仿9GAG製作過程（三）_ZenDei技術網路在線

有話要說：這次準備講述後臺伺服器的搭建以及前臺訪問到數據的過程。成果：準備：搭建伺服器：用eclipse直接創建一個web工程，並將運行環境設置為Tomcat7 接著定義了四個類來實現了一個簡單的介面（通過servlet的方式），下麵來看看這四個類 NewsBean.java 該類是段子類 ...

有話要說：

這次準備講述後臺伺服器的搭建以及前臺訪問到數據的過程。

成果：

準備：

安裝了eclipse
安裝了Tomcat7
安裝了資料庫管理工具：Navicat

搭建伺服器：

用eclipse直接創建一個web工程，並將運行環境設置為Tomcat7

接著定義了四個類來實現了一個簡單的介面（通過servlet的方式），下麵來看看這四個類

NewsBean.java

 1 package com.lanxingren.bean;
 2 
 3 import java.util.List;
 4 
 5 public class NewsBean {
 6     
 7     //段子標識
 8     private int id;
 9     
10     //段子文本
11     private String title;
12     
13     //段子包含的圖片鏈接
14     private List<String> urls;
15     
16     //段子點贊數
17     private int like;
18     
19     //段子點踩數
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 }

該類是段子類的一個bean類，各個屬性代表的意思在代碼里已經說清楚了。

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     //獲取資料庫連接
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     //關閉資料庫連接
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     //關閉資料庫連接
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 }

該類是一個工具類，主要用來創建資料庫連接以及關閉資料庫連接。

其中，由於MySQL更新到了最新的版本，所以設置了useSSL為false，否則連接會出問題。

而且，最新的MySQL其實並不需要通過Class.forName來載入驅動了。

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是頁數，pageSize是每頁條數
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     // 根據段子id獲取段子所包含的圖片
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 }

該類定義了兩個方法，分別為獲取段子信息的方法和獲取圖片的方法。

其中sql用了倒序是為了讓段子按照時間流的順序在前臺展示。

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);
    }
    
}

通過註解的方式來設置servlet的地址，並將數據轉化成json輸出。

通過以上的方式，就完成了後臺查詢段子介面的開發，並且可通過page參數來獲取第page頁的信息，介面URL為：http://localhost:8080/Imitating9GAG/QueryNewsServlet?page=2

接著，將項目在Tomcat下啟動後臺伺服器就正式搭建完成了，通過該URL獲取的數據見下圖：

前臺獲取數據並展示：

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();

由於請求網路是一個耗時操作，因此放進了子線程中。在子線程中請求網路並將返回的數據放入段子集合中。

Handler如下：

 1  // 請求網路結束後的更新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     };

結束語：

這樣，獲取數據+後臺伺服器搭建+前臺頁面展示的過程整個就已經完整了。

下一篇準備講述官方自帶的SwipeRefreshLayout刷新控制項。

由於該控制項沒有上拉載入功能，於是就在RecyclerView中實現了上拉載入功能。

大家如果有什麼疑問或者建議可以通過評論或者郵件的方式聯繫我，歡迎大家的評論~