最新整理源码面试题

public class CircularTest {

    public static void main(String[] args) {
        new CircularTest1();
    }
}
class CircularTest1{
    private CircularTest2 circularTest2 ;
    public CircularTest1(){
	   this.circularTest2 = new CircularTest2();
    }
}

class CircularTest2{
    private CircularTest1 circularTest1 = new CircularTest1();
	public CircularTest2(CircularTest1 circularTest1){
 		this.circularTest1=new CircularTest1();
	}
}

	/**
	 * This implementation handles propagation behavior. Delegates to
	 * {@code doGetTransaction}, {@code isExistingTransaction}
	 * and {@code doBegin}.
	 * @see #doGetTransaction
	 * @see #isExistingTransaction
	 * @see #doBegin
	 */
	@Override
	public final TransactionStatus getTransaction(@Nullable TransactionDefinition definition)
			throws TransactionException {

		// Use defaults if no transaction definition given.
		// 如果没有事务定义信息则使用默认的事务管理器定义信息
		TransactionDefinition def = (definition != null ? definition : TransactionDefinition.withDefaults());

		// 获取事务
		Object transaction = doGetTransaction();
		boolean debugEnabled = logger.isDebugEnabled();

		// 判断当前线程是否存在事务，判断依据为当前线程记录的连接不为空且连接中的transactionActive属性不为空
		if (isExistingTransaction(transaction)) {
			// Existing transaction found -> check propagation behavior to find out how to behave.
			// 当前线程已经存在事务
			return handleExistingTransaction(def, transaction, debugEnabled);
		}

		// Check definition settings for new transaction.
		// 事务超时设置验证
		if (def.getTimeout() < TransactionDefinition.TIMEOUT_DEFAULT) {
			throw new InvalidTimeoutException("Invalid transaction timeout", def.getTimeout());
		}

		// No existing transaction found -> check propagation behavior to find out how to proceed.
		// 如果当前线程不存在事务，但是PropagationBehavior却被声明为PROPAGATION_MANDATORY抛出异常
		if (def.getPropagationBehavior() == TransactionDefinition.PROPAGATION_MANDATORY) {
			throw new IllegalTransactionStateException(
					"No existing transaction found for transaction marked with propagation 'mandatory'");
		}
		// PROPAGATION_REQUIRED，PROPAGATION_REQUIRES_NEW，PROPAGATION_NESTED都需要新建事务
		else if (def.getPropagationBehavior() == TransactionDefinition.PROPAGATION_REQUIRED ||
				def.getPropagationBehavior() == TransactionDefinition.PROPAGATION_REQUIRES_NEW ||
				def.getPropagationBehavior() == TransactionDefinition.PROPAGATION_NESTED) {
			//没有当前事务的话，REQUIRED，REQUIRES_NEW，NESTED挂起的是空事务，然后创建一个新事务
			SuspendedResourcesHolder suspendedResources = suspend(null);
			if (debugEnabled) {
				logger.debug("Creating new transaction with name [" + def.getName() + "]: " + def);
			}
			try {
				return startTransaction(def, transaction, debugEnabled, suspendedResources);
			}
			catch (RuntimeException | Error ex) {
				// 恢复挂起的事务
				resume(null, suspendedResources);
				throw ex;
			}
		}
		else {
			// Create "empty" transaction: no actual transaction, but potentially synchronization.
			// 创建一个空的事务
			if (def.getIsolationLevel() != TransactionDefinition.ISOLATION_DEFAULT && logger.isWarnEnabled()) {
				logger.warn("Custom isolation level specified but no actual transaction initiated; " +
						"isolation level will effectively be ignored: " + def);
			}
			boolean newSynchronization = (getTransactionSynchronization() == SYNCHRONIZATION_ALWAYS);
			return prepareTransactionStatus(def, null, true, newSynchronization, debugEnabled, null);
		}
	}

