说到分页算法，一般WEB开发都会用到，我只是在我的实现技术上用了struts框架，其实原理都一样的。看了网上相当多的分页算法，有对的也有好多是错的，更有好多是不太优化的。还有以前自己在augmentum做的一个分页算法，总结了一些不足。决定重新再写一个分页算法。
首先，应该写个bean来记录存储一些页面的属性。
分页大致需要如下属性：
private int currentPage = 1; // 当前页
private int totalPages = 0; // 总页数
private int pageRecorders = 5;// 每页5条数据
private int totalRows = 0; // 总数据数
private int pageStartRow = 0;// 每页的起始数
private int pageEndRow = 0; // 每页显示数据的终止数
private boolean hasNextPage = false; // 是否有下一页
private boolean hasPreviousPage = false; // 是否有前一页
private int nextPage = 0;//下一页的页码
private int previousPage = 0;//上一页的页码
然后这些属性之间是有联系的，我们可以在构造函数的时候就初始化一些属性有两种方法：
一、根据总的页数，（假设当前页为1）
public PageBean(int totalRows){
this.totalRows = totalRows;
this.currentPage = 1;
hasPreviousPage = false;
if ((totalRows % pageRecorders) == 0) {
totalPages = totalRows / pageRecorders;
} else {
totalPages = totalRows / pageRecorders + 1;
}
if (totalRows >= pageRecorders) {
hasNextPage = true;
nextPage = 2;
this.pageEndRow = pageRecorders;
} else {
this.pageEndRow = totalRows;
hasNextPage = false;
nextPage = 1;
}
this.pageStartRow = 0;
previousPage = 1;
}
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然后在按下一页或者上一页的时候需要如下函数处理：
public void nextPage() {
if(hasNextPage == true)
currentPage = currentPage + 1;
if ((currentPage - 1) > 0) {
hasPreviousPage = true;
} else {
hasPreviousPage = false;
}
if (currentPage >= totalPages) {
hasNextPage = false;
this.nextPage = currentPage;
} else {
hasNextPage = true;
nextPage = currentPage+1;
}
this.pageStartRow = (currentPage -1) * pageRecorders;
if(hasNextPage == true)
this.pageEndRow = pageStartRow + 5;
else{
this.pageEndRow =this.totalPages;
}
previousPage = currentPage - 1;
}
public void previousPage() {
if(hasPreviousPage == true)
currentPage = currentPage - 1;
if (currentPage == 0) {
currentPage = 1;
}
if (currentPage >= totalPages) {
hasNextPage = false;
} else {
hasNextPage = true;
}
nextPage = currentPage + 1;
if ((currentPage - 1) > 0) {
hasPreviousPage = true;
previousPage = currentPage - 1;
} else {
hasPreviousPage = false;
previousPage = currentPage;
}
this.pageStartRow = (currentPage -1) * pageRecorders;
if(hasNextPage == true)
this.pageEndRow = pageStartRow + 5;
else{
this.pageEndRow =this.totalPages;
}
}
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在HTML中按下一页或者上一页的时候有如下代码：
<logic:equal name="page" property="hasNextPage" value="true">
<html:link page="/List.do?action=nextPage">
nextPage
</html:link>
</logic:equal>
<logic:equal name="page" property="hasPreviousPage" value="true">
<html:link page="/List.do?action=previousPage">
PreviousPage
</html:link>
</logic:equal>
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然后在Action中作如下处理：
String currentPage = request.getParameter("currentPage");
HttpSession session = request.getSession();
EmployeeForm employeeForm = (EmployeeForm) form;
String queryString = null;
String queryCon = null;
String action = employeeForm.getAction();
List list = new ArrayList();
PageBean pb = null;
EmployeeDao employeeDao = new EmployeeDao();
if(action == null || action.equals("null")){
int totalRows = employeeDao.getTotalRows();
pb = new PageBean(totalRows);
session.removeAttribute("page");
queryString = employeeForm.getQueryString();
queryCon = employeeForm.getQueryCon();
session.setAttribute("queryString",queryString);
session.setAttribute("queryCon",queryCon);
list = employeeDao.getAllEmployee(queryString, queryCon,
String.valueOf(pb.getPageStartRow()),
String.valueOf(pb.getPageRecorders()));
}else if(action.equals("nextPage")){
queryString = (String)session.getAttribute("queryString");
queryCon = (String)session.getAttribute("queryCon");
employeeForm.setQueryString(queryString);
employeeForm.setQueryCon(queryCon);
pb = (PageBean)session.getAttribute("page");
pb.nextPage();
list = employeeDao.getAllEmployee(queryString, queryCon,
String.valueOf(pb.getPageStartRow()),
String.valueOf(pb.getPageRecorders()));
}else if(action.equals("previousPage")){
queryString = (String)session.getAttribute("queryString");
queryCon = (String)session.getAttribute("queryCon");
employeeForm.setQueryString(queryString);
employeeForm.setQueryCon(queryCon);
pb = (PageBean)session.getAttribute("page");
pb.previousPage();
list = employeeDao.getAllEmployee(queryString, queryCon,
String.valueOf(pb.getPageStartRow()),
String.valueOf(pb.getPageRecorders()));
}
pb.description();
session.setAttribute("page",pb);
request.setAttribute("admin", "admin");
request.setAttribute("employee", list);
return mapping.findForward("showlist");
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然后在数据库查询中有如下代码：
/**
*查询总记录数
*/
public int getTotalRows() {
int totalRows = 0;
String sql = "select count(*) from employee";//假设是员工表
Database db = new Database();
ResultSet rs = db.executeQuery(sql);
try {
while (rs.next()) {
String id = (String) rs.getString(1);
totalRows = Integer.parseInt(id);
}
} catch (SQLException e) {
e.printStackTrace();
}
db.close();
return totalRows;
}
/*
*查询每一页需要查询的页码
*/
public List getAllEmployee(String queryString, String queryCon, String startRow,String num) {
List list = new ArrayList();
String sql = null;
if (queryString == null || queryString.equals("")) {
sql = "select * from employee,dept " +
"where dept.Id = employee.deptId " +
"order by employee.id asc"+ " limit "+startRow+","+num;
} else {
sql = "select * from employee,dept " +
"where dept.Id = employee.deptId order by employee."
