【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;

}

java 复制代码

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

* 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;

}

java 复制代码

/*
 * 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;
    }
}

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);

}

java 复制代码

    /**
     * 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);

   }