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MyBatis 入门(五)--分页查询（2）

分类： Java

2016-04-28 15:30:11

一、Mybatis插件介绍              

摘自官方文档：很晦涩，简单阅读一下即可                                 

MyBatis 允许你在某一点拦截已映射语句执行的调用。默认情况下,MyBatis 允许使用插件来拦截方法调用:

  • Executor (update, query, flushStatements, commit, rollback, getTransaction, close, isClosed)
  • ParameterHandler (getParameterObject, setParameters)
  • ResultSetHandler (handleResultSets, handleOutputParameters)
  • StatementHandler (prepare, parameterize, batch, update, query)

这些类中方法的详情可以通过查看每个方法的签名来发现 ,而且它们的源代码在 MyBatis 的发行包中有。你应该理解你覆盖方法的行为,假设你所做的要比监视调用要多。 如果你尝试修改或覆盖一个给定的方法, 你可能会打破 MyBatis 的核心。 这是低层次的类和方法,要谨慎使用插件。

使用插件是它们提供的非常简单的力量。

简单实现拦截器接口, 要确定你想拦截的指定签名。

上面的插件将会拦截在 Executor 实例中所有的“update”方法调用,它也是负责低层次 映射语句执行的内部对象。 


插件的作用就是在执行预计前，后都可以自定义需要处理的程序（通过责任链模式 ） ，也就是说可以定义多个需要执行的程序。

二、 实现一个自己的拦截器

  1. package com.elements.user.plugins;

  3. import java.sql.Connection;
  4. import java.util.Properties;

  6. import org.apache.ibatis.executor.statement.StatementHandler;
  7. import org.apache.ibatis.plugin.Interceptor;
  8. import org.apache.ibatis.plugin.Intercepts;
  9. import org.apache.ibatis.plugin.Invocation;
  10. import org.apache.ibatis.plugin.Signature;

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

  15.     public Object intercept(Invocation invocation) throws Throwable {
  16.         System.out.println("bbbbbbbbbb");

  18.         return null;
  19.     }

  21.     public Object plugin(Object target) {
  22.         System.out.println("target is :"+target.getClass().getName());
  23.         return target;
  24.  
  25.     }

  27.     public void setProperties(Properties properties) {
  28.         System.out.println(properties.toString());

  30.     }

  32. }

测试输出结果

  1. {someProperty=100}
  2. target is :org.apache.ibatis.executor.CachingExecutor
  3. target is :org.apache.ibatis.scripting.defaults.DefaultParameterHandler
  4. target is :org.apache.ibatis.executor.resultset.DefaultResultSetHandler
  5. target is :org.apache.ibatis.executor.statement.RoutingStatementHandler
 intercept没有被调用
第一步 我们的属性，从配置文件里面获取了，这里是 someProperty 值是 someProperty
 第二步 我们的plugin ，被调用了4次，分别是 CachingExecutor， DefaultParameterHandler ，DefaultResultSetHandler，RoutingStatementHandler
 CachingExecutor ：二级缓存执行器 实现 Executor
DefaultParameterHandler ：参数处理 实现ParameterHandler
 DefaultResultSetHandler ：实现 ResultSetHandler
 ResultSetHandler只负责两件事：
1.处理Statement执行后产生的结果集，生成结果列表
2.处理存储过程执行后的输出参数
 RoutingStatementHandler：实现了StatementHandler

三、分页实现

mybatis-config.xml

  1. <?xml version="1.0" encoding="UTF-8"?>
  2. <!DOCTYPE configuration
  3.   PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
  4.   "">

  6. <configuration>

  8.     <properties resource="jdbc.properties" />

  10.    <!-- 自定义分页拦截器 -->
  11.     <plugins>
  12.         <plugin interceptor="com.elements.user.plugins.PageInterceptor">
  13.             <property name="someProperty" value="100" />
  14.         </plugin>
  15.     </plugins>

  17.     <environments default="dev">
  18.         <environment id="dev">
  19.             <transactionManager type="JDBC" />
  20.             <dataSource type="POOLED">
  21.                 <property name="driver" value="${driver}" />
  22.                 <property name="url" value="${url}" />
  23.                 <property name="username" value="${username}" />
  24.                 <property name="password" value="${password}" />
  25.             </dataSource>
  26.         </environment>
  27.     </environments>



