RESTful Web Services方法

正如我們討論至今認為RESTful web服務使得重用HTTP動詞，以確定要執行所指定的資源(多個)的操作。下表使用HTTP動詞常用狀態的例子。

S.N.	HTTP方法，URI和操作
1	GET http://localhost:8080/UserManagement/rest/UserService/users 獲取使用者列表 (唯讀)
2	GET http://localhost:8080/UserManagement/rest/UserService/users/1 獲取ID為1的使用者 (唯讀)
3	PUT http://localhost:8080/UserManagement/rest/UserService/users/2 使用ID為2插入使用者 (等冪)
4	POST http://localhost:8080/UserManagement/rest/UserService/users/2 更新ID為2的使用者 (N/A)
5	DELETE http://localhost:8080/UserManagement/rest/UserService/users/1 刪除ID為2使用者 (等冪)
6	OPTIONS http://localhost:8080/UserManagement/rest/UserService/users 列出Web服務支援的操作 (唯讀)
7	HEAD http://localhost:8080/UserManagement/rest/UserService/users 僅返回HTTP頭，沒有主體。 (唯讀)

下面是要考慮的重要問題：

GET 僅是讀操作並且是安全的。
PUT 和 DELETE 操作冪等意味著他們的結果總是相同的，無論多少次，這些操作可被呼叫。
PUT 和 POST 動作幾乎相同，區別僅位於在結果其中PUT操作是等冪，POST操作可能導致不同的結果。

例子

讓我們來更新RESTful Web服務建立範例 - 第一應用教學建立Web服務它可以執行CRUD（建立，讀取，更新，刪除）操作。為簡單起見，這裡使用了一個檔案I/O，以取代資料庫操作。

現在更新User.java，UserDao.java和UserService.java檔案在com.yiibai包下。

User.java

package com.yiibai;

import java.io.Serializable;

import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;
@XmlRootElement(name = "user")
public class User implements Serializable {

   private static final long serialVersionUID = 1L;
   private int id;
   private String name;
   private String profession;

   public User(){}

   public User(int id, String name, String profession){
      this.id = id;
      this.name = name;
      this.profession = profession;
   }

   public int getId() {
      return id;
   }
   @XmlElement
   public void setId(int id) {
      this.id = id;
   }
   public String getName() {
      return name;
   }
   @XmlElement
      public void setName(String name) {
      this.name = name;
   }
   public String getProfession() {
      return profession;
   }
   @XmlElement
   public void setProfession(String profession) {
      this.profession = profession;
   }	

   @Override
   public boolean equals(Object object){
      if(object == null){
         return false;
      }else if(!(object instanceof User)){
         return false;
      }else {
         User user = (User)object;
         if(id == user.getId()
            && name.equals(user.getName())
            && profession.equals(user.getProfession())
         ){
            return true;
         }			
      }
      return false;
   }	
}

UserDao.java

package com.yiibai;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.ArrayList;
import java.util.List;

public class UserDao {
   public List<User> getAllUsers(){
      List<User> userList = null;
      try {
         File file = new File("Users.dat");
         if (!file.exists()) {
            User user = new User(1, "Mahesh", "Teacher");
            userList = new ArrayList<User>();
            userList.add(user);
            saveUserList(userList);		
         }
         else{
            FileInputStream fis = new FileInputStream(file);
            ObjectInputStream ois = new ObjectInputStream(fis);
            userList = (List<User>) ois.readObject();
            ois.close();
         }
      } catch (IOException e) {
         e.printStackTrace();
      } catch (ClassNotFoundException e) {
         e.printStackTrace();
      }		
      return userList;
   }

   public User getUser(int id){
      List<User> users = getAllUsers();

      for(User user: users){
         if(user.getId() == id){
            return user;
         }
      }
      return null;
   }

   public int addUser(User pUser){
      List<User> userList = getAllUsers();
      boolean userExists = false;
      for(User user: userList){
         if(user.getId() == pUser.getId()){
            userExists = true;
            break;
         }
      }		
      if(!userExists){
         userList.add(pUser);
         saveUserList(userList);
         return 1;
      }
      return 0;
   }

   public int updateUser(User pUser){
      List<User> userList = getAllUsers();

      for(User user: userList){
         if(user.getId() == pUser.getId()){
            int index = userList.indexOf(user);			
            userList.set(index, pUser);
            saveUserList(userList);
            return 1;
         }
      }		
      return 0;
   }

   public int deleteUser(int id){
      List<User> userList = getAllUsers();

      for(User user: userList){
         if(user.getId() == id){
            int index = userList.indexOf(user);			
            userList.remove(index);
            saveUserList(userList);
            return 1;   
         }
      }		
      return 0;
   }

   private void saveUserList(List<User> userList){
      try {
         File file = new File("Users.dat");
         FileOutputStream fos;

         fos = new FileOutputStream(file);

