mybatis分頁插件pagehleper的基本使用

mybatis使用分頁插件時，多數都是主要是使用pageInfo來作為分頁的。

第一步：使用分頁插件需要引入分頁插件依賴，使用分頁插件時需要注意版本，不同的版本有些區別

<dependency>
    <groupId>com.github.pagehelper</groupId>
    <artifactId>pagehelper</artifactId>
    <version>4.2.1</version>
</dependency>

第二步：在mybati-config.xml文件中配置插件的一些信息，如下

<plugins>
    <!-- com.github.pagehelper為PageHelper類所在包名 -->
    <plugin interceptor="com.github.pagehelper.PageHelper">
        <property name="dialect" value="mysql"/>
        <!-- 該參數默認為false -->
        <!-- 設置為true時，會將RowBounds第一個參數offset當成pageNum頁碼使用 -->
        <!-- 和startPage中的pageNum效果一樣-->
        <property name="offsetAsPageNum" value="false"/>
        <!-- 該參數默認為false -->
        <!-- 設置為true時，使用RowBounds分頁會進行count查詢 -->
        <property name="rowBoundsWithCount" value="false"/>
        <!-- 設置為true時，如果pageSize=0或者RowBounds.limit = 0就會查詢出全部的結果 -->
        <!-- （相當於沒有執行分頁查詢，但是返回結果仍然是Page類型）-->
        <property name="pageSizeZero" value="true"/>
        <!-- 3.3.0版本可用 - 分頁參數合理化，默認false禁用 -->
        <!-- 啟用合理化時，如果pageNum<1會查詢第一頁，如果pageNum>pages會查詢最后一頁 -->
        <!-- 禁用合理化時，如果pageNum<1或pageNum>pages會返回空數據 -->
        <property name="reasonable" value="false"/>
        <!-- 3.5.0版本可用 - 為了支持startPage(Object params)方法 -->
        <!-- 增加了一個`params`參數來配置參數映射，用於從Map或ServletRequest中取值 -->
        <!-- 可以配置pageNum,pageSize,count,pageSizeZero,reasonable,不配置映射的用默認值 -->
        <!--<property name="params" value="pageNum=start;pageSize=limit;pageSizeZero=zero;reasonable=heli;count=contsql"/>-->
    </plugin>
</plugins>

第三步：實際使用如下

/**
 * <p>通過關鍵詞查詢商品接口</p>
 *
 * @author jason
 * @date 2020年8月15日16:07:59
 */
public interface QueryGoodsInfoWithKeyWords {

    /**
     * 通過關鍵詞查詢商品接口
     *
     * @param keyWordsCondition 用戶輸入的關鍵詞,參數為關鍵詞和分頁參數以及二次查詢條件
     * @return Results
     */
    PageInfo selectGoodsInfoByKeywords(KeyWordsCondition keyWordsCondition);

}

public class QueryGoodsInfoWithKeyWordsImpl implements QueryGoodsInfoWithKeyWords {
    @Override
    public PageInfo selectGoodsInfoByKeywords(KeyWordsCondition keyWordsCondition) {
        // md5加密密碼 將入參加密成md5用作redis中的key，不管他的入參是多少個，只要輸入了相同的條件，第二次直接從緩存里面取出就行
        String keyMD5 = DigestUtils.md5DigestAsHex(JSONObject.toJSONString(keyWordsCondition).getBytes());
        // 開啟分頁
        PageHelper.startPage(keyWordsCondition.getPage(), keyWordsCondition.getLimit());

        // 返回給前端的查詢結果list
        List<GoodsSerachKeyWordsDTO> keyWordsDTOList = new ArrayList<>();

        // 查詢緩存，如果緩存中有與之前相同的入參條件則直接返回
        if (redisUtil.existsKey(keyMD5)) {
            logger.info("是從緩存里面取出來的數據：" + JSONObject.toJSONString(redisUtil.getItemKey(keyMD5)));

            // 將json字符串列表list轉換成keyWordsDTOList
            JSONArray jsonArray = JSONArray.fromObject(redisUtil.getItemKey(keyMD5));
            keyWordsDTOList = (List<GoodsSerachKeyWordsDTO>) JSONArray.toCollection(jsonArray, GoodsSerachKeyWordsDTO.class);

            PageInfo pageInfo = new PageInfo(keyWordsDTOList);

            return pageInfo;
        } 

    }

}

需要注意2點：

（1）在使用時需要使用 PageHelper.startPage()方法開啟分頁，只需要傳入頁碼和每頁條數即可，它會自動根據頁碼和每頁條數自動計算偏移量。

（2）返回時把結果封裝為PageInfo，如 PageInfo pageInfo = new PageInfo(你需要返回的數據list);

最后看一下PageInfo里面的源碼

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

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; // 當前頁
    private int pageSize;// 每頁的條數
    private int size;// 當前頁的數據條數
    private String orderBy; // 排序
    private int startRow;// 當前頁第一個元素在數據庫中的行號
    private int endRow;//  當前頁最后一個元素在數據庫中的行號
    private long total;// 總條數
    private int pages;// 總頁數
    private List<T> list;// 結果集list
    private int prePage;// 前一頁
    private int nextPage;// 下一頁
    private boolean isFirstPage;// 是否是第一頁
    private boolean isLastPage;// 是否是最后一頁
    private boolean hasPreviousPage;// 是否有前一頁
    private boolean hasNextPage;// 是否有下一頁
    private int navigatePages;// 導航頁碼數
    private int[] navigatepageNums;// 所有導航頁碼
    private int navigateFirstPage;// 導航第一頁
    private int navigateLastPage;// 導航最后一頁

    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.orderBy = page.getOrderBy();
            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 = 1;
            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.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 String getOrderBy() {
        return this.orderBy;
    }

    public void setOrderBy(String orderBy) {
        this.orderBy = orderBy;
    }

    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();
    }
}

參考博文：

（1） https://www.jianshu.com/p/50fcd7f127f0
（2）https://github.com/pagehelper/Mybatis-PageHelper/blob/master/wikis/en/HowToUse.md