[转]mybatis下的分页，支持所有的数据库

jarod8016b

　　大家都知道，mybatis的自带分页方法只是逻辑分 页，如果数据量很大，内存一定会溢出，不知道为什么开源组织不在里面集成hibernate的物理分页处理方法!在不修改mybatis源代码的情况下，应该怎么使mybatis支持物理分页呢？参考了网上的一些信息，有了下面的解决方法：以oracle为例子
　　1.把hibernate下的dialect包全部拷贝到mybatis包的jdbc目录下，如下图所示：

 　　

　　2.定义一个ResultSetHandler  Interceptor

package cn.machi.utils;
　　import java.sql.Statement;
import java.util.Properties;
　　import org.apache.ibatis.executor.resultset.FastResultSetHandler;
import org.apache.ibatis.executor.resultset.ResultSetHandler;
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.session.RowBounds;
　　@Intercepts( {@Signature(type= ResultSetHandler.class, method = "handleResultSets", args = {Statement.class})})
public class DiclectResultSetHandlerInterceptor implements Interceptor
{
   
    public Object intercept(Invocation invocation) throws Throwable
    {
        FastResultSetHandler resultSet = (FastResultSetHandler)invocation.getTarget();
       
        RowBounds rowBounds = (RowBounds)ReflectUtil.getFieldValue(resultSet,
                "rowBounds");
       
        if (rowBounds.getLimit() > 0
                && rowBounds.getLimit() < RowBounds.NO_ROW_LIMIT)
        {
            ReflectUtil.setFieldValue(resultSet, "rowBounds", new RowBounds());
        }
        return invocation.proceed();
    }
   
    public Object plugin(Object target)
    {
        return Plugin.wrap(target, this);
    }
   
    public void setProperties(Properties properties)
    {
    }
}
　　3.定义一个StatementHandler的Interceptor

package cn.machi.utils;
　　import java.sql.Connection;
import java.util.Properties;
　　import org.apache.ibatis.executor.statement.PreparedStatementHandler;
import org.apache.ibatis.executor.statement.RoutingStatementHandler;
import org.apache.ibatis.executor.statement.StatementHandler;
import org.apache.ibatis.jdbc.dialect.OracleDialect;
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.session.RowBounds;
　　@Intercepts( {@Signature(type= StatementHandler.class, method = "prepare", args = {Connection.class})})
public class DiclectStatementHandlerInterceptor implements Interceptor
{
   
    private static final String DIALECT = "org.apache.ibatis.jdbc.dialect.OracleDialect";
   
    public Object intercept(Invocation invocation) throws Throwable
    {
        RoutingStatementHandler statement = (RoutingStatementHandler)invocation.getTarget();
        PreparedStatementHandler handler = (PreparedStatementHandler)ReflectUtil.getFieldValue(statement,
                "delegate");
        RowBounds rowBounds = (RowBounds)ReflectUtil.getFieldValue(handler,
                "rowBounds");
       
        if (rowBounds.getLimit() > 0
                && rowBounds.getLimit() < RowBounds.NO_ROW_LIMIT)
        {
            BoundSql boundSql = statement.getBoundSql();
            String sql = boundSql.getSql();
           
            OracleDialect dialect = (OracleDialect)Class.forName(DIALECT)
                    .newInstance();
            sql = dialect.getLimitString(sql,
                    rowBounds.getOffset(),
                    rowBounds.getLimit());
           
            ReflectUtil.setFieldValue(boundSql, "sql", sql);
        }
        return invocation.proceed();
    }
   
    public Object plugin(Object target)
    {
        return Plugin.wrap(target, this);
    }
   
    public void setProperties(Properties properties)
    {
    }
}

　　4.定义工具类ReflectUtil

package cn.machi.utils;
　　import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
　　import org.apache.log4j.Logger;
　　
public class ReflectUtil
{
    private static Logger log = Logger.getLogger(ReflectUtil.class);
   
    private static Object operate(Object obj, String fieldName,
            Object fieldVal, String type)
    {
        Object ret = null;
        try
        {
            // 获得对象类型 
            Class<? extends Object> classType = obj.getClass();
            // 获得对象的所有属性 
            Field fields[] = classType.getDeclaredFields();
            for (int i = 0; i < fields.length; i++)
            {
                Field field = fields;
                if (field.getName().equals(fieldName))
                {
                   
