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：
- 安装了eclipse
- 安装了Tomcat7
- 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
1 package com.lanxingren.bean; 2 3 import java.util.List; 4 5 public class NewsBean { 6 7 //段子标识 8 private int id; 9 10 //段子文本 11 private String title; 12 13 //段子包含的图片链接 14 private List<String> urls; 15 16 //段子点赞数 17 private int like; 18 19 //段子点踩数 20 private int unlike; 21 22 public int getId() { 23 return id; 24 } 25 26 public void setId(int id) { 27 this.id = id; 28 } 29 30 public String getTitle() { 31 return title; 32 } 33 34 public void setTitle(String title) { 35 this.title = title; 36 } 37 38 public List<String> getUrls() { 39 return urls; 40 } 41 42 public void setUrls(List<String> urls) { 43 this.urls = urls; 44 } 45 46 public int getLike() { 47 return like; 48 } 49 50 public void setLike(int like) { 51 this.like = like; 52 } 53 54 public int getUnlike() { 55 return unlike; 56 } 57 58 public void setUnlike(int unlike) { 59 this.unlike = unlike; 60 } 61 62 @Override 63 public String toString() { 64 return "NewsBean [id=" + id + ", title=" + title + ", urls=" + urls + ", like=" + like + ", unlike=" + unlike 65 + "]"; 66 } 67 68 }
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
1 package com.lanxingren.util; 2 3 import java.sql.Connection; 4 import java.sql.DriverManager; 5 import java.sql.PreparedStatement; 6 import java.sql.ResultSet; 7 8 public class DatabaseUtil { 9 10 private static String url = "jdbc:mysql://localhost:3306/imitating9gag?serverTimezone=GMT%2B8&useSSL=false"; 11 private static String user = "root"; 12 private static String password = "root"; 13 14 private static Connection conn; 15 16 //获取数据库连接 17 public static Connection getConnection() { 18 19 try { 20 Class.forName("com.mysql.cj.jdbc.Driver"); 21 conn = DriverManager.getConnection(url, user, password); 22 } catch (Exception e) { 23 e.printStackTrace(); 24 } 25 26 return conn; 27 } 28 29 //关闭数据库连接 30 public static void close (Connection conn, PreparedStatement ps) { 31 try { 32 if (ps != null) { 33 ps.close(); 34 } 35 if (conn != null) { 36 conn.close(); 37 } 38 } catch (Exception e) { 39 e.printStackTrace(); 40 } 41 } 42 43 //关闭数据库连接 44 public static void close (Connection conn, PreparedStatement ps, ResultSet rs) { 45 try { 46 if (rs != null) { 47 rs.close(); 48 } 49 if (ps != null) { 50 ps.close(); 51 } 52 if (conn != null) { 53 conn.close(); 54 } 55 } catch (Exception e) { 56 e.printStackTrace(); 57 } 58 } 59 60 }
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
1 package com.lanxingren.dao; 2 3 import java.sql.Connection; 4 import java.sql.PreparedStatement; 5 import java.sql.ResultSet; 6 import java.sql.SQLException; 7 import java.util.ArrayList; 8 import java.util.List; 9 10 import com.lanxingren.bean.NewsBean; 11 import com.lanxingren.util.DatabaseUtil; 12 13 public class NewsDAO { 14 15 //page是页数，pageSize是每页条数 16 public List<NewsBean> queryNewsByPage (int page, int pageSize) { 17 List<NewsBean> newsList = new ArrayList<NewsBean>(); 18 19 Connection conn = DatabaseUtil.getConnection(); 20 21 String sql = "select * from news order by id desc limit " + (page - 1)*pageSize + ", " + pageSize; 22 PreparedStatement pstmt = null; 23 24 try { 25 pstmt = (PreparedStatement)conn.prepareStatement(sql); 26 ResultSet rs = pstmt.executeQuery(); 27 while (rs.next()) { 28 NewsBean nb = new NewsBean(); 29 nb.setId(rs.getInt("id")); 30 nb.setTitle(rs.getString("title")); 31 nb.setLike(rs.getInt("like")); 32 nb.setUnlike(rs.getInt("unlike")); 33 newsList.add(nb); 34 } 35 } catch (SQLException e) { 36 e.printStackTrace(); 37 } 38 finally { 39 DatabaseUtil.close(conn, pstmt); 40 } 41 42 return newsList; 43 } 44 45 // 根据段子id获取段子所包含的图片 46 public List<String> queryUrlsByNewsId (int newsId) { 47 List<String> urls = new ArrayList<String>(); 48 49 Connection conn = DatabaseUtil.getConnection(); 50 51 String sql = "select url from news_pics where newsid = " + newsId; 52 PreparedStatement pstmt = null; 53 try { 54 pstmt = conn.prepareStatement(sql); 55 ResultSet rs = pstmt.executeQuery(); 56 while (rs.next()) { 57 urls.add(rs.getString("url")); 58 } 59 } catch (Exception e) { 60 e.printStackTrace(); 61 } 62 finally { 63 DatabaseUtil.close(conn, pstmt); 64 } 65 66 return urls; 67 } 68 69 }
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：
1 public List<NewsBean> newsBeans = new ArrayList<NewsBean>();// 段子集合 2 private String baseUrl = "http://192.168.10.14:8080/Imitating9GAG/QueryNewsServlet?page=";
1 new Thread(new Runnable() { 2 @Override 3 public void run() { 4 String url = baseUrl + (currentPage); 5 OkHttpClient client = new OkHttpClient(); 6 Request request = new Request.Builder() 7 .url(url) 8 .build(); 9 try { 10 Response response = client.newCall(request).execute(); 11 String json = response.body().string(); 12 if (json != null) { 13 Gson gson = new Gson(); 14 newsBeans.addAll(0, (List<NewsBean>)gson.fromJson(json, new TypeToken<List<NewsBean>>(){}.getType())); 15 } 16 Message message = new Message(); 17 message.what = QUERY_NEWS; 18 handler.sendMessage(message); 19 } catch (IOException e) { 20 e.printStackTrace(); 21 } 22 } 23 }).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：
1 // 请求网络结束后的更新View 2 private Handler handler = new Handler() { 3 @Override 4 public void handleMessage(Message msg) { 5 switch (msg.what) { 6 case QUERY_NEWS: 7 recyclerView.getAdapter().notifyDataSetChanged(); 8 break; 9 case UPDATE_NEWS: 10 recyclerView.getAdapter().notifyDataSetChanged(); 11 swipeRefreshLayout.setRefreshing(false); 12 break; 13 case LOAD_MORE: 14 ((NewsAdapter)recyclerView.getAdapter()).changeStatus(NewsAdapter.UNLOADING); 15 currentState = NewsAdapter.UNLOADING; 16 break; 17 } 18 } 19 };
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~
