<dependency><groupId>org.mybatis.spring.boot</groupId><artifactId>mybatis-spring-boot-starter</artifactId><version>2.0.0</version></dependency><dependency><groupId>com.github.pagehelper</groupId><artifactId>pagehelper</artifactId><version>5.1.2</version></dependency><dependency><groupId>com.github.pagehelper</groupId><artifactId>pagehelper-spring-boot-autoconfigure</artifactId>   ---作用自动配置pagehelper<version>1.2.3</version></dependency>

package com.github.pagehelper.autoconfigure;import com.github.pagehelper.PageInterceptor;
import org.apache.ibatis.session.SqlSessionFactory;
import org.mybatis.spring.boot.autoconfigure.MybatisAutoConfiguration;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.autoconfigure.AutoConfigureAfter;
import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;import javax.annotation.PostConstruct;
import java.util.List;
import java.util.Properties;/*** 自定注入分页插件** @author liuzh*/
@Configuration //表明当前了是一个配置类
@ConditionalOnBean(SqlSessionFactory.class)//当有SqlSesionFactory这个类的时候才实例化当前类
@EnableConfigurationProperties(PageHelperProperties.class)//pagehelpser的配置文件
@AutoConfigureAfter(MybatisAutoConfiguration.class)//当前类是在mybatisAutoconfiguration配置类初始化之后才初始化
public class PageHelperAutoConfiguration {@Autowiredprivate List<SqlSessionFactory> sqlSessionFactoryList;@Autowiredprivate PageHelperProperties properties;//配置文件/*** 接受分页插件额外的属性** @return*/@Bean@ConfigurationProperties(prefix = PageHelperProperties.PAGEHELPER_PREFIX)//将配置文件实例化为propertiespublic Properties pageHelperProperties() {return new Properties();}@PostConstruct//实例化之后条用当前方法，将pagehelper插件添加到myabtis的核心配置文件中（Configuration中） PageInterceptor就是pagehelper的插件public void addPageInterceptor() {PageInterceptor interceptor = new PageInterceptor();Properties properties = new Properties();//先把一般方式配置的属性放进去properties.putAll(pageHelperProperties());//在把特殊配置放进去，由于close-conn 利用上面方式时，属性名就是 close-conn 而不是 closeConn，所以需要额外的一步properties.putAll(this.properties.getProperties());interceptor.setProperties(properties);for (SqlSessionFactory sqlSessionFactory : sqlSessionFactoryList) {sqlSessionFactory.getConfiguration().addInterceptor(interceptor);}}}

@Intercepts(//这个注解是mybatis中的注解{@Signature(type = Executor.class, method = "query", args = {MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class}),@Signature(type = Executor.class, method = "query", args = {MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class, CacheKey.class, BoundSql.class}),}
)
public class PageInterceptor implements Interceptor {//缓存count查询的msprotected Cache<String, MappedStatement> msCountMap = null;private Dialect dialect;//这个是pagehelper的一个接口，里边有数据库的一些方言配置private String default_dialect_class = "com.github.pagehelper.PageHelper";//默认的方言实现类，如果上边那个dialect没有配置的话，默认走这个private Field additionalParametersField;private String countSuffix = "_COUNT";

