Spring Boot 利用Pageable插件实现分页和查询

• Pageable 是spring
Data库中定义的一个接口，该接口是所有分页相关信息的一个抽象，通过该接口，我们可以得到和分页相关所有信息（例如pageNumber、pageSize等）。
• Pageable定义了很多方法，但其核心的信息只有两个：一是分页的信息（page、size），二是排序的信息

第一步

在需要分页的Dao层接口中编辑接口方法

 @Query(value="select * from student inner join classes on classes.cid=student.sid",nativeQuery=true)
    Page<List<Map>> findPage(Pageable pageable);

为什么书写这个page<List<?>>这个返回值呢?

• 将数据交给page类来分页处理
• 在显示页面有首页，上一页，下一页，尾页吧，这个就是原因了

第二步

在service层中实现调用之前定义的Dao层接口

 public Page<List<Map>> findPage(Pageable pageable){
        return studentDao.findPage(pageable);
    }

第三步

这一步就是在控制层（controller）中编写

//    分页
    @RequestMapping("/findPage")

    public String findByPage(Model model, Integer pageNum){
//        当前页面为空时，赋值为一，代表是当前为第一页
        if(pageNum==null){
            pageNum=1;
        }
        Pageable pageable=PageRequest.of(pageNum-1,5);
        Page<List<Map>> page=serviceStudent.findPage(pageable);
        model.addAttribute("pageInfo",page);
        return "index";
    }

PageRequest.of(int PageNum,int PageSize):用来设置页数和每页中显示的数据条数。

• int PageNum: 页数
• int PageSize: 每页显示的数据条数

PageInfo：接收后端接口中的数据，渲染给显示界面。

第四步

现在我们在postman当中请求，看看接口给我返回的数据我们分析下

pageSize: 每页显示的数据条数；
PageNumber： 页数
totalPages： 总页数
totalElements： 总条数

<ul>
    当前第 <span th:text="${pageInfo.number}+1"></span>页&nbsp;&nbsp;&nbsp;|&nbsp;&nbsp;
    总   <span th:text="${pageInfo.totalPages}"></span>页&nbsp;&nbsp;&nbsp;|&nbsp;&nbsp;
    共   <span th:text="${pageInfo.totalElements}"></span> 条&nbsp;&nbsp;&nbsp;|&nbsp;&nbsp;
    <a th:href="@{/student/findPage(pageNum=1)}">首页</a>&nbsp;&nbsp;&nbsp;|&nbsp;&nbsp;
    <a th:href="@{/student/findPage(pageNum= ${pageInfo.hasPrevious()}?${pageInfo.getNumber()}:1)}">上一页</a>&nbsp;&nbsp;&nbsp;|&nbsp;&nbsp;
    <a th:href="@{/student/findPage(pageNum= ${pageInfo.hasNext()}?${pageInfo.getNumber()}+2:${pageInfo.totalPages})}">下一页</a>&nbsp;&nbsp;&nbsp;|&nbsp;&nbsp;
    <a th:href="@{/student/findPage(pageNum= ${pageInfo.totalPages} )}">尾页</a>
</ul>

这个还是可以的，细心点没问题
这些个方法 比如是hasPrevious()（上一页）、pageInfo.hasNext()（下一页）等方法是在哪里来的？
这写个方法是来自Page类的
page 类是继承Slice接口，有兴趣的同学可以看一下

Slice类

/*
 * Copyright 2014-2020 the original author or authors.
 *
 * 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
 *
 *      https://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 org.springframework.data.domain;

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

import org.springframework.core.convert.converter.Converter;
import org.springframework.data.util.Streamable;

/**
 * A slice of data that indicates whether there's a next or previous slice available. Allows to obtain a
 * {@link Pageable} to request a previous or next {@link Slice}.
 *
 * @author Oliver Gierke
 * @since 1.8
 */
public interface Slice<T> extends Streamable<T> {

	/**
	 * Returns the number of the current {@link Slice}. Is always non-negative.
	 *
	 * @return the number of the current {@link Slice}.
	 */
	int getNumber();

	/**
	 * Returns the size of the {@link Slice}.
	 *
	 * @return the size of the {@link Slice}.
	 */
	int getSize();

	/**
	 * Returns the number of elements currently on this {@link Slice}.
	 *
	 * @return the number of elements currently on this {@link Slice}.
	 */
	int getNumberOfElements();

	/**
	 * Returns the page content as {@link List}.
	 *
	 * @return
	 */
	List<T> getContent();

	/**
	 * Returns whether the {@link Slice} has content at all.
	 *
	 * @return
	 */
	boolean hasContent();

	/**
	 * Returns the sorting parameters for the {@link Slice}.
	 *
	 * @return
	 */
	Sort getSort();

	/**
	 * Returns whether the current {@link Slice} is the first one.
	 *
	 * @return
	 */
	boolean isFirst();

	/**
	 * Returns whether the current {@link Slice} is the last one.
	 *
	 * @return
	 */
	boolean isLast();

	/**
	 * Returns if there is a next {@link Slice}.
	 *
	 * @return if there is a next {@link Slice}.
	 */
	boolean hasNext();

	/**
	 * Returns if there is a previous {@link Slice}.
	 *
	 * @return if there is a previous {@link Slice}.
	 */
	boolean hasPrevious();

	/**
	 * Returns the {@link Pageable} that's been used to request the current {@link Slice}.
	 *
	 * @return
	 * @since 2.0
	 */
	default Pageable getPageable() {
		return PageRequest.of(getNumber(), getSize(), getSort());
	}

	/**
	 * Returns the {@link Pageable} to request the next {@link Slice}. Can be {@link Pageable#unpaged()} in case the
	 * current {@link Slice} is already the last one. Clients should check {@link #hasNext()} before calling this method.
	 *
	 * @return
	 * @see #nextOrLastPageable()
	 */
	Pageable nextPageable();

	/**
	 * Returns the {@link Pageable} to request the previous {@link Slice}. Can be {@link Pageable#unpaged()} in case the
	 * current {@link Slice} is already the first one. Clients should check {@link #hasPrevious()} before calling this
	 * method.
	 *
	 * @return
	 * @see #previousPageable()
	 */
	Pageable previousPageable();

	/**
	 * Returns a new {@link Slice} with the content of the current one mapped by the given {@link Converter}.
	 *
	 * @param converter must not be {@literal null}.
	 * @return a new {@link Slice} with the content of the current one mapped by the given {@link Converter}.
	 * @since 1.10
	 */
	<U> Slice<U> map(Function<? super T, ? extends U> converter);

	/**
	 * Returns the {@link Pageable} describing the next slice or the one describing the current slice in case it's the
	 * last one.
	 *
	 * @return
	 * @since 2.2
	 */
	default Pageable nextOrLastPageable() {
		return hasNext() ? nextPageable() : getPageable();
	}

	/**
	 * Returns the {@link Pageable} describing the previous slice or the one describing the current slice in case it's the
	 * first one.
	 *
	 * @return
	 * @since 2.2
	 */
	default Pageable previousOrFirstPageable() {
		return hasPrevious() ? previousPageable() : getPageable();
	}
}