MyBatis物理分页插件——拦截指定对象、返回指定对象

网上有很多MyBatis物理分页插件，基本都是围绕拦截指定分页对象来处理的；网上分页逻辑为，先查出总的列表数，使用分页插件查出分页后列表集合，封装总列表数和分页列表集合到Page结果对象；用起来还要自己封装结果类，相对比较麻烦；我想省去这些复杂的步骤，直接传递分页对象，返回结果对象。

需求：

这里我想像JPA一样传递Pagination分页对象进去，返回Page结果对象。

逻辑：

MyBatis预处理拦截器拦截指定的Pagination，并重写当前的SQL为分页SQL

MyBatis结果集拦截器拦截指定的Pagination，根据分页SQL得到查询总量的SQL执行得到总的列表数，得到原分页后的列表集合，封装为Page对象并返回

代码类：

PaginationStatementInterceptor类为SQL预处理拦截类，拦截指定的分页类，这里我使用的是org.springframework.data.domain.Pageable分页类（Spring-data-commons包下的，如果用Spring-data应该会附带出来这个包的）；如果MyBatis中分页方法有这个分页类，则拦截并修改原来的执行SQL为想要的分页SQL；以MySQL为例比如：之前的SQL为 select * from user 修改后的SQL为 select * from user limit 100, 10利用反射替换原来SQL值的位置delegate.boundSql.sql

下面举例用的方言为MySQL对应的类MySql5Dialect继承了Dialect类，该类的getLimitString得到分页SQL，如果是别的数据库继承Dialect类，重写getLimitString即可

import com.mm.persist.expands.mybatis.dialect.Dialect;
import com.mm.persist.expands.mybatis.dialect.MySql5Dialect;
import com.mm.persist.expands.mybatis.dialect.OracleDialect;
import com.mm.persist.expands.mybatis.dialect.SQLServer2005Dialect;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.ibatis.binding.MapperMethod;
import org.apache.ibatis.executor.parameter.ParameterHandler;
import org.apache.ibatis.executor.statement.StatementHandler;
import org.apache.ibatis.mapping.BoundSql;
import org.apache.ibatis.plugin.*;
import org.apache.ibatis.reflection.MetaObject;
import org.apache.ibatis.reflection.factory.DefaultObjectFactory;
import org.apache.ibatis.reflection.wrapper.DefaultObjectWrapperFactory;
import org.apache.ibatis.session.Configuration;
import org.springframework.data.domain.Pageable;

import java.sql.Connection;
import java.util.Properties;

@Intercepts({@Signature(type = StatementHandler.class, method = "prepare", args = {Connection.class})})
public class PaginationStatementInterceptor implements Interceptor {

    private final static Log log = LogFactory
            .getLog(PaginationStatementInterceptor.class);

    @Override
    public Object intercept(Invocation invocation) throws Throwable {

        StatementHandler statementHandler = (StatementHandler) invocation.getTarget();

        ParameterHandler parameterHandler = statementHandler.getParameterHandler();
        Object parameterObject = parameterHandler.getParameterObject();

        Pageable pagination = null;

        if(parameterObject instanceof MapperMethod.ParamMap){

            MapperMethod.ParamMap paramMapObject = (MapperMethod.ParamMap)parameterObject ;


            if(paramMapObject != null){
                for(Object key : paramMapObject.keySet()){
                    if(paramMapObject.get(key) instanceof  Pageable){
                        pagination = (Pageable) paramMapObject.get(key);
                        break;
                    }
                }
            }
        }

        if (pagination != null) {

            MetaObject metaStatementHandler = MetaObject.forObject(statementHandler, new DefaultObjectFactory(), new DefaultObjectWrapperFactory());
            Configuration configuration = (Configuration) metaStatementHandler.getValue("delegate.configuration");
            Dialect.Type databaseType = null;

            try {
                databaseType = Dialect.Type.valueOf(configuration.getVariables().getProperty("dialect").toUpperCase());
            } catch (Exception e) {
                throw new Exception("Generate SQL: Obtain DatabaseType Failed!");
            }

