仿9GAG制作过程（三）

有话要说：

这次准备讲述后台服务器的搭建以及前台访问到数据的过程。

成果：

准备：

1. 安装了eclipse
2. 安装了Tomcat7
3. 安装了数据库管理工具：Navicat

搭建服务器：

用eclipse直接创建一个web工程，并将运行环境设置为Tomcat7

接着定义了四个类来实现了一个简单的接口（通过servlet的方式），下面来看看这四个类

NewsBean.java

 package com.lanxingren.bean;

 import java.util.List;

 public class NewsBean {

     //段子标识
     private int id;

     //段子文本
     private String title;

     //段子包含的图片链接
     private List<String> urls;

     //段子点赞数
     private int like;

     //段子点踩数
     private int unlike;

     public int getId() {
         return id;
     }

     public void setId(int id) {
         this.id = id;
     }

     public String getTitle() {
         return title;
     }

     public void setTitle(String title) {
         this.title = title;
     }

     public List<String> getUrls() {
         return urls;
     }

     public void setUrls(List<String> urls) {
         this.urls = urls;
     }

     public int getLike() {
         return like;
     }

     public void setLike(int like) {
         this.like = like;
     }

     public int getUnlike() {
         return unlike;
     }

     public void setUnlike(int unlike) {
         this.unlike = unlike;
     }

     @Override
     public String toString() {
         return "NewsBean [id=" + id + ", title=" + title + ", urls=" + urls + ", like=" + like + ", unlike=" + unlike
                 + "]";
     }

 }

该类是段子类的一个bean类，各个属性代表的意思在代码里已经说清楚了。

DatabaseUtil.java

 package com.lanxingren.util;

 import java.sql.Connection;
 import java.sql.DriverManager;
 import java.sql.PreparedStatement;
 import java.sql.ResultSet;

 public class DatabaseUtil {

     private static String url = "jdbc:mysql://localhost:3306/imitating9gag?serverTimezone=GMT%2B8&useSSL=false";
     private static String user = "root";
     private static String password = "root";

     private static Connection conn;

     //获取数据库连接
     public static Connection getConnection() {

         try {
             Class.forName("com.mysql.cj.jdbc.Driver");
             conn = DriverManager.getConnection(url, user, password);
         } catch (Exception e) {
             e.printStackTrace();
         }

         return conn;
     }

     //关闭数据库连接
     public static void close (Connection conn, PreparedStatement ps) {
         try {
             if (ps != null) {
                 ps.close();
             }
             if (conn != null) {
                 conn.close();
             }
         } catch (Exception e) {
             e.printStackTrace();
         }
     }

     //关闭数据库连接
     public static void close (Connection conn, PreparedStatement ps, ResultSet rs) {
         try {
             if (rs != null) {
                 rs.close();
             }
             if (ps != null) {
                 ps.close();
             }
             if (conn != null) {
                 conn.close();
             }
         } catch (Exception e) {
             e.printStackTrace();
         }
     }

 }

该类是一个工具类，主要用来创建数据库连接以及关闭数据库连接。

其中，由于MySQL更新到了最新的版本，所以设置了useSSL为false，否则连接会出问题。

而且，最新的MySQL其实并不需要通过Class.forName来加载驱动了。

NewsDAO.java

 package com.lanxingren.dao;

 import java.sql.Connection;
 import java.sql.PreparedStatement;
 import java.sql.ResultSet;
 import java.sql.SQLException;
 import java.util.ArrayList;
 import java.util.List;

 import com.lanxingren.bean.NewsBean;
 import com.lanxingren.util.DatabaseUtil;

 public class NewsDAO {

     //page是页数，pageSize是每页条数
     public List<NewsBean> queryNewsByPage (int page, int pageSize) {
         List<NewsBean> newsList = new ArrayList<NewsBean>();

         Connection conn = DatabaseUtil.getConnection();

         String sql = "select * from news order by id desc limit " + (page - 1)*pageSize + ", " + pageSize;
         PreparedStatement pstmt = null;

         try {
             pstmt = (PreparedStatement)conn.prepareStatement(sql);
             ResultSet rs = pstmt.executeQuery();
             while (rs.next()) {
                 NewsBean nb = new NewsBean();
                 nb.setId(rs.getInt("id"));
                 nb.setTitle(rs.getString("title"));
                 nb.setLike(rs.getInt("like"));
                 nb.setUnlike(rs.getInt("unlike"));
                 newsList.add(nb);
             }
         } catch (SQLException e) {
             e.printStackTrace();
         }
         finally {
             DatabaseUtil.close(conn, pstmt);
         }

         return newsList;
     }

     // 根据段子id获取段子所包含的图片
     public List<String> queryUrlsByNewsId (int newsId) {
         List<String> urls = new ArrayList<String>();

