MyBatis实现物理分页的实例

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";  }