MyBatis-Plus分页拦截器，源码的重构（重构total总数的计算逻辑）

 1.1创建ThreadLocal工具类（作为业务逻辑结果存放类）

package org.springblade.sample.utils;public class QueryContext {private static final ThreadLocal<Long> totalInThreadLocal = new ThreadLocal<>();public static void setTotalIn(long totalIn) {totalInThreadLocal.set(totalIn);}public static long getTotalIn() {return totalInThreadLocal.get() != null ? totalInThreadLocal.get() : 0;}public static void clear() {totalInThreadLocal.remove();}
}

2.1重构Mybatis-plus分页查询total总数逻辑（通过实现InnerInterceptor接口进行重构,代码如下，根据注释进行对应业务调整即可）

package org.springblade.sample.config;import com.baomidou.mybatisplus.annotation.DbType;
import com.baomidou.mybatisplus.core.metadata.IPage;
import com.baomidou.mybatisplus.core.metadata.OrderItem;
import com.baomidou.mybatisplus.core.toolkit.*;
import com.baomidou.mybatisplus.extension.parser.JsqlParserGlobal;
import com.baomidou.mybatisplus.extension.plugins.inner.InnerInterceptor;
import com.baomidou.mybatisplus.extension.plugins.pagination.DialectFactory;
import com.baomidou.mybatisplus.extension.plugins.pagination.DialectModel;
import com.baomidou.mybatisplus.extension.plugins.pagination.dialects.IDialect;
import com.baomidou.mybatisplus.extension.toolkit.JdbcUtils;
import com.baomidou.mybatisplus.extension.toolkit.PropertyMapper;
import com.baomidou.mybatisplus.extension.toolkit.SqlParserUtils;
import groovy.util.logging.Slf4j;
import lombok.Data;
import lombok.NoArgsConstructor;
import net.sf.jsqlparser.JSQLParserException;
import net.sf.jsqlparser.expression.Alias;
import net.sf.jsqlparser.expression.Expression;
import net.sf.jsqlparser.schema.Column;
import net.sf.jsqlparser.schema.Table;
import net.sf.jsqlparser.statement.select.*;
import org.apache.ibatis.cache.CacheKey;
import org.apache.ibatis.executor.Executor;
import org.apache.ibatis.logging.Log;
import org.apache.ibatis.logging.LogFactory;
import org.apache.ibatis.mapping.BoundSql;
import org.apache.ibatis.mapping.MappedStatement;
import org.apache.ibatis.mapping.ParameterMapping;
import org.apache.ibatis.mapping.ResultMap;
import org.apache.ibatis.session.Configuration;
import org.apache.ibatis.session.ResultHandler;
import org.apache.ibatis.session.RowBounds;
import org.springblade.core.tool.utils.StringUtil;
import org.springblade.sample.utils.QueryContext;import java.sql.SQLException;
import java.util.*;
import java.util.concurrent.ConcurrentHashMap;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.util.stream.Collectors;/*** 分页拦截器* <p>* 默认对 left join 进行优化,虽然能优化count,但是加上分页的话如果1对多本身结果条数就是不正确的** @author hubin* @since 3.4.0*/
@lombok.extern.slf4j.Slf4j
@Data
@NoArgsConstructor
@org.springframework.context.annotation.Configuration
@Slf4j
public class PaginationInnerInterceptor implements InnerInterceptor {/*** 获取jsqlparser中count的SelectItem*/protected static final List<SelectItem> COUNT_SELECT_ITEM = Collections.singletonList(new SelectExpressionItem(new Column().withColumnName("COUNT(*)")).withAlias(new Alias("total")));protected static final Map<String, MappedStatement> countMsCache = new ConcurrentHashMap<>();protected final Log logger = LogFactory.getLog(this.getClass());/*** 表名*/private final String V_SAMPLE_COVID19 = "v_sample_covid19";private final String T_SAMPLE_COVID19 = "t_sample_covid19";private final String