mybatis插件的执行顺序

原理

mybatis插件类型

plugins

MyBatis 允许你在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：

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

那么这些插件的执行顺序是如何的呢？

引入mybatis插件

maven依赖(略)

详见： gitee

配置插件

    <!-- 配置SqlSessionFactory对象 --><bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean"><!-- ..... --><property name="configLocation" value="classpath:mybatis-config.xml"/></bean>

自定义插件

插件的方法内容很简单，即打印当前方法的签名：

 @Intercepts({@Signature(type = Executor.class, method = "query", args = { MappedStatement.class, Object.class, RowBounds.class,ResultHandler.class })
})
@Slf4j
public class Executor_Interceptor implements Interceptor {@Overridepublic Object intercept(Invocation invocation) throws Throwable {log.info("---------------------"+this.getClass().getSimpleName() +"::"+invocation.getMethod().getName());return invocation.proceed();}@Overridepublic Object plugin(Object target) {return Plugin.wrap(target, this);}@Overridepublic void setProperties(Properties properties) {}
}

同理，以此注入如下的插件：

// Executor2_Interceptor ,Executor3_Interceptor 同  Executor_Interceptor//ParameterHandler 监听setParameters方法
@Intercepts({@Signature( type= ParameterHandler.class,method = "setParameters", args = {PreparedStatement.class})
})
public class ParameterHandler_Interceptor implements Interceptor  {}//ResultSetHandler 监听 handleResultSets 方法
@Intercepts({@Signature( type= ResultSetHandler.class,method = "handleResultSets", args = {Statement.class}),
})
public class ResultSetHandler_Interceptor implements Interceptor {}//StatementHandler 监听 prepare和query方法
@Intercepts({@Signature( type= StatementHandler.class,method = "prepare", args = {Connection.class,Integer.class}),@Signature( type= StatementHandler.class,method = "query", args = {Statement.class,ResultHandler.class})
})
public class StatementHandler_Interceptor implements Interceptor {}

同类型插件的执行顺序

mybatis-config.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configurationPUBLIC "-//mybatis.org//DTD Config 3.0//EN""http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration><plugins><plugin interceptor="cn.jhs.framework.mybatis.plugins.Executor2_Interceptor"></plugin><plugin interceptor="cn.jhs.framework.mybatis.plugins.Executor_Interceptor"></plugin><plugin interceptor="cn.jhs.framework.mybatis.plugins.Executor3_Interceptor"></plugin></plugin></plugins>
</configuration>

执行查询方法–日志

结论
相同类型的plugins：按照 注册的 逆序,执行。

不同类型插件的执行顺序

mybatis-config.xml

<plugins><plugin interceptor="cn.jhs.framework.mybatis.plugins.Executor_Interceptor"></plugin><plugin interceptor="cn.jhs.framework.mybatis.plugins.ParameterHandler_Interceptor"></plugin><plugin interceptor="cn.jhs.framework.mybatis.plugins.ResultSetHandler_Interceptor"></plugin><plugin interceptor="cn.jhs.framework.mybatis.plugins.StatementHandler_Interceptor"></plugin>
</plugins>

执行查询方法–日志

猜测
不同类型的plugins：按照 是否注册的顺序影响呢？

随机顺序-不同plugin

  <plugins><plugin interceptor="cn.jhs.framework.mybatis.plugins.ResultSetHandler_Interceptor"></plugin><plugin interceptor="cn.jhs.framework.mybatis.plugins.ParameterHandler_Interceptor"></plugin><plugin interceptor="cn.jhs.framework.mybatis.plugins.StatementHandler_Interceptor"></plugin><plugin interceptor="cn.jhs.framework.mybatis.plugins.Executor_Interceptor"></plugin></plugins>

此时的执行结果，跟上述结果相同

结论
总体顺序
Executor -> StatementHandler ->ParameterHandler -> ResultSetHandler，
但是部分-方法的顺序，不受上述规则的控制。如日志中的StatementHandler.prepare()和StatementHandler.query()

源码分析

我们都知道，XXMapper#selectXXX(); 转换为 DefaultSqlSession#selectList(); 下面从DefaultSqlSession入手，分析，上述插件的执行顺序的原理。

