例如，在数据库的某个表里有1000条数据，我们每次只显示100条数据，在第1页显示第0到第99条，在第2页显示第100到199条，依次类推，这就是分页。
分页可以分为逻辑分页和物理分页。逻辑分页是我们的程序在显示每页的数据时，首先查询得到表中的1000条数据，然后成熟根据当前页的“页码”选出其中的100条数据来显示。
物理分页是程序先判断出该选出这1000条的第几条到第几条，然后数据库根据程序给出的信息查询出程序需要的100条返回给我们的程序。
mybatis使用rowbounds实现的分页是逻辑分页,也就是先把数据记录全部查询出来,然在再根据 offset 和 limit 截断记录返回。
为了在数据库层面上实现物理分页，又不改变原来 mybatis 的函数逻辑,可以编写 plugin 截获 mybatis executor 的 statementhandler，重写sql来执行查询。
经常搭框架的人应该都清楚，框架搭建的核心就是配置文件。
在这里我们需要创建 web 工程。也需要用 mybatis与spring mvc 集成起来，源码在本文结尾处下载，主要有以下几个方面的配置。
整个mybatis分页示例要完成的步骤如下：
1、示例功能描述
2、创建工程
3、数据库表结构及数据记录
4、实例对象
5、配置文件
6、测试执行，输出结果
在本示例中，需要使用 mybatis和spring mvc整合完成分页，完成这样的一个简单功能，即指定一个用户（id=1），查询出这个用户关联的所有订单分页显示出来（使用的数据库是：mysql）。
在本示例中，用到两个表：用户表和订单表，其结构和数据记录如下：
create table `user` (
`id` int(10) unsigned not null auto_increment,
`username` varchar(64) not null default '',
`mobile` varchar(16) not null default '',
primary key (`id`)
) engine=innodb auto_increment=3 default charset=utf8;
-- ----------------------------
-- records of user
-- ----------------------------
insert into `user` values ('1', 'h3', '13838009988');
insert into `user` values ('2', 'saya', '13838009988');
订单表结构和数据如下：
create table `order` (
`order_id` int(10) unsigned not null auto_increment,
`user_id` int(10) unsigned not null default '0',
`order_no` varchar(16) not null default '',
`money` float(10,2) unsigned default '0.00',
primary key (`order_id`)
) engine=innodb auto_increment=17 default charset=utf8;
-- ----------------------------
-- records of order
-- ----------------------------
insert into `order` values ('1', '1', '1509289090', '99.90');
insert into `order` values ('2', '1', '1519289091', '290.80');
insert into `order` values ('3', '1', '1509294321', '919.90');
insert into `order` values ('4', '1', '1601232190', '329.90');
insert into `order` values ('5', '1', '1503457384', '321.00');
insert into `order` values ('6', '1', '1598572382', '342.00');
insert into `order` values ('7', '1', '1500845727', '458.00');
insert into `order` values ('8', '1', '1508458923', '1200.00');
insert into `order` values ('9', '1', '1504538293', '2109.00');
insert into `order` values ('10', '1', '1932428723', '5888.00');
insert into `order` values ('11', '1', '2390423712', '3219.00');
insert into `order` values ('12', '1', '4587923992', '123.00');
insert into `order` values ('13', '1', '4095378812', '421.00');
insert into `order` values ('14', '1', '9423890127', '678.00');
insert into `order` values ('15', '1', '7859213249', '7689.00');
insert into `order` values ('16', '1', '4598450230', '909.20');
用户表和订单表分别对应两个实例对象，分别是：user.java 和 order.java，它们都在 com.h3.pojo 包中。
user.java代码内容如下：
package com.h3.pojo;
import java.util.list;
/**
* @describe: user
* @author: h3
* @version: v1.0
* @copyright http://www.h3.com
*/
public class user {
private int id;
private string username;
private string mobile;
public int getid() {
return id;
}
public void setid(int id) {
this.id = id;
}
public string getusername() {
return username;
}
public void setusername(string username) {
this.username = username;
}
public string getmobile() {
return mobile;
}
public void setmobile(string mobile) {
this.mobile = mobile;
}
}
order.java代码内容如下：
package com.h3.pojo;
/**
* @describe: user - 订单
* @author: h3
* @version: v1.0
* @copyright http://www.h3.com
*/
public class order {
private int orderid;
private string orderno;
private float money;
private int userid;
private user user;
public int getuserid() {
return userid;
}
public void setuserid(int userid) {
this.userid = userid;
}
public int getorderid() {
