MyBatis使用RowBounds实现的分页是逻辑分页,也就是先把数据记录全部查询出来,然在再根据offset和limit截断记录返回
为了在数据库层面上实现物理分页,又不改变原来MyBatis的函数逻辑,可以编写plugin截获MyBatis Executor的statementhandler,重写SQL来执行查询
参考资料: http://blog.csdn.net/hupanfeng/article/details/9265341
下面的插件代码只针对MySQL
plugin代码
package plugin; import java.sql.Connection; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.SQLException; import java.util.Properties; import org.apache.ibatis.executor.parameter.ParameterHandler; import org.apache.ibatis.executor.statement.StatementHandler; import org.apache.ibatis.logging.Log; import org.apache.ibatis.logging.LogFactory; 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.factory.DefaultObjectFactory; import org.apache.ibatis.reflection.factory.ObjectFactory; import org.apache.ibatis.reflection.wrapper.DefaultObjectWrapperFactory; import org.apache.ibatis.reflection.wrapper.ObjectWrapperFactory; import org.apache.ibatis.scripting.defaults.DefaultParameterHandler; import org.apache.ibatis.session.Configuration; import org.apache.ibatis.session.RowBounds; /** * 通过拦截<code>StatementHandler</code>的<code>prepare</code>方法，重写sql语句实现物理分页。 * 老规矩，签名里要拦截的类型只能是接口。 * */ @Intercepts({@Signature(type = StatementHandler.class, method = "prepare", args = {Connection.class})}) public class PaginationInterceptor implements Interceptor { private static final Log logger = LogFactory.getLog(PaginationInterceptor.class); private static final ObjectFactory DEFAULT_OBJECT_FACTORY = new DefaultObjectFactory(); private static final ObjectWrapperFactory DEFAULT_OBJECT_WRAPPER_FACTORY = new DefaultObjectWrapperFactory(); private static String DEFAULT_PAGE_SQL_ID = ".*Page$"; // 需要拦截的ID(正则匹配) @Override public Object intercept(Invocation invocation) throws Throwable { StatementHandler statementHandler = (StatementHandler) invocation.getTarget(); MetaObject metaStatementHandler = MetaObject.forObject(statementHandler, DEFAULT_OBJECT_FACTORY, DEFAULT_OBJECT_WRAPPER_FACTORY); RowBounds rowBounds = (RowBounds) metaStatementHandler.getValue("delegate.rowBounds"); // 分离代理对象链(由于目标类可能被多个拦截器拦截，从而形成多次代理，通过下面的两次循环可以分离出最原始的的目标类) while (metaStatementHandler.hasGetter("h")) { Object object = metaStatementHandler.getValue("h"); metaStatementHandler = MetaObject.forObject(object, DEFAULT_OBJECT_FACTORY, DEFAULT_OBJECT_WRAPPER_FACTORY); } // 分离最后一个代理对象的目标类 while (metaStatementHandler.hasGetter("target")) { Object object = metaStatementHandler.getValue("target"); metaStatementHandler = MetaObject.forObject(object, DEFAULT_OBJECT_FACTORY, DEFAULT_OBJECT_WRAPPER_FACTORY); } // property在mybatis settings文件内配置 Configuration configuration = (Configuration) metaStatementHandler.getValue("delegate.configuration"); // 设置pageSqlId String pageSqlId = configuration.getVariables().getProperty("pageSqlId"); if (null == pageSqlId || "".equals(pageSqlId)) { logger.warn("Property pageSqlId is not setted,use default '.*Page$' "); pageSqlId = DEFAULT_PAGE_SQL_ID; } MappedStatement mappedStatement = (MappedStatement) metaStatementHandler.getValue("delegate.mappedStatement"); // 只重写需要分页的sql语句。通过MappedStatement的ID匹配，默认重写以Page结尾的MappedStatement的sql if (mappedStatement.getId().matches(pageSqlId)) { BoundSql boundSql = (BoundSql) metaStatementHandler.getValue("delegate.boundSql"); Object parameterObject = boundSql.getParameterObject(); if (parameterObject == null) { throw new NullPointerException("parameterObject is null!"); } else { String sql = boundSql.getSql(); // 重写sql String pageSql = sql + " LIMIT " + rowBounds.getOffset() + "," + rowBounds.getLimit(); metaStatementHandler.setValue("delegate.boundSql.sql", pageSql); // 采用物理分页后，就不需要mybatis的内存分页了，所以重置下面的两个参数 metaStatementHandler.setValue("delegate.rowBounds.offset", RowBounds.NO_ROW_OFFSET); metaStatementHandler.setValue("delegate.rowBounds.limit", RowBounds.NO_ROW_LIMIT); } } // 将执行权交给下一个拦截器 return invocation.proceed(); } @Override public Object plugin(Object target) { // 当目标类是StatementHandler类型时，才包装目标类，否者直接返回目标本身,减少目标被代理的次数 if (target instanceof StatementHandler) { return Plugin.wrap(target, this); } else { return target; } } @Override public void setProperties(Properties properties) { //To change body of implemented methods use File | Settings | File Templates. } }
配置plugin
<plugins> <plugin interceptor="plugin.PaginationInterceptor" /> </plugins>
查询SQL
<!-- 测试分页查询 --> <select id="selectUserByPage" resultMap="dao.base.userResultMap"> <![CDATA[ SELECT * FROM user ]]> </select>
调用示例
@Override public List<User> selectUserByPage(int offset, int limit) { RowBounds rowBounds = new RowBounds(offset, limit); return getSqlSession().selectList("dao.userdao.selectUserByPage", new Object(), rowBounds); }
另外,结合Spring MVC,编写翻页和生成页码代码
页码类
package util; /** * Created with IntelliJ IDEA. * User: zhenwei.liu * Date: 13-8-7 * Time: 上午10:29 * To change this template use File | Settings | File Templates. */ public class Pagination { private String url; // 页码url private int pageSize = 10; // 每页显示记录数 private int currentPage = 1; // 当前页码 private int maxPage = Integer.MAX_VALUE; // 最大页数 // 获取offset public int getOffset() { return (currentPage - 1) * pageSize; } // 获取limit public int getLimit() { return getPageSize(); } public String getUrl() { return url; } public void setUrl(String url) { this.url = url; } public int getPageSize() { return pageSize; } public void setPageSize(int pageSize) { this.pageSize = pageSize; } public int getCurrentPage() { return currentPage; } public void setCurrentPage(int currentPage) { if (currentPage < 1) currentPage = 1; if (currentPage > maxPage) currentPage = maxPage; this.currentPage = currentPage; } public int getMaxPage() { return maxPage; } public void setMaxPage(int maxPage) { this.maxPage = maxPage; } }
为了计算最大页码,需要知道数据表的总记录数,查询SQL如下
<!-- 记录总数 --> <select id="countUser" resultType="Integer"> <![CDATA[ SELECT COUNT(*) FROM user ]]> </select>
@Override public Integer countTable() { return getSqlSession().selectOne("dao.userdao.countUser"); }
Controller中的使用
@RequestMapping("/getUserByPage")
public String getUserByPage(@RequestParam
int page, Model model) {
pagination.setCurrentPage(page);
pagination.setUrl(getCurrentUrl());
pagination.setMaxPage(userDao.countTable() / pagination.getPageSize() + 1);
List<User> userList = userDao.selectUserByPage(
pagination.getOffset(), pagination.getLimit());
model.addAttribute(pagination);
model.addAttribute(userList);
return "index";
}
