Mybatis使用篇之十二：实现物理分页

转自http://chenjc-it.iteye.com/blog/1402965

Mybatis 物理分页 

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：

package org.mybatis.extend.interceptor;

 public abstract class Dialect {

     public static enum Type{
        MYSQL,
        ORACLE
    }

     public abstract String getLimitString(String sql, int skipResults, int maxResults);

}

package org.mybatis.extend.interceptor;

public abstract class Dialect {

	public static enum Type{
		MYSQL,
		ORACLE
	}
	
	public abstract String getLimitString(String sql, int skipResults, int maxResults);
	
}

 

 

（2）新建一个Java类OracleDialect.java，该类继承Dialect 类，具体的内容如下：

package org.mybatis.extend.interceptor;

 public class OracleDialect extends Dialect{

     /* (non-Javadoc)
     * @see org.mybatis.extend.interceptor.IDialect#getLimitString(java.lang.String, int, int)
     */
     @Override
     public String getLimitString(String sql, int offset, int limit) {

        sql = sql.trim();
         StringBuffer pagingSelect = new StringBuffer(sql.length() + 100);

         pagingSelect.append("select * from ( select row_.*, rownum rownum_ from ( ");

        pagingSelect.append(sql);

         pagingSelect.append(" ) row_ ) where rownum_ > ").append(offset).append(" and rownum_ <= ").append(offset + limit);

         return pagingSelect.toString();
    }

}

package org.mybatis.extend.interceptor;

public class OracleDialect extends Dialect{

	/* (non-Javadoc)
	 * @see org.mybatis.extend.interceptor.IDialect#getLimitString(java.lang.String, int, int)
	 */
	@Override
	public String getLimitString(String sql, int offset, int limit) {

		sql = sql.trim();
		StringBuffer pagingSelect = new StringBuffer(sql.length() + 100);
		
		pagingSelect.append("select * from ( select row_.*, rownum rownum_ from ( ");
		
		pagingSelect.append(sql);
		
		pagingSelect.append(" ) row_ ) where rownum_ > ").append(offset).append(" and rownum_ <= ").append(offset + limit);
		
		return pagingSelect.toString();
	}

}

 

（3）新建一个Mybaits的拦截器PaginationInterceptor.java，实现Interceptor接口，该类的内容如下：

package org.mybatis.extend.interceptor;

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

 import org.apache.ibatis.executor.parameter.DefaultParameterHandler;
 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.session.Configuration;
 import org.apache.ibatis.session.RowBounds;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;


 @Intercepts({@Signature(type=StatementHandler.class,method="prepare",args={Connection.class})})
 public class PaginationInterceptor implements Interceptor {
     //日志对象
     protected static Logger log = LoggerFactory.getLogger(PaginationInterceptor.class);
     /* (non-Javadoc)
     * @see org.apache.ibatis.plugin.Interceptor#intercept(org.apache.ibatis.plugin.Invocation)
     */
     @Override
     public Object intercept(Invocation invocation) throws Throwable {
        StatementHandler statementHandler = (StatementHandler)invocation.getTarget();
        MetaObject metaStatementHandler = MetaObject.forObject(statementHandler);

         RowBounds rowBounds = (RowBounds)metaStatementHandler.getValue("delegate.rowBounds");
         if(rowBounds == null || rowBounds == RowBounds.DEFAULT){
             return invocation.proceed();
        }

         DefaultParameterHandler defaultParameterHandler = (DefaultParameterHandler)metaStatementHandler.getValue("delegate.parameterHandler");
        Map parameterMap = (Map)defaultParameterHandler.getParameterObject();
         Object sidx = parameterMap.get("_sidx");
         Object sord = parameterMap.get("_sord");

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

         if(sidx != null && sord != null){
             originalSql = originalSql + " order by " + sidx + " " + sord;
        }

         Configuration configuration = (Configuration)metaStatementHandler.getValue("delegate.configuration");

                             Dialect.Type databaseType  = null;
         try{
             databaseType = Dialect.Type.valueOf(configuration.getVariables().getProperty("dialect").toUpperCase());
         } catch(Exception e){
             //ignore
        }
         if(databaseType == null){
             throw new RuntimeException("the value of the dialect property in configuration.xml is not defined : " + configuration.getVariables().getProperty("dialect"));
        }
         Dialect dialect = null;
         switch(databaseType){
             case ORACLE:
                 dialect = new OracleDialect();
                 break;
             case MYSQL://需要实现MySQL的分页逻辑
                 break;