         Connection conn = DatabaseUtil.getConnection();

         String sql = "select url from news_pics where newsid = " + newsId;
         PreparedStatement pstmt = null;
         try {
             pstmt = conn.prepareStatement(sql);
             ResultSet rs = pstmt.executeQuery();
             while (rs.next()) {
                 urls.add(rs.getString("url"));
             }
         } catch (Exception e) {
             e.printStackTrace();
         }
         finally {
             DatabaseUtil.close(conn, pstmt);
         }

         return urls;
     }

 }

该类定义了两个方法，分别为获取段子信息的方法和获取图片的方法。

其中sql用了倒序是为了让段子按照时间流的顺序在前台展示。

QueryNewsServlet.java

package com.lanxingren.servlet;

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

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.google.gson.Gson;
import com.lanxingren.bean.NewsBean;
import com.lanxingren.dao.NewsDAO;

@WebServlet("/QueryNewsServlet")
public class QueryNewsServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    int pageSize = 5;

    public QueryNewsServlet() {
        super();
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/json; charset=utf-8");
        PrintWriter out = response.getWriter();

        String page = request.getParameter("page");
        List<NewsBean> newsList = new ArrayList<NewsBean>();
        List<NewsBean> realList = new ArrayList<NewsBean>();
        NewsDAO dao = new NewsDAO();

        String news = "";

        if (page != null) {
            newsList = dao.queryNewsByPage(Integer.parseInt(page), pageSize);
        }

        if (newsList != null && newsList.size() > 0) {
            for (NewsBean nb : newsList) {
                List<String> urls = dao.queryUrlsByNewsId(nb.getId());
                if (urls != null && urls.size() > 0) {
                    nb.setUrls(urls);
                    realList.add(nb);
                }
            }
        }

        Gson gson = new Gson();
        news = gson.toJson(realList);

        out.print(news);
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

}

通过注解的方式来设置servlet的地址，并将数据转化成json输出。

通过以上的方式，就完成了后台查询段子接口的开发，并且可通过page参数来获取第page页的信息，接口URL为：http://localhost:8080/Imitating9GAG/QueryNewsServlet?page=2

接着，将项目在Tomcat下启动后台服务器就正式搭建完成了，通过该URL获取的数据见下图：

前台获取数据并展示：

 public List<NewsBean> newsBeans = new ArrayList<NewsBean>();// 段子集合
 private String baseUrl = "http://192.168.10.14:8080/Imitating9GAG/QueryNewsServlet?page=";

 new Thread(new Runnable() {
             @Override
             public void run() {
                 String url = baseUrl + (currentPage);
                 OkHttpClient client = new OkHttpClient();
                 Request request = new Request.Builder()
                         .url(url)
                         .build();
                 try {
                     Response response = client.newCall(request).execute();
                     String json = response.body().string();
                     if (json != null) {
                         Gson gson = new Gson();
                         newsBeans.addAll(0, (List<NewsBean>)gson.fromJson(json, new TypeToken<List<NewsBean>>(){}.getType()));
                     }
                     Message message = new Message();
                     message.what = QUERY_NEWS;
                     handler.sendMessage(message);
                 } catch (IOException e) {
                     e.printStackTrace();
                 }
             }
         }).start();

由于请求网络是一个耗时操作，因此放进了子线程中。在子线程中请求网络并将返回的数据放入段子集合中。

Handler如下：

  // 请求网络结束后的更新View
     private Handler handler = new Handler() {
         @Override
         public void handleMessage(Message msg) {
             switch (msg.what) {
                 case QUERY_NEWS:
                     recyclerView.getAdapter().notifyDataSetChanged();
                     break;
                 case UPDATE_NEWS:
                     recyclerView.getAdapter().notifyDataSetChanged();
                     swipeRefreshLayout.setRefreshing(false);
                     break;
                 case LOAD_MORE:
                     ((NewsAdapter)recyclerView.getAdapter()).changeStatus(NewsAdapter.UNLOADING);
                     currentState = NewsAdapter.UNLOADING;
                     break;
             }
         }
     };

结束语：

这样，获取数据+后台服务器搭建+前台页面展示的过程整个就已经完整了。

下一篇准备讲述官方自带的SwipeRefreshLayout刷新控件。

由于该控件没有上拉加载功能，于是就在RecyclerView中实现了上拉加载功能。

大家如果有什么疑问或者建议可以通过评论或者邮件的方式联系我，欢迎大家的评论~