【开端】Java 分页工具类运用

一、绪论

Java系统中，分页查询的场景随处可见，本节介com.baomidou.mybatisplus.core.metadata.IPage;来分页的工具类

二、分页工具类

public class PageUtils implements Serializable {
   private static final long serialVersionUID = 1L;
   /**
   * 总记录数
   */
   private int totalCount;
   /**
   * 每页记录数
   */
   private int pageSize;
   /**
   * 总页数
   */
   private int totalPage;
   /**
   * 当前页数
   */
   private int currPage;
   /**
   * 列表数据
   */
   private List<?> list;

   /**
   * 分页
   * @param list 列表数据
   * @param totalCount 总记录数
   * @param pageSize 每页记录数
   * @param currPage 当前页数
   */
   public PageUtils(List<?> list, int totalCount, int pageSize, int currPage) {
       this.list = list;
       this.totalCount = totalCount;
       this.pageSize = pageSize;
       this.currPage = currPage;
       this.totalPage = (int)Math.ceil((double)totalCount/pageSize);
   }

   /**
   * 分页
   */
   public PageUtils(IPage<?> page) {
       this.list = page.getRecords();
       this.totalCount = (int)page.getTotal();
       this.pageSize = (int)page.getSize();
       this.currPage = (int)page.getCurrent();
       this.totalPage = (int)page.getPages();
   }

   public int getTotalCount() {
       return totalCount;
   }

   public void setTotalCount(int totalCount) {
       this.totalCount = totalCount;
   }

   public int getPageSize() {
       return pageSize;
   }

   public void setPageSize(int pageSize) {
       this.pageSize = pageSize;
   }

   public int getTotalPage() {
       return totalPage;
   }

   public void setTotalPage(int totalPage) {
       this.totalPage = totalPage;
   }

   public int getCurrPage() {
       return currPage;
   }

   public void setCurrPage(int currPage) {
       this.currPage = currPage;
   }

   public List<?> getList() {
       return list;
   }

   public void setList(List<?> list) {
       this.list = list;
   }

}

public class PageUtils implements Serializable {private static final long serialVersionUID = 1L;/*** 总记录数*/private int totalCount;/*** 每页记录数*/private int pageSize;/*** 总页数*/private int totalPage;/*** 当前页数*/private int currPage;/*** 列表数据*/private List<?> list;/*** 分页* @param list        列表数据* @param totalCount  总记录数* @param pageSize    每页记录数* @param currPage    当前页数*/public PageUtils(List<?> list, int totalCount, int pageSize, int currPage) {this.list = list;this.totalCount = totalCount;this.pageSize = pageSize;this.currPage = currPage;this.totalPage = (int)Math.ceil((double)totalCount/pageSize);}/*** 分页*/public PageUtils(IPage<?> page) {this.list = page.getRecords();this.totalCount = (int)page.getTotal();this.pageSize = (int)page.getSize();this.currPage = (int)page.getCurrent();this.totalPage = (int)page.getPages();}public int getTotalCount() {return totalCount;}public void setTotalCount(int totalCount) {this.totalCount = totalCount;}public int getPageSize() {return pageSize;}public void setPageSize(int pageSize) {this.pageSize = pageSize;}public int getTotalPage() {return totalPage;}public void setTotalPage(int totalPage) {this.totalPage = totalPage;}public int getCurrPage() {return currPage;}public void setCurrPage(int currPage) {this.currPage = currPage;}public List<?> getList() {return list;}public void setList(List<?> list) {this.list = list;}}

Ipage接口

/*
* Copyright (c) 2011-2021, baomidou (jobob@qq.com).
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.baomidou.mybatisplus.core.metadata;

import java.io.Serializable;
import java.util.List;
import java.util.function.Function;

import static java.util.stream.Collectors.toList;

/**
* 分页 Page 对象接口
*
* @author hubin
* @since 2018-06-09
*/
public interface IPage<T> extends Serializable {

/**
* 获取排序信息，排序的字段和正反序
*
* @return 排序信息
*/
List<OrderItem> orders();

/**
* 自动优化 COUNT SQL【默认：true 】
*
* @return true 是 / false 否
*/
default boolean optimizeCountSql() {
return true;
}

/**
* {@link com.baomidou.mybatisplus.extension.plugins.inner.PaginationInnerInterceptor#isOptimizeJoin()}
* 两个参数都为 true 才会进行sql处理
*
* @return true 是 / false 否
* @since 3.4.4 @2021-09-13
*/
default boolean optimizeJoinOfCountSql() {
return true;
}

/**
* 进行 count 查询【默认: true 】
*
* @return true 是 / false 否
*/
default boolean searchCount() {
return true;
}

/**
* 计算当前分页偏移量
*/
default long offset() {
long current = getCurrent();
if (current <= 1L) {
return 0L;
}
return Math.max((current - 1) * getSize(), 0L);
}

/**
* 最大每页分页数限制,优先级高于分页插件内的 maxLimit
*
* @since 3.4.0 @2020-07-17
*/
default Long maxLimit() {
return null;
}

/**
* 当前分页总页数
*/
default long getPages() {
if (getSize() == 0) {
return 0L;
}
long pages = getTotal() / getSize();
if (getTotal() % getSize() != 0) {
pages++;
}
return pages;
}

/**
* 内部什么也不干
* <p>只是为了 json 反序列化时不报错</p>
*/
default IPage<T> setPages(long pages) {
// to do nothing
return this;
}

/**
* 分页记录列表
*
* @return 分页对象记录列表
*/
List<T> getRecords();

