MyBatis 插件之拦截器（Interceptor） - M义薄云天的博客 - CSDN博客

安宇雨 - 随手采集
2019-09-02 15:22:56
随手采集
0000-未整理-等待研究

本文链接：https://blog.csdn.net/weixin_39494923/article/details/91534658

一.背景

在很多业务场景下我们需要去拦截sql，达到不入侵原有代码业务处理一些东西，比如：分页操作，数据权限过滤操作，SQL执行时间性能监控等等，这里我们就可以用到Mybatis的拦截器Interceptor

二.Mybatis核心对象介绍

从MyBatis代码实现的角度来看，MyBatis的主要的核心部件有以下几个：

Configuration 初始化基础配置，比如MyBatis的别名等，一些重要的类型对象，如，插件，映射器，ObjectFactory和typeHandler对象，MyBatis所有的配置信息都维持在Configuration对象之中
SqlSessionFactory SqlSession工厂
SqlSession 作为MyBatis工作的主要顶层API，表示和数据库交互的会话，完成必要数据库增删改查功能
Executor MyBatis执行器，是MyBatis 调度的核心，负责SQL语句的生成和查询缓存的维护
StatementHandler 封装了JDBC Statement操作，负责对JDBC statement 的操作，如设置参数、将Statement结果集转换成List集合。
ParameterHandler 负责对用户传递的参数转换成JDBC Statement 所需要的参数，
ResultSetHandler 负责将JDBC返回的ResultSet结果集对象转换成List类型的集合；
TypeHandler 负责java数据类型和jdbc数据类型之间的映射和转换
MappedStatement MappedStatement维护了一条<select|update|delete|insert>节点的封装，
SqlSource 负责根据用户传递的parameterObject，动态地生成SQL语句，将信息封装到BoundSql对象中，并返回
BoundSql 表示动态生成的SQL语句以及相应的参数信息

三. Mybatis执行概要图

四.MyBatis 拦截器原理实现

Mybatis支持对Executor、StatementHandler、PameterHandler和ResultSetHandler 接口进行拦截，也就是说会对这4种对象进行代理
首先从配置文件解析开始