  31.     <mappers>
  32.         <mapper class="com.elements.user.dao.UserMapper" />

  34.     </mappers>

  36. </configuration>

page

  1. package com.elements.user.plugins;

  3. public class Page {

  5.     // 定义分页的默认大小
  6.     private int OnePageSize = 5;

  8.     // 当前页数
  9.     private int nowPage = 1;

  11.     public int getOnePageSize() {
  12.         return OnePageSize;
  13.     }

  15.     public void setOnePageSize(int onePageSize) {
  16.         OnePageSize = onePageSize;
  17.     }

  19.     public int getStartRow() {
  20.         return startRow;
  21.     }

  23.     public void setStartRow(int startRow) {
  24.         this.startRow = startRow;
  25.     }

  27.     public int getEndRow() {
  28.         return endRow;
  29.     }

  31.     public void setEndRow(int endRow) {
  32.         this.endRow = endRow;
  33.     }

  35.     // 开始的行
  36.     private int startRow = 0;
  37.     {
  38.         startRow = (nowPage - 1) * OnePageSize;
  39.     }

  41.     // 结束的行
  42.     private int endRow = 0;
  43.     {
  44.         endRow = nowPage * OnePageSize;
  45.     }

  47.     // 总的页数
  48.     private int AllPages = 0;

  50.     // 总记录数
  51.     private int allRows = 0;

  53.     public int getAllRows() {
  54.         return allRows;
  55.     }

  57.     public void setAllRows(int allRows) {
  58.         this.allRows = allRows;
  59.         this.AllPages = allRows % OnePageSize == 0 ? (int) (allRows / OnePageSize)
  60.                 : (int) (allRows / OnePageSize) + 1;
  61.     }

  63.     public int getNowPage() {
  64.         return nowPage;
  65.     }

  67.     public void setNowPage(int nowPage) {
  68.         this.nowPage = nowPage;
  69.         startRow = (nowPage - 1) * OnePageSize;
  70.         endRow = nowPage * OnePageSize;
  71.     }
  72. }
基础类User

  1. package com.elements.user.model;

  3. import com.elements.user.plugins.Page;

  5.  

  7. public class User extends Page{
  8.     /**
  9.      * This field was generated by MyBatis Generator.
  10.      * This field corresponds to the database column user.userId
  11.      *
  12.      * @mbggenerated Wed Apr 27 15:05:09 CST 2016
  13.      */
  14.     private Integer userid;

  16.     /**
  17.      * This field was generated by MyBatis Generator.
  18.      * This field corresponds to the database column user.UserName
  19.      *
  20.      * @mbggenerated Wed Apr 27 15:05:09 CST 2016
  21.      */
  22.     private String username;

  24.     /**
  25.      * This field was generated by MyBatis Generator.
  26.      * This field corresponds to the database column user.UserEmail
  27.      *
  28.      * @mbggenerated Wed Apr 27 15:05:09 CST 2016
  29.      */
  30.     private String useremail;

  32.     /**
  33.      * This field was generated by MyBatis Generator.
  34.      * This field corresponds to the database column user.createTime
  35.      *
  36.      * @mbggenerated Wed Apr 27 15:05:09 CST 2016
  37.      */
  38.     private String createtime;

  40.     /**
  41.      * This field was generated by MyBatis Generator.
  42.      * This field corresponds to the database column user.updateTime
  43.      *
  44.      * @mbggenerated Wed Apr 27 15:05:09 CST 2016
  45.      */
  46.     private String updatetime;

  48.     /**
  49.      * This method was generated by MyBatis Generator.
  50.      * This method returns the value of the database column user.userId
  51.      *
  52.      * @return the value of user.userId
  53.      *
  54.      * @mbggenerated Wed Apr 27 15:05:09 CST 2016
  55.      */
  56.     public Integer getUserid() {
  57.         return userid;
  58.     }

  60.     /**
  61.      * This method was generated by MyBatis Generator.
  62.      * This method sets the value of the database column user.userId
  63.      *
  64.      * @param userid the value for user.userId
  65.      *
  66.      * @mbggenerated Wed Apr 27 15:05:09 CST 2016
  67.      */
  68.     public void setUserid(Integer userid) {
  69.         this.userid = userid;
  70.     }

