8. mybatis实战教程(mybatis in action)之七:实现mybatis分页(源码下载)

转自：https://blog.csdn.net/tangruyi1992/article/details/52584012

上 一篇文章里已经讲到了mybatis与spring MVC的集成，并且做了一个列表展示，显示出所有article 列表，但没有用到分页，在实际的项目中，分页是肯定需要的。而且是物理分页，不是内存分页。对于物理分页方案，不同的数据库，有不同的实现方法,对于 mysql 来说 就是利用 limit offset,pagesize 方式来实现的。oracle 是通过rownum 来实现的，如果你熟悉相关数据库的操作，是一样的很好扩展，本文以mysql 为例子来讲述.先看一下效果图(源代码在文章最后提供下载):

实现mybatis 物理分页，一个最简单的方式是，是在你的mapper的SQL语句中直接写类似如下方式 :

 <select id="getUserArticles" parameterType="Your_params" resultMap="resultUserArticleList">
        select user.id,user.userName,user.userAddress,article.id aid,article.title,article.content from user,article
               where user.id=article.userid and user.id=#{id} limit #{offset},#{pagesize}
     </select>

请注意这里的 parameterType 是你传入的参数类，或者map ，里面包含了offset,pagesize ,和其他你需要的参数，用这种方式，肯定可以实现分页。这是简单的一种方式。但更通用的一种方式是用 mybatis 插件的方式. 参考了网上的很多资料 ，mybatis plugin 方面的资料。写自己的插件.

 package com.yihaomen.util;

 import java.lang.reflect.Field;
 import java.sql.Connection;
 import java.sql.PreparedStatement;
 import java.sql.ResultSet;
 import java.sql.SQLException;
 import java.util.List;
 import java.util.Map;
 import java.util.Properties;

 import javax.xml.bind.PropertyException;

 import org.apache.ibatis.builder.xml.dynamic.ForEachSqlNode;
 import org.apache.ibatis.executor.ErrorContext;
 import org.apache.ibatis.executor.Executor;
 import org.apache.ibatis.executor.ExecutorException;
 import org.apache.ibatis.executor.statement.BaseStatementHandler;
 import org.apache.ibatis.executor.statement.RoutingStatementHandler;
 import org.apache.ibatis.executor.statement.StatementHandler;
 import org.apache.ibatis.mapping.BoundSql;
 import org.apache.ibatis.mapping.MappedStatement;
 import org.apache.ibatis.mapping.ParameterMapping;
 import org.apache.ibatis.mapping.ParameterMode;
 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.property.PropertyTokenizer;
 import org.apache.ibatis.session.Configuration;
 import org.apache.ibatis.session.ResultHandler;
 import org.apache.ibatis.session.RowBounds;
 import org.apache.ibatis.type.TypeHandler;
 import org.apache.ibatis.type.TypeHandlerRegistry;

 @Intercepts({ @Signature(type = StatementHandler.class, method = "prepare", args = { Connection.class }) })
 public class PagePlugin implements Interceptor {

     private static String dialect = "";
     private static String pageSqlId = "";

     @SuppressWarnings("unchecked")
     public Object intercept(Invocation ivk) throws Throwable {

         if (ivk.getTarget() instanceof RoutingStatementHandler) {
             RoutingStatementHandler statementHandler = (RoutingStatementHandler) ivk
                     .getTarget();
             BaseStatementHandler delegate = (BaseStatementHandler) ReflectHelper
                     .getValueByFieldName(statementHandler, "delegate");
             MappedStatement mappedStatement = (MappedStatement) ReflectHelper
                     .getValueByFieldName(delegate, "mappedStatement");

