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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;
}
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;
}
}
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>
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");
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;
}
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;
}
}
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");
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">
|
<a href="/test/list.do?currentpage=<bean:write name="page" property="previouspage"/>">
previouspage
</a>
</logic:equal>
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。
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