Mybatis分页插件PageHelper的学习与使用

后端程序员都知道，在Web系统中，分页是一种常见的功能，我之前写的分页方法都比较麻烦，移植性也不高，这就很不乐观了。作为一个积极开朗的程序员，怎么能不去了解PageHelper分页插件呢？PageHelper是国内非常优秀的一款开源的mybatis分页插件，它支持基本主流与常用的数据库，一致支持mysql、oracle、mariaDB、DB2、SQLite、Hsqldb等。OK接下来就一起来了解了解PageHelper分页插件！

中文教程

首先，推荐两个PageHelper分页插件项目地址，这里面有中文教程：github 项目gitosc 项目

PageHelper使用

至于怎么使用我想上面提供的两个项目讲的绝逼讲的比我清楚，下面直接进入PageHelper使用实战

首先，集成引入分页插件有下面2种方式，一种是直接下jar包一种是mawen依赖，推荐使用 Maven 方式。

方法一： 直接下载jar包

jar包下载地址，由于使用了sql 解析工具，你还需要下载 jsqlparser.jar

方法二： Maven添加依赖

  <dependency>            <groupId>com.github.pagehelper</groupId>            <artifactId>pagehelper</artifactId>            <version>5.1.2</version>  </dependency>

1.导入maven依赖分页插件

我这里就采用方法二maven依赖

2.各个情况下xml的配置

情况一：如果是mybatis单独使用PageHelper分页插件的时候，就需要在xml配置中添加如下代码：

  <!--plugins在配置文件中的位置必须符合要求，否则会报错，顺序如下properties?, settings?, typeAliases?, typeHandlers?, objectFactory?,objectWrapperFactory?, plugins?,  environments?, databaseIdProvider?, mappers?  -->  <!-- com.github.pagehelper为PageHelper类所在包名 -->    <plugins>     <!-- 使用下面的方式配置参数，推荐的两个项目中有所有的参数介绍 -->        <plugin interceptor="com.github.pagehelper.PageInterceptor">             <property name="param1" value="value1"/>        </plugin>    </plugins>

情况二：显然，我是这个是ssm项目，mybatis是交由spring的IOC容器管理的，就需要在spring的xml配置中添加如下代码（创建工厂中添加）：

  <!-- 把交给IOC管理 SqlSessionFactory --> <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">     <property name="dataSource" ref="dataSource"/>     <!-- 传入PageHelper的插件 -->     <property name="plugins">         <array>             <!-- 传入插件的对象 -->             <bean class="com.github.pagehelper.PageInterceptor">                 <property name="properties">                     <props>                         <prop key="helperDialect">oracle</prop>                         <prop key="reasonable">true</prop>                     </props>                 </property>             </bean>         </array>     </property> </bean>

下面用一个图来分析一下两个参数作用：

3.Controller代码编写

上面我们配置完了，至于为什么从controller代码开始是因为controller调用service嘛，这样编写代码更方便快捷！为了看出差别，未分页的controller代码方法如下：

@Controller@RequestMapping("/orders")public class OrdersController {    @Autowired    private IOrdersService ordersService;//查询所有orders未分页   @RequestMapping("/findAll.do")    public ModelAndView findAll() {        ModelAndView mv = new ModelAndView();        List<Orders> ordersList = ordersService.findAll();        mv.addObject("ordersList", ordersList);        mv.setViewName("orders-list");        return mv;    }}

而采用了分页代码则是如下：

//采用分页代码方法   @RequestMapping("/findAll.do")    public ModelAndView findAll(@RequestParam(name="page",required = true,defaultValue = "1")int page,@RequestParam(name="size",required = true,defaultValue = "4")int size ) {        ModelAndView mv = new ModelAndView();        List<Orders> ordersList = ordersService.findAll(page,size);        //PageInfo就是一个分页Bean        PageInfo pageInfo =new PageInfo(ordersList);        mv.addObject("pageInfo", pageInfo);        mv.setViewName("orders-list");        return mv;    }

