對于表格數據處理的話，displayTag有很大的優勢；但是有些時候還得自己動手做點工作；
我自己寫了一個PageTag的類來處理一些簡單的工作。
PageTag.java
1 package com.blog.utils;
2
3 /**
4 *
5 * @author Chucky
6 */
7 public class PageTag {
8 /* pageNo: the page number of current page
9 * pageSize: how many records in one page
10 * totalPages: the number of totalpages
11 */
12
13 private int pageNo;
14 private int pageSize;
15 private int totalPages;
16
17 public PageTag(int pageNo, int pageSize) {
18 this.pageNo = pageNo;
19 this.pageSize = pageSize;
20 this.totalPages = 1;
21 }
22
23 //accroding to the number of records to calculate the totalpages
24 public PageTag(int pageNo, int pageSize, int records) {
25 this.pageNo = pageNo;
26 this.pageSize = pageSize;
27 this.totalPages = countPages(records);
28 }
29
30 public int getPageNo() {
31 return pageNo;
32 }
33
34 public void setPageNo(int pageNo) {
35 this.pageNo = pageNo;
36 }
37
38 public int getPageSize() {
39 return pageSize;
40 }
41
42 public void setPageSize(int pageSize) {
43 this.pageSize = pageSize;
44 }
45
46 public int getTotalPages() {
47 return totalPages;
48 }
49
50 public void setTotalPages(int totalPages) {
51 this.totalPages = totalPages;
52 }
53
54 public int countPages(int records) {
55 totalPages = records % pageSize == 0 ? records / pageSize : records / pageSize + 1;
56 return totalPages;
57 }
58
59 /* getStartPos： get the start postion of the records
60 */
61 public int getStartPos() {
62 int startPos = (pageNo - 1) * pageSize;
63 return startPos;
64 }
65
66 /* get the page number of previos page
67 */
68 public int getPrePage() {
69 int prePage = pageNo - 1;
70 if (prePage == 0) {
71 prePage = pageNo;
72 }
73 return prePage;
74 }
75
76 /* get the page number of next page
77 */
78 public int getNextPage() {
79 int nextPage = pageNo + 1;
80 if (nextPage > totalPages) {
81 nextPage = totalPages;
82 }
83 return nextPage;
84 }
85
86 /* get the page number of previos page which specified
87 */
88 public int getPrePage(int page) {
89 int prePage = page - 1;
90 if (prePage == 0) {
91 prePage = page;
92 }
93 return prePage;
94 }
95
96 /* get the page number of next page which specified
97 */
98 public int getNextPage(int page) {
99 int nextPage = page + 1;
100 if (nextPage > totalPages) {
101 nextPage = totalPages;
102 }
103 return nextPage;
104 }
105 }
這個類寫的很簡單，注釋也很清楚；還是讓我們結合項目來看看如何使用。
1 List blogs = null;
2
3
4 /* pages proceesor:
5 * get related the number of records (such as blogs number);
6 * then calculate totalpages;
7 * store pageTag to request if nesscessary.
