MyBatis 物理分页

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.    }}

    <plugins>        <plugin interceptor="plugin.PaginationInterceptor" />    </plugins>

    <!-- 测试分页查询 -->    <select id="selectUserByPage" resultMap="dao.base.userResultMap">        <![CDATA[        SELECT * FROM user        ]]>    </select>

    @Override    public List<User> selectUserByPage(int offset, int limit) {        RowBounds rowBounds = new RowBounds(offset, limit);        return getSqlSession().selectList("dao.userdao.selectUserByPage", new Object(), rowBounds);    }

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;    }}

    <!-- 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");    }

    @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";    }