精通SpringBoot——第十二篇：分页查询功能的实现-白红宇

本文将介绍如何实现分页查询功能，推荐使用github的pagehelper插件实现（事实上大家基本都是这么干的），但本文的实现方式和大多数不同，废话少说，现在就带着大家看看区别在哪里。

先看pom.xml依赖：相当简单的mybatis-spring依赖+mysql+pagehelper+fastjson


            
                 
      
       org.springframework.boot
                  
      
       spring-boot-starter-web
              
             
                 
      
       org.mybatis.spring.boot
                  
      
       mybatis-spring-boot-starter
                  
      
       1.3.2
              
             
                 
      
       com.alibaba
                  
      
       fastjson
                  
      
       1.2.44
              
             
                 
      
       mysql
                  
      
       mysql-connector-java
                  
      
       runtime
              
             
             
             
                 
      
       com.github.pagehelper
                  
      
       pagehelper-spring-boot-starter
                  
      
       1.2.5

application.yml配置

spring:  datasource:    username: root    password: 123456    url: jdbc:mysql://localhost:3306/javashop    driver-class-name: com.mysql.jdbc.Driver  http:    encoding:      charset: utf-8      enabled: truemybatis:  type-aliases-package: com.developlee.mybatispagehelper.domain  mapper-locations: classpath:/mapper/*.xmlpagehelper:  helper-dialect: mysql  reasonable: true  support-methods-arguments: true  params: count=countSql

撸代码了，先从controller开始，开干！随便写个简单点的

@RestControllerpublic class UserController {    @Autowired    private UserServiceImpl userService;    @PostMapping("/queryList")    public ResponseEntity queryList(@RequestBody UserEntity userEntity) {        List
    
      userEntities = userService.findUserList(userEntity);        return new ResponseEntity( new PageEntity<>(userEntities), HttpStatus.OK);    }}

仔细看，是不是发现并_没有PageHelper.startPage(int num, int size)_这句话？当然没有最好，每次分页查询都写这句，是不是很烦。。。还有_PageEntity是个啥_？不要着急，让我们慢慢揭开面纱。

service和dao还有userMapper.xml没什么好讲的，就是为了userService.findList能正常查出个list数组来。代码懒得贴了，占位置，相信大家也都会。

Next，就是重点了，看看UserEntity实体做了什么。

public class UserEntity extends BaseEntity {    private Long id;    private String username;    private String password;    private String mobile;    public Long getId() {        return id;    }    public void setId(Long id) {        this.id = id;    }    public String getUsername() {        return username;    }    public void setUsername(String username) {        this.username = username;    }    public String getPassword() {        return password;    }    public void setPassword(String password) {        this.password = password;    }    public String getMobile() {        return mobile;    }    public void setMobile(String mobile) {        this.mobile = mobile;    }}

OMG，继承了一个BaseEntity，那BaseEntity有哪些内容呢，其实相当easy，就是些我们要传的page参数.

public abstract class BaseEntity {    //分页大小    private Integer pageSize;    //分页开始    private Integer pageNum;    private Integer total;    //排序类型DESC  or  AES    private String sort;    private String orderBy;    @JSONField(serialize = false)    public Integer getPageSize() {        return pageSize;    }    public void setPageSize(Integer pageSize) {        this.pageSize = pageSize;    }    @JSONField(serialize = false)    public Integer getPageNum() {        return pageNum;    }    public void setPageNum(Integer pageNum) {        this.pageNum = pageNum;    }    @JSONField(serialize = false)    public Integer getTotal() {        return total;    }    public void setTotal(Integer total) {        this.total = total;    }    @JSONField(serialize = false)    public String getOrderBy() {        return orderBy;    }    public void setOrderBy(String orderBy) {        this.orderBy = orderBy;    }    @JSONField(serialize = false)    public String getSort() {        return sort;    }    public void setSort(String sort) {        this.sort = sort;    }}

注意哦，这些个参数返回给前端时都不需要给的哦。所以用了@JSONField(serialize=false) 来搞定。

讲到这，似乎没什么神奇之处，呃呃呃，是的，这些都是为了传参数。看看PageEntity ,这才是今天的主角儿~~~

import com.github.pagehelper.Page;import java.io.Serializable;import java.util.Collection;import java.util.List;/** * 对Page
    