8 */
9 String page = request.getParameter("page");
10 int pageSize = 10;
11 int pageNo = 1;
12 if (page != null) {
13 pageNo = new Integer(page);
14 }
15 PageTag pageTag = new PageTag(pageNo, pageSize);
16
17 if (cid == null) {
18 sql = "select b.id as id from blog b, category c where category_id = c.id";
19 } else {
20 sql = "select b.id as id from blog b, category c where category_id = " + cid + " and category_id = c.id";
21 }
22 try {
23 blogs = (List) qr.query(sql, new BeanListHandler(Blog.class));
24 if (blogs.size() > 0) {
25 pageTag.countPages(blogs.size());
26 }
27 } catch (SQLException ex) {
28 Logger.getLogger(HomeServlet.class.getName()).log(Level.SEVERE, null, ex);
29 }
30 request.setAttribute("pageTag", pageTag);
31
32
33 /* blog collection
34 * if cid not equals null which means it queries all blogs that belong to specified category
35 * otherwise get all blogs
36 */
37
38 if (cid == null) {
39 //sql = "select b.id as id, title, content, date, c.name as category, c.id as categoryId from blog b, category c where category_id = c.id order by date desc";
40 sql = " select b.id as id,b.title as title,b.content as content,b.date as date,c.name as category,categoryId,comments from " +
41 "(select blog.id as id ,blog.title as title,blog.category_id as categoryId,count(comment.blog_id) as comments,blog.content as content,blog.date as date from blog left join comment on blog.id = comment.blog_id
group by blog.id) as b, category c " +
42 "where categoryId = c.id " +
43 "order by date desc " +
44 "limit " + pageTag.getStartPos() + ","+pageTag.getPageSize();
45 } else {
46 sql = "select id,name from category where id = " + cid;
47 try {
48 List list = (List) qr.query(sql, new BeanListHandler(Category.class));
49 Category category = (Category) list.get(0);
50 request.setAttribute("category", category);
51 } catch (SQLException ex) {
52 Logger.getLogger(HomeServlet.class.getName()).log(Level.SEVERE, null, ex);
53 }
54 //sql = "select b.id as id, title, content, date, c.name as category, c.id as categoryId from blog b, category c where category_id = " + cid + " and category_id = c.id order by date desc";
55 sql = " select b.id as id,b.title as title,b.content as content,b.date as date,c.name as category,categoryId,comments from " +
56 "(select blog.id as id ,blog.title as title,blog.category_id as categoryId,count(comment.blog_id) as comments,blog.content as content,blog.date as date from blog left join comment on blog.id = comment.blog_id
group by blog.id) as b, category c " +
57 "where categoryId = " + cid + " and categoryId = c.id " +
58 "order by date desc " +
59 "limit " + pageTag.getStartPos() + ","+pageTag.getPageSize();
60 }
61 try {
62 blogs = (List) qr.query(sql, new BeanListHandler(Blog.class));
63 } catch (SQLException ex) {
64 Logger.getLogger(HomeServlet.class.getName()).log(Level.SEVERE, null, ex);
65 }
66 request.setAttribute("blogs", blogs);
我們可以看到4-30行是有關pageTag的使用；首先從request取得當前頁(page屬性)，接著創建pageTag對象，根據需求(cid)取得blog的數量；從而得到總頁數；最后將pageTag對象保存至request中。
隨后在查詢blog的時候，我們再次使用
pageTag.getStartPos()和pageTag.getPageSize()這兩個方法，取得查詢數據開始的位置與長度。Job Done！
再看jsp頁面
1 <div id="pagetags">
2 <% if (pageTag.getTotalPages() != 0){
3 int totalPages = pageTag.getTotalPages();
4 if (totalPages > 1) {%>
5 <span class="pagelinks">[<a href="<%=request.getContextPath()%>/HomeServlet?page=1">首頁</a>/<a href="<%=request.getContextPath()%>/HomeServlet?page=<%=pageTag.getPrePage()%>">上一頁</a>]
6
7 <% for (int i=1;i<=10;i++){
8 int base = (pageTag.getPageNo()/10)*10;
9 int remainder =pageTag.getPageNo()%10;
10 if ((i+base)>pageTag.getTotalPages()){
11 break;
12 }
13 if (i != remainder){
14 %>
15 <a href="<%=request.getContextPath()%>/HomeServlet?page=<%=i+base%>"><%=i+base%></a>
16 <%}else{%>
17 <strong><%=pageTag.getPageNo()%></strong>
18 <%}}%>
19
20 [<a href="<%=request.getContextPath()%>/HomeServlet?page=<%=pageTag.getNextPage()%>">下一頁</a>/<a href="<%=request.getContextPath()%>/HomeServlet?page=<%=totalPages%>">尾頁</a>]</span>
21 <%}else{%>
22 <span class="pagelinks">共1頁</span>
23 <% }}%>
24 </div>
首頁很簡單，page設為1即可；尾頁的話就totalPage的值；這里集中要說一下for循環的內容。
line 8 取得一個基數base(類似10，20，30）；
line 9 取得余數；
line 10 如果i加上基數base 大于 總頁數的話，就沒有必要再繼續打印頁碼了；
line 15 如果i不等于余數的話，
line 16 為該頁碼添加鏈接；
line 17 否則，不必為該頁碼添加鏈接。
因為數據不多，之前的pageSize我改成了1；讓我們看下效果：