  72.     /**
  73.      * This method was generated by MyBatis Generator.
  74.      * This method returns the value of the database column user.UserName
  75.      *
  76.      * @return the value of user.UserName
  77.      *
  78.      * @mbggenerated Wed Apr 27 15:05:09 CST 2016
  79.      */
  80.     public String getUsername() {
  81.         return username;
  82.     }

  84.     /**
  85.      * This method was generated by MyBatis Generator.
  86.      * This method sets the value of the database column user.UserName
  87.      *
  88.      * @param username the value for user.UserName
  89.      *
  90.      * @mbggenerated Wed Apr 27 15:05:09 CST 2016
  91.      */
  92.     public void setUsername(String username) {
  93.         this.username = username == null ? null : username.trim();
  94.     }

  96.     /**
  97.      * This method was generated by MyBatis Generator.
  98.      * This method returns the value of the database column user.UserEmail
  99.      *
  100.      * @return the value of user.UserEmail
  101.      *
  102.      * @mbggenerated Wed Apr 27 15:05:09 CST 2016
  103.      */
  104.     public String getUseremail() {
  105.         return useremail;
  106.     }

  108.     /**
  109.      * This method was generated by MyBatis Generator.
  110.      * This method sets the value of the database column user.UserEmail
  111.      *
  112.      * @param useremail the value for user.UserEmail
  113.      *
  114.      * @mbggenerated Wed Apr 27 15:05:09 CST 2016
  115.      */
  116.     public void setUseremail(String useremail) {
  117.         this.useremail = useremail == null ? null : useremail.trim();
  118.     }

  120.     /**
  121.      * This method was generated by MyBatis Generator.
  122.      * This method returns the value of the database column user.createTime
  123.      *
  124.      * @return the value of user.createTime
  125.      *
  126.      * @mbggenerated Wed Apr 27 15:05:09 CST 2016
  127.      */
  128.     public String getCreatetime() {
  129.         return createtime;
  130.     }

  132.     /**
  133.      * This method was generated by MyBatis Generator.
  134.      * This method sets the value of the database column user.createTime
  135.      *
  136.      * @param createtime the value for user.createTime
  137.      *
  138.      * @mbggenerated Wed Apr 27 15:05:09 CST 2016
  139.      */
  140.     public void setCreatetime(String createtime) {
  141.         this.createtime = createtime ;
  142.     }

  144.     /**
  145.      * This method was generated by MyBatis Generator.
  146.      * This method returns the value of the database column user.updateTime
  147.      *
  148.      * @return the value of user.updateTime
  149.      *
  150.      * @mbggenerated Wed Apr 27 15:05:09 CST 2016
  151.      */
  152.     public String getUpdatetime() {
  153.         return updatetime;
  154.     }

  156.     /**
  157.      * This method was generated by MyBatis Generator.
  158.      * This method sets the value of the database column user.updateTime
  159.      *
  160.      * @param updatetime the value for user.updateTime
  161.      *
  162.      * @mbggenerated Wed Apr 27 15:05:09 CST 2016
  163.      */
  164.     public void setUpdatetime(String updatetime) {
  165.         this.updatetime = updatetime;
  166.     }

  168.     @Override
  169.     public String toString() {
  170.         return "User [userid=" + userid + ", username=" + username
  171.                 + ", useremail=" + useremail + ", createtime=" + createtime
  172.                 + ", updatetime=" + updatetime + "]\n";
  173.     }
  174.     
  175.     
  176. }
UserMapper

  1. <?xml version="1.0" encoding="UTF-8" ?>
  2. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "" >
  3. <mapper namespace="com.elements.user.dao.UserMapper" >

