MyBatis分頁

搞清楚什麼是分頁(pagination)

例如，在數據庫的某個表裏有1000條數據，我們每次只顯示100條數據，在第1頁顯示第0到第99條，在第2頁顯示第100到199條，依次類推，這就是分頁。

分頁可以分爲邏輯分頁和物理分頁。邏輯分頁是我們的程序在顯示每頁的數據時，首先查詢得到表中的1000條數據，然後成熟根據當前頁的「頁碼」選出其中的100條數據來顯示。

物理分頁是程序先判斷出該選出這1000條的第幾條到第幾條，然後數據庫根據程序給出的信息查詢出程序需要的100條返回給我們的程序。

MyBatis 物理分頁

MyBatis使用RowBounds實現的分頁是邏輯分頁,也就是先把數據記錄全部查詢出來,然在再根據 offset 和 limit 截斷記錄返回。

爲了在數據庫層面上實現物理分頁，又不改變原來 MyBatis 的函數邏輯,可以編寫 plugin 截獲 MyBatis Executor 的 statementhandler，重寫SQL來執行查詢。

經常搭框架的人應該都清楚，框架搭建的核心就是配置文件。

在這裏我們需要創建 web 工程。也需要用 mybatis與Spring mvc 集成起來，源碼在本文結尾處下載，主要有以下幾個方面的配置。

整個Mybatis分頁示例要完成的步驟如下：

1、示例功能描述

2、創建工程

3、數據庫表結構及數據記錄

4、實例對象

5、配置文件

6、測試執行，輸出結果

1、示例功能描述

在本示例中，需要使用 MyBatis和Spring MVC整合完成分頁，完成這樣的一個簡單功能，即指定一個用戶（ID=1），查詢出這個用戶關聯的所有訂單分頁顯示出來（使用的數據庫是：MySQL）。

2、創建工程

首先創建一個工程的名稱爲：mybatis08-paging，在 src 源代碼目錄下建立文件夾 config，並將原來的 mybatis 配置文件 Configuration.xml 移動到這個文件夾中, 並在 config 文家夾中建立 Spring 配置文件：applicationContext.xml。工程結構目錄如下：

3、數據庫表結構及數據記錄

在本示例中，用到兩個表：用戶表和訂單表，其結構和數據記錄如下：

CREATE TABLE `user` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`username` varchar(64) NOT NULL DEFAULT '',
`mobile` varchar(16) NOT NULL DEFAULT '',
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;

-- Records of user

INSERT INTO `user` VALUES ('1', 'yiibai', '13838009988');
INSERT INTO `user` VALUES ('2', 'saya', '13838009988');

訂單表結構和數據如下：

CREATE TABLE `order` (
`order_id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`user_id` int(10) unsigned NOT NULL DEFAULT '0',
`order_no` varchar(16) NOT NULL DEFAULT '',
`money` float(10,2) unsigned DEFAULT '0.00',
PRIMARY KEY (`order_id`)
) ENGINE=InnoDB AUTO_INCREMENT=17 DEFAULT CHARSET=utf8;

-- Records of order

INSERT INTO `order` VALUES ('1', '1', '1509289090', '99.90');
INSERT INTO `order` VALUES ('2', '1', '1519289091', '290.80');
INSERT INTO `order` VALUES ('3', '1', '1509294321', '919.90');
INSERT INTO `order` VALUES ('4', '1', '1601232190', '329.90');
INSERT INTO `order` VALUES ('5', '1', '1503457384', '321.00');
INSERT INTO `order` VALUES ('6', '1', '1598572382', '342.00');
INSERT INTO `order` VALUES ('7', '1', '1500845727', '458.00');
INSERT INTO `order` VALUES ('8', '1', '1508458923', '1200.00');
INSERT INTO `order` VALUES ('9', '1', '1504538293', '2109.00');
INSERT INTO `order` VALUES ('10', '1', '1932428723', '5888.00');
INSERT INTO `order` VALUES ('11', '1', '2390423712', '3219.00');
INSERT INTO `order` VALUES ('12', '1', '4587923992', '123.00');
INSERT INTO `order` VALUES ('13', '1', '4095378812', '421.00');
INSERT INTO `order` VALUES ('14', '1', '9423890127', '678.00');
INSERT INTO `order` VALUES ('15', '1', '7859213249', '7689.00');
INSERT INTO `order` VALUES ('16', '1', '4598450230', '909.20');

