[Java][MyBatis]物理分页实现

 [Java][MyBatis]物理分页实现

Mybatis3.0出来已有段时间了，其实自己挺喜欢这样的一个持久化框架的，因为它简单实用，学习成本低。Mybatis3.0在整体结构上和ibatis2.X差不多，改进特性如下：

1.        解析xml引进了Xpath，不像ibatis2.x那样业余

2.        动态sql用OGNL解析

3.        加入注解配置sql，感觉没什么特别大的用途，我更喜欢xml方式，代码和配置分离，这也是ibatis的初衷

4.        加强了缓存这块的功能。Mybatis3.0把缓存模块分得更细，分为“持久实现（prepetual）”和“资源回收策略实现（eviction）”，更好的对缓存功能进行自己组合和扩展

5.        终于加入的plugin功能，就像struts一样，这样就可以很好的扩展内部的Executor,，StatementHandler….等内部对象功能。

 

 

MyBatis的分页功能还是基于内存分页（查找出所有记录再取出偏移量的记录，如果jdbc驱支持absolute定位或者rs.next()到指定偏移位置），其实这样的分页实现基本没用，特别是大量数据情况下。不过我们可以通过plugin功能来扩展MyBatis的分页功能、实现物理分页。具体做法如下：

1、编写分页插件类：

/** * 版权所有：华信软件 * 项目名称:ACWS框架类 * 创建者: Wangdf * 创建日期: 2014-4-2 * 文件说明: ACWS框架分页接口类 */package framework.core.interceptor;import java.sql.Connection;import java.util.Map;import java.util.Properties;import org.apache.commons.collections.MapUtils;import org.apache.ibatis.executor.statement.StatementHandler;import org.apache.ibatis.mapping.BoundSql;import org.apache.ibatis.plugin.Interceptor;import org.apache.ibatis.plugin.Intercepts;import org.apache.ibatis.plugin.Invocation;import org.apache.ibatis.plugin.Plugin;import org.apache.ibatis.plugin.Signature;import org.apache.ibatis.reflection.MetaObject;import org.apache.ibatis.reflection.factory.DefaultObjectFactory;import org.apache.ibatis.reflection.factory.ObjectFactory;import org.apache.ibatis.reflection.wrapper.DefaultObjectWrapperFactory;import org.apache.ibatis.reflection.wrapper.ObjectWrapperFactory;import org.apache.ibatis.session.Configuration;import org.apache.ibatis.session.RowBounds;import framework.core.util.DBUtil;/** * ACWS框架分页接口类 * @author Wangdf * */@Intercepts({ @Signature(type = StatementHandler.class, method = "prepare", args = { Connection.class }) })public class PaginationInterceptor implements Interceptor {    private static final ObjectFactory DEFAULT_OBJECT_FACTORY = new DefaultObjectFactory();    private static final ObjectWrapperFactory DEFAULT_OBJECT_WRAPPER_FACTORY = new DefaultObjectWrapperFactory();@Overridepublic Object intercept(Invocation invocation) throws Throwable {StatementHandler statementHandler = (StatementHandler) invocation.getTarget();MetaObject metaStatementHandler =  MetaObject.forObject(statementHandler, DEFAULT_OBJECT_FACTORY,                DEFAULT_OBJECT_WRAPPER_FACTORY);RowBounds rowBounds = (RowBounds) metaStatementHandler.getValue("delegate.rowBounds");if (rowBounds == null || rowBounds == RowBounds.DEFAULT) {return invocation.proceed();}        // 分离代理对象链(由于目标类可能被多个拦截器拦截，从而形成多次代理，通过下面的两次循环可以分离出最原始的的目标类)        while (metaStatementHandler.hasGetter("h")) {            Object object = metaStatementHandler.getValue("h");            metaStatementHandler = MetaObject.forObject(object, DEFAULT_OBJECT_FACTORY, DEFAULT_OBJECT_WRAPPER_FACTORY);        }        // 分离最后一个代理对象的目标类        while (metaStatementHandler.hasGetter("target")) {            Object object = metaStatementHandler.getValue("target");            metaStatementHandler = MetaObject.forObject(object, DEFAULT_OBJECT_FACTORY, DEFAULT_OBJECT_WRAPPER_FACTORY);        }        BoundSql boundSql = (BoundSql) metaStatementHandler.getValue("delegate.boundSql");            String sql = boundSql.getSql();StringBuffer sbSql = new StringBuffer();    // 重写sqlConfiguration configuration = (Configuration)metaStatementHandler.getValue("delegate.configuration");DBUtil dbUtil = new DBUtil(configuration);        if(dbUtil.isMySQL()){        sbSql.append(sql).append(" LIMIT ").append(rowBounds.getOffset()).append(", ").append(rowBounds.getLimit());            metaStatementHandler.setValue("delegate.boundSql.sql", sbSql.toString());                        // 采用物理分页后，就不需要mybatis的内存分页了，所以重置下面的两个参数            metaStatementHandler.setValue("delegate.rowBounds.offset", RowBounds.NO_ROW_OFFSET);            metaStatementHandler.setValue("delegate.rowBounds.limit", RowBounds.NO_ROW_LIMIT);} else if(dbUtil.isOracle()){sbSql.append("SELECT * ");sbSql.append("  FROM (SELECT ROWNUM RN, NOPAGESQL.*   ");sbSql.append("          FROM (").append(sql).append(") NOPAGESQL ");sbSql.append("         WHERE ROWNUM <= ").append(rowBounds.getLimit()+rowBounds.getOffset()).append(")");sbSql.append(" WHERE RN >= ").append(rowBounds.getOffset());        metaStatementHandler.setValue("delegate.boundSql.sql", sbSql.toString());                // 采用物理分页后，就不需要mybatis的内存分页了，所以重置下面的两个参数        metaStatementHandler.setValue("delegate.rowBounds.offset", RowBounds.NO_ROW_OFFSET);        metaStatementHandler.setValue("delegate.rowBounds.limit", RowBounds.NO_ROW_LIMIT);} else {}                // 将执行权交给下一个拦截器        return invocation.proceed();}@Overridepublic Object plugin(Object target) {        // 当目标类是StatementHandler类型时，才包装目标类，否者直接返回目标本身,减少目标被代理的次数        if (target instanceof StatementHandler) {            return Plugin.wrap(target, this);        } else {            return target;        }}@Overridepublic void setProperties(Properties properties) {// TODO Auto-generated method stub}}

 

2、配置读取类

/** * 版权所有：华信软件 * 项目名称:ACWS框架类 * 创建者: Wangdf * 创建日期: 2014-4-2 * 文件说明: ACWS框架数据库相关工具类 */package framework.core.util;import org.apache.commons.lang.StringUtils;import org.apache.ibatis.session.Configuration;import org.slf4j.Logger;import org.slf4j.LoggerFactory;/** * ACWS框架数据库相关工具类 * @author Wangdf */public class DBUtil {private static final String DBTYPE_MYSQL = "MySQL";//支持的类型：MySQL,Oracleprivate static final String DBTYPE_ORACLE = "Oracle";//支持的类型：MySQL,Oracleprivate static Logger logger = LoggerFactory.getLogger(DBUtil.class);private Configuration configuration = null;private String dbType = "";private String defaultDateFormat = "";public DBUtil(Configuration configuration){if(configuration == null){logger.error("系统启动失败：MyBatis Configuration 对象为空！");throw new IllegalArgumentException("系统启动失败：MyBatis Configuration 对象为空！");}this.configuration = configuration;this.dbType = this.configuration.getVariables().getProperty("dbtype");    if(StringUtils.isBlank(dbType)){    logger.error("数据库类型没有配置！");    } else {    logger.info("数据库类型为："+dbType);    }this.defaultDateFormat = this.configuration.getVariables().getProperty("defaultDateFormat");    if(StringUtils.isBlank(this.defaultDateFormat)){    this.defaultDateFormat="yyyy-MM-dd";    logger.info("数据库日期默认格式字符串没有指定！系统默认为：yyyy-MM-dd");    } else {    logger.info("数据库日期默认格式字符串："+this.defaultDateFormat);    }}/** * 判断是否是Oracle数据库 * @return * @author wangdf */public boolean isOracle(){return DBTYPE_ORACLE.equals(this.dbType);}/** * 判断是否是MySQL数据库 * @return * @author wangdf */public boolean isMySQL(){return DBTYPE_MYSQL.equals(this.dbType);}/** * 取得数据库类型 * @return * @author wangdf */public String getDbType(){return this.dbType;}/** * 取得默认日期格式 * @return * @author wangdf */public String getDefaultDateFormat(){return this.defaultDateFormat;}}

 

3、在mybatis全局配置文件设置

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd"><configuration><properties>    <property name="dbtype" value="MySQL"/><!-- 数据库类型：MySQL、Oracle -->    <property name="defaultDateFormat" value="yyyy-MM-dd"/></properties><settings><setting name="cacheEnabled" value="true" /><setting name="lazyLoadingEnabled" value="true" /><setting name="multipleResultSetsEnabled" value="true" /><setting name="useColumnLabel" value="true" /><setting name="defaultExecutorType" value="REUSE" /><setting name="defaultStatementTimeout" value="25000" /></settings><plugins><plugin interceptor="framework.core.interceptor.PaginationInterceptor"></plugin></plugins></configuration>