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[i];
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));