可以发现多了两个参数分别是page和size

4.Service接口代码编写

public interface IOrdersService {    List<Orders> findAll(int page,int size);}

5.Service实现类代码编写

在执行sql之前（ServiceImpl），使用PageHelper分页，参数pageNum 是页码值 参数pageSize 代表是每页显示条数。在ServiceImpl中,使用PageHelper分页操作代码如下：

@Servicepublic class OrdersServiceImpl implements IOrdersService {    @Autowired    private IOrdersDao ordersDao;    @Override    public List<Orders> findAll(int page,int size) {        //参数pageNum 是页码值   参数pageSize 代表是每页显示条数        PageHelper.startPage(page, size);        return ordersDao.findAll();    }}

特别注意：在编写PageHelper分页代码时的 PageHelper.startPage(page, size)这一句必须写在查询方法的上一句，中间不能添加任何代码，否则失效！

6.jsp页面未处理代码

没有更改的jsp页面代码,普通查询关键更改代码块，注意这里接收数据为 ordersList

<c:forEach items="${ordersList}" var="orders">   <tr>		<td><input name="ids" type="checkbox"></td>		...		<td>...</td>		</td>	</tr></c:forEach>

这下面的代码则是未分页逻辑代码

 <div class="box-tools pull-right">                        <ul class="pagination">                            <li>                                <a href="#" aria-label="Previous">首页</a>                            </li>                            <li><a href="#">上一页</a></li>                            <li><a href="#">1</a></li>                            <li><a href="#">2</a></li>                            <li><a href="#">3</a></li>                            <li><a href="#">4</a></li>                            <li><a href="#">5</a></li>                            <li><a href="#">下一页</a></li>                            <li>                                <a href="#" aria-label="Next">尾页</a>                            </li>                        </ul>                    </div>                </div>

7.jsp页面处理后代码

更改后的jsp页面代码,分页查询的关键更改代码块，注意这里接收数据为 ordersList.list

<c:forEach items="${ordersList.list}" var="orders">   <tr>		<td><input name="ids" type="checkbox"></td>		...		<td>...</td>		</td>	</tr></c:forEach>

这下面的代码则是分页逻辑代码

<div class="box-tools pull-right">   <ul class="pagination">		<li>			<a href="${pageContext.request.contextPath}/orders/findAll.do?page=1&size=${pageInfo.pageSize}" aria-label="Previous">首页</a>		</li>		<li><a href="${pageContext.request.contextPath}/orders/findAll.do?page=${pageInfo.pageNum-1}&size=${pageInfo.pageSize}">上一页</a></li>		<c:forEach begin="1" end="${pageInfo.pages}" var="pageNum">			<li><a href="${pageContext.request.contextPath}/orders/findAll.do?page=${pageNum}&size=${pageInfo.pageSize}">${pageNum}</a></li>		</c:forEach>		<li><a href="${pageContext.request.contextPath}/orders/findAll.do?page=${pageInfo.pageNum+1}&size=${pageInfo.pageSize}">下一页</a></li>		<li>			<a href="${pageContext.request.contextPath}/orders/findAll.do?page=${pageInfo.pages}&size=${pageInfo.pageSize}" aria-label="Next">尾页</a>		</li>	</ul></div></div>

8.jsp页面处理前后代码分析

    //PageInfo就是一个分页Bean   PageInfo pageInfo =new PageInfo(ordersList);