  5.  
  6.   <resultMap id="BaseResultMap" type="com.elements.user.model.User" >
  7.     <id column="userId" property="userid" jdbcType="INTEGER" />
  8.     <result column="UserName" property="username" jdbcType="VARCHAR" />
  9.     <result column="UserEmail" property="useremail" jdbcType="VARCHAR" />
  10.     <result column="createTime" property="createtime" jdbcType="VARCHAR" />
  11.     <result column="updateTime" property="updatetime" jdbcType="VARCHAR" />
  12.   </resultMap>
  13.   
  14.   
  15.   <sql id="Base_Column_List" >
  16.     userId, UserName, UserEmail, createTime, updateTime
  17.   </sql>
  18.   
  19.   <select id="selectUserPage" parameterType="com.elements.user.model.User" resultMap="BaseResultMap">
  20.     select
  21.     <include refid="Base_Column_List" />
  22.     from user
  23.      where 1=1
  24.      and UserName like '%%'
  25.   </select>
  26.   
  27. </mapper>
最终要的：PageInterceptor

  1. package com.elements.user.plugins;

  3. import java.sql.Connection;
  4. import java.sql.PreparedStatement;
  5. import java.sql.ResultSet;
  6. import java.sql.SQLException;
  7. import java.util.List;
  8. import java.util.Properties;

  10. import org.apache.ibatis.executor.parameter.ParameterHandler;
  11. import org.apache.ibatis.executor.statement.RoutingStatementHandler;
  12. import org.apache.ibatis.executor.statement.StatementHandler;
  13. import org.apache.ibatis.mapping.BoundSql;
  14. import org.apache.ibatis.mapping.MappedStatement;
  15. import org.apache.ibatis.mapping.ParameterMapping;
  16. import org.apache.ibatis.plugin.Interceptor;
  17. import org.apache.ibatis.plugin.Intercepts;
  18. import org.apache.ibatis.plugin.Invocation;
  19. import org.apache.ibatis.plugin.Plugin;
  20. import org.apache.ibatis.plugin.Signature;
  21. import org.apache.ibatis.scripting.defaults.DefaultParameterHandler;

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

  26.     public Object plugin(Object target) {
  27.         System.out.println("target is :" + target.getClass().getName());
  28.         if (target instanceof RoutingStatementHandler) {
  29.             return Plugin.wrap(target, this);
  30.         }
  31.         return target;
  32.     }

  34.     public void setProperties(Properties properties) {
  35.         System.out.println(properties.toString());

  37.     }

  39.     public Object intercept(Invocation invocation) throws Throwable {

  41.         if (invocation.getTarget() instanceof RoutingStatementHandler) {

  43.             RoutingStatementHandler statementHandler = (RoutingStatementHandler) invocation
  44.                     .getTarget();
  45.             StatementHandler delegate = (StatementHandler) ReflectHelper
  46.                     .getFieldValue(statementHandler, "delegate");
  47.             BoundSql boundSql = delegate.getBoundSql();
  48.             Object obj = boundSql.getParameterObject();

  50.             if (obj instanceof Page) {

  52.                 Page page = (Page) obj;
  53.                 // 通过反射获取delegate父类BaseStatementHandler的mappedStatement属性
  54.                 MappedStatement mappedStatement = (MappedStatement) ReflectHelper
  55.                         .getFieldValue(delegate, "mappedStatement");
  56.                 // 拦截到的prepare方法参数是一个Connection对象
  57.                 Connection connection = (Connection) invocation.getArgs()[0];

  59.                 // 获取当前要执行的Sql语句，也就是我们直接在Mapper映射语句中写的Sql语句
  60.                 String sql = boundSql.getSql();
  61.                 // 给当前的page参数对象设置总记录数
  62.                 this.setTotalRecord(page, mappedStatement, connection);
  63.                 // 获取分页Sql语句
  64.                 String pageSql = this.getPageSql(page, sql);
  65.                 // 利用反射设置当前BoundSql对应的sql属性为我们建立好的分页Sql语句
  66.                 ReflectHelper.setFieldValue(boundSql, "sql", pageSql);
  67.             }
  68.         }

  70.         return invocation.proceed();

  72.     }

  74.     private String getPageSql(Page page, String sql) {

  76.         StringBuffer sqlBuffer = new StringBuffer(sql);

  78.         sqlBuffer.insert(0, "select * from (").append(")temp where 1=1 ")
  79.                 .append(" limit ").append(page.getStartRow()).append(",")
  80.                 .append(page.getOnePageSize());

  82.         return sqlBuffer.toString();
  83.     }

  85.     private void setTotalRecord(Page page, MappedStatement mappedStatement,
  86.             Connection connection) {