	/**
	 * 创建一个DataSourceTransactionObject当作事务，设置是否允许保存点，然后获取连接持有器ConnectionHolder
	 * 里面会存放JDBC的连接，设置给DataSourceTransactionObject,当然第一次是空的
	 *
	 * @return
	 */
	@Override
	protected Object doGetTransaction() {
		// 创建一个数据源事务对象
		DataSourceTransactionObject txObject = new DataSourceTransactionObject();
		// 是否允许当前事务设置保持点
		txObject.setSavepointAllowed(isNestedTransactionAllowed());
		/**
		 * TransactionSynchronizationManager 事务同步管理器对象(该类中都是局部线程变量)
		 * 用来保存当前事务的信息,我们第一次从这里去线程变量中获取 事务连接持有器对象 通过数据源为key去获取
		 * 由于第一次进来开始事务 我们的事务同步管理器中没有被存放.所以此时获取出来的conHolder为null
		 */
		ConnectionHolder conHolder =
				(ConnectionHolder) TransactionSynchronizationManager.getResource(obtainDataSource());
		// 非新创建连接则写false
		txObject.setConnectionHolder(conHolder, false);
		// 返回事务对象
		return txObject;
	}

	/**
	 * Create a TransactionStatus for an existing transaction.
	 */
	private TransactionStatus handleExistingTransaction(
			TransactionDefinition definition, Object transaction, boolean debugEnabled)
			throws TransactionException {

		/**
		 * 判断当前的事务行为是不是PROPAGATION_NEVER的
		 * 表示为不支持事务,但是当前又存在一个事务,所以抛出异常
		 */
		if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_NEVER) {
			throw new IllegalTransactionStateException(
					"Existing transaction found for transaction marked with propagation 'never'");
		}

		/**
		 * 判断当前的事务属性不支持事务,PROPAGATION_NOT_SUPPORTED,所以需要先挂起已经存在的事务
		 */
		if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_NOT_SUPPORTED) {
			if (debugEnabled) {
				logger.debug("Suspending current transaction");
			}
			// 挂起当前事务
			Object suspendedResources = suspend(transaction);
			boolean newSynchronization = (getTransactionSynchronization() == SYNCHRONIZATION_ALWAYS);
			// 创建一个新的非事务状态(保存了上一个存在事务状态的属性)
			return prepareTransactionStatus(
					definition, null, false, newSynchronization, debugEnabled, suspendedResources);
		}

		/**
		 * 当前的事务属性状态是PROPAGATION_REQUIRES_NEW表示需要新开启一个事务状态
		 */
		if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_REQUIRES_NEW) {
			if (debugEnabled) {
				logger.debug("Suspending current transaction, creating new transaction with name [" +
						definition.getName() + "]");
			}
			// 挂起当前事务并返回挂起的资源持有器
			SuspendedResourcesHolder suspendedResources = suspend(transaction);
			try {
				// 创建一个新的非事务状态(保存了上一个存在事务状态的属性)
				return startTransaction(definition, transaction, debugEnabled, suspendedResources);
			}
			catch (RuntimeException | Error beginEx) {
				resumeAfterBeginException(transaction, suspendedResources, beginEx);
				throw beginEx;
			}
		}

		// 嵌套事务
		if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_NESTED) {
			// 不允许就报异常
			if (!isNestedTransactionAllowed()) {
				throw new NestedTransactionNotSupportedException(
						"Transaction manager does not allow nested transactions by default - " +
						"specify 'nestedTransactionAllowed' property with value 'true'");
			}
			if (debugEnabled) {
				logger.debug("Creating nested transaction with name [" + definition.getName() + "]");
			}
			// 嵌套事务的处理
			if (useSavepointForNestedTransaction()) {
				// Create savepoint within existing Spring-managed transaction,
				// through the SavepointManager API implemented by TransactionStatus.
				// Usually uses JDBC 3.0 savepoints. Never activates Spring synchronization.
				// 如果没有可以使用保存点的方式控制事务回滚，那么在嵌入式事务的建立初始简历保存点
				DefaultTransactionStatus status =
						prepareTransactionStatus(definition, transaction, false, false, debugEnabled, null);
				// 为事务设置一个回退点
				status.createAndHoldSavepoint();
				return status;
			}
			else {
				// Nested transaction through nested begin and commit/rollback calls.
				// Usually only for JTA: Spring synchronization might get activated here
				// in case of a pre-existing JTA transaction.
				// 有些情况是不能使用保存点操作
				return startTransaction(definition, transaction, debugEnabled, null);
			}
		}