return orderid;
}
public void setorderid(int orderid) {
this.orderid = orderid;
}
public user getuser() {
return user;
}
public void setuser(user user) {
this.user = user;
}
public string getorderno() {
return orderno;
}
public void setorderno(string orderno) {
this.orderno = orderno;
}
public float getmoney() {
return money;
}
public void setmoney(float money) {
this.money = money;
}
}
这个实例中有三个重要的配置文件，它们分别是：applicationcontext.xml ， configuration.xml 以及 usermaper.xml。
applicationcontext.xml 配置文件里最主要的配置：
<?xml version="1.0" encoding="utf-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/xmlschema-instance" xmlns:aop="http://www.springframework.org/schema/aop"
xmlns:tx="http://www.springframework.org/schema/tx" xmlns:context="http://www.springframework.org/schema/context"
xmlns:p="http://www.springframework.org/schema/p"
xsi:schemalocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-3.0.xsd
http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.0.xsd
http://www.springframework.org/schema/jee http://www.springframework.org/schema/jee/spring-jee-3.0.xsd
http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.0.xsd"
default-autowire="byname" default-lazy-init="false">
<!--本示例采用dbcp连接池，应预先把dbcp的jar包复制到工程的lib目录下。 -->
<context:property-placeholder location="classpath:/config/database.properties" />
<bean id="datasource" class="org.apache.commons.dbcp.basicdatasource"
destroy-method="close" p:driverclassname="com.mysql.jdbc.driver"
p:url="jdbc:mysql://127.0.0.1:3306/h3?characterencoding=utf8"
p:username="root" p:password="" p:maxactive="10" p:maxidle="10">
</bean>
<bean id="transactionmanager"
class="org.springframework.jdbc.datasource.datasourcetransactionmanager">
<property name="datasource" ref="datasource" />
</bean>
<bean id="sqlsessionfactory" class="org.mybatis.spring.sqlsessionfactorybean">
<!--datasource属性指定要用到的连接池-->
<property name="datasource" ref="datasource" />
<!--configlocation属性指定mybatis的核心配置文件-->
<property name="configlocation" value="classpath:config/configuration.xml" />
<!-- 所有配置的mapper文件 -->
<property name="mapperlocations" value="classpath*:com/h3/mapepr/*.xml" />
</bean>
<bean class="org.mybatis.spring.mapper.mapperscannerconfigurer">
<property name="basepackage" value="com.h3.maper" />
</bean>
</beans>
配置文件 configuration.xml 的内容如下：
<?xml version="1.0" encoding="utf-8" ?>
<!doctype configuration public "-//mybatis.org//dtd config 3.0//en"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<typealiases>
<typealias alias="user" type="com.h3.pojo.user"/>
<typealias alias="order" type="com.h3.pojo.order"/>
</typealiases>
<!-- 与spring 集成之后,这些可以完全删除,数据库连接的管理交给 spring 去管理 -->
<!--
<environments default="development">
<environment id="development">
<transactionmanager type="jdbc"/>
<datasource type="pooled">
<property name="driver" value="com.mysql.jdbc.driver"/>
<property name="url" value="jdbc:mysql://127.0.0.1:3306/mybatis?characterencoding=utf8" />
<property name="username" value="root"/>
<property name="password" value="password"/>
</datasource>
</environment>
</environments>
-->
<!-- 这里交给sqlsessionfactory 的 mapperlocations属性去得到所有配置信息 -->
<!--
<mappers>
<mapper resource="com/yihaomen/mapper/user.xml"/>
</mappers>
-->
</configuration>
usermaper.xml 用于定义查询和数据对象映射，其内容如下：
<?xml version="1.0" encoding="utf-8" ?>
<!doctype mapper public "-//mybatis.org//dtd mapper 3.0//en"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.h3.maper.usermaper">
<!-- 为了返回list 类型而定义的returnmap -->
<resultmap type="user" id="resultuser">
<id column="id" property="id" />