     结果进行包装 * 
     
 * 新增分页的多项属性 */@SuppressWarnings({"rawtypes", "unchecked"})public class PageEntity
     
       implements Serializable {    private static final long serialVersionUID = 1L;    //当前页    private int currentPage;    //每页的数量    private int pageSize;    //总记录数    private long total;    //总页数    private int pages;    //结果集    private List
      
        list;    //是否为第一页    private boolean isFirstPage = false;    //是否为最后一页    private boolean isLastPage = false;    public PageEntity() {    }    /**     * 包装Page对象     *     * @param list     */    public PageEntity(List
       
         list) {        if (list instanceof Page) {            Page page = (Page) list;            this.currentPage = page.getPageNum();            this.pageSize = page.getPageSize();            this.pages = page.getPages();            this.list = page;            this.total = page.getTotal();        } else if (list instanceof Collection) {            this.currentPage = 1;            this.pageSize = list.size();            this.pages = 1;            this.list = list;            this.total = list.size();        }        if (list instanceof Collection) {            //判断页面边界            judgePageBoudary();        }    }    /**     * 判定页面边界     */    private void judgePageBoudary() {        isFirstPage = currentPage == 1;        isLastPage = currentPage == pages;    }    public int getCurrentPage() {        return currentPage;    }    public void setCurrentPage(int currentPage) {        this.currentPage = currentPage;    }    public int getPageSize() {        return pageSize;    }    public void setPageSize(int pageSize) {        this.pageSize = pageSize;    }    public long getTotal() {        return total;    }    public void setTotal(long total) {        this.total = total;    }    public int getPages() {        return pages;    }    public void setPages(int pages) {        this.pages = pages;    }    public List
        
          getList() {        return list;    }    public void setList(List
         
           List) { this.list = List; } public boolean isIsFirstPage() { return isFirstPage; } public void setIsFirstPage(boolean isFirstPage) { this.isFirstPage = isFirstPage; } public boolean isIsLastPage() { return isLastPage; } public void setIsLastPage(boolean isLastPage) { this.isLastPage = isLastPage; } @Override public String toString() { final StringBuffer sb = new StringBuffer("PageEntity{"); sb.append("currentPage=").append(currentPage); sb.append(", pageSize=").append(pageSize); sb.append(", total=").append(total); sb.append(", pages=").append(pages); sb.append(", list=").append(list); sb.append(", isFirstPage=").append(isFirstPage); sb.append(", isLastPage=").append(isLastPage); sb.append(", navigatepageNums="); sb.append('}'); return sb.toString(); }}

Watch Out!构造函数PageEntiy(List list) 这里头对pageHelper的Page进行了进一步的完善。看看pageHelper的Page类

public class Page
    
      extends ArrayList
     
       implements Closeable {    private static final long serialVersionUID = 1L;    private int pageNum;    private int pageSize;    private int startRow;    private int endRow;    private long total;    private int pages;    private boolean count;    private Boolean reasonable;    private Boolean pageSizeZero;    private String countColumn;    private String orderBy;    private boolean orderByOnly;    //多余不贴了。。。}

光说不练空把式，postman 工具测试一波看看。

我擦，什么情况，说好的不要这些page参数呢，为什么list里头还是有？嗯哼，SpringBoot默认的消息格式转换，也就是messgeConvert，很明显，我们使用了fastjson ，自然MessageConvert也要改造成用fastjson的。

springboot2.0中实现WebMvcConfiguer接口，然后覆盖该方法

/** * @author Lensen * @desc * @since 2018/8/25 21:45 */@Configuration@EnableWebMvcpublic class WebConfig implements WebMvcConfigurer {    //消息格式转换    @Override    public void configureMessageConverters(List
    
     > converters) {        //1.需要定义一个convert转换消息的对象;        FastJsonHttpMessageConverter fastJsonHttpMessageConverter = new FastJsonHttpMessageConverter();        //2.添加fastJson的配置信息，比如：是否要格式化返回的json数据;        FastJsonConfig fastJsonConfig = new FastJsonConfig();        fastJsonConfig.setSerializerFeatures(SerializerFeature.PrettyFormat,                SerializerFeature.WriteMapNullValue,                SerializerFeature.WriteNullStringAsEmpty,                SerializerFeature.DisableCircularReferenceDetect,                SerializerFeature.WriteNullListAsEmpty,                SerializerFeature.WriteDateUseDateFormat);        //3处理中文乱码问题        List
     
       fastMediaTypes = new ArrayList<>();        fastMediaTypes.add(MediaType.APPLICATION_JSON_UTF8);        //4.在convert中添加配置信息.        fastJsonHttpMessageConverter.setSupportedMediaTypes(fastMediaTypes);        fastJsonHttpMessageConverter.setFastJsonConfig(fastJsonConfig);        //5.将convert添加到converters当中.        converters.add(fastJsonHttpMessageConverter);    }}

@EnableWebMvc别忘了，忘了就不会生效的（我一开始就**忘记了）

在测试，走起

完美~ 代码里我根本不用写PageHelper.startPage(int pageNum, int pageSize)这句话，直接专注自己的逻辑。

省时省力，空出时间来多陪陪家人，陪陪女朋友。bingo!

最后，以上示例代码可在我的中找到。我的个人公众号：developlee的潇洒人生。关注了也不一定更新，更新就不得了了。