mybatis实战教程(mybatis in action)之七：实现mybatis分页

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 :

 程序代码

<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.

 程序代码

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 

 程序代码

   
    <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:

 程序代码

@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:


另外，你还得在前面提到的数据库artilce表里面，多插入一些记录，分页效果就更好。

来源： http://www.yihaomen.com/article/java/326.htm

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