             if (mappedStatement.getId().matches(pageSqlId)) {
                 BoundSql boundSql = delegate.getBoundSql();
                 Object parameterObject = boundSql.getParameterObject();
                 if (parameterObject == null) {
                     throw new NullPointerException("parameterObject error");
                 } else {
                     Connection connection = (Connection) ivk.getArgs()[0];
                     String sql = boundSql.getSql();
                     String countSql = "select count(0) from (" + sql + ") myCount";
                     System.out.println("总数sql 语句:"+countSql);
                     PreparedStatement countStmt = connection
                             .prepareStatement(countSql);
                     BoundSql countBS = new BoundSql(
                             mappedStatement.getConfiguration(), countSql,
                             boundSql.getParameterMappings(), parameterObject);
                     setParameters(countStmt, mappedStatement, countBS,
                             parameterObject);
                     ResultSet rs = countStmt.executeQuery();
                     int count = 0;
                     if (rs.next()) {
                         count = rs.getInt(1);
                     }
                     rs.close();
                     countStmt.close();

                     PageInfo page = null;
                     if (parameterObject instanceof PageInfo) {
                         page = (PageInfo) parameterObject;
                         page.setTotalResult(count);
                     } else if(parameterObject instanceof Map){
                         Map<String, Object> map = (Map<String, Object>)parameterObject;
                         page = (PageInfo)map.get("page");
                         if(page == null)
                             page = new PageInfo();
                         page.setTotalResult(count);
                     }else {
                         Field pageField = ReflectHelper.getFieldByFieldName(
                                 parameterObject, "page");
                         if (pageField != null) {
                             page = (PageInfo) ReflectHelper.getValueByFieldName(
                                     parameterObject, "page");
                             if (page == null)
                                 page = new PageInfo();
                             page.setTotalResult(count);
                             ReflectHelper.setValueByFieldName(parameterObject,
                                     "page", page);
                         } else {
                             throw new NoSuchFieldException(parameterObject
                                     .getClass().getName());
                         }
                     }
                     String pageSql = generatePageSql(sql, page);
                     System.out.println("page sql:"+pageSql);
                     ReflectHelper.setValueByFieldName(boundSql, "sql", pageSql);
                 }
             }
         }
         return ivk.proceed();
     }

     private void setParameters(PreparedStatement ps,
             MappedStatement mappedStatement, BoundSql boundSql,
             Object parameterObject) throws SQLException {
         ErrorContext.instance().activity("setting parameters")
                 .object(mappedStatement.getParameterMap().getId());
         List<ParameterMapping> parameterMappings = boundSql
                 .getParameterMappings();
         if (parameterMappings != null) {
             Configuration configuration = mappedStatement.getConfiguration();
             TypeHandlerRegistry typeHandlerRegistry = configuration
                     .getTypeHandlerRegistry();
             MetaObject metaObject = parameterObject == null ? null
                     : configuration.newMetaObject(parameterObject);
             for (int i = 0; i < parameterMappings.size(); i++) {
                 ParameterMapping parameterMapping = parameterMappings.get(i);
                 if (parameterMapping.getMode() != ParameterMode.OUT) {
                     Object value;
                     String propertyName = parameterMapping.getProperty();
                     PropertyTokenizer prop = new PropertyTokenizer(propertyName);
                     if (parameterObject == null) {
                         value = null;
                     } else if (typeHandlerRegistry
                             .hasTypeHandler(parameterObject.getClass())) {
                         value = parameterObject;
                     } else if (boundSql.hasAdditionalParameter(propertyName)) {
                         value = boundSql.getAdditionalParameter(propertyName);
                     } else if (propertyName
                             .startsWith(ForEachSqlNode.ITEM_PREFIX)
                             && boundSql.hasAdditionalParameter(prop.getName())) {
                         value = boundSql.getAdditionalParameter(prop.getName());
                         if (value != null) {
                             value = configuration.newMetaObject(value)
                                     .getValue(
                                             propertyName.substring(prop
                                                     .getName().length()));
                         }
                     } else {
                         value = metaObject == null ? null : metaObject
                                 .getValue(propertyName);
                     }
                     TypeHandler typeHandler = parameterMapping.getTypeHandler();
                     if (typeHandler == null) {
                         throw new ExecutorException(
                                 "There was no TypeHandler found for parameter "
                                         + propertyName + " of statement "
                                         + mappedStatement.getId());
                     }
                     typeHandler.setParameter(ps, i + 1, value,
                             parameterMapping.getJdbcType());
                 }
             }
         }
     }