T_SAMPLE_FLU = "t_sample_flu";private final String T_SAMPLE_HADV = "t_sample_hadv";private final String T_SAMPLE_HMPV = "t_sample_hmpv";private final String T_SAMPLE_HPIV = "t_sample_hpiv";private final String T_SAMPLE_METAV = "t_sample_metav";private final String T_SAMPLE_RSV = "t_sample_rsv";/*** 溢出总页数后是否进行处理*/protected boolean overflow;/*** 单页分页条数限制*/protected Long maxLimit;/*** 数据库类型* <p>* 查看 {@link #findIDialect(Executor)} 逻辑*/private DbType dbType;/*** 方言实现类* <p>* 查看 {@link #findIDialect(Executor)} 逻辑*/private IDialect dialect;/*** 生成 countSql 优化掉 join* 现在只支持 left join** @since 3.4.2*/protected boolean optimizeJoin = true;public PaginationInnerInterceptor(DbType dbType) {this.dbType = dbType;}public PaginationInnerInterceptor(IDialect dialect) {this.dialect = dialect;}/**** 重构willDoQuery获取序列未上传数量（根据检索结果进行实时更新）* @param executor      Executor(可能是代理对象)* @param ms            MappedStatement* @param parameter     parameter* @param rowBounds     rowBounds* @param resultHandler resultHandler* @param boundSql      boundSql*/public boolean willDoQuery(Executor executor, MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {IPage<?> page = ParameterUtils.findPage(parameter).orElse(null);if (page == null || page.getSize() < 0 || !page.searchCount() || resultHandler != Executor.NO_RESULT_HANDLER) {return true;}BoundSql countSql;BoundSql countSqlIn;MappedStatement countMs = buildCountMappedStatement(ms, page.countId());if (countMs != null) {countSql = countMs.getBoundSql(parameter);countSqlIn = countMs.getBoundSql(parameter);} else {countMs = buildAutoCountMappedStatement(ms);String countSqlStr = autoCountSql(page, boundSql.getSql());PluginUtils.MPBoundSql mpBoundSql = PluginUtils.mpBoundSql(boundSql);countSql = new BoundSql(countMs.getConfiguration(), countSqlStr, mpBoundSql.parameterMappings(), parameter);countSqlIn = new BoundSql(countMs.getConfiguration(), countSqlStr + " and seq_num = '0'", mpBoundSql.parameterMappings(), parameter);PluginUtils.setAdditionalParameter(countSql, mpBoundSql.additionalParameters());PluginUtils.setAdditionalParameter(countSqlIn, mpBoundSql.additionalParameters());}// 执行第一个查询 (result)CacheKey cacheKey = executor.createCacheKey(countMs, parameter, rowBounds, countSql);List<Object> result = executor.query(countMs, parameter, rowBounds, resultHandler, cacheKey, countSql);long total = 0;if (CollectionUtils.isNotEmpty(result)) {// 个别数据库 count 没数据不会返回 0Object o = result.get(0);if (o != null) {total = Long.parseLong(o.toString());}}page.setTotal(total);long totalIn = 0;//获取表名String tableName = getTableFromSql(boundSql.getSql());// 执行第二个查询 (resultIn)if (StringUtil.isNotBlank(tableName)) {//根据表名判断是否进行查询if (this.suitTableName(tableName)) {CacheKey cacheKeyIn = executor.createCacheKey(countMs, parameter, rowBounds, countSqlIn);List<Object> resultIn = executor.query(countMs, parameter, rowBounds, resultHandler, cacheKeyIn, countSqlIn);log.info("未上传序列数：{}", Long.parseLong(resultIn.get(0).toString()));if (CollectionUtils.isNotEmpty(resultIn)) {// 个别数据库 count 没数据不会返回 0Object o = resultIn.get(0);if (o != null) {totalIn = Long.parseLong(o.toString());}}}}// 将 totalIn 设置到 ThreadLocal 中QueryContext.setTotalIn(totalIn);return continuePage(page);}@Overridepublic void beforeQuery(Executor executor, MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql)  {IPage<?