            Dialect dialect = null;
            switch (databaseType) {
                case MYSQL:
                    dialect = new MySql5Dialect();
                    break;
                case ORACLE:
                    dialect = new OracleDialect();
                    break;
                case SQLSERVER:
                    dialect = new SQLServer2005Dialect();
                    break;
            }

            String originalSql = (String) metaStatementHandler.getValue("delegate.boundSql.sql");

            metaStatementHandler.setValue("delegate.boundSql.sql", dialect.getLimitString(originalSql, pagination.getPageNumber() * pagination.getPageSize(), pagination.getPageSize()));

            if (log.isDebugEnabled()) {
                BoundSql boundSql = statementHandler.getBoundSql();
                log.debug("Generate SQL : " + boundSql.getSql());
            }

            return invocation.proceed();
        }

        return invocation.proceed();
    }

    @Override
    public Object plugin(Object target) {
        return Plugin.wrap(target, this);
    }

    @Override
    public void setProperties(Properties properties) {
    }

}

PaginationResultSetInterceptor类为结果拦截类，拦截指定的分页类，这里我使用的是org.springframework.data.domain.Pageable分页类（Spring-data-commons包下的，如果用Spring-data应该会附带出来这个包的）；如果MyBatis中分页方法有这个分页类，则拦截结果集进行重写得到最终想要的org.springframework.data.domain.Page结果类（Spring-data-commons包下的，如果用Spring-data应该会附带出来这个包的）；Page中会包含分页信息和分页后的列表信息。下面举例用的方言为MySQL对应的类MySql5Dialect继承了Dialect类，该类的getCountString方法是根据分页SQL解析获取到对应的查询总记录数的SQL，如果是别的数据库继承Dialect类，重写getCountString即可 invocation.proceed()为原分页结果集，这里根据上面的查询总记录数的SQL执行获取总记录数结果，封装Page对象设置原结果集为分页结果列表，设置总记录数，并返回

import com.mm.persist.expands.mybatis.dialect.Dialect;
import com.mm.persist.expands.mybatis.dialect.MySql5Dialect;
import com.mm.persist.expands.mybatis.dialect.OracleDialect;
import com.mm.persist.expands.mybatis.dialect.SQLServer2005Dialect;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.ibatis.binding.MapperMethod;
import org.apache.ibatis.executor.parameter.ParameterHandler;
import org.apache.ibatis.executor.resultset.DefaultResultSetHandler;
import org.apache.ibatis.executor.resultset.ResultSetHandler;
import org.apache.ibatis.mapping.BoundSql;
import org.apache.ibatis.plugin.*;
import org.apache.ibatis.reflection.MetaObject;
import org.apache.ibatis.reflection.factory.DefaultObjectFactory;
import org.apache.ibatis.reflection.wrapper.DefaultObjectWrapperFactory;
import org.apache.ibatis.session.Configuration;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.PageImpl;
import org.springframework.data.domain.Pageable;
import org.springframework.jdbc.support.JdbcUtils;

import java.sql.*;
import java.util.ArrayList;
import java.util.List;
import java.util.Properties;

@Intercepts({@Signature(type = ResultSetHandler.class, method = "handleResultSets", args = {Statement.class})})
public class PaginationResultSetInterceptor implements Interceptor {

    private final static Log log = LogFactory.getLog(PaginationResultSetInterceptor.class);

    @Override
    public Object intercept(Invocation invocation) throws Throwable {

        DefaultResultSetHandler resultSetHandler = (DefaultResultSetHandler) invocation.getTarget();
        MetaObject metaResultSetHandler = MetaObject.forObject(resultSetHandler, new DefaultObjectFactory(), new DefaultObjectWrapperFactory());
        try {
            ParameterHandler parameterHandler = (ParameterHandler) metaResultSetHandler.getValue("parameterHandler");
            Object parameterObject = parameterHandler.getParameterObject();

