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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

 <dependencies> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency> <dependency> <groupId>org.mybatis.spring.boot</groupId> <artifactId>mybatis-spring-boot-starter</artifactId> <version>1.3.2</version> </dependency> <dependency> <groupId>com.alibaba</groupId> <artifactId>fastjson</artifactId> <version>1.2.44</version> </dependency> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <scope>runtime</scope> </dependency> <!--pageHelper--> <!-- https://mvnrepository.com/artifact/com.github.pagehelper/pagehelper-spring-boot-starter --> <dependency> <groupId>com.github.pagehelper</groupId> <artifactId>pagehelper-spring-boot-starter</artifactId> <version>1.2.5</version> </dependency> </dependencies> 

application.yml配置

spring: datasource: username: root password:  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<UserEntity> 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<E>结果进行包装 * <p/> * 新增分页的多项属性 */ @SuppressWarnings({"rawtypes", "unchecked"}) public class PageEntity<T> 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<T> 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<T> 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<T> getList() { return list; } public void setList(List<T> 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<E> extends ArrayList<E> 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<HttpMessageConverter<?>> 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<MediaType> 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!