		// Assumably PROPAGATION_SUPPORTS or PROPAGATION_REQUIRED.
		if (debugEnabled) {
			logger.debug("Participating in existing transaction");
		}
		if (isValidateExistingTransaction()) {
			if (definition.getIsolationLevel() != TransactionDefinition.ISOLATION_DEFAULT) {
				Integer currentIsolationLevel = TransactionSynchronizationManager.getCurrentTransactionIsolationLevel();
				if (currentIsolationLevel == null || currentIsolationLevel != definition.getIsolationLevel()) {
					Constants isoConstants = DefaultTransactionDefinition.constants;
					throw new IllegalTransactionStateException("Participating transaction with definition [" +
							definition + "] specifies isolation level which is incompatible with existing transaction: " +
							(currentIsolationLevel != null ?
									isoConstants.toCode(currentIsolationLevel, DefaultTransactionDefinition.PREFIX_ISOLATION) :
									"(unknown)"));
				}
			}
			if (!definition.isReadOnly()) {
				if (TransactionSynchronizationManager.isCurrentTransactionReadOnly()) {
					throw new IllegalTransactionStateException("Participating transaction with definition [" +
							definition + "] is not marked as read-only but existing transaction is");
				}
			}
		}
		boolean newSynchronization = (getTransactionSynchronization() != SYNCHRONIZATION_NEVER);
		return prepareTransactionStatus(definition, transaction, false, newSynchronization, debugEnabled, null);
	}

	/**
	 * Start a new transaction.
	 */
	private TransactionStatus startTransaction(TransactionDefinition definition, Object transaction,
			boolean debugEnabled, @Nullable SuspendedResourcesHolder suspendedResources) {

		// 是否需要新同步
		boolean newSynchronization = (getTransactionSynchronization() != SYNCHRONIZATION_NEVER);
		// 创建新的事务
		DefaultTransactionStatus status = newTransactionStatus(
				definition, transaction, true, newSynchronization, debugEnabled, suspendedResources);
		// 开启事务和连接
		doBegin(transaction, definition);
		// 新同步事务的设置，针对于当前线程的设置
		prepareSynchronization(status, definition);
		return status;
	}

	@Override
	protected void doBegin(Object transaction, TransactionDefinition definition) {
		// 强制转化事务对象
		DataSourceTransactionObject txObject = (DataSourceTransactionObject) transaction;
		Connection con = null;

		try {
			// 判断事务对象没有数据库连接持有器
			if (!txObject.hasConnectionHolder() ||
					txObject.getConnectionHolder().isSynchronizedWithTransaction()) {
				// 通过数据源获取一个数据库连接对象
				Connection newCon = obtainDataSource().getConnection();
				if (logger.isDebugEnabled()) {
					logger.debug("Acquired Connection [" + newCon + "] for JDBC transaction");
				}
				// 把我们的数据库连接包装成一个ConnectionHolder对象 然后设置到我们的txObject对象中去
				txObject.setConnectionHolder(new ConnectionHolder(newCon), true);
			}

			// 标记当前的连接是一个同步事务
			txObject.getConnectionHolder().setSynchronizedWithTransaction(true);
			con = txObject.getConnectionHolder().getConnection();

			// 为当前的事务设置隔离级别
			Integer previousIsolationLevel = DataSourceUtils.prepareConnectionForTransaction(con, definition);
			// 设置先前隔离级别
			txObject.setPreviousIsolationLevel(previousIsolationLevel);
			// 设置是否只读
			txObject.setReadOnly(definition.isReadOnly());

			// Switch to manual commit if necessary. This is very expensive in some JDBC drivers,
			// so we don't want to do it unnecessarily (for example if we've explicitly
			// configured the connection pool to set it already).
			// 关闭自动提交
			if (con.getAutoCommit()) {
				//设置需要恢复自动提交
				txObject.setMustRestoreAutoCommit(true);
				if (logger.isDebugEnabled()) {
					logger.debug("Switching JDBC Connection [" + con + "] to manual commit");
				}
				// 关闭自动提交
				con.setAutoCommit(false);
			}

			// 判断事务是否需要设置为只读事务
			prepareTransactionalConnection(con, definition);
			// 标记激活事务
			txObject.getConnectionHolder().setTransactionActive(true);

