project_process_houtai/src/main/java/com/template/common/utils/PageMySqlDialectPlus.java

package com.template.common.utils;

import com.github.pagehelper.Page;
import com.github.pagehelper.dialect.helper.MySqlDialect;
import com.github.pagehelper.util.MetaObjectUtil;
import lombok.extern.slf4j.Slf4j;
import org.apache.commons.lang3.StringUtils;
import org.apache.ibatis.cache.CacheKey;
import org.apache.ibatis.mapping.BoundSql;
import org.apache.ibatis.mapping.MappedStatement;
import org.apache.ibatis.mapping.ParameterMapping;
import org.apache.ibatis.reflection.MetaObject;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

@Slf4j
public class PageMySqlDialectPlus extends MySqlDialect {

    //正则表达式
    private static final String pattern = "([\\s|\\S]*?)/\\*\\s*MAPPINGLIMIT\\s*\\*/\\s*([\\s|\\S]*)";
    private static final Pattern PATTERN = Pattern.compile(pattern, Pattern.CASE_INSENSITIVE);

    /**
     * 把limit语句放到 MAPPINGLIMIT标记所在的位置，也就是主表的位置，对主表进行分页
     *
     * @return 加limit后的sql
     */
    @Override
    public String getPageSql(String sql, Page page, CacheKey pageKey) {
        //如果不匹配正则，走原始的sql
        if (!Pattern.matches(pattern, sql)) {
            return super.getPageSql(sql, page, pageKey);
        }

        String beforeLimitSql = "";
        String afterLimitsql = "";
        Matcher m = PATTERN.matcher(sql);
        if (m.find()) {
            //MAPPINGLIMIT标记前的sql语句
            beforeLimitSql = m.group(1);
            //MAPPINGLIMIT标记后的sql语句
            afterLimitsql = m.group(2);
        }

        String limitSql = "";
        if (page.getStartRow() == 0) {
            limitSql = " LIMIT ? ";
        } else {
            limitSql = " LIMIT ?, ? ";
        }
        String sqlString = beforeLimitSql + " " + limitSql + " " + afterLimitsql;

        return sqlString;
    }

    /**
     * 把分页参数放到参数列表里
     *
     * @return
     */
    @Override
    public Object processPageParameter(MappedStatement ms, Map<String, Object> paramMap, Page page, BoundSql boundSql, CacheKey pageKey) {
        //如果不匹配正则，走原始的sql设置
        if (!Pattern.matches(pattern, boundSql.getSql())) {
            return super.processPageParameter(ms, paramMap, page, boundSql, pageKey);
        }
        //设置参数
        paramMap.put(PAGEPARAMETER_FIRST, page.getStartRow());
        paramMap.put(PAGEPARAMETER_SECOND, page.getPageSize());
        pageKey.update(page.getStartRow());
        pageKey.update(page.getPageSize());

        //设置参数 因为limit放到中间位置，所以要计算出来分页数据的放置位置
        Matcher m = PATTERN.matcher(boundSql.getSql());
        String beforeLimitSql = null;
        int limitIndex;
        if (m.find()) {
            //MAPPINGLIMIT标记前的sql语句
            beforeLimitSql = m.group(1);
        }

        //计算sql里有几个参数，按数据位置添加page
        limitIndex = StringUtils.countMatches(beforeLimitSql, "?");
        if (boundSql.getParameterMappings() != null) {
            List<ParameterMapping> newParameterMappings = new ArrayList<ParameterMapping>(boundSql.getParameterMappings());
            if (page.getStartRow() == 0) {
                newParameterMappings.add(limitIndex,new ParameterMapping.Builder(ms.getConfiguration(), PAGEPARAMETER_SECOND, int.class).build());
            } else {
                newParameterMappings.add(limitIndex,new ParameterMapping.Builder(ms.getConfiguration(), PAGEPARAMETER_FIRST, long.class).build());
                newParameterMappings.add(limitIndex+1,new ParameterMapping.Builder(ms.getConfiguration(), PAGEPARAMETER_SECOND, int.class).build());
            }
            MetaObject metaObject = MetaObjectUtil.forObject(boundSql);
            metaObject.setValue("parameterMappings", newParameterMappings);
        }
        return paramMap;
    }
}