<result column="username" property="username" />
<result column="mobile" property="mobile" />
</resultmap>
<!-- user 联合 order 查询 方法的配置 (多对一的方式) -->
<resultmap id="resultuserorders" type="order">
<id property="orderid" column="order_id" />
<result property="orderno" column="order_no" />
<result property="money" column="money" />
<result property="userid" column="user_id" />
<association property="user" javatype="user">
<id property="id" column="id" />
<result property="username" column="username" />
<result property="mobile" column="mobile" />
</association>
</resultmap>
<select id="getuserorders" parametertype="int" resultmap="resultuserorders">
select u.*,o.* from `user` u, `order` o
where u.id=o.user_id and u.id=#{id}
</select>
<select id="getuserbyid" resultmap="resultuser" parametertype="int">
select *
from user
where id=#{id}
</select>
</mapper>
package com.h3.controller;
import java.util.list;
import javax.servlet.http.httpservletrequest;
import javax.servlet.http.httpservletresponse;
import org.springframework.beans.factory.annotation.autowired;
import org.springframework.stereotype.controller;
import org.springframework.web.bind.annotation.requestmapping;
import org.springframework.web.servlet.modelandview;
import com.h3.maper.usermaper;
import com.h3.pojo.order;
import com.h3.util.page;
// http://localhost:8080/mybatis08-paging/user/orders
@controller
@requestmapping("/user")
public class usercontroller {
@autowired
usermaper usermaper;
/**
* 某一个用户下的所有订单
*
* @param request
* @param response
* @return
*/
@requestmapping("/orders")
public modelandview listall(httpservletrequest request,
httpservletresponse response) {
list<order> orders = usermaper.getuserorders(1);
system.out.println("orders");
modelandview mav = new modelandview("user_orders");
mav.addobject("orders", orders);
return mav;
}
/**
* 订单分页
*
* @param request
* @param response
* @return
*/
@requestmapping("/orderpages")
public modelandview pagelist(httpservletrequest request,
httpservletresponse response) {
int currentpage = request.getparameter("page") == null ? 1 : integer
.parseint(request.getparameter("page"));
int pagesize = 3;
if (currentpage <= 0) {
currentpage = 1;
}
int currentresult = (currentpage - 1) * pagesize;
system.out.println(request.getrequesturi());
system.out.println(request.getquerystring());
page page = new page();
page.setshowcount(pagesize);
page.setcurrentresult(currentresult);
list<order> orders = usermaper.getorderlistpage(page, 1);
system.out.println("current page =>" + page);
int totalcount = page.gettotalresult();
int lastpage = 0;
if (totalcount % pagesize == 0) {
lastpage = totalcount % pagesize;
} else {
lastpage = 1 + totalcount / pagesize;
}
if (currentpage >= lastpage) {
currentpage = lastpage;
}
string pagestr = "";
pagestr = string.format(
"<a href=\"%s\">上一页</a> <a href=\"%s\">下一页</a>", request
.getrequesturi()
+ "?page=" + (currentpage - 1), request.getrequesturi()
+ "?page=" + (currentpage + 1));
// 制定视图，也就是list.jsp
modelandview mav = new modelandview("pagelist");
mav.addobject("orders", orders);
mav.addobject("pagelist", pagestr);
return mav;
}
}
注意，在这个分页工程中，在 com.h3.util 包下新增了几个类，它们分别是：pageplugin.java，page.java, pagehelper.java，其中 pageplugin 是针对 mybatis 分页的插件。由于代码太多，这里列出 pageplugin.java 的代码，其它两个类的代码有兴趣的读者可以在下载代码后阅读取研究。 pageplugin.java 的代码如下所示：
package com.h3.util;
import java.lang.reflect.field;
import java.sql.connection;
import java.sql.preparedstatement;
import java.sql.resultset;
import java.sql.sqlexception;
import java.util.list;
import java.util.map;