         ObjectOutputStream oos = new ObjectOutputStream(fos);		
         oos.writeObject(userList);
         oos.close();
      } catch (FileNotFoundException e) {
         e.printStackTrace();
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

UserService.java

package com.yiibai;

import java.io.IOException;
import java.util.List;

import javax.servlet.http.HttpServletResponse;
import javax.ws.rs.Consumes;
import javax.ws.rs.DELETE;
import javax.ws.rs.FormParam;
import javax.ws.rs.GET;
import javax.ws.rs.OPTIONS;
import javax.ws.rs.POST;
import javax.ws.rs.PUT;
import javax.ws.rs.Path;
import javax.ws.rs.PathParam;
import javax.ws.rs.Produces;
import javax.ws.rs.core.Context;
import javax.ws.rs.core.MediaType;

@Path("/UserService")
public class UserService {
	
   UserDao userDao = new UserDao();
   private static final String SUCCESS_RESULT="<result>success</result>";
   private static final String FAILURE_RESULT="<result>failure</result>";


   @GET
   @Path("/users")
   @Produces(MediaType.APPLICATION_XML)
   public List<User> getUsers(){
      return userDao.getAllUsers();
   }

   @GET
   @Path("/users/{userid}")
   @Produces(MediaType.APPLICATION_XML)
   public User getUser(@PathParam("userid") int userid){
      return userDao.getUser(userid);
   }

   @PUT
   @Path("/users")
   @Produces(MediaType.APPLICATION_XML)
   @Consumes(MediaType.APPLICATION_FORM_URLENCODED)
   public String createUser(@FormParam("id") int id,
      @FormParam("name") String name,
      @FormParam("profession") String profession,
      @Context HttpServletResponse servletResponse) throws IOException{
      User user = new User(id, name, profession);
      int result = userDao.addUser(user);
      if(result == 1){
         return SUCCESS_RESULT;
      }
      return FAILURE_RESULT;
   }

   @POST
   @Path("/users")
   @Produces(MediaType.APPLICATION_XML)
   @Consumes(MediaType.APPLICATION_FORM_URLENCODED)
   public String updateUser(@FormParam("id") int id,
      @FormParam("name") String name,
      @FormParam("profession") String profession,
      @Context HttpServletResponse servletResponse) throws IOException{
      User user = new User(id, name, profession);
      int result = userDao.updateUser(user);
      if(result == 1){
         return SUCCESS_RESULT;
      }
      return FAILURE_RESULT;
   }

   @DELETE
   @Path("/users/{userid}")
   @Produces(MediaType.APPLICATION_XML)
   public String deleteUser(@PathParam("userid") int userid){
      int result = userDao.deleteUser(userid);
      if(result == 1){
         return SUCCESS_RESULT;
      }
      return FAILURE_RESULT;
   }

   @OPTIONS
   @Path("/users")
   @Produces(MediaType.APPLICATION_XML)
   public String getSupportedOperations(){
      return "<operations>GET, PUT, POST, DELETE</operations>";
   }
}

現在使用Eclipse，匯出應用程式為war檔案，並部署在Tomcat中。要使用eclipse建立WAR檔案，按照選項 File -> export -> Web > War File 最後選擇專案UserManagement和目標檔案夾。要將WAR檔案部署在Tomcat，將UserManagement.war檔案放置在Tomcat的安裝目錄下 > webapps 目錄並啟動Tomcat。

測試Web服務

Jersey提供的API來建立Web服務用戶端並測試Web服務。我們已經建立了一個範例測試類 WebServiceTester.java 在com.yiibai下在的同一個專案中。

