後端程式設計師都知道，在Web系統中，分頁是一種常見的功能，我之前寫的分頁方法都比較麻煩，移植性也不高，這就很不樂觀了。作為一個積極開朗的程式設計師，怎麼能不去了解PageHelper分頁外掛呢？PageHelper是國內非常優秀的一款開源的mybatis分頁外掛，它支援基本主流與常用的資料庫，一致支援mysql、oracle、mariaDB、DB2、SQLite、Hsqldb等。OK接下來就一起來瞭解瞭解PageHelper分頁外掛！

中文教程

首先，推薦兩個PageHelper分頁外掛專案地址，這裡面有中文教程： github 專案 gitosc 專案

PageHelper使用

至於怎麼使用我想上面提供的兩個專案講的絕逼講的比我清楚，下面直接進入PageHelper使用實戰

首先，整合引入分頁外掛有下面2種方式，一種是直接下jar包一種是mawen依賴，推薦使用 Maven 方式。

方法一： 直接下載jar包

jar包下載地址，由於使用了sql 解析工具，你還需要下載 jsqlparser.jar

方法二： Maven新增依賴

  <dependency>
            <groupId>com.github.pagehelper</groupId>
            <artifactId>pagehelper</artifactId>
            <version>5.1.2</version>
  </dependency>
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1.匯入maven依賴分頁外掛

我這裡就採用方法二maven依賴

2.各個情況下xml的配置

情況一：如果是mybatis單獨使用PageHelper分頁外掛的時候，就需要在xml配置中新增如下程式碼：

  <!--
plugins在配置檔案中的位置必須符合要求，否則會報錯，順序如下properties?,settings?,typeAliases?,typeHandlers?,objectFactory?,objectWrapperFactory?,plugins?,environments?,databaseIdProvider?,mappers?
  -->
  <!-- com.github.pagehelper為PageHelper類所在包名 -->
    <plugins> 
    <!-- 使用下面的方式配置引數，推薦的兩個專案中有所有的引數介紹 -->
        <plugin interceptor="com.github.pagehelper.PageInterceptor"> 
            <property name="param1" value="value1"/>
        </plugin>
    </plugins>
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情況二：顯然，我是這個是ssm專案，mybatis是交由spring的IOC容器管理的，就需要在spring的xml配置中新增如下程式碼（建立工廠中新增）：

  <!-- 把交給IOC管理 SqlSessionFactory -->
 <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
     <property name="dataSource" ref="dataSource"/>
     <!-- 傳入PageHelper的外掛 -->
     <property name="plugins">
         <array>
             <!-- 傳入外掛的物件 -->
             <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>
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下面用一個圖來分析一下兩個引數作用：

3.Controller程式碼編寫

上面我們配置完了，至於為什麼從controller程式碼開始是因為controller呼叫service嘛，這樣編寫程式碼更方便快捷！為了看出差別，未分頁的controller程式碼方法如下：

@Controller
@RequestMapping("/orders")
public class OrdersController {

    @Autowired
    private IOrdersService ordersService;

//查詢所有orders未分頁
   @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;
    }
}
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而採用了分頁程式碼則是如下：

//採用分頁程式碼方法
   @RequestMapping("/findAll.do")
    public ModelAndView findAll(@RequestParam(name="page",required = true,defaultValue = "1")int page,@RequestParam(name="size",defaultValue = "4")int size ) {
        ModelAndView mv = new ModelAndView();
        List<Orders> ordersList = ordersService.findAll(page,size);

        //PageInfo就是一個分頁Bean
        PageInfo pageInfo =new PageInfo(ordersList);
        mv.addObject("pageInfo",pageInfo);
        mv.setViewName("orders-list");
        return mv;

    }
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可以發現多了兩個引數分別是page和size

4.Service介面程式碼編寫

public interface IOrdersService {
    List<Orders> findAll(int page,int size);
}
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5.Service實現類程式碼編寫

在執行sql之前（ServiceImpl），使用PageHelper分頁，引數pageNum 是頁碼值 引數pageSize 代表是每頁顯示條數。在ServiceImpl中,使用PageHelper分頁操作程式碼如下：

@Service
public class OrdersServiceImpl implements IOrdersService {
    @Autowired
    private IOrdersDao ordersDao;

    @Override
    public List<Orders> findAll(int page,int size) {
        //引數pageNum 是頁碼值   引數pageSize 代表是每頁顯示條數
        PageHelper.startPage(page,size);
        return ordersDao.findAll();
    }
}
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特別注意：在編寫PageHelper分頁程式碼時的 PageHelper.startPage(page,size)這一句必須寫在查詢方法的上一句，中間不能新增任何程式碼，否則失效！

6.jsp頁面未處理程式碼

沒有更改的jsp頁面程式碼,普通查詢關鍵更改程式碼塊，注意這裡接收資料為 ordersList

<c:forEach items="${ordersList}" var="orders">
   <tr>
		<td><input name="ids" type="checkbox"></td>
		...
		<td>...</td>
		</td>
	</tr>
</c:forEach>
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這下面的程式碼則是未分頁邏輯程式碼

 <div class="box-tools pull-right">
                        <ul class="pagination">
                            <li>
                                <a href="#" aria-label="Previous">首頁</a>
                            </li>
                            <li><a href="#">上一頁</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="#">下一頁</a></li>
                            <li>
                                <a href="#" aria-label="Next">尾頁</a>
                            </li>
                        </ul>
                    </div>

                </div>
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7.jsp頁面處理後程式碼

更改後的jsp頁面程式碼,分頁查詢的關鍵更改程式碼塊，注意這裡接收資料為 ordersList.list

<c:forEach items="${ordersList.list}" var="orders">
   <tr>
		<td><input name="ids" type="checkbox"></td>
		...
		<td>...</td>
		</td>
	</tr>
</c:forEach>
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這下面的程式碼則是分頁邏輯程式碼

<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">首頁</a>
		</li>
		<li><a href="${pageContext.request.contextPath}/orders/findAll.do?page=${pageInfo.pageNum-1}&size=${pageInfo.pageSize}">上一頁</a></li>
		<c:forEach begin="1" end="${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=${pageInfo.pageSize}">下一頁</a></li>
		<li>
			<a href="${pageContext.request.contextPath}/orders/findAll.do?page=${pageInfo.pages}&size=${pageInfo.pageSize}" aria-label="Next">尾頁</a>
		</li>
	</ul>
</div>
</div>
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8.jsp頁面處理前後程式碼分析

    //PageInfo就是一個分頁Bean
   PageInfo pageInfo =new PageInfo(ordersList);
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為了能看到上面的pageInfo原始碼，我就把程式碼貼在下面了

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();
    }
}

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到這裡，基本就OK了，我再次強調我推薦的那兩個專案，那裡面講的很詳細大佬寫的，強調完畢，揮爪~