前言

        分页查询在日常开发中无法避免,但每次sql编写时,mybatis 中使用limit,oracle中使用rownum分页,业务场景少的情况下,可以接受.但是随着业务增加每次相同的功能做重复开发又不是那么方便,那么我们有什么方案去解决开发中出现的分页问题呢?

一、PageHelper 框架分页

首先我们看下pageHelper框架的分页核心类PageInterceptor 同样是实现了mybatis的Interceptor

                

二、自定义实现mybatis 插件 Interceptor (与pageHelper类似)

•    当涉及系统中的查询语句,参数为RowBounds时,查询语句会默认根据RowBounds分页

package com.cloud.common;import lombok.extern.slf4j.Slf4j;
import org.apache.ibatis.builder.StaticSqlSource;
import org.apache.ibatis.executor.Executor;
import org.apache.ibatis.mapping.BoundSql;
import org.apache.ibatis.mapping.MappedStatement;
import org.apache.ibatis.plugin.*;
import org.apache.ibatis.session.ResultHandler;
import org.apache.ibatis.session.RowBounds;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.Properties;/*** @author haizhuangbu* @date 2022/6/5 18:25* @mark MybatisIntercepter mybatis 拦截器*/
@Intercepts(@Signature(type = Executor.class, method = "query", args = {MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class}))
@Slf4j
public class MybatisInterceptor implements Interceptor {private Logger logger = LoggerFactory.getLogger(MybatisInterceptor.class);private final Integer MAPPED_STATEMENT_INDEX = 0;private final Integer PARAM = 1;// 默认分页private final Integer ROW_BOUNDS_INDEX = 2;@Overridepublic Object intercept(Invocation invocation) throws Throwable {logger.info("分页拦截器");// 1. 方法获取参数Object[] args = invocation.getArgs();// 分页器RowBounds rowBounds = (RowBounds) args[ROW_BOUNDS_INDEX];// 检查是否为默认分页if (rowBounds == RowBounds.DEFAULT) {return invocation.proceed();}// 设置为默认args[ROW_BOUNDS_INDEX] = RowBounds.DEFAULT;// 执行器MappedStatement mappedStatements = (MappedStatement) args[MAPPED_STATEMENT_INDEX];// 获取执行sqlBoundSql boundSql = mappedStatements.getBoundSql(PARAM);String sql = boundSql.getSql();// 获取数据库类型String databaseProductName = mappedStatements.getConfiguration().getEnvironment().getDataSource().getConnection().getMetaData().getDatabaseProductName();// mysql 的 分页处理if ("MYSQL".equalsIgnoreCase(databaseProductName)) {sql = mysql(sql, rowBounds);}// oracle 的分页处理if ("ORACLE".equalsIgnoreCase(databaseProductName)) {sql = oracle(sql, rowBounds);}logger.info("sql:{}", sql);StaticSqlSource staticSqlSource = new StaticSqlSource(mappedStatements.getConfiguration(), sql, boundSql.getParameterMappings());// 通过反射设置MapperStatment 的sqlSource字段Field field = MappedStatement.class.getDeclaredField("sqlSource");field.setAccessible(true);field.set(mappedStatements, staticSqlSource);return invocation.proceed();}private String oracle(String sql, RowBounds rowBounds) {// 为查询语句给到别名sql = "select * from (select t1.*, rownum rn from (" + sql +") t1 ) t2 where rn > " + (rowBounds.getOffset() - 1) * rowBounds.getLimit() + " and rn <= " + rowBounds.getOffset() * rowBounds.getLimit();return sql;}private String mysql(String sql, RowBounds rowBounds) {// 页数int limit = rowBounds.getLimit();// 页码int offset = rowBounds.getOffset();String format = String.format("LIMIT %d,%d", offset, limit);if (sql.contains(format)) {
//            sql = sql.replaceAll("select", "SELECT COUNT(1) total,");sql = sql.replaceAll(format, "");}sql += " " + format;return sql;}@Overridepublic Object plugin(Object target) {return Plugin.wrap(target, this);}@Overridepublic void setProperties(Properties properties) {Interceptor.super.setProperties(properties);}}

• 将自定义插件交给spring

@Beanpublic ConfigurationCustomizer configurationCustomizer() {return new ConfigurationCustomizer() {@Overridepublic void customize(Configuration configuration) {configuration.addInterceptor(new MybatisInterceptor());}};}