/**
* 设置分页记录列表
*/
IPage<T> setRecords(List<T> records);

/**
* 当前满足条件总行数
*
* @return 总条数
*/
long getTotal();

/**
* 设置当前满足条件总行数
*/
IPage<T> setTotal(long total);

/**
* 获取每页显示条数
*
* @return 每页显示条数
*/
long getSize();

/**
* 设置每页显示条数
*/
IPage<T> setSize(long size);

/**
* 当前页
*
* @return 当前页
*/
long getCurrent();

/**
* 设置当前页
*/
IPage<T> setCurrent(long current);

/**
* IPage 的泛型转换
*
* @param mapper 转换函数
* @param <R> 转换后的泛型
* @return 转换泛型后的 IPage
*/
@SuppressWarnings("unchecked")
default <R> IPage<R> convert(Function<? super T, ? extends R> mapper) {
List<R> collect = this.getRecords().stream().map(mapper).collect(toList());
return ((IPage<R>) this).setRecords(collect);
}

/**
* 老分页插件不支持
* <p>
* MappedStatement 的 id
*
* @return id
* @since 3.4.0 @2020-06-19
*/
default String countId() {
return null;
}
}

/** Copyright (c) 2011-2021, baomidou (jobob@qq.com).** Licensed under the Apache License, Version 2.0 (the "License");* you may not use this file except in compliance with the License.* You may obtain a copy of the License at**     http://www.apache.org/licenses/LICENSE-2.0** Unless required by applicable law or agreed to in writing, software* distributed under the License is distributed on an "AS IS" BASIS,* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.* See the License for the specific language governing permissions and* limitations under the License.*/
package com.baomidou.mybatisplus.core.metadata;import java.io.Serializable;
import java.util.List;
import java.util.function.Function;import static java.util.stream.Collectors.toList;/*** 分页 Page 对象接口** @author hubin* @since 2018-06-09*/
public interface IPage<T> extends Serializable {/*** 获取排序信息，排序的字段和正反序** @return 排序信息*/List<OrderItem> orders();/*** 自动优化 COUNT SQL【 默认：true 】** @return true 是 / false 否*/default boolean optimizeCountSql() {return true;}/*** {@link com.baomidou.mybatisplus.extension.plugins.inner.PaginationInnerInterceptor#isOptimizeJoin()}* 两个参数都为 true 才会进行sql处理** @return true 是 / false 否* @since 3.4.4 @2021-09-13*/default boolean optimizeJoinOfCountSql() {return true;}/*** 进行 count 查询 【 默认: true 】** @return true 是 / false 否*/default boolean searchCount() {return true;}/*** 计算当前分页偏移量*/default long offset() {long current = getCurrent();if (current <= 1L) {return 0L;}return Math.max((current - 1) * getSize(), 0L);}/*** 最大每页分页数限制,优先级高于分页插件内的 maxLimit** @since 3.4.0 @2020-07-17*/default Long maxLimit() {return null;}/*** 当前分页总页数*/default long getPages() {if (getSize() == 0) {return 0L;}long pages = getTotal() / getSize();if (getTotal() % getSize() != 0) {pages++;}return pages;}/*** 内部什么也不干* <p>只是为了 json 反序列化时不报错</p>*/default IPage<T> setPages(long pages) {// to do nothingreturn this;}/*** 分页记录列表** @return 分页对象记录列表*/List<T> getRecords();/*** 设置分页记录列表*/IPage<T> setRecords(List<T> records);/*** 当前满足条件总行数** @return 总条数*/long getTotal();/*** 设置当前满足条件总行数*/IPage<T> setTotal(long total);/*** 获取每页显示条数** @return 每页显示条数*/long getSize();/*** 设置每页显示条数*/IPage<T> setSize(long size);/*** 当前页** @return 当前页*/long getCurrent();/*** 设置当前页*/IPage<T> setCurrent(long current);/*** IPage 的泛型转换** @param mapper 转换函数* @param <R>    转换后的泛型* @return 转换泛型后的 IPage*/@SuppressWarnings("unchecked")default <R> IPage<R> convert(Function<? super T, ? extends R> mapper) {List<R> collect = this.getRecords().stream().map(mapper).collect(toList());return ((IPage<R>) this).setRecords(collect);}/*** 老分页插件不支持* <p>* MappedStatement 的 id** @return id* @since 3.4.0 @2020-06-19*/default String countId() {return null;}
}

三、运用

/**
* 分页查询权限信息
* @param param
* @return
*/
public PageUtils queryPage(Map<String, Object> param) {

IPage<TMenu> page = new Query<TMenu>().getPage(param);
QueryWrapper<TMenu> wrapper = new QueryWrapper<>();
   if (param.containsKey("leftId")) {
       wrapper.eq("left_id", param.get("leftId").toString());
   }
   wrapper.eq("state", "0");
   wrapper.orderByAsc("sort");
IPage<TMenu> tMenuIPage = tMenuMapper.selectPage(page, wrapper);
return new PageUtils(tMenuIPage);

}

    /*** 分页查询权限信息* @param param* @return*/public PageUtils queryPage(Map<String, Object> param) {IPage<TMenu> page = new Query<TMenu>().getPage(param);QueryWrapper<TMenu> wrapper = new QueryWrapper<>();if (param.containsKey("leftId")) {wrapper.eq("left_id", param.get("leftId").toString());}wrapper.eq("state", "0");wrapper.orderByAsc("sort");IPage<TMenu> tMenuIPage = tMenuMapper.selectPage(page, wrapper);return new PageUtils(tMenuIPage);}