import java.util.properties;
import javax.xml.bind.propertyexception;
import org.apache.ibatis.executor.errorcontext;
import org.apache.ibatis.executor.executor;
import org.apache.ibatis.executor.executorexception;
import org.apache.ibatis.executor.statement.basestatementhandler;
import org.apache.ibatis.executor.statement.routingstatementhandler;
import org.apache.ibatis.executor.statement.statementhandler;
import org.apache.ibatis.mapping.boundsql;
import org.apache.ibatis.mapping.mappedstatement;
import org.apache.ibatis.mapping.parametermapping;
import org.apache.ibatis.mapping.parametermode;
import org.apache.ibatis.plugin.interceptor;
import org.apache.ibatis.plugin.intercepts;
import org.apache.ibatis.plugin.invocation;
import org.apache.ibatis.plugin.plugin;
import org.apache.ibatis.plugin.signature;
import org.apache.ibatis.reflection.metaobject;
import org.apache.ibatis.reflection.property.propertytokenizer;
import org.apache.ibatis.scripting.xmltags.foreachsqlnode;
import org.apache.ibatis.session.configuration;
import org.apache.ibatis.session.resulthandler;
import org.apache.ibatis.session.rowbounds;
import org.apache.ibatis.type.typehandler;
import org.apache.ibatis.type.typehandlerregistry;
@intercepts( { @signature(type = statementhandler.class, method = "prepare", args = { connection.class }) })
public class pageplugin implements interceptor {
private static string dialect = "";
private static string pagesqlid = "";
@suppresswarnings("unchecked")
public object intercept(invocation ivk) throws throwable {
if (ivk.gettarget() instanceof routingstatementhandler) {
routingstatementhandler statementhandler = (routingstatementhandler) ivk
.gettarget();
basestatementhandler delegate = (basestatementhandler) reflecthelper
.getvaluebyfieldname(statementhandler, "delegate");
mappedstatement mappedstatement = (mappedstatement) reflecthelper
.getvaluebyfieldname(delegate, "mappedstatement");
if (mappedstatement.getid().matches(pagesqlid)) {
boundsql boundsql = delegate.getboundsql();
object parameterobject = boundsql.getparameterobject();
if (parameterobject == null) {
throw new nullh3erexception("parameterobject error");
} else {
connection connection = (connection) ivk.getargs()[0];
string sql = boundsql.getsql();
string countsql = "select count(0) from (" + sql
+ ") mycount";
system.out.println("总数sql 语句:" + countsql);
preparedstatement countstmt = connection
.preparestatement(countsql);
boundsql countbs = new boundsql(mappedstatement
.getconfiguration(), countsql, boundsql
.getparametermappings(), parameterobject);
setparameters(countstmt, mappedstatement, countbs,
parameterobject);
resultset rs = countstmt.executequery();
int count = 0;
if (rs.next()) {
count = rs.getint(1);
}
rs.close();
countstmt.close();
page page = null;
if (parameterobject instanceof page) {
page = (page) parameterobject;
page.settotalresult(count);
} else if (parameterobject instanceof map) {
map<string, object> map = (map<string, object>) parameterobject;
page = (page) map.get("page");
if (page == null)
page = new page();
page.settotalresult(count);
} else {
field pagefield = reflecthelper.getfieldbyfieldname(
parameterobject, "page");
if (pagefield != null) {
page = (page) reflecthelper.getvaluebyfieldname(
parameterobject, "page");
if (page == null)
page = new page();
page.settotalresult(count);
reflecthelper.setvaluebyfieldname(parameterobject,
"page", page);
} else {
throw new nosuchfieldexception(parameterobject
.getclass().getname());
}
}
string pagesql = generatepagesql(sql, page);