        }


         metaStatementHandler.setValue("delegate.boundSql.sql", dialect.getLimitString(originalSql, rowBounds.getOffset(), rowBounds.getLimit()) );
         metaStatementHandler.setValue("delegate.rowBounds.offset", RowBounds.NO_ROW_OFFSET );
         metaStatementHandler.setValue("delegate.rowBounds.limit", RowBounds.NO_ROW_LIMIT );
         if(log.isDebugEnabled()){
            BoundSql boundSql = statementHandler.getBoundSql();
             log.debug("生成分页SQL : " + boundSql.getSql());
        }
         return invocation.proceed();
    }

     /* (non-Javadoc)
     * @see org.apache.ibatis.plugin.Interceptor#plugin(java.lang.Object)
     */
     @Override
     public Object plugin(Object target) {
         return Plugin.wrap(target, this);
    }

     /* (non-Javadoc)
     * @see org.apache.ibatis.plugin.Interceptor#setProperties(java.util.Properties)
     */
     @Override
     public void setProperties(Properties arg0) {
         // TODO Auto-generated method stub

    }

}

package org.mybatis.extend.interceptor;

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

import org.apache.ibatis.executor.parameter.DefaultParameterHandler;
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.session.Configuration;
import org.apache.ibatis.session.RowBounds;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;


@Intercepts({@Signature(type=StatementHandler.class,method="prepare",args={Connection.class})})
public class PaginationInterceptor implements Interceptor {
	//日志对象
	protected static Logger log = LoggerFactory.getLogger(PaginationInterceptor.class);
	/* (non-Javadoc)
	 * @see org.apache.ibatis.plugin.Interceptor#intercept(org.apache.ibatis.plugin.Invocation)
	 */
	@Override
	public Object intercept(Invocation invocation) throws Throwable {
		StatementHandler statementHandler = (StatementHandler)invocation.getTarget();
		MetaObject metaStatementHandler = MetaObject.forObject(statementHandler);
		
		RowBounds rowBounds = (RowBounds)metaStatementHandler.getValue("delegate.rowBounds");
		if(rowBounds == null || rowBounds == RowBounds.DEFAULT){
			return invocation.proceed();
		}
		
		DefaultParameterHandler defaultParameterHandler = (DefaultParameterHandler)metaStatementHandler.getValue("delegate.parameterHandler");
		Map parameterMap = (Map)defaultParameterHandler.getParameterObject();
		Object sidx = parameterMap.get("_sidx");
		Object sord = parameterMap.get("_sord");
		
		String originalSql = (String)metaStatementHandler.getValue("delegate.boundSql.sql");
		
		if(sidx != null && sord != null){
			originalSql = originalSql + " order by " + sidx + " " + sord;
		}
		
		Configuration configuration = (Configuration)metaStatementHandler.getValue("delegate.configuration");
        
                            Dialect.Type databaseType  = null;
		try{
			databaseType = Dialect.Type.valueOf(configuration.getVariables().getProperty("dialect").toUpperCase());
		} catch(Exception e){
			//ignore
		}
		if(databaseType == null){
			throw new RuntimeException("the value of the dialect property in configuration.xml is not defined : " + configuration.getVariables().getProperty("dialect"));
		}
		Dialect dialect = null;
		switch(databaseType){
			case ORACLE:
				dialect = new OracleDialect();
				break;
			case MYSQL://需要实现MySQL的分页逻辑
				break;
				
		}
		
		
		metaStatementHandler.setValue("delegate.boundSql.sql", dialect.getLimitString(originalSql, rowBounds.getOffset(), rowBounds.getLimit()) );
		metaStatementHandler.setValue("delegate.rowBounds.offset", RowBounds.NO_ROW_OFFSET );
		metaStatementHandler.setValue("delegate.rowBounds.limit", RowBounds.NO_ROW_LIMIT );
		if(log.isDebugEnabled()){
			BoundSql boundSql = statementHandler.getBoundSql();
			log.debug("生成分页SQL : " + boundSql.getSql());
		}
		return invocation.proceed();
	}

	/* (non-Javadoc)
	 * @see org.apache.ibatis.plugin.Interceptor#plugin(java.lang.Object)
	 */
	@Override
	public Object plugin(Object target) {
		return Plugin.wrap(target, this);
	}

	/* (non-Javadoc)
	 * @see org.apache.ibatis.plugin.Interceptor#setProperties(java.util.Properties)
	 */
	@Override
	public void setProperties(Properties arg0) {
		// TODO Auto-generated method stub
		
	}

}

 

 （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：

<?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="dialect" value="oracle"/>
    </properties>

    <plugins>
             <plugin interceptor="org.mybatis.extend.interceptor.PaginationInterceptor"/>
    </plugins>

</configuration>

<?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="dialect" value="oracle"/>
	</properties>
	    
 	<plugins>
	        <plugin interceptor="org.mybatis.extend.interceptor.PaginationInterceptor"/>
	</plugins>
	   
</configuration>

 

（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：

getSqlSession().selectList(sqlId, paramMap,new RowBounds(pageId, pageSize));