			// 设置事务超时时间
			int timeout = determineTimeout(definition);
			if (timeout != TransactionDefinition.TIMEOUT_DEFAULT) {
				txObject.getConnectionHolder().setTimeoutInSeconds(timeout);
			}

			// Bind the connection holder to the thread.
			// 绑定我们的数据源和连接到我们的同步管理器上，把数据源作为key,数据库连接作为value 设置到线程变量中
			if (txObject.isNewConnectionHolder()) {
				// 将当前获取到的连接绑定到当前线程
				TransactionSynchronizationManager.bindResource(obtainDataSource(), txObject.getConnectionHolder());
			}
		}

		catch (Throwable ex) {
			if (txObject.isNewConnectionHolder()) {
				// 释放数据库连接
				DataSourceUtils.releaseConnection(con, obtainDataSource());
				txObject.setConnectionHolder(null, false);
			}
			throw new CannotCreateTransactionException("Could not open JDBC Connection for transaction", ex);
		}
	}

@Autowired
	private UserDao userDao;

	@Autowired
	private PlatformTransactionManager txManager;

	@Autowired
	private LogService logService;

	@Transactional
	public void insertUser(User u) {

		// 1、创建事务定义
		DefaultTransactionDefinition definition = new DefaultTransactionDefinition();

		// 2、根据定义开启事务
		TransactionStatus status = txManager.getTransaction(definition);

		try {
			this.userDao.insert(u);
			Log log = new Log(System.currentTimeMillis() + "", System.currentTimeMillis() + "-" + u.getUserName());
			// this.doAddUser(u);
			this.logService.insertLog(log);
			// 3、提交事务
			txManager.commit(status);
		} catch (Exception e) {
			// 4、异常了，回滚事务
			txManager.rollback(status);
			throw e;
		}
	}

@Override
	@Nullable
	public Object invoke(MethodInvocation invocation) throws Throwable {
		// Work out the target class: may be {@code null}.
		// The TransactionAttributeSource should be passed the target class
		// as well as the method, which may be from an interface.
		Class<?> targetClass = (invocation.getThis() != null ? AopUtils.getTargetClass(invocation.getThis()) : null);

		// Adapt to TransactionAspectSupport's invokeWithinTransaction...
		return invokeWithinTransaction(invocation.getMethod(), targetClass, invocation::proceed);
	}

	@Nullable
	protected Object invokeWithinTransaction(Method method, @Nullable Class<?> targetClass,
			final InvocationCallback invocation) throws Throwable {

		// If the transaction attribute is null, the method is non-transactional.
		// 获取我们的事务属性源对象
		TransactionAttributeSource tas = getTransactionAttributeSource();
		// 通过事务属性源对象获取到当前方法的事务属性信息
		final TransactionAttribute txAttr = (tas != null ? tas.getTransactionAttribute(method, targetClass) : null);
		// 获取我们配置的事务管理器对象
		final TransactionManager tm = determineTransactionManager(txAttr);

		if (this.reactiveAdapterRegistry != null && tm instanceof ReactiveTransactionManager) {
			ReactiveTransactionSupport txSupport = this.transactionSupportCache.computeIfAbsent(method, key -> {
				if (KotlinDetector.isKotlinType(method.getDeclaringClass()) && KotlinDelegate.isSuspend(method)) {
					throw new TransactionUsageException(
							"Unsupported annotated transaction on suspending function detected: " + method +
							". Use TransactionalOperator.transactional extensions instead.");
				}
				ReactiveAdapter adapter = this.reactiveAdapterRegistry.getAdapter(method.getReturnType());
				if (adapter == null) {
					throw new IllegalStateException("Cannot apply reactive transaction to non-reactive return type: " +
							method.getReturnType());
				}
				return new ReactiveTransactionSupport(adapter);
			});
			return txSupport.invokeWithinTransaction(
					method, targetClass, invocation, txAttr, (ReactiveTransactionManager) tm);
		}

		PlatformTransactionManager ptm = asPlatformTransactionManager(tm);
		// 获取连接点的唯一标识  类名+方法名
		final String joinpointIdentification = methodIdentification(method, targetClass, txAttr);

		// 声明式事务处理
		if (txAttr == null || !(ptm instanceof CallbackPreferringPlatformTransactionManager)) {
			// Standard transaction demarcation with getTransaction and commit/rollback calls.
			// 创建TransactionInfo
			TransactionInfo txInfo = createTransactionIfNecessary(ptm, txAttr, joinpointIdentification);

