休息 API 示例

Question

我有一个用 Java 编写的简单 REST 服务器的实现。每个API调用都返回XML格式的数据，如果我想要格式是JSON怎么办？我需要外部库吗？这是我的代码：

用户.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;
}
}

用户道

    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();
        }
    }
}

用户服务.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>";
   }
}

编辑：我在我的项目中包含了 jackson jar，特别是jackson-core-2.7.0.jar、jackson-databind-2.7.0.jar、jackson-annotations-2.2.1.jar但现在我从 Tomcat 得到这个异常：

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

我正在回答将您的问题解释为与 REST 服务 (UserService.java) 有关的问题，如果这不是预期的内容，请发表评论。

您必须首先确保方法中的调用确实以 JSON 形式返回结果。这将需要对 User.java 和 UserDao.java 进行适当的更改以返回 JSON 而不是 XML。

您拥有的 User 类示例使用 Java JAXB 库，基于这些注释 @XMLRootElement、@XMLElement。

您需要使用支持创建 JSON 对象的 Java 库重写此类。

杰克逊图书馆是一个不错的选择。这是 Jackson wiki 的主页，有很好的文档记录。

就 REST 服务本身而言，在 UserService.java 中，您需要更改服务生成的媒体类型。

更改要从中生成 JSON 的方法注释的所有实例

@Produces(MediaType.APPLICATION_XML)

到

@Produces(MediaType.APPLICATION_JSON)