     private String generatePageSql(String sql, PageInfo page) {
         if (page != null && (dialect !=null || !dialect.equals(""))) {
             StringBuffer pageSql = new StringBuffer();
             if ("mysql".equals(dialect)) {
                 pageSql.append(sql);
                 pageSql.append(" limit " + page.getCurrentResult() + ","
                         + page.getShowCount());
             } else if ("oracle".equals(dialect)) {
                 pageSql.append("select * from (select tmp_tb.*,ROWNUM row_id from (");
                 pageSql.append(sql);
                 pageSql.append(")  tmp_tb where ROWNUM<=");
                 pageSql.append(page.getCurrentResult() + page.getShowCount());
                 pageSql.append(") where row_id>");
                 pageSql.append(page.getCurrentResult());
             }
             return pageSql.toString();
         } else {
             return sql;
         }
     }

     public Object plugin(Object arg0) {
         // TODO Auto-generated method stub
         return Plugin.wrap(arg0, this);
     }

     public void setProperties(Properties p) {
         dialect = p.getProperty("dialect");
         if (dialect ==null || dialect.equals("")) {
             try {
                 throw new PropertyException("dialect property is not found!");
             } catch (PropertyException e) {
                 // TODO Auto-generated catch block
                 e.printStackTrace();
             }
         }
         pageSqlId = p.getProperty("pageSqlId");
         if (dialect ==null || dialect.equals("")) {
             try {
                 throw new PropertyException("pageSqlId property is not found!");
             } catch (PropertyException e) {
                 // TODO Auto-generated catch block
                 e.printStackTrace();
             }
         }
     }

 }

此插件有两个辅助类:PageInfo,ReflectHelper,你可以下载源代码参考。
写了插件之后，当然需要在 mybatis 的配置文件Configuration.xml 里配置这个插件

 <plugins>
         <plugin interceptor="com.yihaomen.util.PagePlugin">
             <property name="dialect" value="mysql" />
             <property name="pageSqlId" value=".*ListPage.*" />
         </plugin>
     </plugins>

请注意，这个插件定义了一个规则，也就是在mapper中sql语句的id 必须包含ListPage才能被拦截。否则将不会分页处理.

插件写好了，现在就可以在 spring mvc 中的controller 层中写一个方法来测试这个分页:

 @RequestMapping("/pagelist")
     public ModelAndView pageList(HttpServletRequest request,HttpServletResponse response){
         int currentPage = request.getParameter("page")==null?1:Integer.parseInt(request.getParameter("page"));
         int pageSize = 3;
         if (currentPage<=0){
             currentPage =1;
         }
         int currentResult = (currentPage-1) * pageSize;

         System.out.println(request.getRequestURI());
         System.out.println(request.getQueryString());

         PageInfo page = new PageInfo();
         page.setShowCount(pageSize);
         page.setCurrentResult(currentResult);
         List<Article> articles=iUserOperation.selectArticleListPage(page,1);

         System.out.println(page);

         int totalCount = page.getTotalResult();

         int lastPage=0;
         if (totalCount % pageSize==0){
             lastPage = totalCount % pageSize;
         }
         else{
             lastPage =1+ totalCount / pageSize;
         }

         if (currentPage>=lastPage){
             currentPage =lastPage;
         }

         String pageStr = "";

         pageStr=String.format("<a href=\"%s\">上一页</a>    <a href=\"%s\">下一页</a>",
                         request.getRequestURI()+"?page="+(currentPage-1),request.getRequestURI()+"?page="+(currentPage+1) );

         //制定视图，也就是list.jsp
         ModelAndView mav=new ModelAndView("list");
         mav.addObject("articles",articles);
         mav.addObject("pageStr",pageStr);
         return mav;
     }

然后运行程序，进入分页页面，你就可以看到结果了: