mybatis框架下物理分页的实现（整个工程采用的是springmvc、spring、mybatis框架，数据库是mysql数据库）

(一）关于分页拦截器的简单理解

    首先，要开发MyBatis的插件需要实现org.apache.ibatis.plugin.Interceptor接口，这个接口将会要求实现几个方法：intercept（）、plugin（）及setProperties（），intercept方法是开发人员所要执行的操作，plugin是将你插件放入到MyBatis的插件集合中去，而setProperties这是在你配置你插件的时候将plugins/plugin/properties的值设置到该插件中。
    该方法的第一句话就是获得Intercepts注解，接下来将获得在Intercepts里面的参数@Signature注解内容，在该注解中包含三个参数，分别是type，method，args。Type指定要拦截的类对象，method是指明要拦截该类的哪个方法，第三个是指明要拦截的方法参数集合。在Intercepts中可以配置多个@Signature。那么便对这写值进行遍历，已获得对应的type、method以及args。最终是获得一个HashMap对象，这些对象里面的键是类对象，而值是指定的类中方法对象。执行该端程序之后，更具target的classLoader和接口，来创建一个代理，并且，InvocationHandler是创建一个新的Plugin对象，同时将target，interceptor以及signatureMap传递给Plugin对象，当然，这里的Plugin也实现了Invocation接口。那么target对象所有的方法调用都会触发Plugin中的invoke方法，那么这里将执行开发者所有插入的操作。

    另外对拦截器类里面几个关键的类做出解释：

（1）BoundSql类 ，封装mybatis最终产生sql的类，包括sql语句，参数，参数源数据等。
（2）MappedStatement类，MappedStatement类在Mybatis框架中用于表示XML文件中一个sql语句节点，即一个<select />、<update />或者<insert />标签。Mybatis框架在初始化阶段会对XML配置文件进行读取，将其中的sql语句节点对象化为一个个MappedStatement对象。

   总结，本拦截器实现的目标就是在进行数据库查询操作之前，从配置文件读出相应的sql语句，将相应的参数拼接到其中，然后再进行查询。当然在拼接sql语句之前，先查询了一下数据库中相应记录的总数

（二）拦截器类PageIntercepter.java：

package cn.zyy.paging.intercepter;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.List;
import java.util.Properties;

import org.apache.ibatis.mapping.BoundSql;
import org.apache.ibatis.mapping.MappedStatement;
import org.apache.ibatis.mapping.ParameterMapping;
import org.apache.ibatis.mapping.ParameterMode;
import org.apache.ibatis.mapping.SqlSource;
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.reflection.MetaObject;
import org.apache.ibatis.session.Configuration;
import org.apache.ibatis.session.RowBounds;
import org.apache.ibatis.type.TypeHandler;
import org.apache.ibatis.type.TypeHandlerRegistry;
import cn.zyy.paging.vo.PageObject;
@Intercepts({@org.apache.ibatis.plugin.Signature(method="query", type=org.apache.ibatis.executor.Executor.class, args={MappedStatement.class, Object.class, RowBounds.class, org.apache.ibatis.session.ResultHandler.class})})
public class PageIntercepter implements Interceptor{
    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        MappedStatement mappedStatement = (MappedStatement) invocation.getArgs()[0];
        Object object = invocation.getArgs()[1];
        if(object instanceof PageObject){

            PageObject pageObject = (PageObject) object;
            BoundSql boundSql = mappedStatement.getBoundSql(object);
            String sql = boundSql.getSql();

            int count = getCount(mappedStatement,boundSql);
            pageObject.setCount(count);
            int pages = (pageObject.getCount()+pageObject.getNumber()-1)/pageObject.getNumber();
            pageObject.setPages(pages>0?pages:1);

            int offset = (pageObject.getPage() - 1) * pageObject.getNumber();
            int limit = pageObject.getNumber();
            String pageSql = pageSql(sql, offset, limit);
            BoundSql pageBoundSql = new BoundSql(mappedStatement.getConfiguration(), pageSql, boundSql.getParameterMappings(), boundSql.getParameterObject());
            MappedStatement pageMappedStatement = pageMappedStatement(mappedStatement, new PageSqlSource(pageBoundSql));
            invocation.getArgs()[0] = pageMappedStatement;
            invocation.getArgs()[2] = RowBounds.DEFAULT;
        }
        return invocation.proceed();
    }