WebServiceTester.java

package com.yiibai;

import java.util.List;

import javax.ws.rs.client.Client;
import javax.ws.rs.client.ClientBuilder;
import javax.ws.rs.client.Entity;
import javax.ws.rs.core.Form;
import javax.ws.rs.core.GenericType;
import javax.ws.rs.core.MediaType;

public class WebServiceTester  {

   private Client client;
   private String REST_SERVICE_URL = "http://localhost:8080/UserManagement/rest/UserService/users";
   private static final String SUCCESS_RESULT="<result>success</result>";
   private static final String PASS = "pass";
   private static final String FAIL = "fail";

   private void init(){
      this.client = ClientBuilder.newClient();
   }

   public static void main(String[] args){
      WebServiceTester tester = new WebServiceTester();
      //initialize the tester
      tester.init();
      //test get all users Web Service Method
      tester.testGetAllUsers();
      //test get user Web Service Method 
      tester.testGetUser();
      //test update user Web Service Method
      tester.testUpdateUser();
      //test add user Web Service Method
      tester.testAddUser();
      //test delete user Web Service Method
      tester.testDeleteUser();
   }
   //Test: Get list of all users
   //Test: Check if list is not empty
   private void testGetAllUsers(){
      GenericType<List<User>> list = new GenericType<List<User>>() {};
      List<User> users = client
         .target(REST_SERVICE_URL)
         .request(MediaType.APPLICATION_XML)
         .get(list);
      String result = PASS;
      if(users.isEmpty()){
         result = FAIL;
      }
      System.out.println("Test case name: testGetAllUsers, Result: " + result );
   }
   //Test: Get User of id 1
   //Test: Check if user is same as sample user
   private void testGetUser(){
      User sampleUser = new User();
      sampleUser.setId(1);

      User user = client
         .target(REST_SERVICE_URL)
         .path("/{userid}")
         .resolveTemplate("userid", 1)
         .request(MediaType.APPLICATION_XML)
         .get(User.class);
      String result = FAIL;
      if(sampleUser != null && sampleUser.getId() == user.getId()){
         result = PASS;
      }
      System.out.println("Test case name: testGetUser, Result: " + result );
   }
   //Test: Update User of id 1
   //Test: Check if result is success XML.
   private void testUpdateUser(){
      Form form = new Form();
      form.param("id", "1");
      form.param("name", "suresh");
      form.param("profession", "clerk");

      String callResult = client
         .target(REST_SERVICE_URL)
         .request(MediaType.APPLICATION_XML)
         .post(Entity.entity(form,
            MediaType.APPLICATION_FORM_URLENCODED_TYPE),
            String.class);
      String result = PASS;
      if(!SUCCESS_RESULT.equals(callResult)){
         result = FAIL;
      }

      System.out.println("Test case name: testUpdateUser, Result: " + result );
   }
   //Test: Add User of id 2
   //Test: Check if result is success XML.
   private void testAddUser(){
      Form form = new Form();
      form.param("id", "2");
      form.param("name", "naresh");
      form.param("profession", "clerk");

      String callResult = client
         .target(REST_SERVICE_URL)
         .request(MediaType.APPLICATION_XML)
         .put(Entity.entity(form,
            MediaType.APPLICATION_FORM_URLENCODED_TYPE),
            String.class);
   
      String result = PASS;
      if(!SUCCESS_RESULT.equals(callResult)){
         result = FAIL;
      }

      System.out.println("Test case name: testAddUser, Result: " + result );
   }
   //Test: Delete User of id 2
   //Test: Check if result is success XML.
   private void testDeleteUser(){
      String callResult = client
         .target(REST_SERVICE_URL)
         .path("/{userid}")
         .resolveTemplate("userid", 2)
         .request(MediaType.APPLICATION_XML)
         .delete(String.class);

      String result = PASS;
      if(!SUCCESS_RESULT.equals(callResult)){
         result = FAIL;
      }

      System.out.println("Test case name: testDeleteUser, Result: " + result );
   }
}

現在執行測試，使用Eclipse。右鍵單擊該檔案，並按照選項Run as -> Java Application. 你會看到下面的結果Eclipse控制台：

Test case name: testGetAllUsers, Result: pass
Test case name: testGetUser, Result: pass
Test case name: testUpdateUser, Result: pass
Test case name: testAddUser, Result: pass
Test case name: testDeleteUser, Result: pass