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Mybatis的分页功能很弱，它是基于内存的分页（查出所有记录再按偏移量和limit取结果），在大数据量的情况下这样的分页基本上是没有用的。本文基于插件，通过拦截StatementHandler重写sql语句，实现数据库的物理分页。本文适配的mybatis版本是3.2.7。具体实现如下：
PaginationInterceptor类：
package org.reacher.interceptor.pagination;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Properties;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.ibatis.executor.parameter.ParameterHandler;
import org.apache.ibatis.executor.statement.StatementHandler;
import org.apache.ibatis.mapping.BoundSql;
import org.apache.ibatis.mapping.MappedStatement;
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.reflection.SystemMetaObject;
import org.apache.ibatis.scripting.defaults.DefaultParameterHandler;
import org.apache.ibatis.session.RowBounds;
import org.reacher.interceptor.pagination.dialect.Dialect;
import org.reacher.interceptor.pagination.dialect.DialectFactory;
import org.reacher.interceptor.pagination.model.PageBounds;
/**
* @author reacher
*
* PaginationInterceptor
*/
@Intercepts({@Signature(type = StatementHandler.class, method = "prepare", args = {Connection.class})})
public class PaginationInterceptor implements Interceptor {
private static final Log LOG = LogFactory.getLog(PaginationInterceptor.class);
private Class<?> clazz = null;
@Override
public Object intercept(Invocation invocation) throws Throwable {
if(null == this.clazz) {
LOG.error("Not found has been initialized database dialect!");
return invocation.proceed();
}
final Dialect dialect = DialectFactory.getDialect(this.clazz);
if(null == dialect) {
LOG.error(this.clazz.getName() + " initialized failed!");
return invocation.proceed();
}
final StatementHandler statementHandler = (StatementHandler) invocation.getTarget();
final MetaObject metaStatementHandler = SystemMetaObject.forObject(statementHandler);
final RowBounds rowBounds = (RowBounds) metaStatementHandler.getValue("delegate.rowBounds");
PageBounds pageBounds = null;
if (rowBounds instanceof PageBounds) {
pageBounds = (PageBounds) rowBounds;
}
if(null == pageBounds || 0 >= pageBounds.getSize() || 0 >= pageBounds.getNumber()) {
return invocation.proceed();
}
final MappedStatement mappedStatement = (MappedStatement) metaStatementHandler.getValue("delegate.mappedStatement");
final BoundSql boundSql = statementHandler.getBoundSql();
final Object parameterObject = boundSql.getParameterObject();
final Connection connection = (Connection) invocation.getArgs()[0];
pageBounds.setCount(this.getCount(mappedStatement, connection, parameterObject, dialect));
metaStatementHandler.setValue("delegate.boundSql.sql", dialect.getLimitSql(boundSql.getSql(), pageBounds.getSize() * (pageBounds.getNumber() - 1), pageBounds.getSize()));
metaStatementHandler.setValue("delegate.rowBounds.offset", RowBounds.NO_ROW_OFFSET);
metaStatementHandler.setValue("delegate.rowBounds.limit", RowBounds.NO_ROW_LIMIT);
return invocation.proceed();
}
@Override
public Object plugin(Object target) {
return Plugin.wrap(target, this);
}
@Override
public void setProperties(Properties properties) {
String dialectName = properties.getProperty("dialect");
if(null == dialectName) {
LOG.error("Property dialectName isn't set!");
return;
}
try {
this.clazz = Class.forName(dialectName);
} catch (ClassNotFoundException e) {
LOG.error(e);
}
}
private int getCount(final MappedStatement mappedStatement, final Connection connection, final Object parameterObject, final Dialect dialect) {
final BoundSql boundSql = mappedStatement.getBoundSql(parameterObject);
final String countSql = dialect.getCountSql(boundSql.getSql());
PreparedStatement preparedStatement = null;
ResultSet resultSet = null;
int count = 0;