    @Override
    public Object plugin(Object object) {
        // TODO Auto-generated method stub
        return Plugin.wrap(object, this);
    }

    @Override
    public void setProperties(Properties properties) {
        // TODO Auto-generated method stub

    }

    private int getCount(MappedStatement mappedStatement, BoundSql boundSql) throws SQLException {

        Connection connection = null;
        PreparedStatement ps = null;
        ResultSet rs = null;

        try {
            String countSql = countSql(boundSql.getSql());
            connection = mappedStatement.getConfiguration().getEnvironment().getDataSource().getConnection();
            ps = connection.prepareStatement(countSql);
            BoundSql countBoundSql = new BoundSql(mappedStatement.getConfiguration(), countSql, boundSql.getParameterMappings(), boundSql.getParameterObject());
            setCountParameters(ps, mappedStatement, countBoundSql);
            rs = ps.executeQuery();
            int count = 0;
             if (rs.next())
              {
                count = rs.getInt(1);
              }
            return count;
        } catch (Exception e) {
            return 1000;
        }finally{
             try {
                rs.close();
              } catch (Exception localException4) {
              }
              try {
                ps.close();
              } catch (Exception localException5) {
              }
              try {
                connection.close();
              }
              catch (Exception localException6) {
              }
        }
    }

    private static String countSql(String sql){
        sql = sql.toUpperCase();
        StringBuffer countSql = new StringBuffer();
        countSql.append("SELECT COUNT(1) FROM (");
        countSql.append(sql.substring(0, sql.indexOf("ORDER BY")==-1?sql.length():sql.indexOf("ORDER BY")-1));
        countSql.append(") PAY_PAGE_T");
        return countSql.toString();
    }

    private static void setCountParameters(PreparedStatement ps, MappedStatement mappedStatement, BoundSql boundSql) throws SQLException {
        List<ParameterMapping> parameterMappingList = boundSql.getParameterMappings();
        if (parameterMappingList != null)
        {
          Configuration configuration = mappedStatement.getConfiguration();
          TypeHandlerRegistry typeHandlerRegistry = configuration.getTypeHandlerRegistry();
          Object parameterObject = boundSql.getParameterObject();
          MetaObject metaObject = parameterObject == null ? null : configuration.newMetaObject(parameterObject);

          int n = 1;
          for (ParameterMapping parameterMapping : parameterMappingList)
          {
            if ((parameterMapping.getMode() == ParameterMode.IN) || (parameterMapping.getMode() == ParameterMode.INOUT))
            {
              String property = parameterMapping.getProperty();
              Object value = null;
              if (parameterObject != null)
              {
                if (typeHandlerRegistry.hasTypeHandler(parameterObject.getClass()))
                {
                  value = parameterObject;
                }
                else
                {
                  value = metaObject == null ? null : metaObject.getValue(property);
                }
              }

              TypeHandler typeHandler = parameterMapping.getTypeHandler();
              typeHandler.setParameter(ps, n, value, parameterMapping.getJdbcType());
            }

            n++;
          }
        }
    }

    private String pageSql(String sql, int offset, int limit) {
        sql = sql.toUpperCase();
        StringBuffer pageSql = new StringBuffer();
        pageSql.append(sql);
        pageSql.append(" LIMIT ");
        pageSql.append(offset);
        pageSql.append(", ");
        pageSql.append(limit);
        return pageSql.toString();
      }

    private MappedStatement pageMappedStatement(MappedStatement mappedStatement, SqlSource sqlSource)
      {
        MappedStatement.Builder builder = new MappedStatement.Builder(
          mappedStatement.getConfiguration(),
          mappedStatement.getId(),
          sqlSource,
          mappedStatement.getSqlCommandType());

