MyBatis提供了一种插件(plugin)的功能，虽然叫做插件，其实就是拦截器功能

MyBatis 允许拦截的接口

MyBatis 允许你在已映射语句执行过程中的某一点进行拦截调用。默认情况下，MyBatis 允许使用插件来拦截的方法调用包括：

1. Executor (update, query, flushStatements, commit, rollback, getTransaction, close, isClosed)
2. ParameterHandler (getParameterObject, setParameters)
3. ResultSetHandler (handleResultSets, handleOutputParameters)
4. StatementHandler (prepare, parameterize, batch, update, query)

Executor接口的部分方法，比如update，query，commit，rollback等方法，还有其他接口的一些方法等。

总体概括为：

1. 拦截执行器的方法
2. 拦截参数的处理
3. 拦截结果集的处理,为sql执行之后的结果拦截过滤
4. 拦截Sql语法构建的处理,为sql执行之前的拦截进行sql封装

MyBatis拦截器的接口定义

一共有三个方法intercept 、plugin 、setProperties

setProperties()

方法主要是用来从配置中获取属性。

如果是使用xml式配置拦截器，可在Mybatis配置文件中添加如下节点，属性可以以如下方式传递

<plugins>
	<plugin interceptor="tk.mybatis.simple.plugin.XXXInterceptor">
		<property name="propl" value="valuel" />
		<property name="prop2" value="value2" />
	</plugin>
</plugins>

如果在Spring boot中使用，则需要单独写一个配置类，如下：

@Configuration
public class MybatisInterceptorConfig {
    @Bean
    public String myInterceptor(SqlSessionFactory sqlSessionFactory) {
        ExecutorInterceptor executorInterceptor = new ExecutorInterceptor();
        Properties properties = new Properties();
        properties.setProperty("prop1","value1");
        executorInterceptor.setProperties(properties);
        return "interceptor";
    }
}

如果说不需要配置属性，则在spring boot中，不需要去编写配置类，只需要像我一样在拦截器上加个@Component即可。

plugin()

方法用于指定哪些方法可以被此拦截器拦截。

intercept()

方法是用来对拦截的sql进行具体的操作。

注解实现

MyBatis拦截器用到了两个注解：@Intercepts和@Signature

@Intercepts(
        {
                @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}),
        }
)

type的值与类名相同，method与方法名相同，为了避免方法重载，args中指定了各个参数的类型和个数，可通过invocation.getArgs()获取参数数组。

Executor 拦截器实现

@Intercepts({
        @Signature(
        type= Executor.class,
        method = "query",
        args = {MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class}
        )
})
@Slf4j
@Component
public class ExecutorInterceptor implements Interceptor {
    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        String sql = ExecutorPluginUtils.getSqlByInvocation(invocation);
        //可以对sql重写
        log.error("拦截器ExecutorInterceptor:"+sql);
        //sql = "SELECT id from BUS_RECEIVER where id = ? ";
        ExecutorPluginUtils.resetSql2Invocation( invocation,  sql);
        return invocation.proceed();
    }

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

    @Override
    public void setProperties(Properties properties) {

    }


}

ParameterHandler 拦截器实现

/**
 * @Author: ynz
 * @Date: 2018/12/23/023 12:07
 */
@Intercepts({
        @Signature(type = ParameterHandler.class, method = "setParameters", args = PreparedStatement.class),
})
@Component
@Slf4j
public class ParamInterceptor  implements Interceptor {

    @Override
    public Object intercept(Invocation invocation) throws Throwable {

        log.error("拦截器ParamInterceptor");
        //拦截 ParameterHandler 的 setParameters 方法 动态设置参数
        if (invocation.getTarget() instanceof ParameterHandler) {
            ParameterHandler parameterHandler = (ParameterHandler) invocation.getTarget();
            PreparedStatement ps = (PreparedStatement) invocation.getArgs()[0];