4、實例對象

用戶表和訂單表分別對應兩個實例對象，分別是：User.java 和 Order.java，它們都在 com.yiibai.pojo 包中。

User.java代碼內容如下：

package com.yiibai.pojo;

import java.util.List;

/**
* @describe: User
* @author: Yiibai
* @version: V1.0
* @copyright http://www.yiibai.com
*/
public class User {
private int id;
private String username;
private String mobile;

public int getId() {
    return id;
}
public void setId(int id) {
    this.id = id;
}
public String getUsername() {
    return username;
}
public void setUsername(String username) {
    this.username = username;
}
public String getMobile() {
    return mobile;
}
public void setMobile(String mobile) {
    this.mobile = mobile;
}

}

Order.java代碼內容如下：

package com.yiibai.pojo;

/**
* @describe: User - 訂單
* @author: Yiibai
* @version: V1.0
* @copyright http://www.yiibai.com
*/
public class Order {
private int orderId;
private String orderNo;
private float money;
private int userId;
private User user;

public int getUserId() {
    return userId;
}
public void setUserId(int userId) {
    this.userId = userId;
}
public int getOrderId() {
    return orderId;
}
public void setOrderId(int orderId) {
    this.orderId = orderId;
}
public User getUser() {
    return user;
}
public void setUser(User user) {
    this.user = user;
}
public String getOrderNo() {
    return orderNo;
}
public void setOrderNo(String orderNo) {
    this.orderNo = orderNo;
}
public float getMoney() {
    return money;
}
public void setMoney(float money) {
    this.money = money;
}

}

5、配置文件

這個實例中有三個重要的配置文件，它們分別是：applicationContext.xml ， Configuration.xml 以及 UserMaper.xml。

applicationContext.xml 配置文件裏最主要的配置：

<!--本示例採用DBCP連接池，應預先把DBCP的jar包複製到工程的lib目錄下。 -->
<context:property-placeholder location="classpath:/config/database.properties" />

<bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource"
    destroy-method="close" p:driverClassName="com.mysql.jdbc.Driver"
    p:url="jdbc:mysql://127.0.0.1:3306/yiibai?characterEncoding=utf8"
    p:username="root" p:password="" p:maxActive="10" p:maxIdle="10">
</bean>

<bean id="transactionManager"
    class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
    <property name="dataSource" ref="dataSource" />
</bean>

<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
    <!--dataSource屬性指定要用到的連接池-->
    <property name="dataSource" ref="dataSource" />
    <!--configLocation屬性指定mybatis的核心配置文件-->
    <property name="configLocation" value="classpath:config/Configuration.xml" />
    <!-- 所有配置的mapper文件 -->
    <property name="mapperLocations" value="classpath\*:com/yiibai/mapepr/\*.xml" />
</bean>

<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
    <property name="basePackage" value="com.yiibai.maper" />
</bean>

配置文件  Configuration.xml 的內容如下：

<!-- 這裏交給sqlSessionFactory 的 mapperLocations屬性去得到所有配置信息 -->
<!-- 
<mappers>
    <mapper resource="com/yihaomen/mapper/User.xml"/>
</mappers>
--> 

UserMaper.xml 用於定義查詢和數據對象映射，其內容如下：

    <!-- 爲了返回list 類型而定義的returnMap -->
<resultMap type="User" id="resultUser">
    <id column="id" property="id" />
    <result column="username" property="username" />
    <result column="mobile" property="mobile" />
</resultMap>

<!-- User 聯合 Order 查詢 方法的配置 (多對一的方式)  -->    
<resultMap id="resultUserOrders" type="Order">
    <id property="orderId" column="order\_id" />
    <result property="orderNo" column="order\_no" />
    <result property="money" column="money" />
    <result property="userId" column="user\_id" />

    <association property="user" javaType="User">
        <id property="id" column="id" />
        <result property="username" column="username" />
        <result property="mobile" column="mobile" />            
    </association>        
</resultMap> 

