由于业务关系 巴拉巴拉巴拉
好吧 简单来说就是
原来的业务是 需要再实现类里写 selectCount 和selectPage两个方法才能实现分页功能
现在想要达到效果是 只通过一个方法就可以实现 也就是功能合并 所以就有了下面的实践
既然是基于MyBatis 所以就先搭建一个Mybatis的小项目
1.01导入 mybatis和mysql的包
1.02.配置文件 Configuration.xml 中添加
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<environments default="development"> <environment id="development"> <transactionManager type="JDBC"/> <dataSource type="POOLED"> <property name="driver" value="com.mysql.jdbc.Driver"/> <property name="url" value="jdbc:mysql://localhost:3306/test" /> <property name="username" value="root"/> <property name="password" value=""/> </dataSource> </environment></environments> |
2.01.然后创建一个模块user 创建user表
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DROP TABLE IF EXISTS `user`;CREATE TABLE `user` ( `id` int(11) NOT NULL AUTO_INCREMENT, `name` char(32) NOT NULL, `t1` char(32) DEFAULT NULL, `t2` char(32) DEFAULT NULL, `t3` char(32) DEFAULT NULL, PRIMARY KEY (`id`)) ENGINE=InnoDB AUTO_INCREMENT=10 DEFAULT CHARSET=utf8; |
3.01.写对应bean：User.java
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package lqb.bean;public class User extends Common{ private String id; private String name; private String t1; private String t2; private String t3; //省略get set } |
3.02.对应的mapper： UserMapper.java和UserMapper.xml
简单实现下CRUD
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public interface UserMapper { public User selectByID(int id); public List<User> select(); public int insert(User u); public int update(User u); public int delete(User u); } |
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<mapper namespace="lqb.mapper.UserMapper"> <select id="selectByID" parameterType="int" resultType="lqb.bean.User"> select * from `user` where id = #{id} </select> <select id="select" resultType="lqb.bean.User" parameterType="lqb.bean.User"> select * from `user` </select> <insert id="insert" parameterType="lqb.bean.User"> insert into user (id,name,t1,t2,t3) values (#{id},#{name},#{t1},#{t2},#{t3}) </insert> <update id="update" parameterType="lqb.bean.User"> update user set name=#{name},t1=#{t1},t2=#{t2},t3=#{t3} where id=#{id} </update> <delete id="delete" parameterType="lqb.bean.User"> delete from user where id=#{id} </delete></mapper> |
3.03.然后 在配置文件Configuration.xml中添加user的配置
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<mappers> <mapper resource="lqb/mapper/UserMapper.xml"/></mappers> |
3.04.然后是实现：UserService.java
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public class UserService { private static SqlSessionFactory sqlSessionFactory; private static Reader reader; static{ try{ reader = Resources.getResourceAsReader("Configuration.xml"); sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader); }catch(Exception e){ e.printStackTrace(); } } public static SqlSessionFactory getSession(){ return sqlSessionFactory; }} |
4.01 好 然后是重点了
思路： 截获查询的sql 然后拼成 sqlPage和sqlCount 再进行查找取值 然后赋传入对象
所以我们就需要创建一个基础类来让user.java来继承
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public class Common { private int pagesize; private int pageid; private int pagebegin; private int count; //省略 get set } |
4.02 然后 让User继承Common
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public class User extends Common{ |
4.03 那怎么截获sql呢 我们就要写一个mybatis的拦截器 用来拦截sql请求 PageInterceptor
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@Intercepts({ @Signature(type = StatementHandler.class, method = "prepare", args = {Connection.class}), @Signature(type = ResultSetHandler.class, method = "handleResultSets", args = {Statement.class})}) public class PageInterceptor implements Interceptor { //插件运行的代码，它将代替原有的方法 @Override public Object intercept(Invocation invocation) throws Throwable { } // 拦截类型StatementHandler @Override public Object plugin(Object target) { } @Override public void setProperties(Properties properties) { } |
4.04 首先 设置拦截类型 重写plugin方法
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@Override public Object plugin(Object target) { if (target instanceof StatementHandler) { return Plugin.wrap(target, this); } else { return target; } } |
4.05 然后 就要重写最重要的intercept了
这里我们有一个设定 如果查询方法含有searchpage 就进行分页 其他方法无视
所以就要获取方法名
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StatementHandler statementHandler = (StatementHandler) invocation.getTarget(); MetaObject metaStatementHandler = SystemMetaObject.forObject(statementHandler); MappedStatement mappedStatement=(MappedStatement) metaStatementHandler.getValue("delegate.mappedStatement");String selectId=mappedStatement.getId(); |
4.06 然后判断下 如果含有searchpage 就获取sql
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BoundSql boundSql = (BoundSql) metaStatementHandler.getValue("delegate.boundSql"); // 分页参数作为参数对象parameterObject的一个属性 String sql = boundSql.getSql();Common co=(Common)(boundSql.getParameterObject()); |
4.07 然后 根据这个sql 重新拼写countsql和pagesql
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String countSql=concatCountSql(sql);String pageSql=concatPageSql(sql,co);...public String concatCountSql(String sql){ StringBuffer sb=new StringBuffer("select count(*) from "); sql=sql.toLowerCase(); if(sql.lastIndexOf("order")>sql.lastIndexOf(")")){ sb.append(sql.substring(sql.indexOf("from")+4, sql.lastIndexOf("order"))); }else{ sb.append(sql.substring(sql.indexOf("from")+4)); } return sb.toString(); } public String concatPageSql(String sql,Common co){ StringBuffer sb=new StringBuffer(); sb.append(sql); sb.append(" limit ").append(co.getPagebegin()).append(" , ").append(co.getPagesize()); return sb.toString(); } |
