Mybatis spring plugin详解

1.环境

jdk8
mybatis3.5.2
Spring 5.1.9.RELEASE
spring-jdbc 5.1.9.RELEASE

2.官方解释

mybatis允许自定义拦截执行对数据库操作方法，默认mybatis-plugin支持拦截以下方法:

org.apache.ibatis.executor.Executor中定义（update, query, flushStatements, commit, rollback, getTransaction, close, isClosed）方法
org.apache.ibatis.executor.parameter.ParameterHandler中定义（getParameterObject, setParameters）方法
org.apache.ibatis.executor.resultset.ResultSetHandler中定义（handleResultSets, handleOutputParameters）方法
org.apache.ibatis.executor.statement.StatementHandler中定义 (prepare, parameterize, batch, update, query)方法

以上类中方法通过方法签名进行拦截，要明白覆盖这些方法功能，假如要监控这些方法，需要修改默认方法行为和重写方法功能，增加拦截器可能破坏mybatis核心代码，增加拦截器代码需要小心

3.plugin配置

3.1 .plugin代码

@Intercepts({@Signature( type = Executor.class, method = "update",
                args = {MappedStatement.class,Object.class}),
        @Signature(
                type = Executor.class,
                method = "query",
                args = {MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class, CacheKey.class, BoundSql.class}),
            @Signature(type = Executor.class, method = "query",
                args = { MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class }),
            @Signature(type = Executor.class, method = "query",
                args = { MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class, CacheKey.class, BoundSql.class })
})
public class ExamplePlugin implements Interceptor
{
    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        System.out.println("拦截开始====");
        Object returnObject = invocation.proceed();
        System.out.println("拦截结束====");
        return returnObject;
    }

    @Override
    public Object plugin(Object target) {
        return Plugin.wrap(target, this);
    }

    @Override
    public void setProperties(Properties properties) {

    }
}

3.2. spring中配置

3.3.测试代码

public class MbatisSpringTest
{
    public static void main( String[] args )
    {
        ApplicationContext ctx = new ClassPathXmlApplicationContext("application.xml");
        BlogMapper blogMapper = ctx.getBean(BlogMapper.class);
//        blogMapper.selectBlog(1);

        blogMapper.containsKey("ttt");
    }
}

3.4.plugin源码分析

3.4.1自定义配置plugin初始化代码片段如下：

org.mybatis.spring.SqlSessionFactoryBean#buildSqlSessionFactory


  protected SqlSessionFactory buildSqlSessionFactory() throws Exception {

    final Configuration targetConfiguration;

    …………………………
    //此处代码增加自定义plugin到config中
    if (!isEmpty(this.plugins)) {
      Stream.of(this.plugins).forEach(plugin -> {
        targetConfiguration.addInterceptor(plugin);
        LOGGER.debug(() -> "Registered plugin: '" + plugin + "'");
      });
    }
………………

    return this.sqlSessionFactoryBuilder.build(targetConfiguration);
  }

4.plugin执行流程

mybatis-plugin-01.png

mybatis-plugin-02.png

下面两张图是一起，03图后续流程04图接着，一张图放不下，所以分开

mybatis-plugin-03.png

mybatis-plugin-04.png

5.plugin相关类说明

org.apache.ibatis.plugin.Interceptor：插件接口，自定义plugin需要实现

org.apache.ibatis.plugin.InterceptorChain:用list保存配置plugin，初始化在org.mybatis.spring.SqlSessionFactoryBean#buildSqlSessionFactory中

org.apache.ibatis.plugin.Intercepts：自定plugin类中，说明要拦截方法

org.apache.ibatis.plugin.Plugin：判断执行sql方法是不是在自定义plugin规则中，如果存在自动生成代理包含改插件，不存在不包含。

org.apache.ibatis.executor.Executor：配置org.apache.ibatis.plugin.Signature中，进行要拦截方法