        builder.resource(mappedStatement.getResource());
        builder.fetchSize(mappedStatement.getFetchSize());
        builder.statementType(mappedStatement.getStatementType());
        builder.keyGenerator(mappedStatement.getKeyGenerator());
        builder.timeout(mappedStatement.getTimeout());
        builder.parameterMap(mappedStatement.getParameterMap());
        builder.resultMaps(mappedStatement.getResultMaps());
        builder.cache(mappedStatement.getCache());
        builder.resultSetType(mappedStatement.getResultSetType());
        builder.flushCacheRequired(mappedStatement.isFlushCacheRequired());
        builder.useCache(mappedStatement.isUseCache());
        builder.resultOrdered(mappedStatement.isResultOrdered());
        builder.databaseId(mappedStatement.getDatabaseId());
        builder.lang(mappedStatement.getLang());
        if (mappedStatement.getKeyProperties() != null)
        {
          for (String keyProperty : mappedStatement.getKeyProperties())
          {
            builder.keyProperty(keyProperty);
          }
        }
        if (mappedStatement.getKeyColumns() != null)
        {
          for (String keyColumn : mappedStatement.getKeyColumns())
          {
            builder.keyColumn(keyColumn);
          }
        }

        return builder.build();
      }

     public static class PageSqlSource implements SqlSource {
        private BoundSql boundSql;

        public PageSqlSource(BoundSql boundSql) {
          this.boundSql = boundSql;
        }

        public BoundSql getBoundSql(Object parameterObject)
        {
          return this.boundSql;
        }
      }

}

（三）spring配置文件和mybatis配置文件

mybatis配置文件中主要是配置相关的vo类和拦截器

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spring的配置文件中主要就是实现mybatis和spring框架的整合

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
    xmlns:tx="http://www.springframework.org/schema/tx" xmlns:mvc="http://www.springframework.org/schema/mvc"
    xmlns:aop="http://www.springframework.org/schema/aop"
    xsi:schemaLocation="
        http://www.springframework.org/schema/aop
        http://www.springframework.org/schema/aop/spring-aop-3.2.xsd
        http://www.springframework.org/schema/mvc
        http://www.springframework.org/schema/mvc/spring-mvc-3.0.xsd
        http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
        http://www.springframework.org/schema/tx
        http://www.springframework.org/schema/tx/spring-tx-3.0.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context-2.5.xsd">

        <!-- 读取属性文件 -->
        <bean class = "org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
            <property name = "location" value = "classpath:db.properties"></property>
        </bean>
        <!-- 配置数据源 -->
        <bean id = "dataSource" class = "org.springframework.jdbc.datasource.DriverManagerDataSource">
            <property name = "driverClassName" value = "${driverClass}"></property>
            <property name = "url" value = "${url}"></property>
            <property name = "username" value = "${username}"></property>
            <property name = "password" value = "${password}"></property>
        </bean>
        <!-- 配置 sqlSessionFactory，实现spring和mybatis框架的整合-->
        <bean id = "sqlSessionFactory" class = "org.mybatis.spring.SqlSessionFactoryBean">
            <property name = "dataSource" ref = "dataSource"></property>
            <property name = "configLocation" value = "classpath:mybatis-config.xml"></property>
            <property name = "mapperLocations" value = "classpath:cn/zyy/paging/xml/*.xml"></property>
            <property name = "typeAliasesPackage" value = "cn.zyy.paging.vo"></property>
        </bean>
        <!-- 配置 MapperScannerConfigurer：将Mapper接口生成代理注入到Spring -->
        <bean class = "org.mybatis.spring.mapper.MapperScannerConfigurer">
            <property name = "sqlSessionFactoryBeanName" value = "sqlSessionFactory"></property>
            <property name = "basePackage" value = "cn.zyy.paging.dao"></property>
        </bean>

        <!-- 配置事务管理器 -->
        <bean id = "txManage" class = "org.springframework.jdbc.datasource.DataSourceTransactionManager">
            <property name = "dataSource" ref = "dataSource"></property>
        </bean>

        <!-- 配置事务传播机制 -->
        <tx:advice id = "txAdvice" transaction-manager="txManage">
            <tx:attributes>
                <tx:method name="*" propagation="REQUIRED"/>
            </tx:attributes>
        </tx:advice>
        <!-- 利用aop实现动态代理 -->
        <aop:config>
            <aop:pointcut expression="execution(* cn.zyy.paging.service.*.*(..))" id="pointcut"/>
            <aop:advisor advice-ref="txAdvice" pointcut-ref="pointcut"/>
        </aop:config>
        <!-- 扫描springmvc不能扫描的service类 -->
        <context:component-scan base-package="cn.zyy.paging.service"></context:component-scan>
</beans>