<select id="getUserOrders" parameterType="int" resultMap="resultUserOrders">
   SELECT u.\*,o.\* FROM \`user\` u, \`order\` o 
          WHERE u.id=o.user\_id AND u.id=#{id}
</select>

<select id="getUserById" resultMap="resultUser" parameterType="int">
    SELECT \*
    FROM user
    WHERE id=#{id}
</select>    

6、測試執行，輸出結果

我們創建一個控制器類在包 com.yiibai.controller 下，類的名稱爲：UserController.java，這裏新增了一個方法：pageList， 對應請求URL是 /orderpages，其代碼如下：

package com.yiibai.controller;

import java.util.List;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.servlet.ModelAndView;

import com.yiibai.maper.UserMaper;
import com.yiibai.pojo.Order;
import com.yiibai.util.Page;

// http://localhost:8080/mybatis08-paging/user/orders
@Controller
@RequestMapping("/user")
public class UserController {
@Autowired
UserMaper userMaper;

/\*\*
 \* 某一個用戶下的所有訂單
 \* 
 \* @param request
 \* @param response
 \* @return
 \*/
@RequestMapping("/orders")
public ModelAndView listall(HttpServletRequest request,
        HttpServletResponse response) {
    List<Order> orders = userMaper.getUserOrders(1);
    System.out.println("orders");
    ModelAndView mav = new ModelAndView("user\_orders");
    mav.addObject("orders", orders);
    return mav;
}

/\*\*
 \* 訂單分頁
 \* 
 \* @param request
 \* @param response
 \* @return
 \*/
@RequestMapping("/orderpages")
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());

    Page page = new Page();
    page.setShowCount(pageSize);
    page.setCurrentResult(currentResult);
    List<Order> orders = userMaper.getOrderListPage(page, 1);

    System.out.println("Current page =>" + 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\\">上一頁</a>    <a href=\\"%s\\">下一頁</a>", request
                    .getRequestURI()
                    + "?page=" + (currentPage - 1), request.getRequestURI()
                    + "?page=" + (currentPage + 1));

    // 制定視圖，也就是list.jsp
    ModelAndView mav = new ModelAndView("pagelist");
    mav.addObject("orders", orders);
    mav.addObject("pagelist", pageStr);
    return mav;
}

}

注意，在這個分頁工程中，在 com.yiibai.util 包下新增了幾個類，它們分別是：PagePlugin.java，Page.java, PageHelper.java，其中 PagePlugin 是針對 MyBatis 分頁的插件。由於代碼太多，這裏列出 PagePlugin.java 的代碼，其它兩個類的代碼有興趣的讀者可以在下載代碼後閱讀取研究。 PagePlugin.java 的代碼如下所示：

package com.yiibai.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.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.scripting.xmltags.ForEachSqlNode;
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 NullYiibaierException("parameterObject error");
            } else {
                Connection connection = (Connection) ivk.getArgs()\[0\];
                String sql = boundSql.getSql();
                String countSql = "select count(0) from (" + sql
                        + ") myCount";
                System.out.println("總數sql 語句:" + 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();

                Page page = null;
                if (parameterObject instanceof Page) {
                    page = (Page) parameterObject;
                    page.setTotalResult(count);
                } else if (parameterObject instanceof Map) {
                    Map<String, Object> map = (Map<String, Object>) parameterObject;
                    page = (Page) map.get("page");
                    if (page == null)
                        page = new Page();
                    page.setTotalResult(count);
                } else {
                    Field pageField = ReflectHelper.getFieldByFieldName(
                            parameterObject, "page");
                    if (pageField != null) {
                        page = (Page) ReflectHelper.getValueByFieldName(
                                parameterObject, "page");
                        if (page == null)
                            page = new Page();
                        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, Page 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();
        }
    }
}

}

接下來部署 mybatis08-paging 這個工程，啓動 tomcat ，打開瀏覽器輸入網址：http://localhost:8080/mybatis08-paging/user/orderpages ，顯示結果如下：

工程 mybatis08-paging 的代碼下載：http://pan.baidu.com/s/1pJxhvNt

Jar 包下載：http://pan.baidu.com/s/1bnyRJ9H