精通SpringBoot——第十二篇：分页查询功能的实现
原文链接： https://yq.aliyun.com/articles/629124
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: true
mybatis:
type-aliases-package: com.developlee.mybatispagehelper.domain
mapper-locations: classpath:/mapper/*.xml
pagehelper:
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
@RestController
public 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
@EnableWebMvc
public 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github.com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。