			Object retVal;
			try {
				// This is an around advice: Invoke the next interceptor in the chain.
				// This will normally result in a target object being invoked.
				// 执行被增强方法,调用具体的处理逻辑
				retVal = invocation.proceedWithInvocation();
			}
			catch (Throwable ex) {
				// target invocation exception
				// 异常回滚
				completeTransactionAfterThrowing(txInfo, ex);
				throw ex;
			}
			finally {
				//清除事务信息，恢复线程私有的老的事务信息
				cleanupTransactionInfo(txInfo);
			}

			if (retVal != null && vavrPresent && VavrDelegate.isVavrTry(retVal)) {
				// Set rollback-only in case of Vavr failure matching our rollback rules...
				TransactionStatus status = txInfo.getTransactionStatus();

				if (status != null && txAttr != null) {
					retVal = VavrDelegate.evaluateTryFailure(retVal, txAttr, status);
				}
			}

			//成功后提交，会进行资源储量，连接释放，恢复挂起事务等操作
			commitTransactionAfterReturning(txInfo);
			return retVal;
		}

		else {
			// 编程式事务处理
			Object result;
			final ThrowableHolder throwableHolder = new ThrowableHolder();

			// It's a CallbackPreferringPlatformTransactionManager: pass a TransactionCallback in.
			try {
				result = ((CallbackPreferringPlatformTransactionManager) ptm).execute(txAttr, status -> {
					TransactionInfo txInfo = prepareTransactionInfo(ptm, txAttr, joinpointIdentification, status);
					try {
						Object retVal = invocation.proceedWithInvocation();
						if (retVal != null && vavrPresent && VavrDelegate.isVavrTry(retVal)) {
							// Set rollback-only in case of Vavr failure matching our rollback rules...
							retVal = VavrDelegate.evaluateTryFailure(retVal, txAttr, status);
						}
						return retVal;
					}
					catch (Throwable ex) {
						if (txAttr.rollbackOn(ex)) {
							// A RuntimeException: will lead to a rollback.
							if (ex instanceof RuntimeException) {
								throw (RuntimeException) ex;
							}
							else {
								throw new ThrowableHolderException(ex);
							}
						}
						else {
							// A normal return value: will lead to a commit.
							throwableHolder.throwable = ex;
							return null;
						}
					}
					finally {
						cleanupTransactionInfo(txInfo);
					}
				});
			}
			catch (ThrowableHolderException ex) {
				throw ex.getCause();
			}
			catch (TransactionSystemException ex2) {
				if (throwableHolder.throwable != null) {
					logger.error("Application exception overridden by commit exception", throwableHolder.throwable);
					ex2.initApplicationException(throwableHolder.throwable);
				}
				throw ex2;
			}
			catch (Throwable ex2) {
				if (throwableHolder.throwable != null) {
					logger.error("Application exception overridden by commit exception", throwableHolder.throwable);
				}
				throw ex2;
			}

			// Check result state: It might indicate a Throwable to rethrow.
			if (throwableHolder.throwable != null) {
				throw throwableHolder.throwable;
			}
			return result;
		}
	}

/**
 * 对Controller响应请求的数据做装饰增强
 */
@Configuration
public class InitializingAdviceDecorator implements InitializingBean {

    private final RequestMappingHandlerAdapter adapter;

    public InitializingAdviceDecorator(RequestMappingHandlerAdapter adapter) {
        this.adapter = adapter;
    }

    @Override
    public void afterPropertiesSet() {
        //获取所有的handler对象
        List<HandlerMethodReturnValueHandler> returnValueHandlers = adapter.getReturnValueHandlers();
        //因为上面返回的是unmodifiableList，所以需要新建list处理
        assert returnValueHandlers != null;
        List<HandlerMethodReturnValueHandler> handlers = new ArrayList<>(returnValueHandlers);
        this.decorateHandlers(handlers); // 对 对应的 handler 做装饰增强
        //将增强的返回值回写回去
        adapter.setReturnValueHandlers(handlers);
    }


