://localhost:8100/users/1DELETE REQUEST - Delete an existing user:
curl -X DELETE http://localhost:8100/users/1