Rest API示例

Question

我有一個用Java編寫的簡單REST服務器的實現。 每個API調用都以XML格式返回數據，如果我希望格式為JSON，我該怎么辦？ 我需要外部庫嗎？ 這是我的代碼：

User.java：

package com.leo;

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;
}
}

UserDao.java

    package com.leo;

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.leo;

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>";
   }
}

編輯：我在我的項目中包括傑克遜罐子，特別是jackson-core-2.7.0.jar，jackson-databind-2.7.0.jar，jackson-annotations-2.2.1.jar但現在我從Tomcat得到這個例外：

javax.servlet.ServletException: org.glassfish.jersey.server.ContainerException: java.lang.NoClassDefFoundError: Could not initialize class com.fasterxml.jackson.databind.ObjectMapper
    org.glassfish.jersey.servlet.WebComponent.serviceImpl(WebComponent.java:489)
    org.glassfish.jersey.servlet.WebComponent.service(WebComponent.java:427)
    org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:388)
    org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:341)
    org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:228)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)

Answer 1

我正在回答將您的問題解釋為與REST服務（UserService.java）相關的問題，如果不符合預期，請發表評論。

您必須首先確保方法中的調用確實將結果作為JSON返回。 這將需要對User.java和UserDao.java進行適當的更改以返回JSON而不是XML。

您擁有的User類示例正在使用Java JAXB庫，基於這些注釋@XMLRootElement，@ XMLElement。

您需要使用支持創建JSON對象的Java庫來重寫此類。

傑克遜圖書館是個不錯的選擇。 這是Jackson wiki的主頁，其中有很好的文檔記錄。

就REST服務本身而言，在UserService.java中，您需要更改服務生成的媒體類型。

更改要從中生成JSON的方法注釋的所有實例

@Produces(MediaType.APPLICATION_XML)

至

@Produces(MediaType.APPLICATION_JSON)