            Pageable pagination = null;

            if(parameterObject instanceof MapperMethod.ParamMap){

                MapperMethod.ParamMap paramMapObject = (MapperMethod.ParamMap)parameterObject ;


                if(paramMapObject != null){
                    for(Object key : paramMapObject.keySet()){
                        if(paramMapObject.get(key) instanceof  Pageable){
                            pagination = (Pageable) paramMapObject.get(key);
                            break;
                        }
                    }
                }
            }

            if (pagination != null) {

                BoundSql boundSql = (BoundSql) metaResultSetHandler.getValue("parameterHandler.boundSql");
                Configuration configuration = (Configuration) metaResultSetHandler.getValue("configuration");
                Connection connection = (Connection) metaResultSetHandler.getValue("executor.delegate.transaction.connection");

                String originalSql = boundSql.getSql();

                Dialect.Type databaseType = Dialect.Type.valueOf(configuration.getVariables().getProperty("dialect").toUpperCase());
                Dialect dialect = null;

                switch (databaseType) {
                    case MYSQL:
                        dialect = new MySql5Dialect();
                        break;
                    case ORACLE:
                        dialect = new OracleDialect();
                        break;
                    case SQLSERVER:
                        dialect = new SQLServer2005Dialect();
                        break;
                }


                // 修改sql，用于返回总记录数
                String sql = dialect.getCountString(originalSql);
                Long totalRecord = getTotalRecord(connection, sql, parameterHandler);

                Object result = invocation.proceed();
                Page page = new PageImpl((List)result, pagination, totalRecord);


//                // 设置返回对象类型
//                metaResultSetHandler.setValue("mappedStatement.resultMaps[0].type.name", Page.class.getName());

                // 设置返回值
                List<Page> pageList = new ArrayList<Page>();
                pageList.add(page);

                return pageList;
            }
        } catch (Exception e) {
            throw new Exception("Overwrite SQL : Fail!");
        }

        return invocation.proceed();
    }

    /**
     * 执行 count 操作
     * @param connection  数据库连接
     * @param sql          sql
     * @param parameterHandler  参数设置处理器
     * @return
     */
    private Long getTotalRecord(Connection connection,String sql,ParameterHandler parameterHandler){
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        try {

            preparedStatement = connection.prepareStatement(sql);
            parameterHandler.setParameters(preparedStatement);
            resultSet = preparedStatement.executeQuery();
            resultSet.next();

            return (Long) JdbcUtils.getResultSetValue(resultSet, 1, Long.class);
        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            JdbcUtils.closeResultSet(resultSet);
            JdbcUtils.closeStatement(preparedStatement);
        }
        return 0l;
    }


    @Override
    public Object plugin(Object target) {
        return Plugin.wrap(target, this);
    }

    @Override
    public void setProperties(Properties properties) {
    }
}

这里我仅以MySQL为例，其他需要同学们自己写

public class MySql5Dialect extends Dialect {

	public String getLimitString(String querySqlString, int offset, int limit) {
		return querySqlString + " limit " + offset + " ," + limit;
	}

	@Override
	public String getCountString(String querySqlString) {

		int limitIndex = querySqlString.lastIndexOf("limit");

		if(limitIndex != -1){
			querySqlString = querySqlString.substring(0, limitIndex != -1 ? limitIndex : querySqlString.length() - 1);
		}

                // 用的过程中会发现这里对原有sql进行包装一层select count会有SQL效率低的问题
                // 等待优化
		return "SELECT COUNT(*) FROM (" + querySqlString + ") tem";
	}

	public boolean supportsLimit() {
		return true;
	}
}

public abstract class Dialect {

	public static enum Type {
		MYSQL, ORACLE, SQLSERVER
	}

	public abstract String getLimitString(String querySqlString, int offset, int limit);

	public abstract String getCountString(String querySqlString);

}

以上代码测试并在工作项目中运用，代码可能不全，有时间做个demo并上传

参考文档： http://mybatis.github.io/mybatis-3/zh/configuration.html#plugins

MyBatis物理分页插件——拦截指定对象、返回指定对象

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