                    String firstLetter = fieldName.substring(0, 1)
                            .toUpperCase(); // 获得和属性对应的getXXX()方法的名字 
                    if ("set".equals(type))
                    {
                        String setMethodName = "set" + firstLetter
                                + fieldName.substring(1); // 获得和属性对应的getXXX()方法 
                        Method setMethod = classType.getMethod(setMethodName,
                                new Class[] {field.getType()}); // 调用原对象的getXXX()方法 
                        ret = setMethod.invoke(obj, new Object[] {fieldVal});
                    }
                    if ("get".equals(type))
                    {
                        String getMethodName = "get" + firstLetter
                                + fieldName.substring(1); // 获得和属性对应的setXXX()方法的名字 
                        Method getMethod = classType.getMethod(getMethodName,
                                new Class[] {});
                        ret = getMethod.invoke(obj, new Object[] {});
                    }
                    return ret;
                }
            }
        }
        catch (Exception e)
        {
            log.warn("reflect error:" + fieldName, e);
        }
        return ret;
    }
   
    public static Object getVal(Object obj, String fieldName)
    {
        return operate(obj, fieldName, null, "get");
    }
   
    public static void setVal(Object obj, String fieldName, Object fieldVal)
    {
        operate(obj, fieldName, fieldVal, "set");
    }
   
   
    private static Method getDeclaredMethod(Object object, String methodName,
            Class<?>[] parameterTypes)
    {
        for (Class<?> superClass = object.getClass(); superClass != Object.class; superClass = superClass.getSuperclass())
        {
            try
            {
                //superClass.getMethod(methodName, parameterTypes);
                return superClass.getDeclaredMethod(methodName, parameterTypes);
            }
            catch (NoSuchMethodException e)
            {
                //Method 不在当前类定义, 继续向上转型
            }
        }
       
        return null;
    }
   
   
    private static void makeAccessible(Field field)
    {
        if (!Modifier.isPublic(field.getModifiers()))
        {
            field.setAccessible(true);
        }
    }
   
   
    private static Field getDeclaredField(Object object, String filedName)
    {
        for (Class<?> superClass = object.getClass(); superClass != Object.class; superClass = superClass.getSuperclass())
        {
            try
            {
                return superClass.getDeclaredField(filedName);
            }
            catch (NoSuchFieldException e)
            {
                //Field 不在当前类定义, 继续向上转型
            }
        }
        return null;
    }
   
   
    public static Object invokeMethod(Object object, String methodName,
            Class<?>[] parameterTypes, Object[] parameters)
            throws InvocationTargetException
    {
        Method method = getDeclaredMethod(object, methodName, parameterTypes);
       
        if (method == null)
        {
            throw new IllegalArgumentException("Could not find method ["
                    + methodName + "] on target [" + object + "]");
        }
       
        method.setAccessible(true);
       
        try
        {
            return method.invoke(object, parameters);
        }
        catch (IllegalAccessException e)
        {
           
        }
       
        return null;
    }
   
   
    public static void setFieldValue(Object object, String fieldName,
            Object value)
    {
        Field field = getDeclaredField(object, fieldName);
       
        if (field == null)
            throw new IllegalArgumentException("Could not find field ["
                    + fieldName + "] on target [" + object + "]");
       
        makeAccessible(field);
       
        try
        {
            field.set(object, value);
        }
        catch (IllegalAccessException e)
        {
            e.printStackTrace();
        }
    }
   
   
    public static Object getFieldValue(Object object, String fieldName)
    {
        Field field = getDeclaredField(object, fieldName);
        if (field == null)
            throw new IllegalArgumentException("Could not find field ["
                    + fieldName + "] on target [" + object + "]");
       
        makeAccessible(field);
       
        Object result = null;
        try
        {
            result = field.get(object);
        }
        catch (IllegalAccessException e)
        {
            e.printStackTrace();
        }
       
        return result;
    }
   
}

　　5.更新mapper configuration文件，添加如下几条，注意plugins在整个configuration文件中的顺序
　　<plugins>
<plugin interceptor="functionPoint.db.DiclectStatementHandlerInterceptor"/>
<plugin interceptor="functionPoint.db.DiclectResultSetHandlerInterceptor"/>
</plugins>

　　6.使用方法同mybatis逻辑分页，拦截器会自动拦截执行SQL的地方，加上分页代码：
　　getSqlSession().selectList(mapId, queryKey,new RowBounds(pageId, pageSize));
　　好了，大功告成！