为了能看到上面的pageInfo源代码，我就把代码贴在下面了

package com.github.pagehelper;import java.io.Serializable;import java.util.Collection;import java.util.List;public class PageInfo<T> implements Serializable {    private static final long serialVersionUID = 1L;    private int pageNum;    private int pageSize;    private int size;    private int startRow;    private int endRow;    private long total;    private int pages;    private List<T> list;    private int prePage;    private int nextPage;    private boolean isFirstPage;    private boolean isLastPage;    private boolean hasPreviousPage;    private boolean hasNextPage;    private int navigatePages;    private int[] navigatepageNums;    private int navigateFirstPage;    private int navigateLastPage;    public PageInfo() {        this.isFirstPage = false;        this.isLastPage = false;        this.hasPreviousPage = false;        this.hasNextPage = false;    }    public PageInfo(List<T> list) {        this(list, 8);    }    public PageInfo(List<T> list, int navigatePages) {        this.isFirstPage = false;        this.isLastPage = false;        this.hasPreviousPage = false;        this.hasNextPage = false;        if (list instanceof Page) {            Page page = (Page)list;            this.pageNum = page.getPageNum();            this.pageSize = page.getPageSize();            this.pages = page.getPages();            this.list = page;            this.size = page.size();            this.total = page.getTotal();            if (this.size == 0) {                this.startRow = 0;                this.endRow = 0;            } else {                this.startRow = page.getStartRow() + 1;                this.endRow = this.startRow - 1 + this.size;            }        } else if (list instanceof Collection) {            this.pageNum = 1;            this.pageSize = list.size();            this.pages = this.pageSize > 0 ? 1 : 0;            this.list = list;            this.size = list.size();            this.total = (long)list.size();            this.startRow = 0;            this.endRow = list.size() > 0 ? list.size() - 1 : 0;        }        if (list instanceof Collection) {            this.navigatePages = navigatePages;            this.calcNavigatepageNums();            this.calcPage();            this.judgePageBoudary();        }    }    private void calcNavigatepageNums() {        int i;        if (this.pages <= this.navigatePages) {            this.navigatepageNums = new int[this.pages];            for(i = 0; i < this.pages; ++i) {                this.navigatepageNums[i] = i + 1;            }        } else {            this.navigatepageNums = new int[this.navigatePages];            i = this.pageNum - this.navigatePages / 2;            int endNum = this.pageNum + this.navigatePages / 2;            int i;            if (i < 1) {                i = 1;                for(i = 0; i < this.navigatePages; ++i) {                    this.navigatepageNums[i] = i++;                }            } else if (endNum > this.pages) {                endNum = this.pages;                for(i = this.navigatePages - 1; i >= 0; --i) {                    this.navigatepageNums[i] = endNum--;                }            } else {                for(i = 0; i < this.navigatePages; ++i) {                    this.navigatepageNums[i] = i++;                }            }        }    }    private void calcPage() {        if (this.navigatepageNums != null && this.navigatepageNums.length > 0) {            this.navigateFirstPage = this.navigatepageNums[0];            this.navigateLastPage = this.navigatepageNums[this.navigatepageNums.length - 1];            if (this.pageNum > 1) {                this.prePage = this.pageNum - 1;            }            if (this.pageNum < this.pages) {                this.nextPage = this.pageNum + 1;            }        }    }    private void judgePageBoudary() {        this.isFirstPage = this.pageNum == 1;        this.isLastPage = this.pageNum == this.pages || this.pages == 0;        this.hasPreviousPage = this.pageNum > 1;        this.hasNextPage = this.pageNum < this.pages;    }    public int getPageNum() {        return this.pageNum;    }    public void setPageNum(int pageNum) {        this.pageNum = pageNum;    }    public int getPageSize() {        return this.pageSize;    }    public void setPageSize(int pageSize) {        this.pageSize = pageSize;    }    public int getSize() {        return this.size;    }    public void setSize(int