@Overridepublic Object intercept(Invocation invocation) throws Throwable {try {Object[] args = invocation.getArgs();//获取拦截到的方法的所有参数 下边获取0,1,2,3是进行强制转换对应的类，这个是根据@intercepts注解中的@sisignature中的args得到的MappedStatement ms = (MappedStatement) args[0];Object parameter = args[1];RowBounds rowBounds = (RowBounds) args[2];ResultHandler resultHandler = (ResultHandler) args[3];Executor executor = (Executor) invocation.getTarget();CacheKey cacheKey;BoundSql boundSql;//由于逻辑关系，只会进入一次  分两种情况4个参数和6个参数也是根据注解@signature的args类判断的if(args.length == 4){//4 个参数时boundSql = ms.getBoundSql(parameter);cacheKey = executor.createCacheKey(ms, parameter, rowBounds, boundSql);} else {//6 个参数时cacheKey = (CacheKey) args[4];boundSql = (BoundSql) args[5];}List resultList;//调用方法判断是否需要进行分页，如果不需要，直接返回结果  例如dialect使用的是默认的实现类的话，判断是否要跳过分页，是根据代码中查询数据库是，是否执行过PageHelper.startPage()方法类判断的（一种情况），执行过，则要分页，否则不分页if (!dialect.skip(ms, parameter, rowBounds)) {//反射获取动态参数String msId = ms.getId();Configuration configuration = ms.getConfiguration();Map<String, Object> additionalParameters = (Map<String, Object>) additionalParametersField.get(boundSql);//下边会进行两步：1、总数查询 2、分页查询//判断是否需要进行 count 查询if (dialect.beforeCount(ms, parameter, rowBounds)) {String countMsId = msId + countSuffix;Long count;//先判断是否存在手写的 count 查询MappedStatement countMs = getExistedMappedStatement(configuration, countMsId);if(countMs != null){count = executeManualCount(executor, countMs, parameter, boundSql, resultHandler);} else {countMs = msCountMap.get(countMsId);//自动创建if (countMs == null) {//根据当前的 ms 创建一个返回值为 Long 类型的 mscountMs = MSUtils.newCountMappedStatement(ms, countMsId);msCountMap.put(countMsId, countMs);}count = executeAutoCount(executor, countMs, parameter, boundSql, rowBounds, resultHandler);}//处理查询总数//返回 true 时继续分页查询，false 时直接返回if (!dialect.afterCount(count, parameter, rowBounds)) {//当查询总数为 0 时，直接返回空的结果return dialect.afterPage(new ArrayList(), parameter, rowBounds);}}//判断是否需要进行分页查询if (dialect.beforePage(ms, parameter, rowBounds)) {//生成分页的缓存 keyCacheKey pageKey = cacheKey;//处理参数对象parameter = dialect.processParameterObject(ms, parameter, boundSql, pageKey);//调用方言获取分页 sqlString pageSql = dialect.getPageSql(ms, boundSql, parameter, rowBounds, pageKey);BoundSql pageBoundSql = new BoundSql(configuration, pageSql, boundSql.getParameterMappings(), parameter);//设置动态参数for (String key : additionalParameters.keySet()) {pageBoundSql.setAdditionalParameter(key, additionalParameters.get(key));}//执行分页查询resultList = executor.query(ms, parameter, RowBounds.DEFAULT, resultHandler, pageKey, pageBoundSql);} else {//不执行分页的情况下，也不执行内存分页resultList = executor.query(ms, parameter, RowBounds.DEFAULT, resultHandler, cacheKey, boundSql);}} else {//rowBounds用参数值，不使用分页插件处理时，仍然支持默认的内存分页resultList = executor.query(ms, parameter, rowBounds, resultHandler, cacheKey, boundSql);}return dialect.afterPage(resultList, parameter, rowBounds);} finally {dialect.afterAll();}}

        Page<TUser> startPage = PageHelper.startPage(1, 2);List<TUser> list1 = mapper.selectByEmailAndSex1(params);

 /*** 开始分页** @param pageNum  页码* @param pageSize 每页显示数量*/public static <E> Page<E> startPage(int pageNum, int pageSize) {return startPage(pageNum, pageSize, true);}

   /*** 开始分页** @param pageNum  页码* @param pageSize 每页显示数量* @param count    是否进行count查询*/public static <E> Page<E> startPage(int pageNum, int pageSize, boolean count) {return startPage(pageNum, pageSize, count, null, null);}

   /*** 开始分页** @param pageNum      页码* @param pageSize     每页显示数量* @param count        是否进行count查询* @param reasonable   分页合理化,null时用默认配置* @param pageSizeZero true且pageSize=0时返回全部结果，false时分页,null时用默认配置*/public static <E> Page<E> startPage(int pageNum, int pageSize, boolean count, Boolean reasonable, Boolean pageSizeZero) {Page<E> page = new Page<E>(pageNum, pageSize, count);page.setReasonable(reasonable);page.setPageSizeZero(pageSizeZero);//当已经执行过orderBy的时候Page<E> oldPage = getLocalPage();//查询ThreadLocal中是否已经有了pageif (oldPage != null && oldPage.isOrderByOnly()) {page.setOrderBy(oldPage.getOrderBy());}setLocalPage(page);return page;}