    /**
     * 使用自定义的返回值控制类
     *
     * @param handlers
     */
    private void decorateHandlers(List<HandlerMethodReturnValueHandler> handlers) {
        for (HandlerMethodReturnValueHandler handler : handlers) {
            if (handler instanceof RequestResponseBodyMethodProcessor) {
                //找到返回值的handler并将起包装成自定义的handler
                ControllerReturnValueHandler decorator = new ControllerReturnValueHandler((RequestResponseBodyMethodProcessor) handler);
                int index = handlers.indexOf(handler);
                handlers.set(index, decorator);
                break;
            }
        }
    }

    /**
     * 自定义返回值的Handler
     * 采用装饰者模式
     */
    private static class ControllerReturnValueHandler implements HandlerMethodReturnValueHandler {
        //持有一个被装饰者对象
        private final HandlerMethodReturnValueHandler handler;

        ControllerReturnValueHandler(RequestResponseBodyMethodProcessor handler) {
            this.handler = handler;
        }

        @Override
        public boolean supportsReturnType(MethodParameter returnType) {
            return true;
        }

        /**
         * 增强被装饰者的功能
         *
         * @param returnValue  返回值
         * @param returnType   返回类型
         * @param mavContainer view
         * @param webRequest   请求对象
         * @throws Exception 抛出异常
         */
        @Override
        public void handleReturnValue(Object returnValue, MethodParameter returnType, ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
            //如果是下载文件跳过包装
            IgnoredResultWrapper ignoredResultWrapper = returnType.getMethodAnnotation(IgnoredResultWrapper.class);

            if (ignoredResultWrapper != null) {
                handler.handleReturnValue(returnValue, returnType, mavContainer, webRequest);
                return;
            }

            if (returnValue == null) {
                Optional<String> contentType = Optional.of(webRequest)
                        .map(nativeWebRequest -> ((ServletWebRequest) webRequest))
                        .map(ServletRequestAttributes::getResponse)
                        .map(ServletResponse::getContentType);
                if (contentType.isPresent() && contentType.get().contains("application/vnd.openxmlformats-officedocument")) {
                    return;
                }
            }
            //如果已经封装了结构体就直接放行
            if (returnValue instanceof ResultWrapper) {
                handler.handleReturnValue(returnValue, returnType, mavContainer, webRequest);
                return;
            }
            //正常返回success
            ResultWrapper<Object> success = ResultWrapper.success(returnValue);
            handler.handleReturnValue(success, returnType, mavContainer, webRequest);
        }
    }
}

@Test
public void start() throws Exception{
    // 1. 加载全局配置文件
    InputStream in = Resources.getResourceAsStream("mybatis-config.xml");
    // 2.获取SqlSessionFactory
    // DefaultSqlSessionFactory
    SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(in);
    // 3.获取SqlSession对象 DefaultSqlSession  Executor--> SimpleExecutor --> CachingExecutor --> 插件的逻辑植入
    SqlSession sqlSession = factory.openSession();
    // 4.通过sqlSession的API接口实现数据库操作
    List<User> list = sqlSession.selectList("com.bobo.vip.mapper.UserMapper.selectUserById",2);
    for (User user : list) {
        System.out.println(user);
    }
    // 关闭会话
    sqlSession.close();
}

<setting name="localCacheScope" value="STATEMENT"/>

<!-- 控制全局缓存（二级缓存），默认 true-->
<setting name="cacheEnabled" value="true"/>

<cache />
<!--<cache type="org.mybatis.caches.redis.RedisCache"
       eviction="FIFO"
       flushInterval="60000"
       size="512"
       readOnly="true"/>-->

// ExamplePlugin.java
@Intercepts({@Signature(
  type= Executor.class,
  method = "update",
  args = {MappedStatement.class,Object.class})})
public class ExamplePlugin implements Interceptor {
  private Properties properties = new Properties();
  public Object intercept(Invocation invocation) throws Throwable {
    // implement pre processing if need
    Object returnObject = invocation.proceed();
    // implement post processing if need
    return returnObject;
  }
  public void setProperties(Properties properties) {
    this.properties = properties;
  }
}

<!-- mybatis-config.xml -->
<plugins>
  <plugin interceptor="org.mybatis.example.ExamplePlugin">
    <property name="someProperty" value="100"/>
  </plugin>
</plugins>