+ queryString + " " + queryCon + " limit "+startRow+","+num;
}
Employee employee = null;
Database db = new Database();
ResultSet rs = db.executeQuery(sql);
try {
while (rs.next()) {
String id = (String) rs.getString("employee.id");
String name = (String) rs.getString("employee.name");
String deptId = (String) rs.getString("employee.deptId");
String deptName = (String) rs.getString("dept.deptName");
employee = new Employee();
employee.setId(id);
employee.setName(name);
employee.setDeptId(deptId);
employee.setDeptName(deptName);
list.add(employee);
}
} catch (SQLException e) {
e.printStackTrace();
}
db.close();
return list;
}
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这里我用了hibernate进行数据库操作，你也可以用jdbc进行操作，情况类似。
二、根据总的页数，当前页
这样的话构造函数应该写成：
public PageBean(int totalRows,int currentPage) {
this.totalRows = totalRows;
this.currentPage = currentPage;
if(currentPage < 2)
hasPreviousPage = false;
else
hasPreviousPage = true;
if ((totalRows % pageRecorders) == 0) {
totalPages = totalRows / pageRecorders;
} else {
totalPages = totalRows / pageRecorders + 1;
}
if (currentPage < totalPages) {
hasNextPage = true;
nextPage = currentPage + 1;
pageStartRow = (currentPage - 1)*pageRecorders;
this.pageEndRow = pageStartRow + pageRecorders;
} else if(currentPage == totalPages){
pageStartRow = (currentPage - 1)*pageRecorders;
this.pageEndRow = totalRows;
hasNextPage = false;
nextPage = currentPage;
}
if(currentPage < 2){
previousPage = currentPage;
hasPreviousPage = false;
}else if(currentPage > 1){
previousPage = currentPage-1;
hasPreviousPage = true;
}
}
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在action中应该写成：
if(currentPage == null){
pb = new PageBean(totalRows);
session.removeAttribute("page");
queryString = employeeForm.getQueryString();
queryCon = employeeForm.getQueryCon();
session.setAttribute("queryString",queryString);
session.setAttribute("queryCon",queryCon);
list = employeeDao.getAllEmployee(queryString, queryCon,
String.valueOf(pb.getPageStartRow()),
String.valueOf(pb.getPageRecorders()));
}
else{
pb = new PageBean(totalRows,Integer.parseInt(currentPage));
queryString = employeeForm.getQueryString();
queryCon = employeeForm.getQueryCon();
session.setAttribute("queryString",queryString);
session.setAttribute("queryCon",queryCon);
list = employeeDao.getAllEmployee(queryString, queryCon,
String.valueOf(pb.getPageStartRow()),
String.valueOf(pb.getPageRecorders()));
}
session.setAttribute("page",pb);
request.setAttribute("admin", "admin");
request.setAttribute("employee", list);
return mapping.findForward("showlist");
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在jsp中应该写成：
<logic:equal name="page" property="hasNextPage" value="true">
<a href="List.do?currentPage=<bean:write name="page" property="nextPage"/>">
nextPage
</a>
</logic:equal>
<logic:equal name="page" property="hasPreviousPage" value="true">
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<a href="/test/List.do?currentPage=<bean:write name="page" property="previousPage"/>">
PreviousPage
</a>
</logic:equal>
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数据库查询部分依然适用。
尽管洋洋洒洒贴了一部分代码，不过好像不太想看，包括我，也比较讨厌看一些烦琐的代码，所以如果你想要源代码进行探讨研究的话，欢迎随时找我。那就总结一下这两种方法吧！
首先这两种方法都是取需要显示的数据显示，这样，在数据库庞大的情况下，比一次性把所有数据都取出来的效率要高。
第一种方法是把PageBean存在了一个HttpSession中，在进入到显示列表的时候就进行了初始化，在jsp页面传递的参数action是固定的三个值:null,nextPage,previousPage.这样虽然比较容易理解，但是我发现一个BUG，就是如果你按刷新，他也会翻页，因为他的url就是 .do?aciton=nextPage,这样的话你传进去的action还是有一个值，这样就会导致翻页。
第二种方法是考虑了第一种方法的BUG，在Jsp页面传递的参数currentPage的值是bean中的nextPage的值或者previousPage里的值，用了struts标签库嵌套，把值赋予currentPage，这样的话currentPage的值是：1，2，3，4...totalPages之间。这样的话你即使按刷新按钮，他也是当前页，因为他的url就是.do?currentPage=someNumber（someNumber是1到totalPages中的一个值）。但是这样的话Pagebean在每次访问的时候都要重新生成一个对象，该对象也是根据totalRows（总数据数），currentPage（当前页数）进行构造，从而设置其他的一些属性。个人比较推荐第二种方法。