system.out.println("page sql:" + pagesql);
reflecthelper.setvaluebyfieldname(boundsql, "sql", pagesql);
}
}
}
return ivk.proceed();
}
private void setparameters(preparedstatement ps,
mappedstatement mappedstatement, boundsql boundsql,
object parameterobject) throws sqlexception {
errorcontext.instance().activity("setting parameters").object(
mappedstatement.getparametermap().getid());
list<parametermapping> parametermappings = boundsql
.getparametermappings();
if (parametermappings != null) {
configuration configuration = mappedstatement.getconfiguration();
typehandlerregistry typehandlerregistry = configuration
.gettypehandlerregistry();
metaobject metaobject = parameterobject == null ? null
: configuration.newmetaobject(parameterobject);
for (int i = 0; i < parametermappings.size(); i++) {
parametermapping parametermapping = parametermappings.get(i);
if (parametermapping.getmode() != parametermode.out) {
object value;
string propertyname = parametermapping.getproperty();
propertytokenizer prop = new propertytokenizer(propertyname);
if (parameterobject == null) {
value = null;
} else if (typehandlerregistry
.hastypehandler(parameterobject.getclass())) {
value = parameterobject;
} else if (boundsql.hasadditionalparameter(propertyname)) {
value = boundsql.getadditionalparameter(propertyname);
} else if (propertyname
.startswith(foreachsqlnode.item_prefix)
&& boundsql.hasadditionalparameter(prop.getname())) {
value = boundsql.getadditionalparameter(prop.getname());
if (value != null) {
value = configuration.newmetaobject(value)
.getvalue(
propertyname.substring(prop
.getname().length()));
}
} else {
value = metaobject == null ? null : metaobject
.getvalue(propertyname);
}
typehandler typehandler = parametermapping.gettypehandler();
if (typehandler == null) {
throw new executorexception(
"there was no typehandler found for parameter "
+ propertyname + " of statement "
+ mappedstatement.getid());
}
typehandler.setparameter(ps, i + 1, value, parametermapping
.getjdbctype());
}
}
}
}
private string generatepagesql(string sql, page page) {
if (page != null && (dialect != null || !dialect.equals(""))) {
stringbuffer pagesql = new stringbuffer();
if ("mysql".equals(dialect)) {
pagesql.append(sql);
pagesql.append(" limit " + page.getcurrentresult() + ","
+ page.getshowcount());
} else if ("oracle".equals(dialect)) {
pagesql
.append("select * from (select tmp_tb.*,rownum row_id from (");
pagesql.append(sql);
pagesql.append(") tmp_tb where rownum<=");
pagesql.append(page.getcurrentresult() + page.getshowcount());
pagesql.append(") where row_id>");
pagesql.append(page.getcurrentresult());
}
return pagesql.tostring();
} else {
return sql;
}
}
public object plugin(object arg0) {
// todo auto-generated method stub
return plugin.wrap(arg0, this);
}
public void setproperties(properties p) {
dialect = p.getproperty("dialect");
if (dialect == null || dialect.equals("")) {
try {
throw new propertyexception("dialect property is not found!");
} catch (propertyexception e) {
// todo auto-generated catch block
e.printstacktrace();
}
}
pagesqlid = p.getproperty("pagesqlid");
if (dialect == null || dialect.equals("")) {
try {
throw new propertyexception("pagesqlid property is not found!");
} catch (propertyexception e) {
// todo auto-generated catch block
e.printstacktrace();
}
}
}
}
接下来部署 mybatis08-paging 这个工程，启动 tomcat ，打开浏览器输入网址：http://localhost:8080/mybatis08-paging/user/orderpages ，显示结果如下：
工程 mybatis08-paging 的代码下载：http://pan.baidu.com/s/1pjxhvnt
jar 包下载：http://pan.baidu.com/s/1bnyrj9h