4.08 然后 通过jdbc查询count 然后把值绑定给common
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Connection connection = (Connection) invocation.getArgs()[0]; PreparedStatement countStmt = null; ResultSet rs = null; int totalCount = 0; try { countStmt = connection.prepareStatement(countSql); rs = countStmt.executeQuery(); if (rs.next()) { totalCount = rs.getInt(1); } } catch (SQLException e) { System.out.println("Ignore this exception"+e); } finally { try { rs.close(); countStmt.close(); } catch (SQLException e) { System.out.println("Ignore this exception"+ e); } } //绑定count co.setCount(totalCount); |
4.09 再把pagesql赋给元BoundSql
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metaStatementHandler.setValue("delegate.boundSql.sql", pageSql); |
4.10 最后在配置文件中添加拦截器配置
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<plugins> <plugin interceptor="lqb.interceptor.PageInterceptor"/></plugins> |
4.11 好然后 在UserMapper.java和UserMapper.xml中添加分页代码
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<select id="selectPage" parameterType="lqb.bean.User" resultType="lqb.bean.User"> select * from `user` where id in(3,4,6,8) order by id</select> |
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public List<User> selectPage(User u); |
5.01 最后是测试了
main...请允许本人的懒 就姑且在main方法测下吧
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User u=new User();u.setPagebegin(2);u.setPagesize(3);System.out.println("-u.getCount()------"+u.getCount());List<User> l=userService.selectPage(u);System.out.println(l.size());System.out.println("-u.getCount()------"+u.getCount()); |
5.02 结果 略 然后就成功了
下面附上拦截器的代码
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package lqb.interceptor;import java.util.Properties;import org.apache.ibatis.executor.resultset.ResultSetHandler; import org.apache.ibatis.executor.statement.StatementHandler; import org.apache.ibatis.mapping.BoundSql; import org.apache.ibatis.mapping.MappedStatement; import org.apache.ibatis.plugin.*; import org.apache.ibatis.reflection.MetaObject; import org.apache.ibatis.reflection.SystemMetaObject; import java.sql.*; import lqb.bean.Common;@Intercepts({ @Signature(type = StatementHandler.class, method = "prepare", args = {Connection.class}), @Signature(type = ResultSetHandler.class, method = "handleResultSets", args = {Statement.class})}) public class PageInterceptor implements Interceptor { private static final String SELECT_ID="selectpage"; //插件运行的代码，它将代替原有的方法 @Override public Object intercept(Invocation invocation) throws Throwable { System.out.println("PageInterceptor -- intercept"); if (invocation.getTarget() instanceof StatementHandler) { StatementHandler statementHandler = (StatementHandler) invocation.getTarget(); MetaObject metaStatementHandler = SystemMetaObject.forObject(statementHandler); MappedStatement mappedStatement=(MappedStatement) metaStatementHandler.getValue("delegate.mappedStatement"); String selectId=mappedStatement.getId(); if(SELECT_ID.equals(selectId.substring(selectId.lastIndexOf(".")+1).toLowerCase())){ BoundSql boundSql = (BoundSql) metaStatementHandler.getValue("delegate.boundSql"); // 分页参数作为参数对象parameterObject的一个属性 String sql = boundSql.getSql(); Common co=(Common)(boundSql.getParameterObject()); // 重写sql String countSql=concatCountSql(sql); String pageSql=concatPageSql(sql,co); System.out.println("重写的 count sql :"+countSql); System.out.println("重写的 select sql :"+pageSql); Connection connection = (Connection) invocation.getArgs()[0]; PreparedStatement countStmt = null; ResultSet rs = null; int totalCount = 0; try { countStmt = connection.prepareStatement(countSql); rs = countStmt.executeQuery(); if (rs.next()) { totalCount = rs.getInt(1); } } catch (SQLException e) { System.out.println("Ignore this exception"+e); } finally { try { rs.close(); countStmt.close(); } catch (SQLException e) { System.out.println("Ignore this exception"+ e); } } metaStatementHandler.setValue("delegate.boundSql.sql", pageSql); //绑定count co.setCount(totalCount); } } return invocation.proceed(); } /** * 拦截类型StatementHandler */ @Override public Object plugin(Object target) { if (target instanceof StatementHandler) { return Plugin.wrap(target, this); } else { return target; } } @Override public void setProperties(Properties properties) { } public String concatCountSql(String sql){ StringBuffer sb=new StringBuffer("select count(*) from "); sql=sql.toLowerCase(); if(sql.lastIndexOf("order")>sql.lastIndexOf(")")){ sb.append(sql.substring(sql.indexOf("from")+4, sql.lastIndexOf("order"))); }else{ sb.append(sql.substring(sql.indexOf("from")+4)); } return sb.toString(); } public String concatPageSql(String sql,Common co){ StringBuffer sb=new StringBuffer(); sb.append(sql); sb.append(" limit ").append(co.getPagebegin()).append(" , ").append(co.getPagesize()); return sb.toString(); } public void setPageCount(){ } } |
最后是下载地址：mybatisResolve.rar
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持服务器之家。
原文链接：http://www.cnblogs.com/jethypc/p/5149183.html