try {
preparedStatement = connection.prepareStatement(countSql);
final ParameterHandler handler = new DefaultParameterHandler(mappedStatement, parameterObject, boundSql);
handler.setParameters(preparedStatement);
resultSet = preparedStatement.executeQuery();
if (resultSet.next()) {
count = resultSet.getInt(1);
}
} catch (Exception e) {
LOG.error(e);
} finally {
if (preparedStatement != null) {
try {
preparedStatement.close();
} catch (SQLException e) {
LOG.error(e);
}
}
}
return count;
}
}
Dialect接口：
package org.reacher.interceptor.pagination.dialect;
/**
* @author reacher
*
*/
public interface Dialect {
/**
* 检查数据库是否支持分页
*/
public abstract boolean supportsLimit();
/**
* 得到获取数据总条数的SQL语句
*/
public String getCountSql(String sql);
/**
* 得到分页的SQL语句
*/
public abstract String getLimitSql(String sql, long offset, long limit);
}
DialectFactory工厂类：package org.reacher.interceptor.pagination.dialect;
import java.lang.reflect.Constructor;
import java.util.HashMap;
import java.util.Map;
/**
* @author reacher
*
*/
public final class DialectFactory {
private static Map<String, Dialect> DIALECTS = new HashMap<String, Dialect>();
public static Dialect getDialect(Class<?> clazz) throws Exception {
Dialect dialect = DIALECTS.get(clazz.getSimpleName());
if (dialect == null) {
dialect = newInstance(clazz);
if(null != dialect) {
DIALECTS.put(clazz.getSimpleName(), dialect);
}
}
return dialect;
}
private static Dialect newInstance(Class<?> clazz) throws Exception {
if(null == clazz) {
return null;
}
Constructor<?> constructor = clazz.getConstructor();
constructor.setAccessible(true);
Object object = constructor.newInstance();
Dialect dialect = null;
if(object instanceof Dialect) {
dialect = (Dialect)object;
}
return dialect;
}
}
PageBounds类：
package org.reacher.interceptor.pagination.model;
import org.apache.ibatis.session.RowBounds;
/**
* @author reacher
*
*/
public class PageBounds extends RowBounds {
private int size;//页面大小
private int number;//当前页数
private int count;//数据总条数
private int total;//总页数
public PageBounds() {
this.number = 1;
this.size = 10;
}
public PageBounds(int pageSize) {
this.number = 1;
this.size = pageSize;
}
public int getSize() {
return size;
}
public void setSize(int size) {
this.size = size;
}
public int getNumber() {
return number;
}
public void setNumber(int number) {
this.number = number;
}
public int getCount() {
return count;
}
public void setCount(int count) {
this.count = count;
}
public int getTotal() {
this.total = this.count / this.size + (this.count % this.size > 0 ? 1 : 0);
return this.total;
}
public void setTotal(int total) {
this.total = total;
}
}
实现mysql数据库的分页具体如下：
MySQLDialect类：
package org.reacher.interceptor.pagination.dialect.database;
import org.reacher.interceptor.pagination.dialect.Dialect;
/**
* @author reacher
*
*/
public class MySQLDialect implements Dialect {
@Override
public boolean supportsLimit() {
return true;
}
@Override
public String getCountSql(String sql) {
return "SELECT COUNT(*) FROM (" + sql.replaceAll(";", "") + ") temp";
}
@Override
public String getLimitSql(String sql, long offset, long limit) {
StringBuffer stringBuffer = new StringBuffer(sql.replaceAll(";", ""));
stringBuffer.append(" LIMIT ").append(offset).append(", ").append(limit);
return stringBuffer.toString();
}
}
mybatis-configuration.xml配置如下：<plugins> <span style="white-space:pre"> </span><plugin interceptor="org.reacher.interceptor.pagination.PaginationInterceptor"> <property name="dialect" value="org.reacher.interceptor.pagination.dialect.database.MySQLDialect"/> </plugin> </plugins>
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原文地址：http://blog.csdn.net/awen_c/article/details/44855039