通过SqlSessionFactoryBean去构建Configuration添加拦截器并构建获取SqlSessionFactory

/** * {@code FactoryBean} that creates an MyBatis {@code SqlSessionFactory}. * This is the usual way to set up a shared MyBatis {@code SqlSessionFactory} in a Spring application context; * the SqlSessionFactory can then be passed to MyBatis-based DAOs via dependency injection. * * Either {@code DataSourceTransactionManager} or {@code JtaTransactionManager} can be used for transaction * demarcation in combination with a {@code SqlSessionFactory}. JTA should be used for transactions * which span multiple databases or when container managed transactions (CMT) are being used. * * @author Putthibong Boonbong * @author Hunter Presnall * @author Eduardo Macarron * @author Eddú Meléndez * @author Kazuki Shimizu * * @see #setConfigLocation * @see #setDataSource */public class SqlSessionFactoryBean implements FactoryBean<SqlSessionFactory>, InitializingBean, ApplicationListener<ApplicationEvent> {     private static final Log LOGGER = LogFactory.getLog(SqlSessionFactoryBean.class);     private Resource configLocation;     private Configuration configuration;     private Resource[] mapperLocations;     private DataSource dataSource;     private TransactionFactory transactionFactory;     private Properties configurationProperties;     private SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();     // ... 此处省略部分源码     /**     * Build a {@code SqlSessionFactory} instance.     *     * The default implementation uses the standard MyBatis {@code XMLConfigBuilder} API to build a     * {@code SqlSessionFactory} instance based on an Reader.     * Since 1.3.0, it can be specified a {@link Configuration} instance directly(without config file).     *     * @return SqlSessionFactory     * @throws IOException if loading the config file failed     */    protected SqlSessionFactory buildSqlSessionFactory() throws IOException {          Configuration configuration;        // 根据配置信息构建Configuration实体类        XMLConfigBuilder xmlConfigBuilder = null;        if (this.configuration != null) {            configuration = this.configuration;            if (configuration.getVariables() == null) {                configuration.setVariables(this.configurationProperties);            } else if (this.configurationProperties != null) {                configuration.getVariables().putAll(this.configurationProperties);            }        } else if (this.configLocation != null) {            xmlConfigBuilder = new XMLConfigBuilder(this.configLocation.getInputStream(), null, this.configurationProperties);            configuration = xmlConfigBuilder.getConfiguration();        } else {            if (LOGGER.isDebugEnabled()) {                LOGGER.debug("Property 'configuration' or 'configLocation' not specified, using default MyBatis Configuration");            }            configuration = new Configuration();            if (this.configurationProperties != null) {                configuration.setVariables(this.configurationProperties);            }        }         // ... 此处省略部分源码         if (hasLength(this.typeAliasesPackage)) {            String[] typeAliasPackageArray = tokenizeToStringArray(this.typeAliasesPackage,                    ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);            for (String packageToScan : typeAliasPackageArray) {                configuration.getTypeAliasRegistry().registerAliases(packageToScan,                        typeAliasesSuperType == null ? Object.class : typeAliasesSuperType);                if (LOGGER.isDebugEnabled()) {                    LOGGER.debug("Scanned package: '" + packageToScan + "' for aliases");                }            }        }         if (!isEmpty(this.typeAliases)) {            for (Class<?> typeAlias : this.typeAliases) {                configuration.getTypeAliasRegistry().registerAlias(typeAlias);                if (LOGGER.isDebugEnabled()) {                    LOGGER.debug("Registered type alias: '" + typeAlias + "'");                }            }        }        // 查看是否注入拦截器，有的话添加到Interceptor集合里面        if (!isEmpty(this.plugins)) {            for (Interceptor plugin : this.plugins) {                configuration.addInterceptor(plugin);                if (LOGGER.isDebugEnabled()) {                    LOGGER.debug("Registered plugin: '" + plugin + "'");                }            }        }         // ... 此处省略部分源码         return this.sqlSessionFactoryBuilder.build(configuration);    }     // ... 此处省略部分源码}

通过原始的XMLConfigBuilder 构建configuration添加拦截器

public class XMLConfigBuilder extends BaseBuilder {    //解析配置    private void parseConfiguration(XNode root) {        try {            //省略部分代码            pluginElement(root.evalNode("plugins"));         } catch (Exception e) {            throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);        }    }     private void pluginElement(XNode parent) throws Exception {        if (parent != null) {            for (XNode child : parent.getChildren()) {                String interceptor = child.getStringAttribute("interceptor");                Properties properties = child.getChildrenAsProperties();                Interceptor interceptorInstance = (Interceptor) resolveClass(interceptor).newInstance();                interceptorInstance.setProperties(properties);                //调用InterceptorChain.addInterceptor                configuration.addInterceptor(interceptorInstance);            }        }    }}

上面是两种不同的形式构建configuration并添加拦截器interceptor，上面第二种一般是以前XML配置的情况，这里主要是解析配置文件的plugin节点，根据配置的interceptor 属性实例化Interceptor 对象，然后添加到Configuration 对象中的InterceptorChain 属性中

3.定义了拦截器链，初始化配置文件的时候就把所有的拦截器添加到拦截器链中

org.apache.ibatis.plugin.InterceptorChain 源代码如下：

public class InterceptorChain {    private final List<Interceptor> interceptors = new ArrayList<Interceptor>();   public Object pluginAll(Object target) {    //循环调用每个Interceptor.plugin方法    for (Interceptor interceptor : interceptors) {      target = interceptor.plugin(target);    }    return target;  }   // 添加拦截器  public void addInterceptor(Interceptor interceptor) {    interceptors.add(interceptor);  }    public List<Interceptor> getInterceptors() {    return Collections.unmodifiableList(interceptors);  } }