  88.         // delegate里面的boundSql也是通过mappedStatement.getBoundSql(paramObj)方法获取到的。
  89.         BoundSql boundSql = mappedStatement.getBoundSql(page);
  90.         // 获取到我们自己写在Mapper映射语句中对应的Sql语句
  91.         String sql = boundSql.getSql();
  92.         // 通过查询Sql语句获取到对应的计算总记录数的sql语句
  93.         String countSql = this.getCountSql(sql);

  95.         // 通过BoundSql获取对应的参数映射
  96.         List<ParameterMapping> parameterMappings = boundSql
  97.                 .getParameterMappings();
  98.         // 利用Configuration、查询记录数的Sql语句countSql、参数映射关系parameterMappings和参数对象page建立查询记录数对应的BoundSql对象。
  99.         BoundSql countBoundSql = new BoundSql(
  100.                 mappedStatement.getConfiguration(), countSql,
  101.                 parameterMappings, page);
  102.         // 通过mappedStatement、参数对象page和BoundSql对象countBoundSql建立一个用于设定参数的ParameterHandler对象
  103.         ParameterHandler parameterHandler = new DefaultParameterHandler(
  104.                 mappedStatement, page, countBoundSql);
  105.         // 通过connection建立一个countSql对应的PreparedStatement对象。
  106.         PreparedStatement pstmt = null;
  107.         ResultSet rs = null;
  108.         try {
  109.             pstmt = connection.prepareStatement(countSql);
  110.             // 通过parameterHandler给PreparedStatement对象设置参数
  111.             parameterHandler.setParameters(pstmt);
  112.             // 之后就是执行获取总记录数的Sql语句和获取结果了。
  113.             rs = pstmt.executeQuery();
  114.             if (rs.next()) {
  115.                 int totalRecord = rs.getInt(1);
  116.                 // 给当前的参数page对象设置总记录数
  117.                 page.setAllRows(totalRecord);
  118.             }
  119.         } catch (SQLException e) {
  120.             e.printStackTrace();
  121.         } finally {
  122.             try {
  123.                 if (rs != null)
  124.                     rs.close();
  125.                 if (pstmt != null)
  126.                     pstmt.close();
  127.             } catch (SQLException e) {
  128.                 e.printStackTrace();
  129.             }
  130.         }

  132.     }

  134.     private String getCountSql(String sql) {
  135.         StringBuffer sqlBuffer = new StringBuffer(sql);
  136.         sqlBuffer.insert(0, "select count(*) from (").append(
  137.                 ")temp where 1=1 ");
  138.         return sqlBuffer.toString();
  139.     }

  141. }
测试类：
  1. package com.elements.user;

  3. import java.io.IOException;
  4. import java.io.InputStream;
  5. import java.util.List;

  7. import org.apache.ibatis.io.Resources;
  8. import org.apache.ibatis.session.SqlSession;
  9. import org.apache.ibatis.session.SqlSessionFactory;
  10. import org.apache.ibatis.session.SqlSessionFactoryBuilder;
  11. import org.junit.Test;
  12. import com.elements.user.dao.UserMapper;
  13. import com.elements.user.model.User;

  15. public class TestUserPage {

  17.     @Test
  18.     public void TestUserPageSelect() throws IOException {
  19.         String resource = "mybatis-config.xml";
  20.         InputStream inputStream = Resources.getResourceAsStream(resource);
  21.         SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder()
  22.                 .build(inputStream);

  24.         SqlSession session = sqlSessionFactory.openSession();
  25.         try {
  26.  
  27.             
  28.             UserMapper user = (UserMapper) session
  29.                     .getMapper(UserMapper.class);
  30.  
  31.             User u=new User();
  32.             
  33.             List<User> list =user.selectUserPage(u);
  34.             
  35.             System.out.print(list);

  37.         } finally {
  38.             session.close();
  39.         }

  41.     }

  43. }

四、总结

     只要你的查询参数继承Page类，就会自动分页，查询总记录，总页数（在page内  ）。方式一要自己一一实现。

项目代码地址：  
                                                                                       
本文章参考了：
（1）http://blog.csdn.net/hfmbook/article/details/41985853

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