> page = ParameterUtils.findPage(parameter).orElse(null);if (null == page) {return;}// 处理 orderBy 拼接boolean addOrdered = false;String buildSql = boundSql.getSql();List<OrderItem> orders = page.orders();if (CollectionUtils.isNotEmpty(orders)) {addOrdered = true;buildSql = this.concatOrderBy(buildSql, orders);}// size 小于 0 且不限制返回值则不构造分页sqlLong _limit = page.maxLimit() != null ? page.maxLimit() : maxLimit;if (page.getSize() < 0 && null == _limit) {if (addOrdered) {PluginUtils.mpBoundSql(boundSql).sql(buildSql);}return;}handlerLimit(page, _limit);IDialect dialect = findIDialect(executor);final Configuration configuration = ms.getConfiguration();DialectModel model = dialect.buildPaginationSql(buildSql, page.offset(), page.getSize());PluginUtils.MPBoundSql mpBoundSql = PluginUtils.mpBoundSql(boundSql);List<ParameterMapping> mappings = mpBoundSql.parameterMappings();Map<String, Object> additionalParameter = mpBoundSql.additionalParameters();model.consumers(mappings, configuration, additionalParameter);mpBoundSql.sql(model.getDialectSql());mpBoundSql.parameterMappings(mappings);}/*** 获取分页方言类的逻辑** @param executor Executor* @return 分页方言类*/protected IDialect findIDialect(Executor executor) {if (dialect != null) {return dialect;}if (dbType != null) {dialect = DialectFactory.getDialect(dbType);return dialect;}return DialectFactory.getDialect(JdbcUtils.getDbType(executor));}/*** 获取指定的 id 的 MappedStatement** @param ms      MappedStatement* @param countId id* @return MappedStatement*/protected MappedStatement buildCountMappedStatement(MappedStatement ms, String countId) {if (StringUtils.isNotBlank(countId)) {final String id = ms.getId();if (!countId.contains(StringPool.DOT)) {countId = id.substring(0, id.lastIndexOf(StringPool.DOT) + 1) + countId;}final Configuration configuration = ms.getConfiguration();try {return CollectionUtils.computeIfAbsent(countMsCache, countId, key -> configuration.getMappedStatement(key, false));} catch (Exception e) {logger.warn(String.format("can not find this countId: [\"%s\"]", countId));}}return null;}/*** 构建 mp 自用自动的 MappedStatement** @param ms MappedStatement* @return MappedStatement*/protected MappedStatement buildAutoCountMappedStatement(MappedStatement ms) {final String countId = ms.getId() + "_mpCount";final Configuration configuration = ms.getConfiguration();return CollectionUtils.computeIfAbsent(countMsCache, countId, key -> {MappedStatement.Builder builder = new MappedStatement.Builder(configuration, key, ms.getSqlSource(), ms.getSqlCommandType());builder.resource(ms.getResource());builder.fetchSize(ms.getFetchSize());builder.statementType(ms.getStatementType());builder.timeout(ms.getTimeout());builder.parameterMap(ms.getParameterMap());builder.resultMaps(Collections.singletonList(new ResultMap.Builder(configuration, Constants.MYBATIS_PLUS, Long.class, Collections.emptyList()).build()));builder.resultSetType(ms.getResultSetType());builder.cache(ms.getCache());builder.flushCacheRequired(ms.isFlushCacheRequired());builder.useCache(ms.isUseCache());return builder.build();});}/*** 获取自动优化的 countSql** @param page 参数* @param sql  sql* @return countSql*/protected String autoCountSql(IPage<?