论坛 › Mybatis › (转)Mybatis使用篇之十二：实现物理分页

sdfouhdso888 发表于 2016-11-27 07:18:11

(转)Mybatis使用篇之十二：实现物理分页

转自http://chenjc-it.iyunv.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：

Java代码  




[*]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：

Java代码  




[*]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：

Java代码  




[*]<?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：

Java代码  




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

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