pagehelper的使用和一些坑！

[toc]
##1.1 pagehelper介绍和使用
PageHelper是一款好用的开源免费的Mybatis第三方物理分页插件。
原本以为分页插件，应该是很简单的，然而PageHelper比我想象的要复杂许多，它做的很强大，也很彻底，强大到使用者可能并不需要这么多功能，彻底到一参可以两用。
###1.1.1 springboot下使用

• 依赖包导入（这里划重点！！！有坑！！）

<dependency>
    <groupId>com.github.pagehelper</groupId>
    <artifactId>pagehelper</artifactId>
    <version>最新版本</version>
</dependency>

这是从官网上的标准形式，但是注意了。pagehelper与springboot集成的话，不能用这个包，这样会导致分页失效！

正确的是下面这种导入方式：

 <dependency>
            <groupId>com.github.pagehelper</groupId>
            <artifactId>pagehelper-spring-boot-starter</artifactId>
            <version>1.2.3</version>
 </dependency>

可以看到跟springboot集成的包大多数后面都是以spring-boot-starter结尾。。。。

刚开始我用的第一种，代码也全都正确，就是没有分页效果。。。这坑！！

• User

public class User {
    private Integer id;

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", password='" + password + '\'' +
                ", uid=" + uid +
                ", admin=" + admin +
                ", email='" + email + '\'' +
                ", phonenumber=" + phonenumber +
                ", classid=" + classid +
                '}';
    }

    private String name;

    private String password;

    private Integer uid;

    private Integer admin;

    private String email;

    private Integer phonenumber;

    private Integer classid;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name == null ? null : name.trim();
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password == null ? null : password.trim();
    }

    public Integer getUid() {
        return uid;
    }

    public void setUid(Integer uid) {
        this.uid = uid;
    }

    public Integer getAdmin() {
        return admin;
    }

    public void setAdmin(Integer admin) {
        this.admin = admin;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email == null ? null : email.trim();
    }

    public Integer getPhonenumber() {
        return phonenumber;
    }

    public void setPhonenumber(Integer phonenumber) {
        this.phonenumber = phonenumber;
    }

    public Integer getClassid() {
        return classid;
    }

    public void setClassid(Integer classid) {
        this.classid = classid;
    }
}

• UserMapper

@Repository
public interface UserMapper {
    long countByExample(UserExample example);

    int deleteByExample(UserExample example);

    int insert(User record);

    int insertSelective(User record);
    List<User> selectAllUser();
    User selectByExample(UserExample example);
    User selectBynameANDpassword(String name,String password);

    int updateByExampleSelective(@Param("record") User record, @Param("example") UserExample example);

    int updateByExample(@Param("record") User record, @Param("example") UserExample example);

}

这里只用selectAllUser()这个方法就行了！

• UserMapper.xml

<select id="selectAllUser" resultType="com.hifix.springbootmyfirstproject.pojo.User">
    select *from user
  </select>

鄙人还是比较喜欢这种xml的方式声明sql，并不是觉得注解的不好，只是觉得这种方式使得代码的整体可读性更好！

• controller

//测试分页信息
@RequestMapping("/UserInfo")
public String presentUser(Model model,
                                  @RequestParam(required = false,defaultValue="1",value="pageNum")Integer pageNum,
                                  @RequestParam(defaultValue="2",value="pageSize")Integer pageSize)throws  Exception {

    if(pageNum == null){
        pageNum = 1;   //设置默认当前页
    }
    if(pageNum <= 0){
        pageNum = 1;
    }
    if(pageSize == null){
        pageSize = 2;    //设置默认每页显示的数据数
    }
    System.out.println("当前页是："+pageNum+"显示条数是："+pageSize);
//1.引入分页插件,pageNum是第几页，pageSize是每页显示多少条,默认查询总数count
//2.紧跟的查询就是一个分页查询-必须紧跟.后面的其他查询不会被分页，除非再次调用PageHelper.startPage
    PageHelper.startPage(pageNum,pageSize);
    List<User> userList =pageimpl.getAllUser();

        System.out.println("分页数据："+userList);
        //3.使用PageInfo包装查询后的结果,5是连续 显示的条数,结果list类型是Page<E>
        PageInfo<User> pageInfo = new PageInfo<User>(userList,pageSize);
        //4.使用model/map/modelandview等带回前端

        model.addAttribute("pageInfo",pageInfo);

return "bootstraptable";

}

• 前端

<!doctype html>
<html lang="en" xmlns:th="http://www.thymeleaf.org" xmlns:c="http://www.w3.org/1999/xhtml">
<head>
    <!-- Required meta tags -->
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
    <title>Hello, Bootstrap Table!</title>

