Mybatis的自带分页方法只是逻辑分页，如果数据量很大，内存会溢出，不知道为什么开源组织不在里面实现类似Hibernate的物理分页处理方法。在不改动Mybatis源代码的情况下，怎么使Mybatis支持物理分页呢？下面我们来看看。
（1）新建一个Java类Dialect.java，该类的内容如下：
java代码：
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Java代码
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package org.mybatis.extend.interceptor;
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public abstract class Dialect {
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public static enum Type{
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MYSQL,
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ORACLE
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}
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public abstract String getLimitString(String sql, int skipResults, int maxResults);
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}
（2）新建一个Java类OracleDialect.java，该类继承Dialect
类，具体的内容如下：
java代码：
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Java代码
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package org.mybatis.extend.interceptor;
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public class OracleDialect extends Dialect{
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@Override
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public String getLimitString(String sql, int offset, int limit) {
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sql = sql.trim();
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StringBuffer pagingSelect = new StringBuffer(sql.length() + 100);
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pagingSelect.append("select * from ( select row_.*, rownum rownum_ from ( ");
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pagingSelect.append(sql);
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pagingSelect.append(" ) row_ ) where rownum_ > ").append(offset).append(" and rownum_ <= ").append(offset + limit);
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return pagingSelect.toString();
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}
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}
（3）新建一个Mybaits的拦截器PaginationInterceptor.java，实现Interceptor接口，该类的内容如下：
java代码：
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Java代码
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package org.mybatis.extend.interceptor;
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import java.sql.Connection;
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import java.util.Map;
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import java.util.Properties;
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import org.apache.ibatis.executor.parameter.DefaultParameterHandler;
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import org.apache.ibatis.executor.statement.StatementHandler;
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import org.apache.ibatis.mapping.BoundSql;
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import org.apache.ibatis.plugin.Interceptor;
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import org.apache.ibatis.plugin.Intercepts;
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import org.apache.ibatis.plugin.Invocation;
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import org.apache.ibatis.plugin.Plugin;
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import org.apache.ibatis.plugin.Signature;
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import org.apache.ibatis.reflection.MetaObject;
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import org.apache.ibatis.session.Configuration;
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import org.apache.ibatis.session.RowBounds;
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import org.slf4j.Logger;
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import org.slf4j.LoggerFactory;
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@Intercepts({@Signature(type=StatementHandler.class,method="prepare",args={Connection.class})})
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public class PaginationInterceptor implements Interceptor {
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//日志对象
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protected static Logger log = LoggerFactory.getLogger(PaginationInterceptor.class);
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@Override
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public Object intercept(Invocation invocation) throws Throwable {
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StatementHandler statementHandler = (StatementHandler)invocation.getTarget();
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MetaObject metaStatementHandler = MetaObject.forObject(statementHandler);
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RowBounds rowBounds = (RowBounds)metaStatementHandler.getValue("delegate.rowBounds");
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if(rowBounds == null || rowBounds == RowBounds.DEFAULT){
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return invocation.proceed();
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}
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DefaultParameterHandler defaultParameterHandler = (DefaultParameterHandler)metaStatementHandler.getValue("delegate.parameterHandler");
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Map parameterMap = (Map)defaultParameterHandler.getParameterObject();
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Object sidx = parameterMap.get("_sidx");
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Object sord = parameterMap.get("_sord");
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String originalSql = (String)metaStatementHandler.getValue("delegate.boundSql.sql");
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if(sidx != null && sord != null){
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originalSql = originalSql + " order by " + sidx + " " + sord;
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}
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Configuration configuration = (Configuration)metaStatementHandler.getValue("delegate.configuration");
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Dialect.Type databaseType = null;
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try{
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databaseType = Dialect.Type.valueOf(configuration.getVariables().getProperty("dialect").toUpperCase());
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} catch(Exception e){
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//ignore
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}
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if(databaseType == null){
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throw new RuntimeException("the value of the dialect property in configuration.xml is not defined : " + configuration.getVariables().getProperty("dialect"));
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}
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Dialect dialect = null;
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switch(databaseType){
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case ORACLE:
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dialect = new OracleDialect();
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break;
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case MYSQL://需要实现MySQL的分页逻辑
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break;
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}
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metaStatementHandler.setValue("delegate.boundSql.sql", dialect.getLimitString(originalSql, rowBounds.getOffset(), rowBounds.getLimit()) );
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metaStatementHandler.setValue("delegate.rowBounds.offset", RowBounds.NO_ROW_OFFSET );
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metaStatementHandler.setValue("delegate.rowBounds.limit", RowBounds.NO_ROW_LIMIT );
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if(log.isDebugEnabled()){
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BoundSql boundSql = statementHandler.getBoundSql();
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log.debug("生成分页SQL : " + boundSql.getSql());
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}
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return invocation.proceed();
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}
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@Override
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public Object plugin(Object target) {
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return Plugin.wrap(target, this);
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}
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@Override
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public void setProperties(Properties arg0) {
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// TODO Auto-generated method stub
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}
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}
（4）将Mybatis的拦截器配置到Mybatis的全局配置文件(mybatis.cfg.xml)中，具体如下：
5）使用方法同Mybatis逻辑分页一样，拦截器会自动拦截执行SQL的地方，加上分页代码：
java代码：
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getSqlSession().selectList(sqlId, paramMap,new RowBounds(pageId, pageSize));
