MyBatis 拦截器 （实现分页功能）

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

 <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

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

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

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);
    
}

<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

<mappers>
        <mapper resource="lqb/mapper/UserMapper.xml"/>
</mappers>

3.04.然后是实现：UserService.java

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

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

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

@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

@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

 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

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 

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

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

   metaStatementHandler.setValue("delegate.boundSql.sql", pageSql);  

4.10 最后在配置文件中添加拦截器配置

 <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

 <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>

 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

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

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(){
        
    }
    
}  

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