> page, String sql) {if (!page.optimizeCountSql()) {return lowLevelCountSql(sql);}try {Select select = (Select) JsqlParserGlobal.parse(sql);SelectBody selectBody = select.getSelectBody();// https://github.com/baomidou/mybatis-plus/issues/3920  分页增加union语法支持if (selectBody instanceof SetOperationList) {return lowLevelCountSql(sql);}PlainSelect plainSelect = (PlainSelect) select.getSelectBody();Distinct distinct = plainSelect.getDistinct();GroupByElement groupBy = plainSelect.getGroupBy();// 包含 distinct、groupBy 不优化if (null != distinct || null != groupBy) {return lowLevelCountSql(select.toString());}// 优化 order by 在非分组情况下List<OrderByElement> orderBy = plainSelect.getOrderByElements();if (CollectionUtils.isNotEmpty(orderBy)) {boolean canClean = true;for (OrderByElement order : orderBy) {// order by 里带参数,不去除order byExpression expression = order.getExpression();if (!(expression instanceof Column) && expression.toString().contains(StringPool.QUESTION_MARK)) {canClean = false;break;}}if (canClean) {plainSelect.setOrderByElements(null);}}for (SelectItem item : plainSelect.getSelectItems()) {if (item.toString().contains(StringPool.QUESTION_MARK)) {return lowLevelCountSql(select.toString());}}// 包含 join 连表,进行判断是否移除 join 连表if (optimizeJoin && page.optimizeJoinOfCountSql()) {List<Join> joins = plainSelect.getJoins();if (CollectionUtils.isNotEmpty(joins)) {boolean canRemoveJoin = true;String whereS = Optional.ofNullable(plainSelect.getWhere()).map(Expression::toString).orElse(StringPool.EMPTY);// 不区分大小写whereS = whereS.toLowerCase();for (Join join : joins) {if (!join.isLeft()) {canRemoveJoin = false;break;}FromItem rightItem = join.getRightItem();String str = "";if (rightItem instanceof Table) {Table table = (Table) rightItem;str = Optional.ofNullable(table.getAlias()).map(Alias::getName).orElse(table.getName()) + StringPool.DOT;} else if (rightItem instanceof SubSelect) {SubSelect subSelect = (SubSelect) rightItem;/* 如果 left join 是子查询，并且子查询里包含 ?(代表有入参) 或者 where 条件里包含使用 join 的表的字段作条件,就不移除 join */if (subSelect.toString().contains(StringPool.QUESTION_MARK)) {canRemoveJoin = false;break;}str = subSelect.getAlias().getName() + StringPool.DOT;}// 不区分大小写str = str.toLowerCase();if (whereS.contains(str)) {/* 如果 where 条件里包含使用 join 的表的字段作条件,就不移除 join */canRemoveJoin = false;break;}for (Expression expression : join.getOnExpressions()) {if (expression.toString().contains(StringPool.QUESTION_MARK)) {/* 如果 join 里包含 ?(代表有入参) 就不移除 join */canRemoveJoin = false;break;}}}if (canRemoveJoin) {plainSelect.setJoins(null);}}}// 优化 SQLplainSelect.setSelectItems(COUNT_SELECT_ITEM);return select.toString();} catch (JSQLParserException e) {// 无法优化使用原 SQLlogger.warn("optimize this sql to a count sql has exception, sql:\"" + sql + "\", exception:\n" + e.getCause());} catch (Exception e) {logger.warn("optimize this sql to a count sql has error, sql:\"" + sql + "\", exception:\n" + e);}return lowLevelCountSql(sql);}/*** 无法进行count优化时,降级使用此方法** @param originalSql 原始sql* @return countSql*/protected String lowLevelCountSql(String originalSql) {return SqlParserUtils.getOriginalCountSql(originalSql);}/*** 查询SQL拼接Order By** @param originalSql 需要拼接的SQL* @return ignore*/public String concatOrderBy(String originalSql, List<OrderItem> orderList) {try {Select select = (Select) JsqlParserGlobal.parse(originalSql);SelectBody selectBody = select.getSelectBody();if (selectBody