构建DefaultSqlSession — 初始化


--DefaultSqlSessionFactory#openSessionFromDataSource()
----configuration#newExecutor();                //1.    创建 executor
------executor = new SimpleExecutor();             //1.1   创建SimpleExecutor
------executor = new CachingExecutor(executor);    //1.2   包装成： CachingExecutor
------executor = (Executor) interceptorChain.pluginAll(executor);  //1.3   使用 interceptorChain.代理executor
----------for-each -> interceptor.plugin(target);                    //1.3.1 内部调用： Plugin.wrap(target, this);
----------Plugin#wrap(target, this);                                //1.3.1.1 生成executor代理对象public static Object wrap(Object target, Interceptor interceptor) {//a. 获取代理interceptor所有签名的<接口，Set<接口methods>>Map<Class<?>, Set<Method>> signatureMap = getSignatureMap(interceptor);//b. target = CachingExecutor;Class<?> type = target.getClass();//c. type(CachingExecutor.class)与interceptor签名接口 交集;  // 此时CachingExecutor实现了Executor接口， 故只有@Signature中包含Executor接口的interceptor，会生成代理对象;Class<?>[] interfaces = getAllInterfaces(type, signatureMap);//d. 如果存在交集， 则生成代理对象if (interfaces.length > 0) {return Proxy.newProxyInstance(type.getClassLoader(),interfaces,new Plugin(target, interceptor, signatureMap));}//e. 如果不存在交集，则返回原始对象return target;}
------返回一个可能存在多重Plugin..warp的(CachingExecutor(SimpleExecutor)) 对象；
-----new DefaultSqlSession(configuration, executor, autoCommit);    // 2.  构造DefaultSqlSession对象

此时构建出一个DefaultSqlSession对象,它的内容如下：

public class DefaultSqlSession implements SqlSession {private Configuration configuration;private Executor executor; // 仅包含 plugins中，@Signature中包含Executor接口的interceptorpublic <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {MappedStatement ms = configuration.getMappedStatement(statement);return executor.query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER);}
}

执行查询

接上一节内容，所有的查询都会转换为executor.query, 此时的executor为@Signature中包含Executor接口的interceptor生成的Plugin代理对象。

1. 执行Plugin<Executor.class>

Plugin执行代理方法的逻辑如下。此时的Plugin代理的是Executor

  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {Set<Method> methods = signatureMap.get(method.getDeclaringClass());    //1.1 查看当前Plugin支持的方法类型setif (methods != null && methods.contains(method)) {                  //1.2 检验执行mapper方法类型，与当前Plugin设置的方法 是否一致return interceptor.intercept(new Invocation(target, method, args));  //1.3. 链式调用*执行插件interceptor.intercept方法}return method.invoke(target, args); //1.4 执行原始对象 CachingExecutor();}

2. 执行CachingExecutor#query()

上一步执行完成之后，最终执行真实对象查询方法CachingExecutor#query.

-------delegate.<E> query(ms, parameterObject, rowBounds, resultHandler, key, boundSql); //delegate = SimpleExecutor //SimpleExecutor extends BaseExecutor//delegate.query() 执行 BaseExecutor#query(), 而BaseExecutor内部调用抽象方法doQuery,由 SimpleExecutor实现
---------SimpleExecutor#doQuery(); // 2.1
-----------StatementHandler handler = configuration.newStatementHandler() // 2.1.1
-------------StatementHandler statementHandler = new RoutingStatementHandler(); //2.1.1.1 构造 RoutingStatementHandler
---------------delegate = new PreparedStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql); //2.1.1.1.1 内部delegate//delegate 构造内容public class PreparedStatementHandler extends BaseStatementHandler {protected BaseStatementHandler() { this.parameterHandler = configuration.newParameterHandler(); //a. 内部调用创建 ParameterHandlerthis.resultSetHandler = configuration.newResultSetHandler(); //b. 内部调用创建 ResultSetHandler}}
-------------statementHandler = (StatementHandler) interceptorChain.pluginAll(statementHandler); //2.1.1.2 最终通过Plugin.warp(=RoutingStatementHandler);它的delegate类型为PreparedStatementHandler
-----------Statement stmt = prepareStatement(handler, ms.getStatementLog());// 2.1.2
-------------Connection connection = getConnection(statementLog);          // 2.1.2.1 获取数据库连接
-------------stmt = handler.prepare(connection, transaction.getTimeout()); // 2.1.2.2 PreparedStatementHandler->BaseStatementHandler#prepare ;
-------------handler.parameterize(stmt);                                    // 2.1.2.3 PreparedStatementHandler#parameterize ; -----------return handler.<E>query(stmt, resultHandler);// 2.1.3
------------PreparedStatementHandler#query()public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {PreparedStatement ps = (PreparedStatement) statement;ps.execute(); //2.1.3.1 执行psreturn resultSetHandler.<E> handleResultSets(ps); //2.1.3.2  resultSetHandler 渲染执行结果}

关键类图

执行顺序

handler.prepare : StatementHandler
handler.parameterize: StatementHandler + ParameterHandler
handler.<E>query : StatementHandler + ParameterHandler
resultSetHandler.<E> handleResultSets(ps) : ResultSetHandler