size) {        this.size = size;    }    public int getStartRow() {        return this.startRow;    }    public void setStartRow(int startRow) {        this.startRow = startRow;    }    public int getEndRow() {        return this.endRow;    }    public void setEndRow(int endRow) {        this.endRow = endRow;    }    public long getTotal() {        return this.total;    }    public void setTotal(long total) {        this.total = total;    }    public int getPages() {        return this.pages;    }    public void setPages(int pages) {        this.pages = pages;    }    public List<T> getList() {        return this.list;    }    public void setList(List<T> list) {        this.list = list;    }    /** @deprecated */    @Deprecated    public int getFirstPage() {        return this.navigateFirstPage;    }    /** @deprecated */    @Deprecated    public void setFirstPage(int firstPage) {        this.navigateFirstPage = firstPage;    }    public int getPrePage() {        return this.prePage;    }    public void setPrePage(int prePage) {        this.prePage = prePage;    }    public int getNextPage() {        return this.nextPage;    }    public void setNextPage(int nextPage) {        this.nextPage = nextPage;    }    /** @deprecated */    @Deprecated    public int getLastPage() {        return this.navigateLastPage;    }    /** @deprecated */    @Deprecated    public void setLastPage(int lastPage) {        this.navigateLastPage = lastPage;    }    public boolean isIsFirstPage() {        return this.isFirstPage;    }    public void setIsFirstPage(boolean isFirstPage) {        this.isFirstPage = isFirstPage;    }    public boolean isIsLastPage() {        return this.isLastPage;    }    public void setIsLastPage(boolean isLastPage) {        this.isLastPage = isLastPage;    }    public boolean isHasPreviousPage() {        return this.hasPreviousPage;    }    public void setHasPreviousPage(boolean hasPreviousPage) {        this.hasPreviousPage = hasPreviousPage;    }    public boolean isHasNextPage() {        return this.hasNextPage;    }    public void setHasNextPage(boolean hasNextPage) {        this.hasNextPage = hasNextPage;    }    public int getNavigatePages() {        return this.navigatePages;    }    public void setNavigatePages(int navigatePages) {        this.navigatePages = navigatePages;    }    public int[] getNavigatepageNums() {        return this.navigatepageNums;    }    public void setNavigatepageNums(int[] navigatepageNums) {        this.navigatepageNums = navigatepageNums;    }    public int getNavigateFirstPage() {        return this.navigateFirstPage;    }    public int getNavigateLastPage() {        return this.navigateLastPage;    }    public void setNavigateFirstPage(int navigateFirstPage) {        this.navigateFirstPage = navigateFirstPage;    }    public void setNavigateLastPage(int navigateLastPage) {        this.navigateLastPage = navigateLastPage;    }    public String toString() {        StringBuffer sb = new StringBuffer("PageInfo{");        sb.append("pageNum=").append(this.pageNum);        sb.append(", pageSize=").append(this.pageSize);        sb.append(", size=").append(this.size);        sb.append(", startRow=").append(this.startRow);        sb.append(", endRow=").append(this.endRow);        sb.append(", total=").append(this.total);        sb.append(", pages=").append(this.pages);        sb.append(", list=").append(this.list);        sb.append(", prePage=").append(this.prePage);        sb.append(", nextPage=").append(this.nextPage);        sb.append(", isFirstPage=").append(this.isFirstPage);        sb.append(", isLastPage=").append(this.isLastPage);        sb.append(", hasPreviousPage=").append(this.hasPreviousPage);        sb.append(", hasNextPage=").append(this.hasNextPage);        sb.append(", navigatePages=").append(this.navigatePages);        sb.append(", navigateFirstPage=").append(this.navigateFirstPage);        sb.append(", navigateLastPage=").append(this.navigateLastPage);        sb.append(", navigatepageNums=");        if (this.navigatepageNums == null) {            sb.append("null");        } else {            sb.append('[');            for(int i = 0; i < this.navigatepageNums.length; ++i) {                sb.append(i == 0 ? "" : ", ").append(this.navigatepageNums[i]);            }            sb.append(']');        }        sb.append('}');        return sb.toString();    }}

到这里，基本就OK了，我再次强调我推荐的那两个项目，那里面讲的很详细大佬写的，强调完毕，挥爪~