instanceof PlainSelect) {PlainSelect plainSelect = (PlainSelect) selectBody;List<OrderByElement> orderByElements = plainSelect.getOrderByElements();List<OrderByElement> orderByElementsReturn = addOrderByElements(orderList, orderByElements);plainSelect.setOrderByElements(orderByElementsReturn);return select.toString();} else if (selectBody instanceof SetOperationList) {SetOperationList setOperationList = (SetOperationList) selectBody;List<OrderByElement> orderByElements = setOperationList.getOrderByElements();List<OrderByElement> orderByElementsReturn = addOrderByElements(orderList, orderByElements);setOperationList.setOrderByElements(orderByElementsReturn);return select.toString();} else if (selectBody instanceof WithItem) {// todo: don't known how to resolereturn originalSql;} else {return originalSql;}} catch (JSQLParserException e) {logger.warn("failed to concat orderBy from IPage, exception:\n" + e.getCause());} catch (Exception e) {logger.warn("failed to concat orderBy from IPage, exception:\n" + e);}return originalSql;}protected List<OrderByElement> addOrderByElements(List<OrderItem> orderList, List<OrderByElement> orderByElements) {List<OrderByElement> additionalOrderBy = orderList.stream().filter(item -> StringUtils.isNotBlank(item.getColumn())).map(item -> {OrderByElement element = new OrderByElement();element.setExpression(new Column(item.getColumn()));element.setAsc(item.isAsc());element.setAscDescPresent(true);return element;}).collect(Collectors.toList());if (CollectionUtils.isEmpty(orderByElements)) {return additionalOrderBy;}// github pull/3550 优化排序，比如：默认 order by id 前端传了name排序，设置为 order by name,idadditionalOrderBy.addAll(orderByElements);return additionalOrderBy;}/*** count 查询之后,是否继续执行分页** @param page 分页对象* @return 是否*/protected boolean continuePage(IPage<?> page) {if (page.getTotal() <= 0) {return false;}if (page.getCurrent() > page.getPages()) {if (overflow) {//溢出总页数处理handlerOverflow(page);} else {// 超过最大范围，未设置溢出逻辑中断 list 执行return false;}}return true;}/*** 处理超出分页条数限制,默认归为限制数** @param page IPage*/protected void handlerLimit(IPage<?> page, Long limit) {final long size = page.getSize();if (limit != null && limit > 0 && (size > limit || size < 0)) {page.setSize(limit);}}/*** 处理页数溢出,默认设置为第一页** @param page IPage*/protected void handlerOverflow(IPage<?> page) {page.setCurrent(1);}@Overridepublic void setProperties(Properties properties) {PropertyMapper.newInstance(properties).whenNotBlank("overflow", Boolean::parseBoolean, this::setOverflow).whenNotBlank("dbType", DbType::getDbType, this::setDbType).whenNotBlank("dialect", ClassUtils::newInstance, this::setDialect).whenNotBlank("maxLimit", Long::parseLong, this::setMaxLimit).whenNotBlank("optimizeJoin", Boolean::parseBoolean, this::setOptimizeJoin);}protected String getTableFromSql(String sql) {String regex = "(?i)from\\s+([a-zA-Z0-9_]+)";Pattern pattern = Pattern.compile(regex);Matcher matcher = pattern.matcher(sql);if (matcher.find()) {return matcher.group(1);}return null;}/*** 判断是否进行未上传序列数计算* @param tableName 表名*/private boolean suitTableName(String tableName) {switch (tableName) {case V_SAMPLE_COVID19:case T_SAMPLE_RSV:case T_SAMPLE_COVID19:case T_SAMPLE_FLU:case T_SAMPLE_HADV:case T_SAMPLE_HMPV:case T_SAMPLE_HPIV:case T_SAMPLE_METAV:return true;default:return false;}}
}