** 4.从以下代码可以看出mybatis 在实例化Executor、ParameterHandler、ResultSetHandler、StatementHandler四大接口对象的时候调用interceptorChain.pluginAll() 方法插入进去的。其实就是循环执行拦截器链所有的拦截器的plugin() 方法，
mybatis官方推荐的plugin方法是Plugin.wrap() 方法,这个类就是我们上面的TargetProxy类
org.apache.ibatis.session.Configuration 类，其代码如下：**

public class Configuration {     protected final InterceptorChain interceptorChain = new InterceptorChain();    //创建参数处理器    public ParameterHandler newParameterHandler(MappedStatement mappedStatement, Object parameterObject, BoundSql boundSql) {        //创建ParameterHandler        ParameterHandler parameterHandler = mappedStatement.getLang().createParameterHandler(mappedStatement, parameterObject, boundSql);        //插件在这里插入        parameterHandler = (ParameterHandler) interceptorChain.pluginAll(parameterHandler);        return parameterHandler;    }     //创建结果集处理器    public ResultSetHandler newResultSetHandler(Executor executor, MappedStatement mappedStatement, RowBounds rowBounds, ParameterHandler parameterHandler,                                                ResultHandler resultHandler, BoundSql boundSql) {        //创建DefaultResultSetHandler        ResultSetHandler resultSetHandler = new DefaultResultSetHandler(executor, mappedStatement, parameterHandler, resultHandler, boundSql, rowBounds);        //插件在这里插入        resultSetHandler = (ResultSetHandler) interceptorChain.pluginAll(resultSetHandler);        return resultSetHandler;    }     //创建语句处理器    public StatementHandler newStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {        //创建路由选择语句处理器        StatementHandler statementHandler = new RoutingStatementHandler(executor, mappedStatement, parameterObject, rowBounds, resultHandler, boundSql);        //插件在这里插入        statementHandler = (StatementHandler) interceptorChain.pluginAll(statementHandler);        return statementHandler;    }     public Executor newExecutor(Transaction transaction) {        return newExecutor(transaction, defaultExecutorType);    }     //产生执行器    public Executor newExecutor(Transaction transaction, ExecutorType executorType) {        executorType = executorType == null ? defaultExecutorType : executorType;        //这句再做一下保护,囧,防止粗心大意的人将defaultExecutorType设成null?        executorType = executorType == null ? ExecutorType.SIMPLE : executorType;        Executor executor;        //然后就是简单的3个分支，产生3种执行器BatchExecutor/ReuseExecutor/SimpleExecutor        if (ExecutorType.BATCH == executorType) {            executor = new BatchExecutor(this, transaction);        } else if (ExecutorType.REUSE == executorType) {            executor = new ReuseExecutor(this, transaction);        } else {            executor = new SimpleExecutor(this, transaction);        }        //如果要求缓存，生成另一种CachingExecutor(默认就是有缓存),装饰者模式,所以默认都是返回CachingExecutor        if (cacheEnabled) {            executor = new CachingExecutor(executor);        }        //此处调用插件,通过插件可以改变Executor行为        executor = (Executor) interceptorChain.pluginAll(executor);        return executor;    }}