            // 反射获取 BoundSql 对象，此对象包含生成的sql和sql的参数map映射
            Field boundSqlField = parameterHandler.getClass().getDeclaredField("boundSql");
            boundSqlField.setAccessible(true);
            BoundSql boundSql = (BoundSql) boundSqlField.get(parameterHandler);
            // 反射获取 参数对像
            Field parameterField = 
                    parameterHandler.getClass().getDeclaredField("parameterObject");
            parameterField.setAccessible(true);
            Object parameterObject = parameterField.get(parameterHandler);

            if (parameterObject instanceof Map) {
                //将参数中的name值改为2
                ((Map) parameterObject).put("name","2");
            }

            // 改写的参数设置到原parameterHandler对象
            parameterField.set(parameterHandler, parameterObject);
            parameterHandler.setParameters(ps);


            log.error(JSON.toJSONString(boundSql.getParameterMappings()));
            log.error(JSON.toJSONString(parameterObject));
        }
        return invocation.proceed();
    }

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

    @Override
    public void setProperties(Properties properties) {

    }
}

ResultSetHandler 拦截器实现

@Intercepts({
        @Signature(type = ResultSetHandler.class, method = "handleResultSets", args={Statement.class})
})
@Component
@Slf4j
public class ResultInterceptor implements Interceptor {

    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        log.error("拦截器ResultInterceptor");
       // ResultSetHandler resultSetHandler1 = (ResultSetHandler) invocation.getTarget();
        //通过java反射获得mappedStatement属性值
        //可以获得mybatis里的resultype
        Object result = invocation.proceed();
        if (result instanceof ArrayList) {
            ArrayList resultList = (ArrayList) result;
            for (int i = 0; i < resultList.size(); i++) {
                Object oi = resultList.get(i);
                Class c = oi.getClass();
                Class[] types = {String.class};
                Method method = c.getMethod("setAddress", types);
                // 调用obj对象的 method 方法
                method.invoke(oi, "china");
            }
        }
        return result;
    }

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

    @Override
    public void setProperties(Properties properties) {

    }
}

StatementHandler 拦截器实现

/**
 * @Author: ynz
 * @Date: 2018/12/23/023 14:22
 */
@Intercepts(
        {@Signature(
                type = StatementHandler.class,
                method = "prepare",
                args = {Connection.class, Integer.class}
                )
        })
@Component
@Slf4j
public class StatementInterceptor implements Interceptor {

    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        StatementHandler statementHandler = 
                (StatementHandler) PluginUtils.realTarget(invocation.getTarget());
        MetaObject metaStatementHandler = SystemMetaObject.forObject(statementHandler);
        MappedStatement mappedStatement = 
                (MappedStatement) metaStatementHandler.getValue("delegate.mappedStatement");
        //只拦截select方法
        if (!SqlCommandType.SELECT.equals(mappedStatement.getSqlCommandType())) {
            return invocation.proceed();
        }
        BoundSql boundSql = (BoundSql) metaStatementHandler.getValue("delegate.boundSql");
        //获取到sql
        String originalSql = boundSql.getSql();
        //可以对originalSql进行改写
        log.error("拦截器StatementInterceptor:"+originalSql);
        metaStatementHandler.setValue("delegate.boundSql.sql", originalSql);
        Object parameterObject = boundSql.getParameterObject();
        return invocation.proceed();
    }

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

    @Override
    public void setProperties(Properties properties) {

    }
}

Spring Boot整合

方法1：手写一个配置类

@Configuration
public class MybatisInterceptorConfig {
    @Bean
    public String myInterceptor(SqlSessionFactory sqlSessionFactory) {
        ExecutorInterceptor executorInterceptor = new ExecutorInterceptor();
        Properties properties = new Properties();
        properties.setProperty("prop1","value1");
        executorInterceptor.setProperties(properties);
        sqlSessionFactory.getConfiguration().addInterceptor(executorInterceptor);
        sqlSessionFactory.getConfiguration().addInterceptor(new ParamInterceptor());
        sqlSessionFactory.getConfiguration().addInterceptor(new ResultInterceptor());
        return "interceptor";
    }
}

方法2：在拦截器上加@Component注解