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Spring Boot 利用Pageable插件实现分页和查询

2020-06-06 06:11 519 查看

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Dao包中书写个数据库的接口

@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包中实现Dao接口

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

这样就把pageable这个分页插件给实现了

第三步

这一步就是在Controller这个包中编写

//    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):用来设置页面的位置和展示的数据条目数，我们设置每页展示5条数据。PageInfo用来封装页面信息，返回给前台界面。

第四步

这个就是设置一下他的显示效果，单纯的显示层

<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.w3.org/1999/xhtml">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<center>
<h1>山东柏瑞软件科技有限公司</h1>
<table border="1" width="80%"height="80%">
<tr >
<td colspan="6">
<form action="/student/findName">
<input type="text" name="name">
<input type="submit"value="查询">
</form>
</td>
</tr>
<tr>
<td>编号</td>
<td>姓名</td>
<td>成绩</td>
<td>生日</td>
<td>班级</td>
<td>操作</td>
</tr>
<tr th:each="student:${pageInfo.content}">
<td th:text="${student.id}"></td>
<td th:text="${student.name}"></td>
<td th:text="${student.score}"></td>
<td th:text="${student.birthday}"></td>
<td th:text="${student.cname}"></td>
<td>
<a href="/student/toAdd">添加</a>
<a th:href="@{/student/doDelete(id=${student.id})}">删除</a>
<a th:href="@{/student/toUpdate(id=${student.id})}">修改</a>
</td>
</tr>
</table>
<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>
</center>
</body>
</html>

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接口中的
展示一下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();
}
}

那么number，totalElements 这些个方法在哪里呢？

这里的totalPages（总页） total Elements：（数据的总条数） size :(一个界面中有多少条数据)

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