5.Mybatis的Plugin动态代理

org.apache.ibatis.plugin.Plugin 源代码如下

public class Plugin implements InvocationHandler {     public static Object wrap(Object target, Interceptor interceptor) {    //从拦截器的注解中获取拦截的类名和方法信息    Map<Class<?>, Set<Method>> signatureMap = getSignatureMap(interceptor);    //取得要改变行为的类(ParameterHandler|ResultSetHandler|StatementHandler|Executor)    Class<?> type = target.getClass();    //取得接口    Class<?>[] interfaces = getAllInterfaces(type, signatureMap);    //产生代理，是Interceptor注解的接口的实现类才会产生代理    if (interfaces.length > 0) {      return Proxy.newProxyInstance(type.getClassLoader(),interfaces,new Plugin(target, interceptor, signatureMap));    }    return target;  }      @Override  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {    try {      //获取需要拦截的方法      Set<Method> methods = signatureMap.get(method.getDeclaringClass());      //是Interceptor实现类注解的方法才会拦截处理      if (methods != null && methods.contains(method)) {        //******调用Interceptor.intercept，也即插入了我们自己的逻辑********        return interceptor.intercept(new Invocation(target, method, args));      }      //最后还是执行原来逻辑        return method.invoke(target, args);    } catch (Exception e) {        throw ExceptionUtil.unwrapThrowable(e);    }  }      //取得签名Map,就是获取Interceptor实现类上面的注解，要拦截的是那个类（Executor   //,ParameterHandler， ResultSetHandler，StatementHandler）的那个方法 private static Map<Class<?>, Set<Method>> getSignatureMap(Interceptor interceptor) {    //取Intercepts注解，例子可参见ExamplePlugin.java    Intercepts interceptsAnnotation =interceptor.getClass().getAnnotation(Intercepts.class);    // issue #251    //必须得有Intercepts注解，没有报错    if (interceptsAnnotation == null) {      throw new PluginException("No @Intercepts annotation was found in interceptor " + interceptor.getClass().getName());          }    //value是数组型，Signature的数组      Signature[] sigs = interceptsAnnotation.value();    //每个class里有多个Method需要被拦截,所以这么定义      Map<Class<?>, Set<Method>> signatureMap = new HashMap<Class<?>, Set<Method>>();     for (Signature sig : sigs) {      Set<Method> methods = signatureMap.get(sig.type());        if (methods == null) {          methods = new HashSet<Method>();          signatureMap.put(sig.type(), methods);      }      try {         Method method = sig.type().getMethod(sig.method(), sig.args());         methods.add(method);      } catch (NoSuchMethodException e) {         throw new PluginException("Could not find method on " + sig.type() + " named " + sig.method() + ". Cause: " + e, e);      }    }    return signatureMap;  }     //取得接口 private static Class<?>[] getAllInterfaces(Class<?> type, Map<Class<?>, Set<Method>> signatureMap) {    Set<Class<?>> interfaces = new HashSet<Class<?>>();      while (type != null) {        for (Class<?> c : type.getInterfaces()) {        //拦截其他的无效        if (signatureMap.containsKey(c)) {          interfaces.add(c);        }      }      type = type.getSuperclass();    }    return interfaces.toArray(new Class<?>[interfaces.size()]);  }}

6.我们自己实现的拦截器

@Slf4j@Component@Intercepts({@Signature(method = "prepare", type = StatementHandler.class, args = {Connection.class, Integer.class}),            @Signature(method = "query", type = Executor.class, args = {MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class, CacheKey.class, BoundSql.class})})@SuppressWarnings("unchecked")public class SqliteDataSourceInterceptor implements Interceptor {     @Override    public Object plugin(Object target) {        // 调用插件        return Plugin.wrap(target, this);    }     @Override    public void setProperties(Properties properties) {    }     @Override    public Object intercept(Invocation invocation) throws Exception {        // 该方法写入自己的逻辑        if (invocation.getTarget() instanceof StatementHandler) {            String dataSoureType = DynamicDataSourceContextHolder.getDateSoureType();            // judge dataSource type ,because sqlite can't use internal.core_project this express            // so we need to add "" for it or delete this 'internal.'            if (DataSourceType.SQLITE.name().equals(dataSoureType)) {                RoutingStatementHandler handler = (RoutingStatementHandler) invocation.getTarget();                StatementHandler delegate = (StatementHandler) ReflectUtil.getFieldValue(handler, "delegate");                BoundSql boundSql = delegate.getBoundSql();                String sql = boundSql.getSql();                sql = sql.replace("internal.", " ");                ReflectUtil.setFieldValue(boundSql, "sql", sql);            }        }        // SQL execute start time        long startTimeMillis = System.currentTimeMillis();        // get execute result        Object proceedReslut = invocation.proceed();        // SQL execute end time        long endTimeMillis = System.currentTimeMillis();        log.debug("<< ==== sql execute runnung time：{} millisecond ==== >>", (endTimeMillis - startTimeMillis));        return proceedReslut;    }}

Mybatis拦截器用到责任链模式+动态代理+反射机制；

通过上面的分析可以知道，所有可能被拦截的处理类都会生成一个代理类,如果有N个拦截器，就会有N个代理，层层生成动态代理是比较耗性能的。而且虽然能指定插件拦截的位置，但这个是在执行方法时利用反射动态判断的，初始化的时候就是简单的把拦截器插入到了所有可以拦截的地方。所以尽量不要编写不必要的拦截器；

附：如果采用SqlSessionFactoryBean的形式配置拦截器不起作用，需要在SqlSessionFactoryBean设置添加即可，如下红框框