原生Mybitas的Interceptor和Plugin

落日映苍穹つ 2023-06-25 10:15 2阅读 0赞

借鉴了读写分离框架，大概了解了实现原理，顺手写了这篇博客

*  **Mybitas的Dao层实际上是一个代理对象，在执行的时候先走MapperProxy.invoke()**

## 主要代码 ##

pom.xml

<dependencies>
            
            <dependency>
                <groupId>log4j</groupId>
                <artifactId>log4j</artifactId>
                <version>1.2.16</version>
            </dependency>
    
            
            <dependency>
                <groupId>org.mybatis</groupId>
                <artifactId>mybatis</artifactId>
                <version>3.2.6</version>
            </dependency>
    
            
            <dependency>
                <groupId>mysql</groupId>
                <artifactId>mysql-connector-java</artifactId>
                <version>5.1.12</version>
            </dependency>
    
        </dependencies>

mybitas.xml

<?xml version="1.0" encoding="UTF-8" ?>
    <!DOCTYPE configuration
            PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
            "http://mybatis.org/dtd/mybatis-3-config.dtd">
    <configuration>
    
        
        <settings>
            <setting name="logImpl" value="LOG4J"/>
        </settings>
    
        <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/test1"/>
                  <property name="username" value="root"/>
                  <property name="password" value="root"/>
                </dataSource>
            </environment>
        </environments>
    
        
        <mappers>
            <mapper resource="com/dao/userDao-mapping.xml"/>
        </mappers>
    
    </configuration>

Main

package com;
    
    import com.dao.UserDao;
    import com.entity.User;
    import org.apache.ibatis.executor.Executor;
    import org.apache.ibatis.io.Resources;
    import org.apache.ibatis.mapping.MappedStatement;
    import org.apache.ibatis.plugin.*;
    import org.apache.ibatis.session.*;
    
    import java.io.IOException;
    import java.util.Properties;
    
    /** * @author ：liujipeng * @date ：Created in 2019/12/27 14:58 * @description：${description} */
    public class Application { 
        public static void main(String[] args) { 
            SqlSession sqlSession = getSessionFactory().openSession();
            UserDao userMapper = sqlSession.getMapper(UserDao.class);
            User user = userMapper.findUserById(1);
        }
    
        private static SqlSessionFactory getSessionFactory() { 
            SqlSessionFactory sessionFactory = null;
            String resource = "mybitas.xml";
            try { 
                sessionFactory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsReader(resource));
            } catch (IOException e) { 
                e.printStackTrace();
            }
            MyInterceptor myInterceptor = new MyInterceptor();
            sessionFactory.getConfiguration().addInterceptor(myInterceptor);
            return sessionFactory;
        }
    //拦截器
        @Intercepts({  @Signature(type = Executor.class, method = "query", args = { MappedStatement.class, Object.class,
                RowBounds.class, ResultHandler.class}),
                @Signature(type = Executor.class, method = "update", args = { MappedStatement.class,
                        Object.class})})
        static class MyInterceptor implements Interceptor { 
            public Object intercept(Invocation invocation) throws Throwable { 
                return invocation.proceed();
            }
            public Object plugin(Object target) { 
                return Plugin.wrap(target, this);
            }
            public void setProperties(Properties properties) { 
            }
        }
    
    }

userDao-mapping.xml

<?xml version="1.0" encoding="UTF-8" ?>
    <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
    <mapper namespace="com.dao.UserDao">
    
        <select id="findUserById" resultType="com.entity.User" >
            select * from user where id = #{ id}
        </select>
        <update id="updateUser" >
            update user set name = "sds" where id = #{ id}
        </update>
    
    </mapper>

关于Mapper.xml 文件的加载和`"select|insert|update|delete"`的解析此次先不进行说明，全部被解析后封存在`Configuration.mappedStatements<String, MappedStatement>` key就是`namespace+id`形式储存的

## Interceptor和Plugin ##

我的application里面在SqlSessionFactory初始化完成的时候会将自己写的 MyInterceptor添加到 InterceptorChain 里面。  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3h1eGllMTM_size_16_color_FFFFFF_t_70]

## 在什么时候进行调用呢 ##

在获得SqlSessionFactory后就要获取SqlSession,此时就会发生第一次拦截

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3h1eGllMTM_size_16_color_FFFFFF_t_70 1]  
根据openSession（）方法进来，我们会看到如下得到一个执行器  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3h1eGllMTM_size_16_color_FFFFFF_t_70 2]  
在打开获取执行器的方法里面我们可以看到获取了所有的拦截器  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3h1eGllMTM_size_16_color_FFFFFF_t_70 3]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3h1eGllMTM_size_16_color_FFFFFF_t_70 4]  
这个interceptor.plugin(target)就进入了自己设置的interceptor里面  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3h1eGllMTM_size_16_color_FFFFFF_t_70 5]  
这个`Plugin.wrap`方法继续跟进去  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3h1eGllMTM_size_16_color_FFFFFF_t_70 6]  
`signatureMap`获取的是自己在Interceptor的注解上定义的内容，key 就是type值对象，value存的是Executor.class里面通过nethid和args得到的方法  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3h1eGllMTM_size_16_color_FFFFFF_t_70 7]  
target是newExecutor里面传进去的，有此处可见是`CachingExecutor`对象  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3h1eGllMTM_size_16_color_FFFFFF_t_70 8]  
因此`interfaces`里面会得到一个`CachingExecutor`数组对象，如下  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3h1eGllMTM_size_16_color_FFFFFF_t_70 9]  
回头再看这个三元运算符，则会返回Plugin针对`CachingExecutor`的代理对象。  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3h1eGllMTM_size_16_color_FFFFFF_t_70 10]  
然后的方法就是一路返回，直到返回`SqlSession`![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3h1eGllMTM_size_16_color_FFFFFF_t_70 11]  
上面这一步返回的是 `MapperProxy`的代理对象，在执行`xxxMapper.find()`方法的时候会走如下  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3h1eGllMTM_size_16_color_FFFFFF_t_70 12]  
![!\[在这里插入图片描述\](https://img-blog.csdnimg.cn/20191228133944939.png?x-oss-process=image/watermark,type\_ZmFuZ3poZW5naGVpdGk,shadow\_10,text\_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3h1eGllMTM=,size\_16,color\_FFFFFF,t\_70][https_img-blog.csdnimg.cn_20191228133944939.png_x-oss-process_image_watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3h1eGllMTM_size_16_color_FFFFFF_t_70]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3h1eGllMTM_size_16_color_FFFFFF_t_70 13]  
然后就会走到上面这个地方，这个 `executor`就是上面Plugin产生的代理对象，当执行的时候会先走 `Plugin.invoke()`  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3h1eGllMTM_size_16_color_FFFFFF_t_70 14]  
`method.getDeclaringClass()` 得到的是进入Plugin的这个方法的方法对象，在wrap（）的时候已经初始化了signatureMap数据，此次是大于0的，因此就又走了  
`this.interceptor.intercept(new Invocation(this.target, method, args))` 这个就是自定义的intercept方法中  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3h1eGllMTM_size_16_color_FFFFFF_t_70 15]  
至此，mybitas的Interceptor就结束了，后面的就是mybitas 自己的初始化各种链接查询了。

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