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 Restlet

Posted by Philippe Van Nuijs at 16:12

Restlet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/1

POST REQUEST - Create a new user:

curl -d "user[name]=John" http://localhost:8100/users

PUT REQUEST - Update an existing user:

curl -X PUT -d "user[name]=Jane" http://localhost:8100/users/1

DELETE REQUEST - Delete an existing user:

curl -X DELETE http://localhost:8100/users/1

Labels: Java, Rest, Restlet