    <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css" integrity="sha384-ggOyR0iXCbMQv3Xipma34MD+dH/1fQ784/j6cY/iJTQUOhcWr7x9JvoRxT2MZw1T" crossorigin="anonymous">
    <link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.6.3/css/all.css" integrity="sha384-UHRtZLI+pbxtHCWp1t77Bi1L4ZtiqrqD80Kn4Z8NTSRyMA2Fd33n5dQ8lWUE00s/" crossorigin="anonymous">
    <link rel="stylesheet" href="https://unpkg.com/bootstrap-table@1.17.1/dist/bootstrap-table.min.css">
</head>
<body>
<table data-toggle="table">
    <thead>
    <tr>
        <th>name</th>
        <th>password</th>
        <th>uid</th>
    </tr>
    </thead>
    <tbody >
    <tr  th:each="c:${pageInfo.list}">
        <td>[[${c.name}]]</td>
        <td>[[${c.password}]]</td>
        <td>[[${c.uid}]]</td>
    </tr>

    </tbody>

</table>
<br/>
<div class="modal-footer no-margin-top">
    <div class="col-md-6">
        当前第 [[${pageInfo.pageNum}]]页,共 [[${pageInfo.pages}]] 页.一共 [[${pageInfo.total}]] 条记录
    </div>

    <ul class="pagination pull-right no-margin">
        <li th:if="${pageInfo.hasPreviousPage}">
            <a th:href="'/UserInfo?pageNum=1'">首页</a>
        </li>

        <li class="prev" th:if="${pageInfo.hasPreviousPage}">
            <a th:href="'/UserInfo?pageNum='+${pageInfo.prePage}">
                <i class="ace-icon fa fa-angle-double-left"></i>
            </a>
        </li>
        <!--遍历条数-->
        <li th:each="nav:${pageInfo.navigatepageNums}">
            <a th:href="'/UserInfo?pageNum='+${nav}" th:text="${nav}" th:if="${nav != pageInfo.pageNum}"></a>
            <span style="font-weight: bold;background: #6faed9;" th:if="${nav == pageInfo.pageNum}" th:text="${nav}" ></span>
        </li>

        <li class="next" th:if="${pageInfo.hasNextPage}">
            <a th:href="'/UserInfo?pageNum='+${pageInfo.nextPage}">
                <i class="ace-icon fa fa-angle-double-right"></i>
            </a>
        </li>

        <li>
            <a th:href="'/UserInfo?pageNum='+${pageInfo.pages}">尾页</a>
        </li>
    </ul>
</div>

<div>当前页号：<span th:text="${pageInfo.pageNum}"></span></div>
<div>每页条数：<span th:text="${pageInfo.pageSize}"></span></div>
<div>起始行号：<span th:text="${pageInfo.startRow}"></span></div>
<div>终止行号：<span th:text="${pageInfo.endRow}"></span></div>
<div>总结果数：<span th:text="${pageInfo.total}"></span></div>
<div>总页数：<span th:text="${pageInfo.pages}"></span></div>
<hr />
<div>是否为第一页：<span th:text="${pageInfo.isFirstPage}"></span></div>
<div>是否为最后一页：<span th:text="${pageInfo.isLastPage}"></span></div>
<div>是否有前一页：<span th:text="${pageInfo.hasPreviousPage}"></span></div>
<div>是否有下一页：<span th:text="${pageInfo.hasNextPage}"></span></div>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.min.js" integrity="sha512-bLT0Qm9VnAYZDflyKcBaQ2gg0hSYNQrJ8RilYldYQ1FxQYoCLtUjuuRuZo+fjqhx/qtq/1itJ0C2ejDxltZVFg==" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.7/umd/popper.min.js" integrity="sha384-UO2eT0CpHqdSJQ6hJty5KVphtPhzWj9WO1clHTMGa3JDZwrnQq4sF86dIHNDz0W1" crossorigin="anonymous"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/js/bootstrap.min.js" integrity="sha384-JjSmVgyd0p3pXB1rRibZUAYoIIy6OrQ6VrjIEaFf/nJGzIxFDsf4x0xIM+B07jRM" crossorigin="anonymous"></script>
<script src="https://unpkg.com/bootstrap-table@1.17.1/dist/bootstrap-table.min.js"></script>
</body>
</html>

• 效果

##2.1 总结
相比其他分页插件而言，pagehelper强大的很多。个人觉得用起来还是挺香的。